USGS Professional Paper 1361 - State of Arizona Department of ...

Geology and Gold Mineralization of theGold Basin-Lost Basin Mining Districts,Mohave County, ArizonaBy TED G. THEODORE, WILL N. BLAIR, and J. THOMAS NASHWith a section on K-AR CHRONOLOGY OF MINERALIZATION ANDIGNEOUS ACTIVITYBy EDWIN H. McKEEand a section on IMPLICATIONS OF THE COMPOSITIONS OF LODEAND PLACER GOLDBy J.C. ANTWEILER and w.L. CAMPBELLu.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1361UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1987

DEPARTMENT OF THE INTERIORDONALD PAUL HODEL, SecretaryU.S. GEOLOGICAL SURVEYDallas L. Peck, DirectorLibrary of Congress Cataloging-in-Publication DataTheodore, Ted G,Geology and gold mineralization of the Gold Basin-Lost Basin mining districts, Mohave County, Arizona,m.s. Geological Survey Professional Paper 1361)BibliographySupt. of Docs. No.: I 19.16:13611. Geology-Arizona-Mohave County. 2. Gold ores-Arizona-Mohave County. I. Blair, Will N. II. Nash, J. Thomas (JohnThomas), 1941- . III. Title. IV. Series: Geological Survey Professional Paper 1361. V. Title: Gold Basin-Lost Basinmining districts, Mohave County, Arizona.QE86.M63T48 1987 557.91'59 87-600286For sale by the Books and Open-File Reports Section,U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225

VIIICONTENTSPageTABLE 20. Semiquantitative spectrographic analyses for minor metals in heavy-mineral concentrates from a selected lodeoccurrence and previously worked placer deposits and occurrences in the Gold Basin-Lost Basin miningdistricts - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 9921. Compilation of signatures of placer gold samples, Lost Basin mining district - - - - - - - - - - - - - - - - - - 10222. Variation of silver and copper content of lode gold samples from Lost Basin and Gold Basin mining districts asshown by replicate emission-spectrograplric analyses - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 10323. Comparison of signatures of placer gold and possible lode gold sources - - - - - - - - - - - - - - - - - - - - - 10424. Compilation of signatures of lode gold, Lost Basin mining district- - - - - - - - - - - - - - - - - - - - - - - - 10625. Compilation of lode gold signatures, Gold Basin mining district - - - - - - - - - - - - - - - - - - - - - - - - - 10826. Signatures of gold from Lost Basin and Gold Basin mining districts that are somewhat similar to those of goldfrom porphyry copper deposits in other areas - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 11027. Homogenization temperatures and salinity data from fluid-inclusion studies in the Gold Basin-Lost Basin miningdistricts - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 114CONVERSION FACTORS1 micrometer (",m) = 1x 10- 6 meter (m)1 meter (m) = 3.281 feet (ft)1 kilometer (km) = 0.6214 mile (mi)1 gram (g) = 0.0022 pound, avoirdupois (lb avdp)1 gram (g) = 0.035 ounce, avoirdupois (oz avdp)1 kilogram (kg) = 2.205 pounds, avoirdupois (lb avdp)1 tonne (t) = 1.102 tons, short (2,000 lb)1 tonne (t) = 0.9842 ton, long (2,240 lb)1 kilogram per square centimeter (kg/cm 2 ) = 0.98 bar (0.9869 atm)1x10 6 pascals (MPa) = 10 barsdegree Celsius (0C) = 1.8 (temp °C)+32 degrees Fahrenheit (OF)

GEOLOGY AND GOLD MINERALIZATION OF THEGOLD BASIN-LOST BASIN MINING DISTRICTS,MOHAVE COUNTY, ARIZONABy TED G. THEODORE, WILL N. BLAIR, and J. THOMAS NASHABSTRACTThe Gold Basin and adjacent Lost Basin mining districts are in northwesternArizona, south of Lake Mead and justwest ofthe Grand WashCliffs. Gold in quartz veins was apparently first discovered in the areain the 1870's. Recorded production from the districts between 1901 and1942 includes 13,508 oz gold and 6,857 oz silver and has a value ofabout$359,000, of which 98 percent is credited to gold. Most recorded productionfrom lode deposits was from mines in the Gold Basin district,which is in the southern White Hills, whereas the bulk of placer productionwas along the east flank of the Lost Basin Range, about 16 kmto the northeast across Hualapai Valley. The districts have been idlesince about 1942, except for very small scale placer mining.Most known occurrences of lode gold in the districts are associatedwith widespread quartz-cored pegmatite vein systems that were probablyemplaced episodically during Early Proterozoic, Middle Proterowic,and Late Cretaceous time into Early Proterozoic metamorphic andigneous rocks. Most of the veins apparently were emplaced during theLate Cretaceous, and they were localized along both high- and low-anglestructures in the Early Proterozoic rocks. These veins are associatedspatially and possibly genetically with two-mica magmatism of presumedLate Cretaceous age. A Late Cretaceous two-mica monzogranite, whichincludes some- episyenite, crops out in an area of 4 to 5 km 2 in thesouthern part of the Gold Basin district. Some gold is found also in smallepisyenitic alteration pipes and in veins along a regionally extensive,low-angle detachment surface that has been traced for at least 30 kmalong the western flank of the White Hills and crops out conspicuouslyin their southern part.Hydrothermal micas from selected veins in the districts give K-Arages of 822, 712, 69, 68, and 65 Ma, and those from pipes give agesof 130 and 127 Ma. The oldest ages (822 and 712 Ma) may reflect resettingof veins emplaced penecontemporaneously with the 1,400-m.y.-oldgranite of Gold Butte, which crops out just to the north of Lake Mead.The ages from pipes (130 and 127 Ma) must reflect either the presenceofexcess radiogenic argon in the hydrothermal environment ofthe evolvingpipes or contamination ofthe dated mineral separates by Proterozoicmica and (or) feldspar. Primary white mica from the two-mica monzogranitegives a K-Ar age of 72 Ma.Most occurrences of gold in the veins and pipes probably reflect eitherremobilization of gold from gold-bearing, near-surface Proterozoicmetabasite or anatectic incorporation of gold into Late Cretaceous,two-mica magmas from very deep gold-bearing Proterozoic sources.Deposition of gold occurred in a mesothermal environment during thegalena-, chalcopyrite-, and ferroan-carbonate-bearing stages ofthe veins.Homogenization studies of fluid inclusions prominent in the veins andpipes yield temperatures mostly in the range 150 to 280°C. Early-stagetrapping temperatures in the pipes were probably about 330°C, andpressures in the range 50 to 70 MPa can be inferred. Fluids weremoderately saline, mostly 4 to 16 weight percentNaCI equivalent, nonboiling,and contained appreciable amounts of carbon dioxide and, inplaces, fluorine. Such fluids associated with the deposition of gold inthese districts largely bridge the fluid-composition interval between fluidsassociated with other epithermal precious-metal and porphyry copperdeposits.Approximately 350 compositional analyses of samples of native goldfrom 20 mines in the Gold Basin district and from 48 veins in the LostBasin district show silver contents from 6 to approximately 50 weightpercent, and copper contents from 0.01 to 0.5 weight percent. Metalzonation and a possible relation to a porphyry copper system at depthcan be inferred from some ofthese chemical data. Differences betweenthe composition of placer gold from 24 occurrences in the Lost Basindistrict and that ofgold in nearby lode sources suggest that other sourcescontributed gold to the placers or that locally derived grains were enrichedby oxidation and weathering of the lodes.INTRODUCTIONThe Gold Basin-Lost Basin mining districts of northwesternArizona are in Mohave County, 120 km southeastof Las Vegas, Nev., and about 95 km north of Kingman,Ariz. (fig. 1). These districts comprise primarily goldbearingvein deposits containing minor byproduct lead,silver, and copper, and placer gold deposits. Gold was firstdiscovered there in the 1870's. The districts lie adjacentto each other south of Lake Mead and west of the GrandWash Cliffs, which mark the boundary of the ColoradoPlateau. The Gold Basin district is mostly in the southernWhite Hills, and the Lost Basin district is to the east,across Hualapai Wash; they are mostly in the GarnetMountain 15-minute quadrangle (fig. 2). In this report, wefollow a broadly defined, strictly geographic assembly ofmineral deposits and occurrences into mining districts.Our Gold Basin mining district includes the Gold Basin,Cyclopic, and Gold Hill mineral districts of Welty andothers (1985), and our Lost Basin mining district includesthe Lost Basin and Garnet Mountain mineral districts ofWelty and others (1985). In their classification, Welty andothers (1985) grouped known metallic mineral occurrencesand deposits according to metallogenic criteria. Thisreport summarizes field and laboratory investigations inwhich a remarkable suite of gold-bearing samples werecollected from wide-ranging localities in these districts.Included are discussions of the environment(s) and age1

2 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAof gold deposition based on geochemical studies, fluidinclusionstudies, and K-Ar isotopic dating, all supplementedby observations with the scanning electronmicroscope (SEM). For our investigations, lode and placersamples containing visible gold were collected from morethan 30 localities.ACKNOWLEDGMENTSThe preceding geologic investigations of P.M. Blacet(1975) ofthe U.S. Geological Survey in the Garnet Mountainquadrangle during the late 1960's and early 1970'sand of E.J. Krish (1974) and A.J. Deaderick (1980) pro-120 0 114 0EXPLANATION40 035 0oI:", c~~~ ~/I~.., MOUNTAINVA/ ~I,~" MINING'\'j0., ~TRICT LAS ~\>'"I-'~ \ VEGAS,,0/ (j "1.-''''~I'''- I ISTUDY\-, ,,~ M )AREA \ SOUTH VIRGINOJAVE \ MOUNTAINSDESERT 0 \I, Kingman ,,IIThrust fault- Sawteeth onupper plateBatholithic rocks/---//-- -- --- -f­// III;1 III,." z.. Boundary of Colorado/// Plateaus province//6\ ELDORAD,O "~ MOUNTAINS ",~ ~ "'" ,f MESQUITE MINING DISTRICT"'"100 200Ir~~ /~\

HISTORY OF MINING ACTIVITY 3vided the geologic framework upon which we built muchof our studies. Further, Blacet collected many of the goldbearingsamples used in this study. R.L. Oscarson introducedus to the scanning electron microscope methodsneeded in the development of electron micrographs andaided our usage of the X-ray detector (EDAX) during thequalitative chemical analyses of selected mineral grains.Fluid-inclusion studies were conducted in the laboratoryof W.E. Hall, U.S. Geological Survey.HISTORY OF MINING ACTIVITYThe Gold Basin district is situated mostly in the easternpart of the White Hills and is bounded on the east byHualapai Wash (fig. 2). Gold in quartz veins apparentlywas discovered in the district in the early 1870's, and mostof the production until 1932 came from a small group ofmines, including the EI Dorado, Excelsior, Golden Rule,Jim Blaine, Never-Get-Left, O.K., and Cyclopic (fig. 3).About 1880 there was a small boom in the area, and by1881 the ores were being worked in two stamp mills(Burchard, 1882, p. 253); in 1882 the EI Dorado mine produced26,000 tons of developed ore (Burchard, 1883, p.305). Table 1 summarizes information concerning the millspreviously operated in the Gold Basin-Lost Basin districts.The first stamp mill, a cooperative venture by the miners,was built about 1880 at "Grass Springs" near the present(1986) headquarters of the Diamond Bar Ranch, andin 1881 a second five-stamp mill was constructed, probablyat Red Willow Spring, 4.0 km southwest of the Cyclopicmine. By 1883, most of the important mines in the districthad been located, were developed, and had producedrelatively small tonnages of free-milling, gold-quartz oresranging from 0.5 to 3.0 oz gold per ton.A third stamp mill was built along Hualapai Wash about1886 and soon became the nucleus of a settlement calledGold Basin. About this time the gold-bearing veins in theLost Basin district were discovered, and the centrallylocated Gold Basin mill soon became the most importantin the region. Several years of relative inactivity precededand followed the burning of the Gold Basin mill in 1893,but in 1896 it was rebuilt with 10 stamps and a cyanideplant. Water was piped about 10 km from water tunnelsat Patterson's well (SWI/4 sec. 36, T. 29 N., R. 17 W.),because two wells drilled at Gold Basin had penetratednothing but dry alluvial gravels to depths of 150 and230 m (Lee, 1908, p. 78). Most of the mines in bothdistricts had passed their peaks of production when thesecond burning of the Gold Basin mill occurred in 1906;in June 1907 the post office at "Basin" was discontinued,and postal service was transferred entirely to a post officeestablished in 1905 at the Cyclopic mine.In 1904, the Cyclopic mine was purchased by theCyclopic Gold Mining Company, and the next year a40-ton-per-day cyanide mill was built along Cyclopic Washjust below the mine. From this time on, "Cyclopic" wasthe main population center of the district, supporting apost office until 1917. After several years of idleness,intermittent production began again at the Cyclopic in1919, and the old mill was remodeled in 1923 after themine was taken over by the Gold Basin Exploration Company.In 1926 a new ore body was discovered, so the millwas again remodeled and its daily capacity increased to100 tons.Although the Cyclopic was one of the earliest discoveriesand also was one of the largest overall producersof ore in the district, it was apparently inactive duringthe late 1920's. However, in 1929 the Kiowa Gold MiningCompany built the San Juan mill about 1.6 km north ofCyclopic. Water for this then-new 60-ton mill evidentlywas obtained from the Cyclopic pumping station, previouslybuilt about 1905 to pipe water to an earlier mill atthe same site. The actual source of the water was a well5 km to the southwest (Sl/2 sec. 35, T. 28 N., R. 19 W.).About this time there was renewed interest in the Harmonica(Climax) mine, 3.2 km north of the San Juan mill.This mill may have processed ore from several small nearbymines until the Cyclopic mill was reactivated about1932. The Cyclopic mine produced intermittently during1932-34, when the shallow underground workings wereabandoned in favor of a large-volume opencut operation.By late 1933 a cyanide mill operated at a daily capacityof 125 tons, and a total of about 40 men were employedat the mine and mill. Much of the ore mined in 1934reportedly averaged 0.2 oz gold per ton (Wilson andothers, 1934, p. 77). In 1936 the Cyclopic property wasacquired by Manta de Oro Mines, Inc., and the mine producedsomewhat steadily through 1940. From 1941 toabout 1967 the mine was idle, and all mine buildings arenow (1986) gone. Exploration drilling in 1968 failed tolocate any additional ore. However, some attempts toheap-leach at the site of the Cyclopic mine apparentlywere undertaken in 1981. In 1984-85 Saratoga Mines Inc.of Blackhawk, Colo. apparently conducted some additionalexploration near the Cyclopic mine (Engineering andMining Journal, 1984; Saratoga Mines, Inc, QuarterlyReport to Stockholder, March 31, 1984).In addition to the Cyclopic, O.K., and Excelsior mines,which were relatively steady producers over the years,the following mines had intermittent production duringthe Depression-era mining revival from 1930 to 1942: Harmonica,Eldorado, Fry, Gold Hill, Golden Link, GoldenRule, M.O., Morning Star, and San Juan. Most of the orefrom these and several smaller mines and prospects wastreated at the Cyclopic or Malco mills. In 1942, four lodemines in the Gold Basin district had a recorded productionof 108 oz gold and 24 oz silver from 249 short tonsof treated ore (Woodward and Luff, 1943). The district

__"__4 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONA36°00' r---------------------,.--:;:--;-----.:..~7_v;;;:;;'\~::_""'\-___, :__-_;::;=_z;:;_.____--55'• •Gold Hil~mine •Qs:

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6 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAUnconformityUnconformity8UnconformityCORRELATION OF MAP UNITSDESCRIPTION OF MAP UNITS~ Sedimentary deposits (Quaternary)-Includes sand and gravel alongactive stream washes. talus. colluvium. poorly consolidatedfanglomerate currently being dissected, and landslide deposits;also may include extensive high-level fanglomeratic deposits. westof Grand Wash Cliffs in general area of Grapevine Mesa, that maybe Tertiary and (or) Quaternary in ageIOTgIFanglomerate (Qullternary and (or) Tertiary)-Locally derivedfanglomerate deposits that include mostly clasts of metamorphicrock south-southeast of Senator Mountain and that do notcontain clasts of rapakivi granite or any interbedded tuffsMuddy Creek Formation (Tertiary)ITml I Hualapai Limestone Member-Includes limestone interbedded withthin beds of limy claystone, mudstone, and siltstone. Weatheredlimestone beds have a predominantly reddish color and form steepcliffs where they are dissected by Hualapai WashITmblIOTglUnconformityTmlTmbTmfUnconformityUnconformityI YdblUnconformity1".1"'I} I xgclIXbm11 x1ml~} I XfgI Xmg Xm0 IxmllIxgnl} Quaternary}Quaternary and(or) TertiaryTertiary} CretaceousCENOZOIC} MESOZOIC} PALEOZOICEARLYPROTEROZOICBasalt- As shown, flows at Senator Mountain. near west edgeof map area. and at Iron Spring Basin, near east edge. Basalt inthese two areas correlates probably with basalt Dows (not shown)that conformably underlie the Hualapai Limestone Member andalso are interbedded with fanglomerate 01 the Muddy Creek Formationnear northwest corner of map area. Whole-rock K-Ar agedetermination of basalt from this area yields age of 10.9 Ma (seesection by E.H. McKee, this report)}MIDDLEPROTEROZOICFanglomerate-Alluvial fanglomeratic deposits that include conglomerate.sandstone. siltstone. mudstone. and locally abundantgypsum lenses. Locally includes lenses and beds of rhyolitic tuffand, as shown near southwest corner of map area. fanglomeratemapped previously by Blacet (1975) as unit n. Unit is also intrudedby minor basalt dikes, especially in general area of Senator Mountain.Near northwest corner of map area. unit includes wellexposedDows of basaltG Volcanic rocks (Tertiary)-Includes mostly andesite. Map unit nearnorthwest corner of map area internally is highly broken bynumerous faults, and near here, unit also includes air-fall tuff andreddish·brown sandstone interbedded with chaotic sedimentarybreccia composed of fragments of Early Proterozoic gneiss. Inplaces, unit also includes massive porphyritic hornblende andesiteand basalt Dows and breccia and overall minor amounts of tightlycemented volcaniclastic rocks. Flow layering and bedding gener·ally dip at angles of 35' in contrast with shallow dips of about 5'in unconformably overlying basal fanglomerate of the MuddyCreek Formation. Age ranges of 11.8 to 14.6 Ma are reported neartype section of the Mount Davis Volcanics (Anderson and others,1972), whereas K·Ar age determination on sanidlne from air-Ialltuff near Salt Creek Wash in northwestern part of area yields ageof 15.4 Ma. The volcanic rocks may be equivalent of the MountDavis Volcanics or the Patsy Mine Volcanics (see section by E.H.McKee, this report).G Rhyolitic tuffaceous sedimentary rocks and fanglomerate (Tertiary)­Includes well·bedded mudDows and rhyolitic tuffaceous sedlmen·tary rocks and minor amounts of fanglomerate. Crops out as steeplydipping sequence of rocks, bounded by north-striking faults, nearsouth end of Lost Basin Range. Possibly equivalent to the MountDavis VolcanicsG Fanglomerate (Tertiary)-Coarse fanglomeratic deposits that locallyinclude landslide or mudDow breccia. Overlain unconlormably byfanglomeratic deposits of the Muddy Creek Formation, and apparentlyIntercalated with andesite possibly equivalent to theMount Davis VolcanicsI Tmf IFIGURE 2.-Continued.Two·mica monzogranite (Cretaceous)-Includes mostly highlyleucocratic muscovite-biotite monzogranite and some minoramounts of felsic muscovite granodiorite and episyenitic-alteredmuscovite-biotite monzogranite. Some facies are fluorite bearing.Porphyritic variants contain as much as 5 percent quartzphenocrysts. In places, contains very weakly defined primary layeringof dimensionally oriented potassium feldspar and biotite8 Sedimentary rocks, undivided (Paleozoic)-Includes Cambrian TapeatsSandstone, Bright Angel Shale, and Muav LimestoneIYdb I Diabase (Middle Proterozoic)-·Includes normally zoned laths ofplagioclase set In very fine grained matrix of granules of opaquemineral(s) and clinopyroxene. Close to chilled margins of some&esh outcrops of undeformed diabase. olivine is found in concentrationsof as much as 10 volume percent. Small masses of finegraineddiabase crop out sporadically in Early Proterozoic igneousand metamorphic rocks. Most extensive exposures are about 2 kmeast of Gamet Mountain. Subophitlc textures are dominant. Lowerchilled margins of some sills contain sparse hornblende and biotitemicroveinlets. Presumed to be correlative with the diabase ofSierra Ancha, Ariz., having an emplacement age of 1,150 Ma(Silver, 1963)IXpm I Porphyritic monzogranite of Garnet Mountain (Early Proterozoic)­Includes conspicuous. large potassium feldspar phenocrysts, setin a Iight·pinkish-gray, coarse-grained hypidiomorphic ground·mass. Many exposures show tabular phenocrysts as much as 10cm long. Some phases are predominantly subporphyritic seriateand show an almost continual gradation in size of their euhedralpotassium feldspar phenocrysts. Most widely exposed mass cropsout in the general area of Garnet Mountain, in the southeasternpart of the area, and extends discontinuously from there to northalong the low hills leading to Grand Wash Cliffs. Dated by Wasserburgand Lanphere (1965) to be about 1,660 Ma

HISTORY OF MINING ACTIVITY 7has been idle generally from about 1942 to the mid-1970's,except for small-scale placer mining that recovered a littledetrital gold. In 1985-86 at least three major mining companieswere active in the district; some relatively closelyspaced drill holes were put down in the general area ofthe Owens mine.The Lost Basin district contains a wide-ranging groupof placer and lode mines in a belt lying between HualapaiWash on the west and the Grand Wash Cliffs on the east(fig. 3). It extends from the Colorado River at the mouthof the Grand Canyon southward through the Grand WashCliffs for a total length of about 32 km. This district,although much larger in areal extent, has not been asactive nor as productive as the adjacent Gold Basindistrict. The principal gold veins were discovered in 1886,and the production of the district was reported bySchrader (1909) to be "many thousand dollars," chieflyin gold. Placers apparently were first worked in 1931 andresulted in a minor local boom. However, recorded productionin copper, gold, and silver during 1904-32 wasvalued at less than $45,000 (Hewett and others, 1936).The King Tut placers, discovered in 1931, were the mostimportant placers in the Lost Basin district. Systematicsampling of the King Tut placers by G.E. Pitts in 1932.delineated approximately 90,000 tons of indicatedreserves and 250,000 tons of probable reserves beforemining operations on a relatively large scale began(Mining Journal, 1933, p. 10). All of this was confined toapproximately one section of land. In the last four monthsof 1933 the King Tut yielded 117 oz of gold (Gerry andIXgd IGranodiorite border facies of porphyritic monzogranite (Early Pro·terozoic)-Gray granodiorite that Includes variable proportions ofbiotite. hornblende, quartz, plagioclase, and potassium feldspar.fncludes less abundant porphyritic granodiorite and porphyriticmonzogranite phases. Locally coarse grained and sparsely por·phyritic. Porphyritic phases show potassium feldspar phenocrystsset In coarse.gralned hornblende·biotite hypldlomorphlc granularmatrix that Is very magnetite rich. Crops out along west andsouthwest Danks of Garnet Mountain as mafic border facies of por·phyritic monzogranite of Garnet Mountain. Found ashomogeneous discrete bodies and also in the mixed granodioritecomplex (Xgc)IXbml Biotite monzogranite (Early Proterozoic)-Includes a homogeneouslight-gray, fine·gralned monzogranite and some porphyritic faciescontaining potasslum.feldspar and quartz phenocrysts. Crops outsouth·southeast of Garnet Mountain and In the southern part ofthe Gold Basin mining district. In southern Gold Basin district,forms host rock for numerous fluorlte..bearing. quartz-carbonateveins, presumably Late Cretaceous in age, some of which containvisible goldIXlm ILeucocratic monzogranite (Early Proterozoic)-Typically light.yellowlsh.gray rock and generally nonporphyritlc. Partly chlorit·ized biotite makes up less than 5 percent of most outcrops. Cropsout as discontinuous, lensoid masses along western front of GarnetMountain. Where well exposed, contacts with porphyritic monozogranite of Garnet Mountain (Xpm) show irregular dike offshootsofporphyritic monzogranite of Garnet Mountain cutting leucocraticmonzograniteIXgc IMixed granodiorite complex (Early Proterozolc)- Composite unit thatincludes mainly granodiorite (Xgd), some of which is porphyritie.and porphyritic monzogranite of Garnet Mountain (X pm). Also In·c1udes some leucocratic monzogranite (Xlm)IXggIGnelssie granodiorite (Early Proterozoie)-Generally, well.foliated,medlum.gray.green rock containing highly variable alkali feldsparto plagioclase ratios. Biotite makes up about 20 volume percentof unit. Crops out In elongate body In southern White Hillso Leucogranite (Early Proterozoic)-Includes coarse.gralned leucograniteto pegmatltlc leucogranite that contains potassium feldsparphenocrysts as much as 8 em wide. Largest mass Is I.km.longsill cropping out 3 km northeast of Cyclopic mine. Stringers severalcentimeters wide parallel layering throughout much of the gneiss(Xgn). Fabrics grade from relatively undeformed to intenselymylonitic. Northeast of Gold Hill mine, large sills of pegmatitlcleucogranite Increase in abundance and eventuaUy grade into complexesof mlgmatitic leucogranite (Xml). Most facies show modalcompositions that plot in the field of granite; some outcrops ofgneissic leucogranite contain garnetFIGURE 2.-Continued.Feldspar gneiss (Early Proterozolc)-Generally. light gray to lightpinkish gray; compositionally homogeneous and typified by astrongly Iineated fabric. Includes minor amounts of amphibolite,mafic gneiss, highly crenulated quartz tourmaline schist, and tour·mallnlte. Crops out In a 5·km.long and 0.8-km·wlde sliver,bounded by faults In southern Lost Basin Range. Cut by quartzfeldsparveins, some of which contain goldMigmatitie leucogranite complex (Early Proterozoic)-Composite unitthat Includes swarms of leucogranite (XI), aplite, and pegmatitedikes, together with pegmatoid quartz veins all culling gneiss(Xgn). Complex and highly deformed by a ductile (mylonitic andgneissic) style of deformationIXgn I Gneiss (Early Proterozolc)-Includes variably metamorphosed gneissand some metaquartzite in northern parts of the Lost Basin Range.and in northern White Hills. Exposed sequence of gneiss insouthern parts of the Lost Basin Range includes abundantmetabasite and amphibolite consisting partly of metagabbro,metaclinopyroxenite. metawehrlite. metadiabase, and metabasalt.Intruded to varying degrees by porphyritic monzogranite of GarnetMountain (Xpm). biotite monzogranite (Xbm).leucocratic mon.zogranlte (Xlml, leucogranite (Xi), and diabase (YdblIXmgIMigmatltic gneiss (Early Proterozoie)-Composite unit that includesmostly gneiss (Xgn) intruded to varying degrees by porphyriticmonzogranite of Garnet Mountain (Xpm). biotite monzogranite(Xbm), and granodiorite (Xgd)8 Mlgmatlte (Early Proterozoic)-Composlte unit that Includes mostlymedium-grained, sparsely porphyritic monzogranite of GarnetMountain (Xpm) complexly intruded into gneiss (Xgn)---?Contact-Queried where location uncertain--- Fault-Dashed where approximately located; dotted where concealed---"-i-.? Detachment fault- Dashed where apprOXimately located; dotted whereconcealed; queried where uncertain. Sawteeth on upper plate• Lode-gold locality-Collected for this report or observed (see Blacet,1975; and section by J.C. Antweiler and W.L. Campbell, thisreport).........?Fluorite occurrence-Outer limit observed either in veins ordisseminated in the Late Cretaceous two-mica monzogranite;dashed where approximately located; queried where uncertain8Area of placer deposit and (or) mine

8 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAAAncestral White Hills- )southern Virgin Mountainshighland'\,',- \"'; ...'-' _\~\"/"'::.'~(\... \ .. ~ ....\ ",'I'" 1\ I ........\, .... IJ "\\~"I'"/j ,I"'\~"~"\,-\",,, , __.... -"1'1'''''\1''­ . /--........ .... ,- \. '"Porphyritic monzogranite ofGarnet Mountail and relatedintrusive rocksSlig hI basil filled by anarm of Hualapai Lime·B stone Member ofMuddy Creek FormationLow hillsUpturned rhyohtic ashflows and mudflowsNontuffaceous locally derived,gold.bearing gravel of\\\'I~;;:;;:*,__ late Muddy Creek age--Retreating Grand/ Wash Cliffs----DRelatively level crest --..of Bluebird Ridge --... Relatively gold-rich, localy_ Lone Jack derived fanglomerate loneUpturned rhyohtlc a,iil - _ ~ r-- placers ----... Ouaternaryflows and mudflows ...~,L~el. ':'~T~"~:-----=--:u aceous gold' . ~ '. ".' ..."of the MUddy C poor fanglomerateteek FormatIOn

GENERAL GEOLOGY OF THE DISTRICTS 9Miller, 1935). By 1936 the gold output from the King Tutwas 450 oz, which represented the bulk of the entire productionfrom the Lost Basin district. In 1939 Mr. CharlesDuncan placered 13 oz of gold in 16 days, using only asluice box and wash tub, near the King Tut placers(Engineering and Mining Journal, 1939), whereas theKing Tut placers themselves were only worked intermittentlyuntil 1942. Eventually, placer mining of unconsolidatedgravel from the upper reaches of present-dayarroyos extended across approximately 25 km 2 in thegeneral area ofthe King Tut placers (Blacet, 1969). Nonetheless,by 1942 no additional production was recordedfrom the Lost Basin district. However, in the middle andlate 1960's several small operators using dry washerswere active intermittently in the general area of the KingTut placers. These washers were powered by smallportable gasoline motors. Because of the surge in the priceofgold during 1978-80, small-scale placer operations andextensive exploration efforts, centered on an areajust tothe north of the King Tut placers, began again. Theseefforts were continuing intermittently through 1986.A summary of the recorded metal production from thelode mines in the Gold Basin-Lost Basin districts between1901 and 1942 reveals that 13,508 oz gold, 6,857 oz silver,5,9181b (2,684 kg) copper, and 43,6521b (19,797 kg) leadwere produced from a total of 69,189 tons of treated ore(table 2). The value of these metals was approximately$359,000, and approximately 98 percent of the dollarvalue is credited to gold. Recorded production from theGold Basin district in the period 1904 to 1932 was 15,109tons of ore yielding 6,244.91 oz gold, 5,059 oz silver, 4,738lbs copper, and 1,765 lb lead, valued in all at $133,014(Hewett and others, 1936; table 2). Most of this production,excluding 4,711 lb copper produced during 1918,came from the Eldorado mine. The 4,711lb of copper isassigned questionably to an unknown mine in the GoldBasin district. A total of 19 oz of placer gold was alsorecovered from the Gold Basin district in 1942 (Woodwardand Luff, 1943).GENERAL GEOLOGY OF THE DISTRICTSThe Gold Basin-Lost Basin mining districts are in theBasin and Range province, just south of Lake Mead andwest of the Colorado Plateau. The west edge of the Colo-FIGURE 3.-Schematic east-west cross section from ancestral highlandof the White Hills-southern Virgin Mountains to Grand Wash Cliffsshowing inferred geologic relations. Arrows, direction of relative movement;dashed line, previous position or approximate location; query,where uncertain. Modified from P.M. Blacet (unpub. data, 1967-72)and Deaderick (1980). A, About 15-18 Ma. B, About 8 Ma. C, About5 Ma. D, Present day.rado Plateau is approximately 3 km west of the east edgeof the Garnet Mountain quadrangle (fig. 1), where thegenerally gently east dipping to flat-lying lower Paleozoicbasal formations of the Colorado Plateau crop out alongthe Grand Wash Cliffs. The districts are present in anuplifted region near the leading edge ofthe North Americanplatform (see Burchfiel, 1979; Dickinson, 1981) andstraddle several north-trending ranges of mostly Proterozoicbasement rocks from which the rocks of thePaleozoic stable platform have been removed by erosion.Lake Mead occupies a structurally complex area to thenorth marked by the junction of several regionally extensivemajor geologic features (see Anderson and Laney,1975; Angelier and others, 1985). These features includethe boundary between the Paleozoic miogeocline andstable platform, the Mesozoic Sevier orogenic belt, andthe Las Vegas shear zone. Further, the districts are presentalong the southern extension of the Virgin Mountainsstructural block of Longwell (1936) and Anderson andLaney (1975). The districts include two ranges of mostlyEarly Proterozoic metamorphic and igneous rocks, theWhite Hills and the next range to the east, herein termedthe Lost Basin Range but referred to as the InfernalRange by Lucchitta (1966), and two intervening valleysfilled by Tertiary and Quaternary deposits (Blacet, 1975).These two valleys are drained by Hualapai Wash andGrapevine Wash, and the latter valley also cuts throughGrapevine Mesa. The Grapevine geomorphic trough includesthe Grand Wash fault zone, a N. 10°-15° E.­striking system of Miocene normal faults (west blockdown) now covered by Tertiary fanglomerate and Quaternarygravel (see Longwell, 1936; Lucchitta, 1966, 1979).The trace of the Grand Wash fault zone is inferred to passbetween Lost Basin Range and Garnet Mountain, southwestof which the Grand Wash fault zone is inferred onthe basis of relations apparent in satellite imagery (Goetzand others, 1975, fig. IV-B-2) to terminate against ayounger northwest-striking structure, herein named theHualapai Valley fault. The Hualapai Valley fault is inferredto change its strike gradually to almost north-southas it passes west of the Lost Basin Range along the maindrainage of Hualapai Wash (Liggett and Childs, 1977).Major offsets along the Hualapai Valley fault may bepenecontemporaneous with deposition of the uppermostsequences of the upper Miocene limestone. However,along the Grand Wash trough basin-and-range faultingwas active during the early stages of basin fill, althoughmovement(s) along some faults apparently continued afterdeposition of the upper Miocene limestone, (Lucchitta,1972; also note displacements shown along the Wheelerfault in figure 6 of Lucchitta, 1979). Similarly, initialmovements along the Hualapai Valley fault may have contributedtoward local development of an embayment inwhich the limestone was deposited.

I-'oName of siteWillow mill(Gold Spring)Grass Springs(Grass Valley)Patterson's wellButcher CampO.K. mill(Gold Basinor Burnt mill)Old Senator millSalt Springs millCyclopic millSan Juan millLost Basin mill(Scanlon)Malco mill(Excel sior •Eldorado)Type of millArrastre and stampStampArrastreArrastreArrastre and stampStampStampCyanideAmalgamatingand cyanideBall mill withflotation andcyanideBall mill withflotation andcyanide(?)TABLE I.-Descriptions ofgold-quartz mills in the Gold Basin-Lost Basin mining districts, ArizonaLocationRed Willow Spring, NW1/4 sec. 12,T. 27 N., R. 19 W.At the headquarters of the DiamondBar Ranch, NW1/4 sec. 27, T. 29 N.,R. 16 W.SE 114 sec. 36. T. 29 N., R. 17 W.NW1/4 sec. 7. T. 27 N•• R. 18 W.Along Hualapai Wash, NE1/4 sec. 13,T. 28 N., R. 18 W.Near the Colorado River east of themouth of Salt Springs Wash, SW1/4sec. 5, T. 30 N., R. 18 W.At Salt Springs near center ofsec. 18, T. 30 N•• R. 18 W.At Cyclopic mine, SW1/4 sec. 30,T. 28 N., R. 18 W.In canyon 1 mi north ofCyclopic mine, SE1/4 sec. 19,T. 28 N., R. 18 W.About 1 mi northeast of theGolden Gate mine, SW1/4 sec. 28,T. 30 N., R. 17 W.At Excelsior mine, NW1/4 sec. 22,T. 28 N., R. 18 W.History and remarksPossibly the location of the first arrastre in the district,bUilt in the early 1870's. A stamp mill was built here priorto 1915, perhaps as early as 1881.An inefficient four- or five-stamp mill, the first for thedistrict, was constructed at Grass Springs about 1880 as acooperative venture by the early miners.Robert Patterson, a pioneer rancher and miner, built an arrastrenear his well (water tunnels) in 1883.Two arrastres at shallow well. History unknown.This stamp mill operated intermittently at the settlement of GoldBasin from 1887 to 1890; it burned in 1893, but was rebuilt in1896 and its 10 stamps and cyanide plant ran intermittentlyuntil it burned again in 1906 (Schrader, 1909, p. 120-121).A 1a-stamp mill was built here about 1892, operating for about6 months on low-grade ore hauled 16 mi from the Senator Mine.History uncertain, probably built by the Salt Springs Mining Co.about 1900. This mill apparently operated as late as 1917.A 40-ton-per-day mill was built in 1905 by the Cyclopic GoldMining Co., producing considerable bullion during the next fewyears. In 1923, the Gold Basin Exploration Co. acquired theproperty and remodeled the mill. After discovery of a new orebody in 1926, the mill was again remodeled, and its capacityincreased to 100 tons per day. The mill operatedintermittently during 1932-40 and was enlarged to 125 tonsdaily capacity in late 1933.In 1929, the Kiowa Gold Mining Co. built a 60-ton-per-dayamalgamating and cyanide mill to process ore from the San Juangroup of claims. This plant may have provided custom millingfor several small miners during the early 1930's (MiningJournal, 1929).In the mid-1930's, the Lost Basin Gold Mining Co. was apparentlyoperating a diesel-powered 50-ton-per-day ball mill at the oldScanlon mine. Prior to the filling of Lake Mead, this companymay have operated a mill near the Colorado River along HualapaiWash.A 35-ton-per-day diesel-powered ball mill was built in 1938 bythe Malco Mining Co. (Mining Journal, 1938). About 1908, astamp mill may have been built at this site by the Arizona­Minnesota Gold Mining Co.~~oSl~t;:18t--3~~.1:12~N~ >

GENERAL GEOLOGY OF THE DISTRICTS 11Early Proterozoic rocks crop out widely in both the GoldBasin and Lost Basin mining districts. These rocks consistmostly of gneiss that presumably is 1,750 Ma and thatincludes both paragneiss and orthogneiss, the coarsegrainedporphyritic monzogranite of Garnet Mountain,and relatively small masses of medium-grained leucocraticmonzogranite that crop out as part of the plutonic complexof Garnet Mountain (fig. 2). In this report, we usethe classification of Streckeisen and others (1973). Assuch, the porphyritic monzogranite of Garnet Mountainand the leucocratic monzogranite correspond to the porphyriticquartz monzonite and leucocratic quartz monzoniteof Blacet (1975), who followed the classification ofBateman (1961). The porphyritic monzogranite of GarnetMountain intrudes gneiss and most likely was emplacedabout 1,660 Ma (Wasserburg and Lanphere, 1965). TheProterozoic terrane in the quadrangle also includes smallbodies of granodiorite, gneissic granodiorite, alaskite,various mappable migmatite units, feldspathic gneiss, amphibolitederived from igneous and sedimentary protoliths,and other metasedimentary rocks, including somefairly widespread metaquartzite. In addition, some minoramounts of diabase that presumably is of Middle Proterozicage are exposed mostly as thin northwest-strikingdikes in the general area of Iron Spring Basin (fig. 2).The most widespread unit of Early Proterozoic age tocrop out in the districts is the gneiss unit (Xgn, fig. 2).TABLE 2.-Production ofgold, silver, copper, and leadfrom lode depositsin the Gold Basin-Lost Basin mining districts, 1901-42[Quantities furnished by the U.S. Bureau of Mines; ----. no production recorded]Ore treated Gold SilverYear (short tons) (ounces) (ounces)1901---- 30 59 151902-- 3.900 260 8101903-- 4,723 2,361 3001904-- 2,000 1.429 3511905--- 360 1,356 2091906-- 903 380 1151907-- 101 27 151908--- 55 29 101910--- 412 203 681911-- 431 197 471913--- 600 228 411914-- 600 280 421915---- 600 300 701917---- 560 280 501918-- 639 248 8271919--- 2,813 270 7841920-- 800 275 501922--- 3 21923--- 5 6 11929---- 9 4 41933-- 3,425 371 771934--- 3.306 317 51935-- 502 209 1141936--- 2.231 326 941937--- 13,354 923 2751938--- 7,968 370 8091939--- 3,170 655 3071940-- 14,299 1.453 9731941-- 1,141 582 3701942-- 249 ~ 24Total- 69.189 13,508 6.857Copper(pounds)Lead(pounds)27 149As such, it hosts most of the known gold-quartz veindeposits. These deposits are concentrated in a belt thattrends approximately N. 15°-20° E. and that spans theGold Basin and Lost Basin districts. The deposits arefound mostly in the western half of the Garnet Mountainquadrangle (fig. 3). The remaining gold-quartz veins areconcentrated mostly in the southern part of the Gold Basindistrict, east of the Cyclopic mine. The veins here arehosted by gneissic granodiorite and porphyritic monzograniteof Garnet Mountain.The Early Proterozoic gneiss, and here we paraphraseBlacet's (1975) descriptions for the most part, consists ofan assemblage of metasedimentary rocks, mostly quartzofeldspathicgneiss interlayered with subordinate cordieritegneiss, biotite-garnet-sillimanite schist, and amphibolite.Locally, dark-gray to black amphibolite forms a large partof the gneiss unit, especially in the southern part of theLost Basin Range where the amphibolite sequence consistsof metagabbro, metadiabase, metaclinopyroxenite,and metawehrlite. Generally, the amphibolite crops outdiscontinuously in lensoid masses ofvarious sizes. In addition,thin lenses of marble, calc-silicate gneiss, banded ironformation, and metachert crop out sporadically within thegneiss. All these metamorphic rocks have been deformedintensely during several episodes of deformation in EarlyProterozoic time (Blacet, 1975). The presence of Paleozoicrocks in the eastern part of the study area and theirabsence in the western part results from regional downwardtilting to the northeast and consequent erosionalstripping of the Paleozoic rocks. As pointed out byLucchitta (1966), the tilt results from a belt of uplift southwestofthe present-day edge of the Colorado Plateau. Thisuplift is presumably of early to middle Tertiary (orLaramide) age and predated the basin-and-range riftingin the area, exemplified by the Grand Wash fault zone.Displacements along the Grand Wash fault zone areestimated to range from 1,000 to more than 5,000 m(Lucchitta, 1966). However, north of the Colorado River,the Grand Wash fault zone apparently has displaced6.9-Ma basalt by as much as 305 m (Hamblin, 1984). Thesestudies by Hamblin suggest that the eastern block(s) hasbeen elevated, whereas the western block(s) remainedrelatively stationary.East of the Lost Basin district, well-exposed Paleozoicformations crop out at the base of the Grand Wash Cliffs,near the east boundary of the Garnet Mountain quadrangle.These Cambrian formations include the conformableTapeats Sandstone, Bright Angel Shale, and MuavLimestone (Blacet, 1975). The Tapeats Sandstone restsunconformably on the porphyritic monzogranite of GarnetMountain. All of these formations are included within thePaleozoic undivided unit of figure 2.An undeformed leucocratic two-mica monzogranite intrudesgneiss about 1.5 km north of the Cyclopic mine in

12 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAthe southern part of the Gold Basin district (fig. 2). Thetwo-mica monzogranite crops out across an area of about4 to 5 km 2 and is Late Cretaceous in age (Blacet, 1972);it includes some zones of episyenite, with minor aplite andpegmatite. The two-mica monzogranite in the Gold Basindistrict is part of the Wilderness "strato-tectonic" assemblageof Keith and Wilt (1985), which apparently makesup the most widespread and most voluminous type ofmagmatism during the Late Cretaceous and (or) earlyTertiary in Arizona (see also Keith, 1984).Three types of lode gold deposits are known in the GoldBasin-Lost Basin districts (Blacet, 1969, 1975). Most lodegold deposits in the districts are present as veins, presumablyof Late Cretaceous age, and are localized alongpreexisting structures in Early Proterozoic rocks. In addition,some of the gold-bearing quartz veins probably areof Proterozoic age. A minor yet geologically significanttype of lode gold deposit in the Gold Basin district consistsof small masses of Late Cretaceous fluorite-bearingepisyenite containing macroscopically visible disseminatedgold (Blacet, 1969). Most likely, the emplacement of theseepisyenite bodies is related genetically to the intrusion ofLate Cretaceous two-mica monzogranite. The third typeof lode gold deposit, exemplified by the Cyclopic mine,consists of Late Cretaceous gold-quartz veins that mayhave been originally deposited as cap-rock silica brecciasand then brecciated further as they were caught up alonga regionally extensive Miocene low-angle fault. This faultcrops out in the southern part of the Gold Basin districtand has been traced to the north along the west flank ofthe White Hills (fig. 2).The oldest Tertiary rocks in the general area of thedistricts are volcanic rocks presumably equivalent to theTertiary Mount Davis Volcanics or Patsy Mine Volcanicsas mapped by Longwell (1963) and Anderson and others(1972; unit Tv, fig. 2), rhyolitic tuffaceous sedimentaryrocks and fanglomerate (unit Ts), and Tertiary fanglomerate(unit Tf). The volcanic rocks include mostly andesite.Their base in the general area of the districts is not exposedbut instead is marked apparently by a low-angledetachment surface. In the Eldorado Mountains, Nev.,just west of the Colorado River and south-southwest ofLake Mead, andesite and rhyolite lavas of the Patsy MineVolcanics are overlain successively by rhyolitic ash-flowtuff of the tuff of Bridge Spring and by basaltic andrhyodacitic lavas of the Mount Davis Volcanics (Andersonand others, 1972). A sequence oftuffaceous mudflowsand rhyolitic water-laid tuffaceous sedimentary rocks andfanglomerate crops out near the south end of the LostBasin Range (fig. 2) and was mapped in detail by Deaderick(1980). This sequence is steeply dipping, is partlybounded by north-striking faults on the west, and possiblyis equivalent in age to the Tertiary volcanic rocks; on theeast, the sequence is overlain unconformably by conglomeratesbelonging to the Muddy Creek Formation(Blacet, 1975). In addition, Deaderick (1980) reported thatthe mudflows and rhyolitic tuffaceous sedimentary rockslocally are in depositional contact with Early Proterozoicmigmatitic gneiss and that the mudflows and tuffaceoussedimentary rocks may be equivalent in age to theMiocene Patsy Mine Volcanics (or formerly the GoldenDoor Volcanics of Longwell, 1963). In the northwest cornerofthe study area (fig. 2), Tertiary fanglomerate (unitTf) apparently is intercalated with the Tertiary volcanicrocks. These coarse fanglomeratic deposits locally includelandslide or mudflow breccia and are overlain unconformablyby younger fanglomeratic deposits (unit Tmf).Although the stratigraphic nomenclature for nonmarineTertiary sedimentary rocks in the Lake Mead area hasbeen modified recently by Bohannon (1984), the nomenclatureused for purposes of this report follows that ofLongwell (1936), Lucchitta (1966, 1972, 1979), Blacet(1975), and Blair (1978). The Muddy Creek Formation ofMiocene age in the study area consists of conglomerate,claystone, mudstone, and gypsum; basalt, possibly equivalentto the Fortification Basalt Member of the MuddyCreek Formation, at Senator Mountain and Iron SpringBasin near the Grand Wash Cliffs; and an upper carbonatemember that has been called the Hualapai LimestoneMember. The conglomerate appears to have beendeposited in small basins and topographic lows in an environmentof interior drainage. Small patches of landslideor mudflow breccia containing Proterozoic clasts occurwithin the fanglomerate of the Muddy Creek Formationsoutheast of the Lost Basin Range. Stratigraphically,much of the Fortification Basalt Member and the HualapaiLimestone Member of the Muddy Creek Formation occupiesapproximately the same position near the top ofthe section (Longwell, 1936; Lucchitta, 1979), althoughAnderson (1977, 1978) shows lenses of the FortificationBasalt Member cropping out throughout the entire sequenceof the Muddy Creek Formation. The HualapaiLimestone Member may have been deposited in a marineenvironment (Blair, 1978; Blair and Armstrong, 1979),although Lucchitta (1979) has reinterpreted Blair's datato suggest that the Hualapai Limestone Member wasdeposited in saline lakes at or below sea level. Further,the low contents of bromide, six to seven parts per millionin salt from the Muddy Creek Formation near Overton,Nev. (85 km northwest of the study area), suggested toHolser (1970) that these salts could have been derivedfrom evaporites on the Colorado Plateau. Nonetheless,some paleontological and chemical evidence at least suggeststhat the Hualapai Limestone Member may reflectdeposition at the north end of an extended embaymentof the Gulf of California beginning more than 8.9 Ma (Blairand others, 1977) or 5 to 6 Ma according to Lucchitta(1979). The type locality for the Hualapai Limestone

GENERAL GEOLOGY OF THE DISTRICTS 13Member is along Hualapai Wash, and the thickest partof the limestone at the type locality is almost 300 m. Somebeds of this limestone cover the Grand Wash fault zonenear the base of the Grand Wash Cliffs where the ColoradoRiver emerges from the Grand Canyon (Longwell,1936; Lucchitta, 1966). Thus, apparently no major movementoccurred along this fault zone after the last severalhundred meters of deposition of the Muddy Creek Formation.However, northwest of the Cyclopic mine, rocksassigned to the Muddy Creek Formation apparently havebeen faulted against Proterozoic metamorphic and igneousrocks and the Late Cretaceous two-mica monzogranitealong the regionally extensive low-angle Miocenefault, which crops out there (fig. 2; see also Blacet,1975).Exposures of the actual surface of this low-angle detachmentfault are extremely difficult to find. Locally, nevertheless,indurated conglomerate of the Muddy CreekFormation containing boulders of coarse-grained porphyriticmonzogranite of Garnet Mountain are faultedagainst crushed migmatitic gneiss and crushed porphyriticmonzogranite of Garnet Mountain. This detachment faultborders the White Hills along the entire west margin andthus establishes an eastern leading edge for low-angledetachment terranes in the Lake Mead area (see Anderson,1971; Davis and others, 1979, fig. 1).The overall tectonic history of this low-angle structureis still poorly resolved. The detachment fault does notappear, however, to be similar to dislocation surfaces(decollement) immediately associated spatially with closelyunderlying cordilleran metamorphic core complexes,owing to the absence of pervasive penetrative linear structuresassociated with widespread mylonitic or cataclasticfabrics (see Crittenden and others, 1980). The fabric ofthe two-mica monzogranite is not mylonitic or cataclastic.In addition, such core-complex-associated dislocation surfacestypically show an underlying microbreccia about 1 mthick, which is in tum underlain by a zone of chloritebreccia. Furthermore, the detachment fault, which cropsout along the west margin of the White Hills and at theCyclopic mine, must not reflect the eastern distal effectof near-surface distension associated with the emplacementof plutons coeval with the Miocene Mount DavisVolcanics (see Anderson, 1971; Anderson and others,1972). The detachment fault apparently is younger thanthe Mount Davis Volcanics because it cuts rocks assignedto the Muddy Creek Formation (fig. 2). The overall extensionassociated with this structure appears to have anazimuthal bearing of approximately east-west based onthe roughly north-south trend of its trace along the westflank of the White Hills. In the general area of theCyclopic mine, some sequences of fanglomerate assignedto the Muddy Creek Formation crop out in the upper plateof the detachment fault; however, as mapped, parts of theMuddy Creek Formation apparently crop out also in thelower plate of the detachment fault farther to the northwest(fig. 2). Several splays of the detachment fault arewell exposed in the general area of the Cyclopic mine.Some additional field relations along this fault are providedin the section "Veins Along the Miocene DetachmentFault." Nonetheless, the geologic relations shownon figure 2 must be amplified by studies beyond the intendedscope of this present report. As pointed out byLucchitta (1979; written commun., 1983) only the lowermostbasin-fill deposits are substantially deformed and cutby detachment-type faults elsewhere in the region. Rarelyin the region have such faults been reported to cut basinfillrocks of Muddy Creek age. To the west near theEldorado Mountains, south of Boulder City, Nev., Anderson(1971) provided some of the first comprehensivedescriptions of thin-skin Tertiary distension. There, alongthe northwest flank of the Eldorado Mountains, some ofthe flat-lying Muddy Creek Formation rests unconformablyacross some of the listric normal faults. However,just to the northeast of Boulder City, rocks of the MuddyCreek are cut by a number of high-angle faults (Anderson,1977), and the Muddy Creek Formation in the easternpart of the Eldorado Mountains is involved significantlyin detachment-type faulting, particularly in its lowermostsequences (Anderson, 1978).Displacements along the low-angle fault may haveoccurred in response to either of two other tectonicphenomena. First, the low-angle displacements mayreflect the near-surface uplift of the White Hills associatedwith strike-slip offsets along a southeast-striking faultpostulated to go through Lake Mead (Anderson, 1973, fig.8), south of the Virgin Mountains. Second, the possibilityof local gravity sliding off the White Hills cannot bediscounted.The next younger sequence of rocks in the Gold Basin­Lost Basin districts includes some unconsolidated sediment(Blacet, 1975), but because of their patchy distribution,they are not shown as separate map units on thegeologic sketch map (fig. 2). Well-rounded cobbles andgravels derived from the Colorado Plateau lie scatteredunconformably on the Hualapai Limestone Member andsome ridges of the Muddy Creek Formation. These cobblesand gravels probably represent Pliocene high-levelremnants of the ancestral Colorado River (Lucchitta,1966).Some late Tertiary gravels are present as dissectedalluvial fan remnants along Grapevine Wash at the baseof the Grand Wash Cliffs and are included with theQuaternary sedimentary deposits of figure 2 (unit Qs).The Grand Wash fault zone near the base of the GrandWash Cliffs has had a profound impact on the overallgeomorphic evolution of the region. However, any viableregional interpretation must include the critical geologicrelations mapped by Blacet (1975) at the Lost Basin

14 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONARange, approximately 10 km west of the Grand WashCliffs and almost at the very center of the GarnetMountain quadrangle. Our hypotheses of the geologicgeomorphichistory of the region during the past 18 to15 m.y. is shown schematically, in an east-west crosssection (fig. 3). Inferred structural relations are shownextending from the ancestral highland of the White HillssouthernVirgin Mountains on the west, through the rocksof the Lost Basin Range, and finally to the Grand WashCliffs on the east.Prolonged but episodic regional extensional tectonismin the late Tertiary seems to have affected the predominantlyEarly Proterozoic crystalline terrane of thedistricts, and this in turn apparently contributed towardthe eventual distribution of the productive placer golddeposits. The development of the relatively deep middleto late Tertiary basin along the Grand Wash fault zonewas apparently controlled primarily by regional east-westextension (fig. 3A; Lucchitta, 1966). This extension mustalso be reflected in the low-angle detachment surfaces atthe base of the volcanic rocks possibly equivalent in ageto the Mount Davis Volcanics and through the generalarea of the Cyclopic mine workings and along the westmargin of the White Hills, described previously (fig. 2).Sediment was shed into the basin along the Grand Washtrough mostly from a highland at the ancestral White Hillsand southern Virgin Mountains as suggested previouslyby Longwell (1936) and Lucchitta (1966). Sometime afterdeposition of the lowermost sequences of tuffaceous goldpoorfanglomerate belonging to the Muddy Creek Formationinto the basin, local tilting toward the east in responseto movements along the Grand Wash fault zone may haveoccurred during the late Tertiary in the general area ofthe Lost Basin Range to yield the steeply dipping andpartly overturned sequence of mudflows and rhyolitic tuffaceoussedimentary rocks (fig. 3B). Early Proterozoicgneiss, migmatitic gneiss, feldspathic gneiss, and amphibolitein turn may have been faulted against this sequenceof steeply dipping and locally overturned mudflows andrhyolitic tuffaceous sedimentary rocks and fanglomerate(fig. 2, unit Ts; see also Deaderick, 1980, pI. 1). Such lateTertiary faulting must have been a near-surface phenomenonand contributed to the development of low hills atand ancestral to the present-day Lost Basin Range. Continuedeast-west extension is reflected by steeply west dippingnormal faults (west side down) along both the eastand west range fronts of the Lost Basin Range. Thesenorth-south normal faults seem to reflect a westwardmigration in extensional phenomena away from the GrandWash fault zone (see Longwell, 1936; Lucchitta, 1966).Some of the past major normal displacements here wereconcentrated along the Hualapai Valley fault and predateddeposition of the nearby Hualapai Limestone Member.The initiation of block faulting at the Lost Basin Rangeprobably occurred at nearly the same time as depositionof nontuffaceous locally derived gold-bearing gravels oflate Muddy Creek age. These gravels, which contain goldin noneconomic concentrations, most likely were derivedin part from the now-eroded upper portions of veins exposedalong Lost Basin Range and uplifted possibly as aresult of faulting during the late Tertiary. However, continuedmovements along the normal fault inferred tobound Lost Basin Range immediately on the west,together with the deep post-Muddy Creek erosion just tothe west of Lost Basin Range led to the relative upliftingof the gold-bearing gravels at the leading edge of GrapevineMesa and the reworking of these gravels during theQuaternary into important placer deposits (Lone Jackplacers, SW1J4 sec. 15, T. 29 N., R. 17 W.). These goldbearingplacers are now perched approximately 500 mabove the main drainage of Hualapai Wash, about 5 kmto the west.The relations between the detachment fault, whichcrops out just east and southeast of Senator Mountain andalong the west margin of the White Hills (fig. 2), and theLost Basin Range are difficult to resolve. The detachmentfault probably continues to the southeast from the areaof the Cyclopic mine, where it last crops out before beingcovered by Quaternary gravels (P.M. Blacet, unpub. data,1967-72). The trace of the detachment fault probably liesto the east of Table Mountain Plateau, approximately 10km to the southeast of the Cyclopic mine area.K-AR CHRONOLOGY OF MINERALIZATIONAND IGNEOUS ACTIVITYBy EDWIN H. McKEEA total of 11 samples were dated by the K-Ar method.These samples include 10 purified mineral separates (eightwhite mica, one biotite, and one sanidine) and one wholerocksample (table 3). Sample preparation and argon andpotassium analyses were done in the U.S. GeologicalSurvey laboratories, Menlo Park, Calif. Potassium analyseswere performed by a lithium metaborate flux fusionflame-photometrytechnique, and argon analyses wereperformed by standard isotope-dilution procedures. Nineofthe samples were analyzed using a 60 0sector 15.2-cmradiusNeir-type 1 mass spectrometer operated in the staticmode in which six manual scans of 40 Ar, 38Ar, 36Ar peakswere made during a time interval of about 10 minutes.Two samples (table 3, samples 837,999) were analyzedon a five-collector, first-order, direction-focusing, 22.9-cmradiusmass spectrometer controlled by a PDP8/3 minicomputerthat takes peak heights simultaneously from the1Any use oftrade names and trademarks in this publication is for descriptivepurposes only and does not constitute endorsement by the U.S. GeologicalSurvey.

K-AR CHRONOLOGY OF MINERALIZATION AND IGNEOUS ACTIVITY 15three argon collectors. The constants used in age calculationsare:A£=0.581x10- 10 /yr, AfJ=4.963x10- 10 /yr, and40KlKtota l = 1.167x10-4 mole/mole.The precision or analytical reproducibility reported asa ± value is at a.In a general way, it reflects the relativeamount of 40Arrad to 40Artotah the higher percent of40Arrad the smaller the ±. The ± value is determined byassessment of the various analytical procedures, includingflame-photometer and spectrometer reproducibility andstandard and argon tracer calibration. The precision ofthe eight ages reported ranges from 0.7 to 6.5 percentof the calculated age.CRETACEOUS PLUTONIC ROCKSSeveral small two-mica leucocratic monzogranite plutonscrop out in the southwestern part ofthe study area(fig. 2). Muscovite from a sample of one of these bodiesabout 2 km north of the Cyclopic mine was dated at72.0±2.1 Ma, which is Late Cretaceous (Laramide) andtypical of many granitic rocks in central and westernArizona.Biotite from a sample of Proterozoic gneiss from about2 km east of this pluton was dated to see what effect, ifany, the Cretaceous plutons have had on surroundingrocks. A number of dikes of presumed and (or) knownCretaceous age intrude the gneiss and much or most ofthe hydrothermal alteration and mineralization is also ofCretaceous age. Radiogenic 40Ar in biotite in the gneiss,which is easily lost at moderately low temperatures, wouldhopefully reflect the extent of pervasive regional heatingduring the Late Cretaceous. The biotite yielded an ageof 76.3 ±3.0 Ma, which is very near that of the pluton andsubstantiates the widespread character of the Laramideevent.CRETACEOUS VEINSThree quartz-muscovite veins were sampled for agedetermination. Two of the veins cut granitic rocks knownor assumed to be Late Cretaceous in age, and one cutsgneissic rocks of Proterozoic age. Sample 923 (table 3)TABLE 3.-K-Ar analytical data and agesSample Mineral K 2 0 40 rrad 40 Ar rad Apparent ageand location Unit name dated percent 1O- t1 mol/g percent (Ma)733C Basalt flow in Muddy Creek Whole-rock 1.045 1.6619 17 .1 10.9:1;0.635°59'54" Formation basalt 1.067114°17'40"728A Air-fall tuff Sanidine 8.48 11.9251 77 .2 15.4:1;0.235°52'00"114°07 '00"837 Quartz-muscovite-fluorite- Muscovite 10.75 103.001 21.1 65.4:1;2.635°46'00" pyrite vein114°14' 00"278A Quartz vein containing Muscovite 10.95 108.991 79.4 67.8:1;2.035°53'15"hydrothermal muscovite114°08'04"923 Muscovite from quartz- Muscovite 10.73 108.465 88.5 68.8:1;1.835°48'22" muscovite-fluorite-pyrite 10.75114°15' 15"vein cutting two-micamonzogranite884 Two-mica monzogranite Muscovite 10.67 112.823 76.9 72.0:1;2.135°48' 22"114°15' 15"999 Gneissic granodiorite Biotite 9.06 101.666 85.1 76.3:1;3.035°48'03"114°12'44"79GM8b Episyenitic alteration Sericite 11.64 220.225 90.8 126.9:1;3.835°46'42" pipe, gold-bearing114°11'07"79GM8b Episyenitic alteration Sericite 11.64 226.550 87.8 130.3:1;3.935°46'42" pipe, gold-bearing114°11'07"735 Secondary mica in quartz Muscovite 10.62 1.3342xl0- 8 98.0 712:1;5.035°58'45"114°15'42"735-1 Secondary mica in quartz Muscovite 10.67 1.6007xl0- 8 95.0 822:1;6.035°58'45"114°15'42"

16 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAcuts the leucocratic monzogranite dated at 72.0±2.1Ma-it yielded an age of 68.8 ± 1.8 Ma, which is the sameas the pluton (within the overlap of the ± values). Thesecond vein in granitic rock is 4 km southeast of the datedpluton and vein described above. Its K-Ar age is 65.4±2.6Ma, the same, considering the analytical precision, as thefirst vein.Both veins contain fluorite and pyrite as well as whitemica and quartz as major components. Gold in traceamounts is also present in the veins and is the metal mostsought after in the numerous prospects and small abandonedmines throughout the area. On the basis of theseage determinations, mineralization is considered to beLate Cretaceous in age and to be a late stage of the periodof Laramide plutonism prevalent throughout the Basinand Range region of Arizona.The third dated vein (sample 287A) cuts Proterozoicgneiss about 1 km east ofthe Bluebird mine in the centerofthe study area. Hand samples of this vein contain whatappears to be hydrothermal white mica along with traceamounts of gold. The white mica yields a K-Ar age of67.8±2.0 Ma and is within the age span ofthe two veinsreported above and about the same as the age of primarymuscovite from the leucocratic monzogranite. This agesubstantiates the thesis that Laramide igneous activitywas associated with significant gold mineralizationthroughout the Gold Basin-Lost Basin area, approximatelyat the same time as the widespread Laramide porphyrycopper deposits formed elsewhere in the Southwest.Two ages were determined on fine muscovite from agold-bearing episyenitic alteration pipe in Proterozoicbiotite monzogranite about 5 km southeast of the datedLate Cretaceous two-mica leucocratic pluton. This alterationpipe is in the same general area as the dated LateCretaceous veins, and its mineral assemblage and geologicsetting suggest that it is related to and probably the sameage as the other veins in the area. The ages from this pipeare 126.9±3.8 and 130.3±3.9 Ma, or twice as old as expected.If the pipe is Late Cretaceous, as field evidenceindicates, some type of contamination has affected thesample. Two possibilities that seem most likely include:Excess radiogenic Ar picked up by hydrothermal solutionspassing through the surrounding Proterozoic rocks wasincorporated into the hydrothermal-vein sericite duringits formation, or mineral contamination was caused by inclusionof some Proterozoic muscovite or feldspar fromthe host gneiss during collection of the vein sample. Fromthe data available, the mechanism that accounts for theanomalously old age of the pipe's muscovite is impossibleto verify.PROTEROZOIC(?) VEINTwo samples of secondary coarse-grained hydrothermalwhite mica from a gold-bearing quartz vein about 3 kmsouthwest of Salt Spring Bay on Lake Mead (15 km northof the study area) were dated. The vein, which cuts Proterozoicgneiss, looks like the other veins in the region,some of which yielded Late Cretaceous or Laramide ages.This vein was thought to be Laramide in age as well;however, the apparent ages are discordant-712 ±5 and822 ±6 Ma. Interpretation of these values is difficult. Proterozoicgneiss of similar appearance as the host rock ofthe vein described here is intruded by porphyritic monzogranitethat was dated by Rb-Sr methods (a well-definedisochron) at 1,660 Ma (Wasserburg and Lanphere, 1965,p. 746 and fig. 4). This age is similar to many ages ofProterozoicrocks in central and western Arizona and is consideredan established age for major regional igneousevents in this region (Silver, 1964, 1966, 1967; Ludwig,1973). The discordant K-Ar ages on the vein white micacould represent partial and different amounts of argonloss from a Proterozoic vein related either to the widespread1,660-Ma event or a less well documented goldmineralization event at 1,440 Ma. The partial argon lossand accompanying partial resetting ofthe so-called K-Arclock may have been caused by slight heating during theLate Cretaceous or early Tertiary Laramide event documentedelsewhere in the area. If the rocks near the veinwere not heated sufficiently to release all the radiogenicallyproduced 40Ar, the age would be some indeterminableamount less than the original1,660-Ma age-the711 and 822 Ma determined here. Alternatively, the partialargon loss could also represent small but continuousargon diffusion from the white mica caused by generalregional geothermal elevation throughout the past 1,660m.y. In either case a reset age that does not record thetime of any single event is the result. The vein wasassumed to be about the same age as the dated gneiss,or approximately 1,660 Ma.The possibility exists that the white mica mineral separatefrom the vein contained a small amount of Proterozoicmuscovite from the enclosing host gneiss. A small anddifferent amount of 1,660-Ma contaminant muscovite witha larger amount of Late Cretaceous vein white mica couldcause the two aberrant ages. The possibility ofthis mechanismcausing the 711- and 822-Ma ages is impossible toevaluate. Assumedly, the ages do not represent the timeofvein emplacement. We believe, however, that the overwhelmingbulk of the white mica composing these twomineral separates dated by the K-Ar method crystallizedduring the vein's emplacement.Textural relations between white mica and vein quartzfrom the sample site at locality 735, yielding the 711- and822-Ma ages, were studied using the scanning electronmicroscope (SEM; fig. 4). These studies strongly suggestthat the white mica there composing the dated samplesis secondary. An initially unknown 1.5-l-Im-long bladedmineral (fig. 4A) was chemically verified by its SEM X-rayspectra as having the same overall proportions of aluminum,silicon, potassium, and iron as a known muscovitestandard (compare fig. 4B and C). In addition, some of

K-AR CHRONOLOGY OF MINERALIZATION AND IGNEOUS ACTIVITY 17these very fine grained bladed crystals, which can reasonablybe asswned to be white mica, appear to be growinginto 3- to 5-~ irregularly shaped cavities in vein quartz.This relation suggests the white mica is secondary; thatis, it crystallized initially during vein formation. Thesesmall crystals of mica are probably not daughter mineralsbut are instead trapped or captured mineral grains (seeRoedder, 1972, p. JJ24).TERTIARY VOLCANIC ROCKS25002000'" ....~ 1500ou::t 1000'""50050004000'" ~3000::>o u>-2000"'"" 10002000 4000 6000ELECTRON VOLTSSamples 733C. basalt. and 728A, rhyolite ash-flow tuff.were dated to aid in establishing the chronology of Tertiaryrocks and tectonic events in the Gold Basin·LostBasin area. The ages were used in conjunction withstratigraphic relations for correlation between units in thecomplex lenticular sequences of Tertiary basin and subaerialdeposits of the region. They also provide limits onthe age of low-angle faulting (regional sliding) that hasdisplaced most of the Tertiary rocks in the region.The 15.4±O.2-Ma age on sanidine from a rhyolitewelded ash-flow tuff from a large tectonic block along SaltCreek Wash suggests correlation with the middle part ofthe Patsy Mine Volcanics or possibly the lower part ofthe Mount Davis Volcanics as described by Anderson andothers (1972). The Patsy Mine Volcanics are composed ofmore than 1,000 m of lenticular volcanogenic rock includinga variety of rhyolitic to dacitic lava flows and tuffbeds. The type section for the Patsy Mine Volcanics is inthe Eldorado Mountains of Nevada about 70 km due westof the sample site of the tuff reported here. UnspecifiedTertiary volcanic rocks, of which the Patsy Mine Volcanicsare a part. are shown on figure 2 of Anderson and others8000 (1972) as extending into the Gold Basin-Lost Basin area.Because the middle part of this composite volcanic unitis rhyolite lavas and interstratified tuffaceous sedimentaryrocks with K-Ar ages in the range of 14.5 to 18.6Ma. the correlation with our 15.4±0.2-Ma rhyolite tuffseems good. In fact, Anderson and others (1972, table 1and appendix, samples 36-40) record three rhyolite flowswith ages that are the same, within analytical uncertainty,as the tuff reported here. Furthermore, sanidinemineral separates used to date the Patsy Mine rocks andOle Gold Basin-Lost Basin ash flow have a similar unusuallylow K20 content. suggesting a genetic relation.A sample of basalt collected from the lower oftwo flowsbeneath the late Miocene Hualapai Limestone Member ofthe Muddy Creek Formation near the north-central edge2

18 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN·LOST BASIN MINING DISTRICTS, ARIZONAof the study area and 6.8 km south of 1'emple Baryields a K-Ar age of 10.9±0.6 Ma. This age is the same(11.3±0.3, 11.1±0.5, and 10.6± 1.1 Ma), within the analyticaluncertainty, as that of the Fortification BasaltMember of the Muddy Creek Formation as reported byAnderson and others (1972). These ages were subsequentlydiscarded and a new set ofages of 4.9,5.8, and 5.9 Mawere adopted for the age of the Fortification BasaltMember of the Muddy Creek Formation (Lucchitta, 1979).The locality south of Temple Bar is at least 30 km eastof Fortification Hill and 45 and 50 km east·southeast ofthe collection sites of the other basalt samples, so thesesamples are probably not from the same lava flow. Theconcordant ages on basalts indicate that basaltic volcanismwas widespread and from a number of vents in theregion from 11 Ma to 5-6 Ma.All of the silicic and intermediate volcanic rocks in theGold Basin-Lost Basin area (those correlated with thePatsy Mine Volcanics or Mount Davis Volcanics) are infault contact with surrounding older rocks. This low-anglefault is apparently some type of regional slide surface andnot a thrust fault. Other areas in southern Arizona, southeasternCalifornia, western Utah, and eastern Nevada inwhich the terrane is characterized by large slide blocksofTertiary rocks have almost universally been related tometamorphic core complexes. Gravity tectonics caused bydoming of the core complex is the driving force that causesmovement of these large slide blocks. In the Gold Basin­Lost Basin area, sliding postdates the rhyolite unit datedat 15.4±0.2 Ma. A second period of sliding is recordedby low-angle fault surfaces between Tertiary conglomerateof the Muddy Creek Formation that is dated about10.9 Ma and older rocks including Proterozoic gneiss andthe Late Cretaceous two-mica monzogranite (see fig. 2).This second period ofsliding is probably not much youngerthan about 10.9 Ma because the Hualapai LimestoneMember of the Muddy Creek Formation, a thick carbonateunit in the region about 8 Ma (Blair, 1978), is somewhatyounger (Lucchitta, 1979), is largely undeformed, and isnot in low-angle fault contact with older rocks.PETROCHEMISTRY OF CRYSTALLINE ROCKS ANDTHEIR RELATION TO MINERALIZATIONMetamorphic rocks in the Gold Basin-Lost Basin miningdistricts have been derived from igneous and sedimentaryprotoliths that were regionally metamorphosed to as highas upper-amphibolite-facies (Miyashiro, 1973) assemblagesand complexly deformed syntectonically during the olderEarly Proterozoic Mazatzal orogeny (see Wilson, 1939,1962). This orogeny occurred 1,650 to 1,750 Ma (Silver,1967). The Mazatzal orogeny thus correlates temporallywith the upper half of the Hudsonian orogeny in the CanadianShield, with final metamorphism in the Front Range,Colorado, and with the pre-Belt basement, Montana(King, 1969). Early Proterozoic metamorphic rocks inArizona broadly compose three tectonic belts, of whichthe northwesternmost one, in the general region of theGold Basin-Lost Basin mining districts, is mostly gneissderived largely from an epiclastie protolith (Anderson andGuilbert, 1979); it also includes schist in the Vishnu Complexof Brown and others (1979) derived from shale andgraywacke protoliths and some thick sequences ofgneissand amphibolite derived from mafic and, very locally,ultramafic protoliths. Metamorphic rocks in the districtsalso include metaquartzite, thin lenses of marble, calcsilicategneiss, banded iron formation, and metachert. Theprotolith(s) of these metamorphic rocks is difficult to correlateconvincingly with specific well-studied sequencesof Proterozoic rocks in central Arizona (see Donnelly andHahn, 1981, for descriptions of these sequences). TheEarly Proterozoic Bagdad Belt of Donnelly and Hahn(1981) includes relatively thick sequences of coarse- tofine-grained metamorphosed wackes ncar the top of theoverall metamorphic pile there. Some of these metamorphosedwackes may be correlative with quartzofeldspathicgneiss at Gold Basin-Lost Basin.The gneiss exposed in the Gold Basin-Lost Basin miningdistricts contains highly deformed and lithologically complexsequences that commonly grade or change abruptlyinto one another across short distances. Although aquartz-plagioclase (oligoclase or andesine) or quartzofeldspathicgneiss is probably the predominant rock typeoverall of the gneiss unit, quartzofeldspathic gneiss is complexlyinterlayered with other lithologies in many outcrops(fig. M). In addition, moderately thick, layered sequencesof predominantly quartzofe1dspathic gneiss may gradeinto sequences consisting mostly ofamphibolite by subtleyet marked changes in the relative proportions ofquartzo.feldspathic gneiss and amphibolite along strike. Some ofthe amphibolite in the districts will be shown, in the followingsection, to have an igneous protolith. In some sequenceswithin the gneiss unit, rather abrupt transitionsare also present across conformable contacts, perpendicularto lithologic layering between predominantlyquartzofe1dspathic gneiss and mixed zones of amphiboliteand associated gneissic. pegmatoid leucogranite dikes andthin sills (fig. 58). However, most ofthesc contacts couldnot be laterally extended sufficiently to be shown at ascale of 1:48,000, the scale of the map published by Blacet(1975). Further, many outcrops show an overall bandedaspect resulting from complex and close interlaminationand interlayering of quartzofeldspathic gneiss and amphibolite.In fact, many outcrops in the gneiss unit containabundant 0.3- to 5.Q-an, highly planar and continuousbands of amphibolite, some bands reaching thicknessesas great as 40 cm. Many such outcrops commonly showa pulling apart or boudinage of the amphibolite layers. In

PETROCHEMISTRY OF CRYSTALLINE ROCKS 19these outcrops, the foliation in the surrounding quartzofeldspathicgneiss converges dramatically in the neckeddomains of the amphibolite, suggesting the preferred concentrationofductileflow in the quartzofeldspathic gneissduring defonnation. Additional evidence for the brittlebehavior of blocks of layered amphibolite during igneousinjection includes the infilling ofleucogranite along fracturesbetween separated blocks of amphibolite (fig. 6).Some further evidence for the complexity of the prolongeddefonnation(s) to affect the Early Proterozoic gneiss terraneis reflected in highly contorted and isoclinally foldedsequences of gneiss containing locally pervasive cataclasiteand mylonite, and mylonitized coarse-grainedleucogranite cutting amphibolite and quartz-plagioclasegneiss. The cataclastically deformed rocks must reflecta brittle-type deformation, whereas the largely recrystallizedmylonite, including mylonitic schist and myloniticgneiss, must reflect syntectonic recrystallization accompanyingductile flow.Widespread and pervasive injection of the gneiss byEarly Proterozoic granitic magmas yielded migmatiticcomplexes now concentrated mostly along the lower westflanks ofGarnet Mountain and near the southernmost extentof Lost Basin Range (fig. 2, units Xgc, Xmg, Xm,and XmI). Migmatitic gneiss (Xmg) and migmatite (Xm)were mapped separately mostly on the basis of the relativeproportion of granitic injecta. Migmatitic gneiss includesmostly pelitic gneiss and lesser amounts of, but nonethelessrelatively abundant, granitic material; whereas migmatite(Xm) contains mostJy Proterozoic granitic rock (fig.5C). Swarms of leucogranite, aplite, and pegmatite dikes,including varying amounts of pegmatoid quartz veins andirregular quartz masses, cut gneiss locally in the north·western part of the Garnet Mountain quadrangle andtogether compose a migmatitic leucogranite complex(Xml).Approximately 200 thin sections, prepared from meta·morphic rocks showing wide-ranging overdll bulk chern·istries, were studied petrographically. These Proterozoicmetamorphic rocks host many of the lode gold depositsknown in the districts. For the most part, the metamorphicrocks show prograde mineral assemblages of upperF1CllRl: S.-Outcropsofgneiss lieQUt'nces at various localities in the LostBasin Range and in the White IliUs. A. Typical exposure ofdistinctlyIarered gneiss sho..;ng similar ..·eU-developed folds plunging aboutN. 3C>"·75" W. Quartz "fin cutli gneiss near base of JiKltograph. Notepocket knife near uppercenter for scale. B, Zone offolded thin 1eueogranite1a)'e1'S confined to 3().cm~ofchJoritized amphibolitewithn unif

20 GEOUX;Y AND GOLD MINERALIZATION OF THE GOLD BASIN·LOST BASIN MINING DISTRICTS, ARIZONAamphibolite facies that have been retrograded partly orcompletely to greenschist assemblages; approximately 70percentofour thin-sectioned samples contain such retrogradeassemblages. In addition to greenschist-faciesmineral assemblages locally developed syntectonicallyduring recrystallization of a fabric showing strongcrystallographic and dimensional preferred orientatton ofquartz and various phyllosilicate minerals, some of themetamorphic rocks also are altered deuterically to propyliticassemblages and even phyllic and potassic (seeCreasey, 1966; Beane and TitJey, 1981) assemblages. Thepropylitic assemblages are especially well developed in thegeneral area of the major north-striking faults in thesouthern Lost Basin Range (Deaderick, 1980, pI. 1), andFICURE 6.-Coarse.grai.ned quartz·feldspar IeucognInite eroueultingdistoSty in 4

PETROCHEMISTRY OF CRYSTALLINE ROCKS 21Epldo'~ amphibolll~ Amphiboli'~Chlo,il~Epido'~Mu.cOYl'~Blotll~T""rmalin~Almaodin~ lIa.n~ISla".olil~AndaJ".Il~Kyanil~S~lImanl'~=======-----=-==---------------------,---.-H~T

22 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING D1STRlcrs, ARIWNAto biotite +chlorite +quartz + H20. However, these temperatureestimates are based on the assumption that thepartial pressure of water (PH 20) equalled total pressure(Plot) during the prograde event. This assumption probablyis not valid, however, as will be discussed subsequently.Therefore, the 425 to 460 °C temperature range shouldbe considered only as the highest temperatures one wouldinfer for the onset of such white mica-biotite assemblages.Miyashiro (1973) notes that stilpnomelane may occur inhigh-pressure metamorphic terranes and very rarely inlow-pressure ones, a relation that may further constrainthe thermal implications of the absence of stilpnomelane.Some of the mica schists also show textural relationssuggesting compatibility between biotite and carbonate,probably calcite, during the prograde metamorphism ofthe area(fig. 9C). From the absence of talc and tremoliteas the first silicate minerals to crystallize in this assemblageand the appropriate experimentally determinedcarbonate-silicate equilibria (Skippen, 1971; Winkler,-1974, p. 113), we infer that the molecular fraction of carbondioxide, at least locally, must have been very high inthe fluid(s) associated with metamorphism. Winkler (1974)further suggests that such a high molecular fraction ofcarbon dioxide in the fluid(s) may have been maintainedby a reaction such as3 Fe-Mg carbonate+l potassium feldspar + 1 H 2 0-1 biotite+3 calcite+3 CO2. (1)However, the early biotite (dark brown, Z axis}carbonatequartzassemblage in the fine-grained schist, exemp.lifiedby sample GM-339 (fig. 9C), has been replaced significantlyby a retrograde greenschist assemblage of chlorite,epidote (clinozoisite), white mica, and minor rutile. Thewhite mica probably is mostly muscovite, but it mayinclude some margarite. Where ductile flow was con·centrated in these micaceous rocks during the biotitedestructivegreenschist metamorphic event, the rockswere converted into chlorite-rich phyllonitic schist. Suchchanges commonly occur across sharp boundaries and arereflected by marked modal differences. These changes areprimarily an increased abundance of chlorite and whitemica, whereas there are sharply decreased amounts ofbiotite. Further, in these domains of chlorite-richA~? ~o~-:~ "'ILU",ETEASoO.6"'UI",nEAL' -----.:,B?? -.:: ",...lMnEAFIOURE 9.-Schist containing relatively abundant concentrations ofmuseovite(M)and (or) biotite (8). Planc-polariwd light. Q. quartz. A.Unret.rograded quartz-biotite-.museovite schist containing minortourmaline (T), apatite (A), opaque mincrals (Ol, and oligoclase feldspar(F). Sample GM·233. B. Crenulated quartz·biotite-musoovit.e schistshowing incipient nCOCry!ltallization of quartz and museovit.e alongzones of axial·plane e1eavage, which eut dominant foliation in rockat high angles. Sparse porphyroblasts of chlorite (chi) aligned withtheir lOOt} cleavage traces parallel t.o the axial-plane cleavage. SampleGM·273. C, Apparently compatible relict biotite (8) and carbonat.e(C) in a highly retrograded biotit.e-ehlorite-white mica-epidote(clinoroisite) schist. Sample GM-339.

PETROCHEMISTRY OF CRYSTALLINE ROCKS 23phyllonitic schist, calcite is a conspicuous relict from theearlier biotite-stable metamorphic event, and it showsmostly an intensification of its dimensional orientationwherein the short axes ofthe calcite grains are transverseto the trace of the foliation. A chemical analysis of a sampleof heavily retrograded biotite-carbonate schist showsa very low Na20 content of 0.1 weight percent, a C02content of 3.1 weight percent, and a relatively high Ti02content of 1.9 weight percent (table 4, analysis 1).roURMALINE SCHIST AND GNEISSTourmaline, a complex boron-bearing silicate typicallycontaining 8 to 10 weight percent B20s (Deer and others,1962a), is present in significant concentrations at severallocalities in the gneiss terrane. However, within most ofthe gneiss, tourmaline is a relatively sparse mineral thatcrystallized during the early metamorphism of the area.In those rocks containing tourmaline in relatively abundantconcentrations of perhaps as much as 30 volume percent,the prismatic crystals of tourmaline show a verystrong preferred orientation that defines the metamorphicfoliation or 8 surface. Generally, the known tourmalineschists or tourmalinites form zones that may beseveral centimeters thick, mostly in sequences of quartzofeldspathicgneiss. Many of these zones show welldeveloped,small-scale, composite folds that reflect acombination of shear along an axial-plane cleavage andbuckling due to lateral compression (fig. lOA). In suchfolded rocks, the leucocratic layers include mostly quartz,muscovite, tourmaline, and sparse oligoclase. Theseleucocratic layers show a more ductile behavior duringdeformation than the dark, tourmaline-rich layers. Underthe microscope, the tourmaline-rich layers are composedof aggregates of fine-grained crystals that measure approximately0.1 mm across their basal sections. The tourmalineis strongly pleochroic from very pale light olivegray to dark greenish blue. Such a pleochroic scheme suggeststhat the tourmaline in these rocks is the ironcontainingvariety known as schorl (Deer and others,1962a). However, the identification of the compositionalvariety of tourmaline primarily by color may be misleading(Jones, 1979). In addition, tourmaline in these rocksshows apparently stable compatabilities with a broad spectrumof the characteristic minerals used typically as zonalindicators in pelitic metamorphic terranes. As describedabove, it is present in sparse concentrations with progradequartz-muscovite-biotite assemblages. Tourmaline is alsopresent in epidote-quartz-microcline-muscovite-plagioclase-opaquemineral assemblages that compose the wispybanded layers within quartzitic sequences of the gneiss.Tourmaline is also abundant in somewhat higher gradeschists containing a muscovite-biotite-almandine(?) garnetquartz-sparsepotassium feldspar assemblage. The texturalrelations and crystal forms of the garnets in thisassemblage suggest they are in their initial stages ofcrystallization (fig. lOB). Some quartz-kyanite clots in themetamorphic rocks, which will be discussed fully in afollowing section describing kyanite relations, also containtourmaline. However, tourmaline was not found tobe associated with sillimanite, cordierite, or staurolite.Nonetheless, it has been reported to occur with staurolitein mica schist of the Alto Aldige region, Italy (Gregnaninand Piccirillo, 1969), with garnet and staurolite in theeastern Alps, Austria (Ackermand and Morteani, 1977),with staurolite and sillimanite in metamorphic rocks ofthe Kamchatka Peninsula, U.S.S.R. (Lebedev and others,1967), and with staurolite and kyanite in the Black Mountainarea, New Hampshire (Rumble, 1978). A tourmalinequartzassociation is also present in some rocks of theEarly Proterozoic Yavapai Series (Anderson and others,1971) of the Jerome, Ariz., area (S.C. Creasey, oralcommun., 1979), and tourmaline is a common accessoryin amphibolite-facies micaceous and quartzofeldspathicschist of the Early Proterozoic Vishnu Complex in theGrand Canyon (Brown and others, 1979).Experimental studies further substantiate the wideranging,pressure-temperature stability of tourmaline.Reynolds (1965) showed that a marked redistribution ofboron occurs at metamorphic conditions near the greenschistfacies. He concluded that boron typically is expelledfrom a boron-bearing, 1 Md lattice ofillite in sedimentaryrocks when recrystallized during metamorphism to the2 Mpolymorph and that the expelled boron is fixed finallyin tourmaline. However, the extremely high concentrationsof boron required locally by these stratiform occurrencesof tourmaline schist (fig. lOA), or tourmalinite inthe usage of Nicholson (1980), indicate that boron-bearingclays could not have been the primary source ofboron here(see Ethier and Campbell, 1977). Further, the tourmalinein the tourmaline schist obviously reflects recrystallizationdating from the prograde metamorphism of the area.Although detrital. tourmaline grains commonly act asnucleii for any newly crystallized tourmaline, carefulpetrographic examination of these tourmaline-bearingrocks revealed that the tourmaline does not now showovergrowths, broken crystals, or any variably roundedcrystal forms. Thus, the tourmaline-bearing biotite-stableschists in the Gold Basin-Lost Basin districts are wellbeyond the lower stability limit of tourmaline. At the highmetamorphic end of the spectrum, the experimentalstudies of Robbins and Yoder (1962) in the system dravite­H20 suggest temperatures greater than 800°C at pressures(PH 20) greater than 50 MPa are needed to decomposedravite, the Fe-free Mg-bearing tourmaline, intomostly cordierite bearing assemblages.The provenance of the protolith and the overall petrogenesisof the tourmaline schist remain nonetheless

24 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONATABLE 4. -Chemical analyses ofselected schist and gneissfrom the Gold Basin-Lost Basin mining districts compared with analyses ofslate, argillite,shale, graywacke, and arkose[Chemical analyes by rapid-rock methods; analysts, P.L.D. Elmore and S. Botts. Methods used are those described by Shapiro (1967). Spectrol;.l"aphic analyses by Chris Heropoulos. Resultsare identified WIth geometric brackets whose boundaries are 1.2, 0.83, 0.56, 0.38, 0.26. 0.18, 0.12. and so forth, but are reported arbitrarily as midpomts of these brackets, 1,0.7,0.5,0.3, 0.2, 0.15, 0.1: and so forth. The prec~sion of a reported value is approximately plus or mmu~ one bracket at 68.p~rcentconfidence ~r two brackets at .95-p,ercent confidence. Lookedfor but not found. Ag, As, Au, B, Be. Bt, Cd, Mo. Pd, Pt, Sb, Sn, Te, V, W, Zn, Ge, Hf, In, Lt, Re, Ta, Th, TI. Eu, ----, not detected, N.D.. not determmed; Tr, trace]Analysis ----- 1 2 3 4 5 6Sample -------- GM-339 GM-555 GM-312b GM-255 GM-295 GM-4987 8 9 10 11Chemical analyses (weight percent)Si02 ---------- 50.9 66.8 76.3 75.4 75.0 72.3A1 2 0 3 -------- 13.6 17 12.3 12.4 12.7 14Fe203 --------- 3.4 1.2 1 1.6 1.7 2.8FeO --------- 10.4 4.4 .68 1.9 1.7 2.2MgO ----------- 5 1.7 .6 1.7 .4 .7CaO --------- 5.7 .90 3.3 2.1 3 4.3Nat ---------- .1 1.4 3 2.7 3 32.4 4K2 ----------1.3 1.3 1 .7H20+ ----------3.4 1.8 .87 .98 1 1.1H~O- ---------- .05 •08 .02 .02 .05 .04T 02 ----------1.9 .74 .08 .13 .12 .01P205 ---------- .24 .05 .00 .01 .04 .07MnO ----------- .06 .12 .02 .06 .09 .06CO2 ---------- 3.1

PETROCHEMISTRY OF CRYSTALLINE ROCKS 25the schist composes wispy stratiform zones containingsparse concentrations of other minerals that also haverelatively high specific gravities. The specific gravity oftounnaline is approximately 3.00 to 3.20 (Deer and others,1962a). These relations suggestthat the tourmaline schistor tourmalinite may reflect local syngenetic exhalativeemanations of boron-rich fluids onto the sea floor, wherethe protolith of the Proterozoic metamorphic rocks occurred.Such a syngenetic model for similar rocks elsewherehas been proposed recently (Ethier and Campbell,1977; Nicholson, 1980; Plimer, 1980; Slack, 1980). Theexploration implications of these rocks will be discussedin the section entitled "Suggestions for ExploratoryPrograms,"BFICHU IO.-Stn..:turaI and textural reIationsoftounnaline in metam0rphicroch. Plane-polarized light. A. Compollite small-scale folM intourma1illt lIChilit.~ eM·296. B, Disseminated euhedral ttyIlta!lIof fiIJeolT&ined garnet in a tourmaIine-biotite-museovite lldrist. T.tourmaline; Q. quartz; G. garnet; M,rnicroctine.SampIe GM·297LALMANOINE·BIOTITE±STAUROUTE SCHIST AND GNEISSPelitic schist and gneiss in the Proterozoic metamorphicterrane also include almandine-biotite-quartzpotassiumfeldspar-plagioclase assemblages. The potas·sium feldspar is mostly microcline, and the plagioclase ismostly oligoclase or andesine, although some of theserocks rarely contain albite. Minor aceessory minerals includeapatite, opaque mineral(s), and rutile. Some of theinitial crystallization stages ofalmandine are recorded byrocks still containing muscovite and biotite, as describedin the preceding section. In such a mineral association,almandine garnet is present aseuhedraJ O.l-mm-wXle porphyroblastsin a fabric wherein the schistosity and subsequentstrain-slip cleavage are defined by muscovite andbiotite. Textural relations suggesting specific reactionsthat controlled the crystallization and growth of almandineare very difficult to ascertain. Generally, however,increased modal abundances ofalmandine and microclineappear to have been compensated by (1) a decrease inoverall abundance and eventual disappearance of muscoviteand (2) a change in the color of biotite from darkbrown (Z axis) to reddish brown (Z axis). These changesare accompanied also by an apparent increase in grainsize. The first crystallization ofalmandine-rich garnet inthese rocks is not sharply defined areally and is notmarked by the disappearance ofa phyllosilicate phase. Instead,we infer from our petrographic observations thatthe initial crystallization of garnet reflects a reaction suchasbiotite! +m phengitic white mica....biotiten +a1mandine gamet+m potassium feldspar+ H20. (2)We suggest that early dark-brown (Z axis) biotite! is aniron-rich variety and that the ensuing red-brown (Z axis)biotiteu is a variety containing more magnesium thanbiotite!_ If reaction (2) is mostly correct for the onset ofthe biotiteu-almandine-potassium feldspar compatibility,then the magnesium content of biotiten may be derivedprincipally from the breakdown of phengitic white mica,which may have magnesium substituted for aluminum inits octahedral structural sites (Deer and others, 1962b).Further, m in reaction (2) may be greater than one, thusreflecting a preferred consumption of white mica relativeto biotite). In addition, reaction (2) provides a mechanismwhereby biotiteJl in the rocks becomes more magnesianand thus stable to higher temperatures than biotite).Staurolite (ideally F~A19S40d:OH» was found at onlyone locality (GM-922), near the south edge of the GoldBasin district, approximately 5 km south of the Cyclopicmine. Ribboned and spotted migmatitic gneisses there areretrograded partly to a chlorite-white mica greenschistassemblage. However, the melanosomes of these rocks

26 GEOLOGY AND GOLD MINERALIZATION Of' THE GOLD BASIN-LOST BASIN MINING DISTRlcrs. ARIZONAcontain a weU-developed, gamet-biotite-stauroli~andalusiU(r)assemblage with an absence of potassiumfeldspar and plagioclase. Andalusite is possibly presentin the rock in trace amounts as crystals apparently compatiblewith garnetduring the progradeevent, but subsequentlyhighly altered to white mica during the retrogradeevenl Equant to stubby-prismatic crystals of staurolitemeasure typically 0_5 to 1.0 rom wide and they form, inplaces, 120° dihedral angles against euhedral porphyroblastsof garnet (fig. IlA). Under the microscope, thestaurolite is strongly pleochroic from colorless (X axis) topale golden yellow (Z axis); some crystals are twinned.In the melanosomes of these staurolite-bearing rocks.chlorite and white mica partly replace mostly biotite asfine-grained porphyroblasts at high angles to the traceof the foliation defined by the biotite. Many of the staurolitecrystals are also rimmed by aggregates of very finegrained white mica. However, the crystalsofgarnet hereare remarkably free of replacement phenomena relatedto the retrograde evenlThe presena! ofstaurolite in the a1mandine-biotite schistand gneiss allows us to make some inferences concerningthe prograde metamorphism of the area during theEarly Proterozoic. The onset of the crystallization ofstaurolite is generally accepted to be at temperaturessomewhat higher than almandine garnet(Miyashiro, 1973)and to indicate thereby that regionally metamorphosedrocks have reached alleast a medium grade, or temperaturesin the 500 to 550°C range (Winkler, 1974).Although staurolite can apparently fonn across a broadspectrum of pressure environments (Miyashiro, 1973), itsmaximum stability determined experimentally in thepresence of quartz, muscovite, and biotite appears to beabout 675°C at 550 MPa and about 575 DC at 200 MPa,P H 2P = Plot and Mg/(Mg+Fe) - 0.4 (Hoschek, 1969).G. Hoschek further found that a relatively high FeJ(Mg+Fe) ratio will expand the stability field ofstaurolite.Thus, the very restricted presence of staurolite in contrastwith the very wide distribution of cordierite in theProterozoic terrane of the Gold Basin-Lost Basin districtsmay reflect such chemical controls. Although stauroliteis present here in an assemblage questionably containingandalusite, staurolite-bearing assemblages elsewhere arecF\cuRl: 11.-Textunli reIationa M'lOl'"C' minerals in gameWlearinggneiaG. garnet; S. staurolite; B. biotite; C. chkIrite; M. white mica; Q,~f'Iane.~ I:igttLA. Textural reIationr; in gamet·mwroote-biotitegneis& relict &om prograde evenL Odorite and ,,'hite mica a')"itallizedduring subeequent greenschist retrograde e\~nL SampleGM-922&. B. Rounded and higtlly a1tenxl crystals ofgarnet in retrogradt.odgarnetiIerotIlS Ieut'ogneia. Partially chloritiz.ed garneta arereplac:ed by aggregates oC very fine grained white mica. SampleGM-462. C. Mylonitic fabric COn9sting oflnotite-d1lorite-wrute mica·clinoww1e-()llartz _mblage superpo:l6ed during greenschi6t retrogradeewnt OIl an E'Jlrlier gamet-bearingassemblage. Sample GM·555.

PETROCHEMISTRY OF CRYSTALLINE ROCKS 27reported commonly to include all three aluminosilicatepolymorphs (Hietanen, 1973; Carmichael, 1978; Dusel­Bacon and Foster, 1983).Almandine-biotite prograde assemblages are also presentin some rocks intermediate in composition betweenthe pelitic and quartzofeldspathic gneisses. However,many of these rocks are retrograded intensely, as exem~plified by garnet-bearing leucogneiss that is interlayeredwith quartzofeldspathic and amphibolite gneisses (fig.lIB). In the garnet-bearing leucogneiss, partially chloriti7.edcrystals ofgarnet are as much as J cm across in someof the layers. The cores of many of the garnets hostrounded fine-grained crystals of quartz, engulfed possiblyby rapid growth of garnet during its early stages ofcrystallization. Further, the garnets are replaced at theirmargins and along fractures by pale-green chlorite andsome white mica. The light~colored matrix of the rocksconsists of quartz, clouded feldspar, and a few relicts ofbiotite now replaced largely by interlayered chlorite. Mostoligoclase grains are partly replaced by white mica andclinozoisite and (or) epidote. The almandine, which ispresent in some gneiss, is intermediate chemically betweenthe pelitic and quartzofeldspathic end members andshows excellent textural relations indicating the crystallizationof some retrograde biotite (fig. lIe). In theserocks, fractured crystals of garnet (.'ontain alteration rimsof biotite. In addition, the garnets are microveined bybiotite, chlorite, and white mica, which together withc1inozoisite and quartz make up the predominant mineralsin the mylonitic fabric that developed contemporaneouslywith retrograde metamorphism and isoclinal folding ofsome sequences ofgneiss. Chemical analysis of such a rockshows contents of AJz03. of total alkalis (KzO+NazO),and ratios of Si~/Alz03 similar to fine-grained detritalrocks (table 4, (.'ompare analysis 2 with analyses 8-10).KYANITE-BEARING GNEISSKyanite (AlzSi05) is present in at least three localitiesin the Early Proterozoic gneiss terrane of the Gold Basin­Lost Basin districts. and it has been reported only fromabout 12 widespread localities across aU three Proterozoicmetamorphic belts of Arizona (Espenshade, 1969; Gal·braith and Brennan, 1970). However, kyanite may occurmore commonly in the Proterozoic rocks of Arizona thanbelieved previously because systematic petrographic examinationofsome relatively highly metamorphosed. EarlyProterozoic Pinal Schist at Mineral Mountain southeastof Phoenix (Theodore and others, 1978) revealed its presencethere also (T.G. Theodore, unpub. data, 1979). Indeed.,the anhydrous chemistry of kyanite and its polymorphs,sillimanite and andalusite, make paragenesesinvolving these minerals excellent diagnostic pressuretemperatureindicators for moderate temperature regionallymetamorphosed pelitic assemblages (Kepezhinskasand Khlestov, 1977; and many others). As describedbelow, one can make certain barometric inferences fromkyanite and sillimanite parageneses using the appropriatethermodynamically generated equilibrium curves and theappropriate experimentally determined phase relations(Helgeson and others, 1978, fig. 49). Early progradeassemblages in kyanite-bearing pelitic paragneiss in theGold Basin-Lost Basin districts include:kyanite-quartz-tourmaline-opaque mineral (3)kyanite-biotite-quartz ± magnetite(?)±graphite±apatite. (4)The kyanite-bearing assemblages (3) and (4) were foundat three widely separated localities in the districts.Assemblage (3) is present in gneissic schlieren within amixed granodioritic complex (unit Xmg of figure 2) on thelower west flanks of Gamet Mountain (SWI/4 sec. 15, T.28 N., R. 17 W.). Assemblage (4) is present in samplescollected from two localities: the first is in a thin layerof pelitic biotite schist within foliated and lineated hornblendeamphibolite on the west flank of the Lost BasinRange (SEI/4 sec. 18, T. 29 N., R. 17 W.), and the secondlocality is in migmatitic gneiss that crops out in GrapevineWash, approximately 2.5 km southwest of the GrandWash Cliffs. This last sample locality containing kyaniteassemblage (4) falls well within the projected outer limitof the suite of Early Proterozoic plutonic igneous rocksexposed predominantly in the general area of GarnetMountain. Thus, two of the kyanite-bearing assemblagesarc related spatially with the igneous rocks of GarnetMountain.The kyanite-bearing assemblages known in the GarnetMountain quadrangle now appear to be of two genetictypes. The first includes locally preserved relicts initiallycrystallized prior to and separately from the enclosingschist and possibly shed detritally into the metamorphicterrane's protolith or. more likely, preserved in situ froman earlier stage of the metamorphic event. The otherkyanite-bearing assemblage crystallized syntectonically,penecontemporaneous with development of the enclosingschistose fabric, which is strongly lineated. The firstassemblage in fact shows textural relations strongly suggestingphysicochemical incompatibility with its enclosingphyllosilicate-dominant fabric. Kyanite in assemblage(4) thus is present in 0.6- to 1.0-mm, sieve-textured clotscontaining minute, highly rounded crystals of quartz.These cry.,tals of quartz are aligned in trains defining ssurfacesat very high angles to the schistosity in a quartzmuscovite-chlorite-albite-cordierite(?)fine-grained schist.In addition, the kyanite is altered partially along its rimsto white mica, probably muscovite (fig. 12.4). Kyanite inone of the two samples of assemblage (4) shows a verystrong preferred orientation ofits c axis which lies in. and

28 GEOLOGY AND GOLD MINERALIZATION m' THE GOLD BASIN·LOST BASIN MIl'.'1NG DISTRICTS, ARIWNApartly defines, the foliation of sample GM-283 (fig. 128).Kyanite and biotite are apparently compatible in this sam·pie because they are juxtaposed along sharp, straightcrystal contacts showing athigh magnifications no indicationin either mineral of replacement by the other (fig.128). In addition, the kyanite in this rock shows relationsindicative of partial replacement by two subsequentgenerations of muscovite. The two generations of muscovitecomprise (1) large single crystals and (2) very finegrained crystals of muscovite aggregated into microveinletsthat cut the earlier crystallized kyanite. We wantto emphasize again that the important feature of sampleGM·283 is its apparent hosting of syntectonically crystallizedkyanite. Finally, two of the kyanit.e-bearing samplesstudied (samples GM-283 and GM-IOlOc)oontain anotherAI2Si05 polymorph, sillimanite. However. the twominerals in these samples do not show textural relationsof apparent mutual compatibility. Sillimanite appears topostdate crystallization ofkyanite. In sample GM-IOIOc.fibrous sillimanite partly replaces kyanite as a directnucleation product. but more commonly sillimanite replacesan intervening muscovite, possibly by a paired orA~_.. '',-,'0;' ..lU.atETEII.-co 0.6 ..I.UIIII£IIIt'--,---~,8,'-__---"".66 ..lI.J.JIO£TEIt'~,~o,!- MUJIoOETUIfo'IGliRE 12.-Tenul'lli relationll of kyanite. Plane-polarized lighL D,biotite; K, k)'af\ite; 0, opaque mineral; Q, quartz; S, sillimanite; T,tourmaline. A, Clot or k)1UUte containing quartz.. tourmaline, andopaque mineral Kyanite is partiallyaltered~ its rim to ....il.ite mica(M, pl"Obably muaeovite). Sample GM-235; SW'4 see. 15, T. 28 N., R17 W. B, ~'oliation defined partly by \-ef)' strong prefen-ed orientationof!c)'anite c:: axes thatlie in plane offoliatiorl and by dimensional·Iy oriented flakes of biotite; M, postkyanite .....hite mica porphyroblast(probably mullCOYite). Sample GM·283, SE'4 sec. 18, T. 2S N., R 17W. C. K)'anite and biotite in oontaci with each other and shooAing novisible signs of mutual incompatibi.lit)'. Sample GM-283, SEV. sec. 18,T. 29 N., R 17 W. D, A91emblage ofkyanite, quartz, and biotite sh0wingpattial replaoement of k)1UUte by white mica eM, probablymUlICO\'ite), .....hich is in tum partially repIaoed by fibrous sillimanite.Sample GM·IOlOe, NWV. sec. 21, T. 29 N., R. 16 W.

PETROCHEMISTRY OF CRYSI'ALLINE ROCKS 29cyclic reaction (Cannichael, 1969). [n sample GM-283,fibrous sillimanite partly replaces biotite in a quartz-richdomain of the rock that contains no kyanite.SILLIMANITE- AND CORDIERITE·BEARINGGNEISS AND SCHISTSillimanite- and cordierite-bearing gneiss and schist inthe Early Proterozoic metamorphic rocks show complexcompatibilities, manyofwhich are confined to very smalldomains (table 5). Textural and fiekl relations documentedduring our petrologic studies suggest that some initiallyvery high grade assemblages developed in these rocks,including:garnel-sillimanite(1).biotif.e.quartz:t potassium feldspar:t plagioclase:t opaque minera1(s):t hercynite (5)biotit.e-sillimanite-quartz-opaque mineral (6)sillimanite-quartz:t muscovite:t rutile (7)cordierite·biotite-quartz±garnet± plagioclase±potassium feldspar±rutile (8)oordierite-sillimanite·hercynite-quartz·potassium feldspar-plagioclase. (9)Garnet, presumably rich in the almandine molecular endmember, in muscovite-free assemblage (5) containsisolated apparently stable inclusions of biotite, quartz,opaque mineral(s), plagioclase (in trace amounts), and hercynite(in trace amounts), thereby oorroborating ourjudg·ment that these minerals together constitute one of theTABU: So -GmtporiU tU8tIIIbllIgetill riUimmtiU- axd ~rUIg~ cn&d -eJWt ill Owl Eo.rly Proternwie Mtto.morp\ic rot:b til 1M gl'MnJio.nn ofIiwl Gold fkuUl..u.t Bo..riK ftIilltll9 districU[X, ....... ~Tr......... ~in"-_-._~r.~_1SaIIple ----- GII-ll3-' ....'25 GM-126a GM-l26b ....,.. ~06 G~101Oc lG~1010e ~1077Quartz ______X X X X X X X X XBiotite X X X XX X XGarnet _________X X X XSillimanite ________ X X X X X X X X XPotaulU11l feldspar - X X X X X X XPlagioclase ______ T, X X X X X X XWhite mica__ T, T, 'X X X X XCord1erite X X X XHercynite _____X X XOpaque ~ineral(s) -- 1< X X X T, X T, T,Rutile ________XT, XApatiteXZircon T, T, 1< 1< 1< 1< T, 1-116 Gt'>-116b G1'.-126a-1 Gt'>-135 GH-1010b Gt'>-111]11 Gt'>-126cQUllrtz. X X X X X X X X XBiotit____ X X X X X X X X XGlIrnet X X X X X X X XSilli~nlte -----__ X XPotassium feldspar - X X T, X X X X XPlagioclaseXX1< XWhitw ~icll 'X Ix IxIx 'r, t,Cordierite ______ X X X X X 1

30 GEOLOGY Ai'\'D GOLD MINERAliZATION Of THE GOLD BASIN·LOST BASIN MINING DISTRICTS, ARIZONAearliest stable assemblages in the gneiss. However, theparagenetic position ofsillimanite in garnet-biotite assemblage(5) is problematicaL Careful examination ofgarnetsillimanitetextural relations reveals the crystals ofgarnetto be corroded marginally and embayed locally by stoutcrystals of sillimanite (fig. 1M). Further, excellent texturalevidence in such rocks shows that garnet is veinedand partially replaced by assemblage (6). Nonetheless,many garnet crystals contain swarms of very fine grainedneedlelike crystals of sillimanite aligned parallel to thetrace of the flowlines in the enclosing matrix of gneiss.Such sillimanite elsewhere has been interpreted by others(Reinhardt, 1968) as an early relict phase initially stablewith its host garnet as a two-phase subsystem. However,the overall fabric of such needles of sillimanite in garnethere suggests to us that crystallization of these needlesoccurred penecontemporaneously with the crystallizationof the surrounding stout sillimanite, which in places embaysand thus somewhat postdates the parageneticallyearlier garnet. Nonetheless, because textural criteria arehighly interpretive as to compatibilities and because somebiotite seems to have replaced an early sillimanite (fig.138), we assign sillimanite tentatively as a queried phasein early assemblage (5).D '-l --"o,~ ..lLI.IMfTUlFIGURE 13.-Textural relations ofsillimanite. Plane-polarized light. A,Embayed IU1d highly corroded crysta.l ofgarnet (G) showing replacementand microveining by assemblage of biotite (B), sillimanite (5),quartz(Q), and opaque mineral(O). Sample GM-406. B, Greenish·brownbiotite (8) completely replacing pseudomorphieaUy earlier crystallizedsillimanite in l-em-Iong Iensoid domains within IU1 assemblage ofgarnet, biotite (red-brown, Z axis), cordierite, pIagjoclase(Anlly, andquartt, where biotite is partially replseed by serpentine. SampleGM·I25. C, Sillimanite (5) partially replaced by biotite (B). SampleGM·406. D, Rounded porphyroclasts of garnet (G) in a qUllrtr. (Q)­5illimanite (5) mylonitic schist. Sillimanite is apparently replacing Ixlthgarnet and biotite (B). Sample GM-83-1.

Sillimanite shows additional apparently metastable-relationswith biotite and muscovite in the gneiss and schist.Some sillimanite appears to be in the initial stages ofreplacement by biotite (fig. 13C). Most of this biotite thatpartly or wholly replaces sillimanite is various shades ofgreenish brown (Z axis) W1der plane light in contrast tothe more typical reddish-brown (Z axis) cdorsofthe otherbiotites. We have already briefly described the growth ofsillimanite in muscovite, which previously had replacedkyanite (fig. 12D). Such textural relations among thesethree minerals may be interpreted most simply as reflectingthe following cyclic orpaired reactions wherein muscoviteoccurs as an intermediate phase (Carmichael, 1969):3 kyanite+3 quartz+2K ++3H~2 muscovite +2H +(10)2 musoovite+2H+-3 sillimanite+2K+. (11)A critical implication of reactions (10) and (11) is theapparent immobility of A13+ (Carmichael, 1969). However,as pointed out by Glen (1979), if overall volumetricchanges and half reactions in physically separate domainsof the rocks during metamorphism also are considered insuch metapelites. then some elements (A13+, Si 4 +) mayindeed be relatively mobile.The metamorphic rocks thus contain textural evidencedocumenting repeated and possibly prolonged periods ofsillimanite crystallization after the onsetofcrystallizationof a biotite-gamet-quartz±potassium feldspar±plagioclase±opaque minerals ± hercynite assemblage. Thepelitic gneiss also may have included sillimanite as an earlyphase.Some high-grade-metamorphic rocks host an assemblageofquartz and sillimanite, (7), which together makeup the bulk of the blastomylonitic matrix of these rocks(fig. laD). These mylonitic rocks crop outdiscontinuouslyin the metamorphic terrane, and the white mica in themis present as poorly developed coronas that surrOW1dsillimanite. In these rocks, which also contain previouslycrystallized porphyroclasts of garnet and biotite, thephyllonitic structure is defined mostly by sillimanite,which crystallized preferentially along the mylonitic s sur·face. In addition, quartz shows a strong crystallographicand dimensional orientation wherein the orientations ofits 0001 axes coincide closely with the s surface of themylonite. Although quartz in the matrix of the blastomyloniticrocks shows complex and highly sutured boundaries,the bulk of the quartz is strain free and t.riple jW1Ctionsof 120 0dihedral angles are common. In somemylonitic rocks. white mica partly replaces sillimanite andmay reflect continued late-stage mylonitization underhydrous conditions. Thus, local mylonitization apparentlyoccurred initially during the metamorphic peak of theregion at upper·amphibolite-facies conditions, and perhapscontinued sporadically into the subsequent greenschistmetamorphism (see fig. 7).PETROCHEMIS1"RY OF CRYSrALLINE ROCKS 31The cordierite-bearing rocks most commonly include acordierite-biotite-garnet-potassium feldspar association,(8) (table 5), which does not contain white mica that isparagenetically the same age as the cordierite. The bulkof the white mica in the cordierite-bearing assemblage(table 5) is a very late mineral that partly replaces feklsparand (or) cordieritein the rocks. Thus, the progressive andconsistent decrease in the modal abundance ofearly whitemica in these rocks suggests that the peak of the progrademetamorphism occurred at physical conditions whereinthe white mica-quartz assemblage was not stable. Althoughcordierite isograds elsewhere commonly have beenmapped fairly concisely as halos around intrusive rocksemplaced into metapelitic terranes (Loomis, 1979; andmany others), we have established only a very approximateboundary for the distribution of con::l.ierite in theGold Basin-Lost Basin districts. Con::l.ierite in the districtsseems generally to be confined to relatively fresh nonretrogradedmetamorphic rocks associated spatially withthe suite of Early Proterozoic igneous rocks that crop out.in the general area ofGarnet Mountain east of the traceof the Grand Wash fault zone and northeast of the intersectionof the inferred traces of the Grand Wash andHualapai Valley faults. In these rocks, cordierite does notreflect thermal recrystallization during a relatively drynondynamic contact event related primarily to fmalemplacement of nearby igneous rocks. Cordierite in manyof these rocks forms an integral part of the gneissic fabricof the g'.lrnet-biotite assemblage(s). Many of the rocks containingcordierite are metamorphic schlieren and pendantsof metapelites engulfed by more widespread igneousrocks. However, many pelitic rocks in these schlieren andpendants do not contain cordierite very close to their contactswith adjoining plutonic igneous rocks. Some peliticmigmatitic gneiss within 3 m of very large Early Proterozoicigneous bodies show quartz+biotite + plagioclase(oligoclase to even albite, in places)+microcline±whitemica ±garnet composite assemblages but also includecarbonate and clinozoisite-epidote alteration of earlierplagioclase. The only contact phenomena noted are theporphyroblastic growthsofwhite mica and feldspar (bothalbite and microcline) and the alteration of plagioclase.Cordierite, as listed in reactions (8) and (9), is presentin at least two parageneses in nonretrograded peliticgneiss and migmatite. The more common, and probablyearly, association is with biotite and garnet (table 5), anassociation (8) that partly defines the schistose fabric ofthe host pelitic gneiss. Presumably early cordierite is alsopresent with biotite and garnet in the melanosome(Mehnert, 1968), or dark portion of migmatites, againstwhich the light micropegmatitic portion, or leuoosome, apparentlyhas advanced (fW- 14A). We herein use the termsmelanosome and leucosome in a purely descriptive sense.It is beyond the intended scope of our present study to

32 GEOLOGY AND GOLD MINERALIZATION Ot' THE GOLD BASIN·LOST BASlN MINING D1STRlCI'S, ARIZONAattempt a full documentation of the overall genesis ofthese extremely complex rocks. For example, we have notestablished whether the melanosomes reflect simply anin situ residue from the parent rock (paJeosome ofMehnert, 1968) or whether the melanosomes are chemicallytransformed even partially. However, modal analysesof adjoining layers of melanosomes and leucosomes inthese rocks show approximately equivalent abundancesof the felsic minerals (quartz and feldspars). The majordifference between the two is the almost complete absenceof biotite from the leucosome whereas the melanosomeA',-,:::;o~~Ltypically includes about 25 volume percent biotite.Further, in the melanosome some cordierite is concentratedin biotite-potassium feldspar (mostly microcIine)­plagioclase (An2(}-zs) domains away from garnet-quartzdomains. Within these latter domains, xeooblastic garnetalso commonly shows highly irregular skeletal outlinesresulting from its growth along quartz crystal boundaries.In the melanosomes, garnet appears to be associatedstably with biotite. Biotite shows invariably an increasedabundance within about 0.2 mm ofthe sharply adjoiningleucosome, especially along fronts convex toward themelanosome. The leucosomes of these migmatitic rockscommonly contain a cordierite-sillimanite-hercyniteassemblage (9) (fig. 148). Contents of Al,o, and K,

PETROCHEMISTRY OF CRYSTALLINE ROCKS 33place the triple point in the system Al20g-Si02-H20 at approximately370 Mpa and 500°C, or close to the 510 °Cand 400 MPa coordinates of the triple point proposed byNewton (1966) and Holdaway (1971). We cannot ascertainhow far beyond the kyanite-sillimanite transition thekyanite initially crystallized. However, this crystallizationmay not have been far from the transition, becausekyanite was found to occur only sparingly, althoughunknown amounts of kyanite may have been destroyedduring the widespread retrograde metamorphism of thearea. Further, Kepezhinskas and Khlestov (1977) cautionedthat the boundaries of the PT stability regions ofnaturally occurring aluminosilicates may in fact be not sowell defined. They envision the boundaries to contain afield in PT space rather than a line. Nonetheless, theoverall transition from kyanite to sillimanite must reflectan increase in the geothermal gradient that created theregional metamorphic maximum for the area. Assemblagesof Fe-Mg cordierite that include potassium feldsparand that occurred at PT conditions of muscovite-quartzinstability define extremely wide ranging stability fieldsthat also are a function of PH 20 (Holdaway and Lee,1977). Holdaway and Lee (1977) showed that under suchconditions and at PHzO = P tot but still below the granitesolidus, Mg cordierite +potassium feldspar +vapor isstable to a maximum pressure ofabout 500 MPa whereasat P H2 0 = 0.4 Ptot. this assemblage is stable to about600 MPa. These pressures are probably reasonable upperpressure limits to the cordierite- and sillimanite-bearingassemblages created during the prograde Early Proterozoicregional metamorphic event in the districts. Last,the absence of hypersthene from the cordierite-bearingassemblages suggests that the upper-temperature stabilitylimit ofcordierite here did not exceed a biotite +quartzbreakdown reaction (see Hess, 1969).Q.UARTZOFELDSPATHIC GNEISSEpiclastic rocks, best termed quartzofeldspathic gneiss,are probably the most common rock type in the mappedEarly Proterozoic gneiss. However, quartzofeldspathicgneiss typically does not make up extensive monolithologicsequences ofgneiss throughout the unit. Instead, thequartzofeldspathic gneiss is interlayered with many otherlithologies, including amphibolite and marble. Locally, thinlayers of quartzofeldspathic gneiss are present withinlarger masses of amphibolite; some of these masses of amphiboliteare large enough to be shown as separate mapunits (see Blacet, 1975), and others are included withinthe rocks mapped as paragneiss by him. In the amphibolite,the quartzofeldspathic gneiss ranges from sharplydefined layers a few millimeters to as much as 20 em thick.However, either of these rocks, quartzofeldspathic gneissor amphibolite, locally may grade into the other by interbeddingacross an interval of2 to 3 m. In fact, quartzofeldspathicgneiss and amphibolite together impart abanded aspect to many outcrops within the gneiss unit.These outcrops may be nearly homoclinal sequences ofrock, or they may be complexly isoclinally folded at theoutcrop scale. In addition, some ofthe thicker sequencesof quartzofeldspathic gneiss show sporadic pegmatoidclots, inferred to be "sweatouts," that formed during thepeak ofprograde regional metamorphism. These clots consistof, in decreasing abundance, feldspar, quartz, andbiotite, and they show gradational boundaries with thesurrounding more uniformly sized quartzofeldspathicgneiss. Further, layering throughout the quartzofeldspathicgneiss provided the local structural controls thatdetermined the attitude and geometry of subsequently introducedquartz+sulfide lenses and (or) veins that will bediscussed in the section "Gold Deposits and Occurrences."MicroclineAOrthoclaseBOrthoclaseFIGURE 15.-Thompson (1957) projected AFM diagrams for medium-pressure progressive metamorphism. Small dots at Al 2 0 S (A), FeO (F), andMgO (M). Large dots, assemblages pbserved in metamorphic rocks from Gold Basin-Lost Basin districts. A, Kyanite zone. B, Sillimanite zone.

34 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONABy using a microscope, visual estimates of representativesamples of quartzofeldspathic gneiss reveal thatmany samples may have consisted of mostly quartz andoligoclase prior to metamorphism. Polycrystalline quartzgrains that are round to subround are fairly common inthe size range 0.1 to 0.4 mm. These relations suggest thatthe protolith of the quartzofeldspathic gneiss consistedof fine-grained arkosic to possibly subarkosic sandstone,on the basis of the classification of McBride (1963). Wehave not recognized any lithic fragments in the samplesstudied. The polycrystalline quartz grains show very complexsutured intragranular crystal boundaries for the mostpart, but many grains have retained their overall subroundedto well-rounded detrital outlines through thesuperposed metamorphic events. Although oligoclase wasprobably the predominant feldspar in most samples priorto metamorphism, it now has been replaced variably inmost samples by a very finely crystallized shreddy aggregateof white mica, chlorite, actinolite, sphene (trace), andopaque minerals (including some ilmenite), with or withoutepidote-clinozoisite, calcite, and albite. This assemblageof minerals, predominantly reflecting the retrograde800Ul-.J~uUl~a..~(9w ~ 400~Wa:::;)UlUlwa:a..6002000'-----'-----'------'-__...L...._---l._~..L-_--.J200KyaniteAndalusite400600TEMPERATURE, IN DEGREES CELSIUSFIGURE 16.-Equilibrium curves generated from thermodynamic databy Helgeson and others (1978) in system AI 0 2 a -Si0 2 -H 20 at highpressures and temperatures. Dashed lines indicate metastable projectionsof equilibrium curves.metamorphic event, is also present as a matrix which supportsthe quartz and feldspar framework minerals.However, the intense development of retrograde assemblagesin the plagioclase feldspars and matrix generallyobscures significantly the premetamorphic textural relationsin the rocks between framework feldspars andmatrix. In fact, the matrix may have consisted of veryfine granules of plagioclase, including varying amountsof diagenetic phyllosilicate minerals and minor amountsof calcite cement. Although relict oligoclase grains are theonly recognizable feldspar in many samples of the quartzofeldspathicgneiss, overall plagioclase to potassium feldsparratios are inferred to have varied highly prior tometamorphism. Some samples contain oligoclase to potassiumfeldspar ratios of approximately 10 to 1. The potassiumfeldspar, including both perthite and locally abundantmicrocline, typically has not been replaced by mineralassemblages diagnostic of the retrograde event. Heavyminerals in the quartzofeldspathic gneiss include 0.01- to0.05-mm-wide subrounded prisms to well-rounded ellipsoidsof zircon and, less commonly, sphene and apatite.Chemical analyses of four samples of quartzofeldspathicgneiss (table 4, analyses 3-6) reveal compositions mostsimilar to published analyses of eugeoclinal sandstone orgraywacke. The content of Si02 in these analyzed samplesof quartzofeldspathic gneiss ranges from 72.3 to 76.3weight percent, only slightly higher than the 71 weightpercent geometric mean determined for the eugeosynclinalgraywackes by Middleton (1960). However, themean Si02 content of 61 graywackes (table 4, analysis 10)compiled by Pettijohn (1963) is 66.7 weight percent. Further,the analyses of quartzofeldspathic gneiss show lowK20 to Na20 ratios that range from 0.23 to 0.48 (table4). Such low ratios are a feature common to graywackes(Middleton, 1960; Pettijohn, 1963, fig. 2), but they aresomewhat lower than the 0.69 ratio of K20 to Na20 inthe average graywacke (table 4, analysis 10), and significantlylower than the 1.9 ratio in the average arkose(table 4, analysis 11). The low ratios ofless than one confirmour petrographic estimates for the overall low ratioof potassium feldspar to plagioclase in the detrital frameworkminerals. In addition, the content of Al203 in theserocks ranges from 12.3 to 14.0 weight percent, which isclose to the mean value of 13.5 (Pettijohn, 1963) but issignificantly higher than the 8.7 weight percent meanAl20 3 content of arkose (table 4, analysis 11). The contentsof CaO in the four rocks range from 2.1 to 4.3 weightpercent; thus they are not much different from the 2.5and 2.7 weight percent content of CaO in the averagegraywacke and arkose. Such contents of CaO in the foursamples of quartzofeldspathic gneiss are somewhat higherthan the contents of CaO reported for the Early ProterozoicVishnu Complex by Brown and others (1979; fig.17). MgO in the quartzofeldspathic gneiss analyzed ranges

PETROCHEMISTRY OF CRYSTALLINE ROCKS 35from 0.4 to 1.7 weight percent and is thus less than themean MgO composition of 61 graywackes (2.1 weight percent;table 4, analysis 10). Such low contents ofMgO mayreflect the very low content oflithic volcanic detritus shedinto the protolith of the gneiss. Although these chemicalanalyses of quartzofeldspathic gneiss from the Gold Basin­Lost Basin mining districts show similarities generally tograywacke, all of these samples have been affectedmoderately to strongly by retrograde alteration phenomena.The rocks have been subjected to severed intense andprolonged metamorphic events and weathering phenomenathat contributed to the final chemical composition ofthe gneiss. 1'he chemical changes, if any, that accompaniedeach of the events cannot be ascertained.AMPHIBOLITEAmphibolite bodies of varying sizes are presentthroughout the Proterozoic metamorphic terrane in theGold Basin-Lost Basin mining districts. However, only afew of these amphibolite bodies are shown as separate'O',--;;;;:-_~~~ ~ _'0"z• u•••"I0"• '0•"z•"z0u~.."••'OooL-------,cC-;:------.,O-----,!2.0 4.0 6.0CaO CONTENT. IN WEIGHT PERCENTFiCURe 17.-Si~ versus Cao in four sample!:! (dotll) of quaJ1.zofeJdspathiegneiss (analyses 3-6. table 4); field (shaded area) establishedby Brown and others(l979) for 16 analyses oflTl4JtAsedimentary rocksfrom the Early Proteromie Vishnu Complex of Brown and others(1979).map units in the district-wide geologic map by Blacet(1975) because of the scale of the quadrangle map, theirdiscontinuous structure, and the overall highly irregularsize distribution of many individual outcrops. Most amphiboliteis present within the gneiss (fig. 2, unit Xgn),which includes mainly quartzofeldspathic gneiss asdescribed previously. Lesser amounts of amphibolite arepresent in the migmatitic units and also scattered aspendants in the various Early Proterozoic igneous rocks.In the gneiss unit, some outcrops consist of 30-m-thicklayers that are as much as 80 to 90 percent dark-greengrayto dark-greenish-black to black amphibolite (see fig.58). Such masses of amphibolite may grade across severalmeters into quartzofeldspathic gneiss by decreasednumbers oflayers of amphibolite along strike of the foliation.Layers of amphibolite also may terminate abruptlyor be crosscut by coarse-grained, quartz-feldspar-richleucogranite which in tum then grades into the surroundingquartzofeldspathic gneiss. The overall abundance ofamphibolite in the Proterozoic terrane here in the GoldBasin-Lost Basin mining districts is much greater thanin similar metamorphic terranes just to the north aroundLake Mead (P.M. Blacet, unpub. data, 1967-72). However,even within the districts themselves there is a widevariation in the proportion of amphibolite in the EarlyProterozoic gneiss map unit (fig. 2). Near the south endof the Lost Basin Range, amphibolite is derived largelyfrom igneous protoliths, an assessment based on the occurrenceof widespread relict gabbroic and diabasic textures.Careful examination of outcrops there furtherreveals that rarely some amphibolite definitely crosscutsthe lithologic layering in the enclosing paraschist andparagneiss and clearly shows preserved chilled marginsagainst these rocks.Amphibolite in the Proterozoic terrane is eithermassive, showing no readily apparent macroscopic structure,or more commonly it contains a well-developedfabric. Generally, the fabric consists of at least one obviousfoliation and possibly a less well-developed lineation.The principal foliation (sd is defined by millimeter-sizelayers of different compositions and by differences ingrain size between adjoining domains of similar mineralogy(fig. 1M). Most commonly, the attitude of SI in theamphibolite is the sameas that in the surrounding gneiss,and 81 may be better developed near the margins of theamphibolite bodies. Lineation in the amphibolite locallyis defined by a strong preferred orientation ofamphibolecrystals within 81. In addition, other types of lineation inamphibolite include minor fold axes and well-developedmullion structures consisting of aggregates of hornblendeshowing a strong preferred orientation of their [001] axesparallel to the mullions. The fold axes and mullion structurescommonly are coaxial. lsoclinally folded amphiboliteinterlayered with quartzofeldspathic gneiss is especially

36 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOS'f BASIN MINING DISTRICTS, ARIWNAabundant along the west flank of the Lost Basin Range.Lineation in amphibolite may also be defined by the intersectionof a subsequent fracture cleavage (80 with 81.Locally, in amphibolite, ripplelike corrugations on 81plunge shallowly (about 10°) and reflect the intersectionof 81 with the S2 fracture cleavage. Typically, such S2 frac·ture cleavages are more widely spaced than the 8} layering.In addition, chloritization occurred ooncurrently withthe development of 82, and thus the fracture cleavageFIGURE 18.-Stucture llIld textures obsen'oo in amphibolite. A, amphibole;Q, quartz:; P, plagioclase or retrogrnde aheration productsof plagiodaae, including white mka, carbonate, and cla}'(s). A. Principalfoliation ('1) defined by tithokJgic Ia}'cring of varying compositionLSample GM-290, 5Eo,I, IiOC- 18, T. 29 N., R. 17 W. B, Fabricof hombleflde.clinop)'1'Oxene-pIagioclase (A~-biotite (B) amphiloIiteCf)1Itallizedat upper-~facieI;

PETROCHEMISTRY OF CRYSTALLINE ROCKS 37The protolith for many individual outcrops of amphiboliteor cluster of outcrops can be ascertained primarilyusing relict textures or geologic field relations withother lithologies of known provenance. In addition, wehave supplemented and refined these observations byextensive microscopic examination of thin sections of amphiboliteand chemical analyses of a few selected samplesof amphibolite in this report and reported elsewhere (Pageand others, 1986). However, some of the amphiboliteexposed in the districts cannot be classified as to protolithbecause of the absence of diagnostic macroscopic,microscopic, or chemical criteria. Locally, amphibolite inthe gneiss derived from a sedimentary protolith includesrelict beds which consist of calc-silicate minerals andmarble and is finer grained than amphibolite derived fromigneous rocks. Some of these beds reach a maximumthickness of about 30 cm along a continuously exposedstrike length of about 15 m. The calc-silicate beds are conformablewith the layering in the adjoining amphibolite,and in places they neck down to about 2.5 cm or less. Thedelicate interlayering of many amphibolite layers withquartzofeldspathic beds a few millimeters to approximately20 cm thick is additional evidence for a sedimentaryorigin. This evidence for a sedimentary protolith for someamphibolite in the gneiss is especially convincing if werecall from our descriptions above that the quartzofeldspathicgneiss shows abundant textural and chemicalevidence for a sedimentary protolith. Lastly, we will showbelow that many hornblende crystals in this type of amphibolitehave trapped well-rounded to ovoid grains ofquartz that obviously had been through a sedimentarycycle.In all, 37 samples of amphibolite from 27 localities werestudied petrographically (table 6). Almost all of thesesamples contain mixed mineral assemblages, which reflectcrystallization during the Early Proterozoic upperamphibolite-faciesmetamorphism and retrograde metamorphismat greenschist conditions. The amphibolitelocally includes some cataclastic or mylonitic fabrics andfinally some local thermal and (or) hydrothermal alterationphenomena associated with Cretaceous plutonism andvein-type gold mineralization. The latter mineralogicchanges in a selected suite of amphibolite samples will bediscussed in the section entitled "Gold Deposits andOccurrences." Nonetheless, the mineral assemblageformed during anyone of the above events is relativelysimple. For example, amphibolite that shows the leastmodification by subsequent events contains a greenishbrownto brown (Z axis) hornblende-plagioclase (An70)­quartz-clinopyroxene-biotite (trace)-opaque mineralassemblage that includes apatite and sphene as minor accessories(fig. 18B). In outcrop, this 5- to 6-m-thick zoneof amphibolite shows a sparkling fresh granoblastic fabricand is present within some garnet-biotite migmatiticgneiss. Red-brown (Z axis) biotite in trace amounts is apparentlycompatible with the other minerals in the assemblage.Normally zoned very calcic plagioclase (An70) ispresent as generally untwinned, stubby to equant prisms.Miyashiro (1973) and Mason (1978), and many others, havenoted the general tendency for the calcium content ofplagioclase to increase and the color of hornblende to gofrom blue green to various shades of brown during an increasein the grade of metamorphism of metabasites fromthe lower to the upper amphibolite facies. These relationsare present in amphibolite from the Gold Basin-Lost Basindistricts (table 6) and suggest the amphibolite reachedprograde metamorphic peaks similar perhaps to zone-Cmetabasites in the low-pressure central Abukuma Plateau,Japan (Miyashiro, 1958), or to zone-B metabasites in themedium-pressure Broken Hill area, Australia (Binns,1965a, b, c).Quartz makes up a significant proportion of many ofthe samples of amphibolite and is present in all but fiveof the samples studied (table 6). Quartz in these rocks isof several different parageneses. Some quartz is premetamorphicand is from the protolith of the amphibolite,whereas the bulk of the quartz crystallized either duringthe prograde or the retrograde events. The hornblendein some samples includes abundant, small, well-rounded,monocrystalline grains of quartz and much lesser quantitiesof rounded grains of plagioclase. Such quartz inplaces is rimmed partially by an extremely fine grainedunknown silicate. Many such grains of quartz werestrained moderately and are inferred to reflect relictdetrital quartz grains engulfed by a subsequent overgrowthof hornblende during the upper-amphibolite-faciesmetamorphism of the area (fig. 18C). The fabric of muchof the quartz that recrystallized during either the earlyamphibolite-facies metamorphism or the subsequentgreenschist and contact events differs markedly fromthese grains of quartz showing well-rounded outlines.Such metamorphic quartz typically has a blebby orshredded overall aspect and is associated very closely withblue-green (Z axis) hornblende and (or) tremolite-actinolitethat replaces partially the early green or brown hornblende.The quartz-quartz boundaries in such associationsare very complexly sutured. Further, contact effects arenotable in outcrops of some amphibolite as much as 3 mfrom the Cretaceous two-mica monzogranite that cropsout in the southern part of the Gold Basin district. Underthe microscope, such rock shows a well-developed granoblastictexture of tightly intergrown fine-grained crystalsof mostly blue green (Z axis) hornblende and quartz (fig.18D).Some quartz-free metabasite in the gneiss was probablyderived from clinopyroxenite. Such metabasite includesblack, dense, highly magnetic rocks that locally arelayered and that crop out predominantly along a strike

Ci:l00TABLE 6.-Composite mineral assemblages in amphibolite and altered amphibolite from the Gold Basin-Lost Basin mining districts[Color of am¥hibole under microscope is down Z axis using plane-rcolarized li~ht. Biotite is present as primary and (or) secondary mineral. TremoIite-actinolite, epidote group, chlorite, white mica, and carbonate minerals aTe present mostlyas part 0 regional greenschist retrograde assemblage and (or) Deal hydrot ermal assemblage adjacent to mineralized veins. X. mineral present; Tr, present in trace amounts; 50, An content ofplagioclase; ----, not found;?, presence uncertain]AmphiboleSample Blue Gray green to Green brown Opaque Tremolite Epidote Whitegreen olive-gray green to brown Quartz Plagioclase Clinopyroxene Biotite minera Is Apatite Sphene actinolite group Chlorite mica CarbonateGM-92a ------ ---- X ---- X Tr ---- ---- X ---- ---- ---- XGM-124 ------ ---- X ---- X X X X X Tr ---- ---- ---- X TrGM-191 ------ X ---- ---- ---- ---- ---- ---- X X ---- ---- X X ---GM-191a ----- X ---- ---- Tr X ---- ---- X X X ---- X ---- ---- XGM-209 ------ ---- X ---- X ---- ---- ---- Tr ---- Tr ---- X X XGM-213 ------ ---- XI---- ---- Tr X ---- X 2 X ---- X ---- ---- X 3GM-213a ----- ---- X ---- ---- ---- ---- ---- X ---- X X ---- X ---- TrGM-242 ------ ---- X ---- Tr X ---- ---- X ---- ---- X X X ---- ?GH-246 ------ ---- ---- X X 40 ---- ---- X X ---- X X X X ---GM-254 ------ ---- ---- X Tr 30 ---- X ---- ---- X X X ---- XGM-290a ----- ---- ---- X X X ---- X ---- X ---- X X X ---GM-290 ------ ---- ---- X ---- Tr ---- ---- X Tr ---- ---- X X ---- XGM-298a ----- ---- ---- X ---- Tr ---- Tr X X X X X X ---- XGM-371 4 ----- X ---- ---- X 30 ---- X X X X ---- X X X ---GM-382a 5 ---- X ---- ---- X 30 ---- Tr X Tr X X X X XGM-382b 5 ---- X ---- ---- Tr 10 ---- ---- Tr X Tr X X X Tr XGH-382c 5 ---- ---- ---- ---- X 10 ---- X X X ---- X X X XGM-392d 5 ---- ---- ---- ---- X 10 ---- X X X ---- ---- ---- X Tr XGM-382e 5 ---- ---- ---- ---- X 10 ---- X X X ---- ---- X X XGM-412f ----- X ---- ---- Tr ---- ---- ---- X Tr X ---- X TrGM-461b ----- ---- ---- X X Tr ---- ---- X Tr ---- X X TrGM-468 ------ X ---- X X ---- X X X ---- X Tr XGH-529 ------ X ---- ---- X 35 ---- ---- X X ? ---- X X XGM-529a ----- X ---- ---- X X ---- ---- X X X ---- X X XGM-539 ------ X ---- ---- Tr ---- ---- Tr X X X ---- Tr X X XGM-634a ----- X ---- ---- Tr ---- ---- ---- X X X X X X ---- XGM-634a I ____X ---- ---- Tr ---- ---- ---- X X X ---- X X ---- XGM-665 ------ ---- X X X ---- ---- X X Tr X X X X TrGH-669 ------ ---- X ---- X Tr ---- ---- X X X X X X Tr TrGM-697 ------ X ---- ---- X X ---- X X X ---- X X X X TrGH-699 ------ ---- X ---- X X ---- X X X X X X X TrGM-855 ------ ---- X ---- X 65 ---- X X X X X Tr Tr TrGH-962 ------ X ---- Tr ---- ---- ---- X ---- X Tr X X ---- XGM-I063 ----- ---- ---- X X Tr X ---- X X ---- X X X TrGH-I063b ---- ---- ---- X X 55 X ---- X X ---- ---- X Tr TrGM-II 03. ---- X ---- ---- X 35 ---- X X X X ---- X X X TrGM-11I7 ----- ---- ---- X X 70 X X Tr X ---- ---- Tr ---- XlCummingtonite.21ncludes green spinel, and probable chromite.3Includes serpentine.41ncludes potassium feldspar in hairline microveinlets cutting metamorphic fabric of amphibolite; biotite is secondary.SSample included in alteration suite studied near a vein (see text and fig. 47>.~~o~~8 bis:~;:0~N?:3o zo'7j~l"j~t:l~UJZ t-

PETROCHEMISTRY OF CRYSTALLINE ROCKS 39length measuring about 100 m, as exemplified by locality213 (pI. 1, see table 11). Here the contacts of these rockswith the enclosing gneiss are obscured by rubble. However,close examination of these rocks reveals that theyare unquestionably pods of metamorphosed ultramaficrocks. These rocks are very magnesian in composition(page and others, 1986). They show marked petrologic differencesfrom the bulk of the amphibolite in the gneiss.Under the microscope, no evidence of an ophitic or subophitictexture common to most of the amphibolite derivedfrom gabbroic protoliths can be seen. The amphibole inthe metamorphosed ultramafic rocks is colorless to veryTABLE 7.-Analyses ofmafic rocksfrom the Early Proterozoic terranein the Gold Basin-Lost Basin mining districts[Chemical analyses by rapid-rock methods; analysts, P.L.D. Elmore and S. Botts. Methods usedare those descrihed m Shapiro and Brannock (1962), supplemented hy atomic absorption(Shapiro, 1967). Spectrographic analyses by Chris Heropoulos. Results are reported to thenearest numher in the senes 1, 0.7(. 0.5, 0.3, 0.2, 0.15, 0.1, 0.70, and so forth, whichrepresents approximate midpoints 0 interval data on a geometric scale. The precision ofa reported value is approximately plus or minus ODe series interval at 68-percent confidenceor two intervals at 95-percent confidence. Looked for but not found: Ag, As, Au, B, Bi,Cd, Mo, Ni, Pd, Pt, Sh, Sn, Te, U, W, Zn, Hf, In, Li, Re, Ta, Th, TI, Pr, Sm, Eu]Analysis --- 1Sample ------- GH-290a5a -------_ 0.05 0.03 0.02 0.05 0.03Co ---------__ .007 .005 .005 .005 .007Cr ------_ .1 .05 .001 .02 .02Cu ---------_ .007 .0015 .01 .007 .01Ni ---____Sc __________ .03 .01 .005 .01 .01.005 .005 .005 .005 .005Sr V ------_ __________ .03 .05 .05 .07 .03.02 .03 .03 .015 .05YZr-------- --________ .003 .002 .002 .003 .002.007 .005 .007 .01 .003Ga ------_ .0015 .0015 .002 .0015 .002Yb -------__ .0003 .0003 .0003 .0003 .0003Niggli values3GH-529Chemical analyses (weight peroent)4GH-5785GH-245SiO~ ------__ 46.0 49.6 55.2 47.5 45.0Al2 3 ------- 15 15.4 13.7 17.2 15.93.2 3.2 6.5 6.7 5.89.7 8.5 7.4 3 9.3~:tC-=:=--=HgO ------__ 8.4 5.7 3.9 6 5.7CaO ------- 10.5 10.5 8.3 10.1 10.9Na~o -----__ 2.1 2 2 2.7 1.5K2 ------ .70 1 .8 .40 .50":1 0 + ------- 1.3 1.1 1.5 1.2 1.9Ht- .03 .08 .06 1.3 .13T O 2 -------__ 1.3 1 1.4 1.2 1.7P2 0 5 ------- .15 .12 .24 .24 .16HuO -------_ .15 .22 .22 .12 .21CO2, --------- .11 .12

40 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONATABLE B.-Analysesfor minor metals in selected samples ofamphibolite and associated soil from the general area ofthe Bluebirdmine in the Lost Basin mining districtfSpectrogr~phic an~ys~s by ~eon A. Bradley. Results are rer.0rted to the nearest number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1, 0.07, and so forth, which representapproXl!Ilate mldpomts of mterval data on a geometric sea e. The precision of a reported value is approximately plus or minus one series interval at 68:percent confidenceor two mtErvalsat 95-percent confidence. Looked for but not found: Ag, As, Au, Bi, Cd, Mo, Pd, Pt, Sb Sn, Te. D, W, Hf, In, Li, Re, Ta, Th, Tl, Pr, Sm Eu; L, lessthan detErnunabon value; --, not detected; N.D.. not determined. Chemical analyses by Joseph Haffty, l.w. Haubert, and J. McDade using techniques of Haffty andRtley (1968) for Pd, Pt, and Rh; and Haffty, Haubert, and Page (1980) for Ir and RujAnalysis ------- 1 2 3 4 5 6 7 8Sample --------- 79GM-l 79GM-2 79GM-3 79GM-4 79GM-5 79GM-6 79GM-7 79GM-7aSemiquantitative spectrographic analyses (weight percent)B -------------- 0.002 L N.D.Ba ------------- .015 0.015 0.007 0.02 0.015 0.02 0.015 N.D.Co ------------- .007 .005 .003 .0007 .005 .003 .003 N.D.Cr ------------ .1 .3 .05 .007 .2 .07 .15 N.D.Cu ------------- .00015 .0007 .015 .0015 .007 .02 •015 N.D •Mn ------------- .15 .15 .1 .05 .07 .15 •1 N.D •Ni ------------- .007 .02 .01 .0015 .07 .015 .03 N.D.Pb ------------- .0015 .003 •0015 N.D •Sc ------------- .007 .005 .003 .001 .002 .003 •003 N.D •Sr ------------- .02 .01 .007 .015 .0015 .007 •01 N.D •V ------------- .07 .02 .015 .005 .01 .02 •015 N.D •Y -------------- L .003 .0015 .0015 L .0015 .0015 N.D.Zr ------------- .003 .0015 .0015 .0015 .003 •003 N.D •Ga ------------- .0015 .0015 .002 .0015 .001 .002 .0015 N.D.Chemical analyses (parts per million)Pd ------------- 0.029

PETROCHEMISTRY OF CRYSTALLINE ROCKS41TABLE 9.-Average major-element compositions, in weight percent, ofGold Basin-Lost Basin amphiboliteand various groups ofigneous rocks and other amphibolites[N.D., not determined]Analysis ------- 2 3 4 5 6 7 85i08----------- 50.3 49.9 49.58 57.94 48.87 52.8 49.3 55.5Al2 3 14.7 16.2 14.79 17.02 112.26 14.7 16.3 16.1Fe8 03 ---------- 4.3 3 3.38 3.27 11.89 4.5 2.5 2.8Fe ------------ 8.5 7.8 8.03 4.04 N.D. 6.6 8.5 5MgO ------------ 6 6.3 7.30 3.33 10.13 6.5 6 5.7CaO ------------ 9.8 9.8 10.36 6.79 9.84 8.8 10.7 6.9Na20 ----------- 2 2.8 2.37 3.48 1.91 2.5 3.1 3.4K20 ---------- .83 1.1 .43 1.62 1.90 .68 .59 1.7H20+ ---------- 1.3 1 •91 .83 N.D • 1.2 1.2 1.3H20- ---------- .06 N.D. .50 .34 N.D. .39 .10 .10Ti02 ----------- 1.2 1.6 1.98 .87 .62 1.1 1.1 .78P205 ----------.17 .30 .24 .21 .09 .15 .23 .32MnO ------------ .19 .17 .18 .14 .34 .19 .17 .12CO2 ------------ .09 N.D. .03 •05 N.D • .04 .18 .04Total ------ 99 100 100.08 99.93 97.85 100.2 100 100lTotal Fe calculated as Fe203.1. Average amphibolite, analyses 1-3 (table 6), this report.2. Average continental basalt (Manson, 1967, table III, p. 222).3. Average tholeiite (LeMaitre, 1976, No. 28).4. Average andesite (LeMaitre, 1976, No. 16).5. Selected amphibolite from Early Proterozoic Vishnu Schist in the Grand Canyon(Clark, 1979, table II, analysis 4).6. Average of five amphibolites in Early Proterozoic Pinal Schist from theMineral Mountain area, Arizona (T.G. Theodore, unpub. data, 1982).7. Average of 12 amphibolites from Condrey Mountain, Klamath Mountains, Calif.(Hotz, 1979, table 5, p. 16).8. Average amphibolite, central Beartooth Mountains, Montana-Wyoming(Armbrustmacher and Simons, 1977).a diagram, the analyzed diabase appears to be less differentiatedthan the three analyzed amphibolite samples.On a Niggli c versus Niggli al-alk diagram, the data forthe amphibolite again cluster and fall just outside thevalues most expected for shale-carbonate mixtures butstill within a field of possible values for shale-carbonatemixtures (fig. 21). Again, the clustering of the smallnumber of data points (three amphibolite, and onepyroxene-banded gneiss) follow clearly neither a sedimentarynor an igneous trend. Therefore, only one of the plots(fig. 20) yields a trend for the amphibolite that might beinterpreted as an igneous one. The minor-element data,particularly the concentration of chromium and nickel insome of the samples of amphibolite analyzed (tables 7, 8),also suggest derivation from igneous protoliths. Further,the presence of detectable platinum-group metals in eightsamples of amphibolite analyzed from the general areaof the Bluebird mine (table 8), in the Lost Basin Range,implies an igneous protolith, as does the relict igneousfabric in these samples and in most other metabasitesthroughout the southern part of the Lost Basin Range.Plots of all available chemical analyses of amphibolite fromthe districts (page and others, 1986) suggest that igneouscLimestone100 mgEXPLANATION• Amphibolite@ DiabaseA Pyroxene-bandedgneissShaleal-alkFIGURE 19.-Niggli 100 mg, c, and al-alk values for amphibolite, diabase,and pyroxene-banded gneiss from Gold Basin-Lost Basin miningdistricts. Analysis numbers same as in table 7. Solid lines indicatetielines between end-member compositions for dolomite, shale, andlimestone.

42 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS,----ARIZONA30,...-------,------,...--------,------,-------,-,---.--==-==-_=-----.-----r-------,//-----Field for Karroo /'.3-- "-\\dolerites ~ /'/Trendline of/'/'Karroo dolerites20/'/'.//'./10 EXPLANATION• Amphibolite@ Diabase£ Pyroxene-bandedgneissOL- --l.- ---L ...........L .L- .....L ...."-L.,,..-- -=''::-_---'o 0.1 0.2 0.3 0.4 0.5 0.6 0.7NIGGLI mgFIGURE 20.-Niggli c versus my values for amphibolite, diabase, and pyroxene-banded gneiss from Gold Basin-Lost Basin mining districts. Analysisnumbers same as in table 7. Field and trendline for Karroo dolerites are from Evans and Leake (1960).:!!:l'1i:::::i(.:J(.:J50 r-----.;;:----r-----,-----,------,-----,--------,-----,------,4030Shalefield'" '"\\\/////4/ // // /// // // I// \/ \// \/ \\\\\\\ \IEXPLANATION• Amphibolite® Diabase& Pyroxene-bandedgneissZ 20 ///////10 /Field of/igneous rocks///// Dolomiteo '-- -----i --"--- .....L -.L._L.-__..l..- L- ----' ----'o10203050607080FIGURE 21.-Niggli c versus al-alk values for amphibolite, diabase, and pyroxene-banded gneiss from Gold Basin-Lost Basin mining districts.Analysis numbers same as in table 7. Solid lines, potential trends of variation in mixtures of shale and carbonate (van de Kamp, 1969).

PETROCHEMISTRY OF CRYSTALLINE ROCKS 43protoliths of amphibolite varied from ultramafic komatiiteto basaltic komatiite to tholeiite in the classificationscheme of Jensen (1976). Eight of the samples analyzedby Page and others (1986) contain as much as 1,000 ppmchromium and 300 ppm nickel. However, these observa·tions and geologic relations together with those in thequartz-rich, sedimentary-derived amphibolite suggestvery strongly that amphibolite in the districts was derivedfrom both igneous and sedimentary protoliths.METACHERT, BANDED IRON FORMATION,AND METARHYOLITEThin lenses of metachert, discontinuous beds of bandediron fonnation (see Stanton, 1972), and scattered outcropsof metarhyolite are fOWld in the Proterozoic metamorphicrocks of the districts. Most of these rocks are in the gneiss(fig. 2, Wlit Xgn) and the three types commonly are associatedspatially with one another. They are rarely presentin the migmatitic gneiss unit. Most are quite thin, generally20 to 90 em thick. Metachert typically is weJllaminated,probably reflecting relict bedding. The metachert consistsof irregularly handed quartz- and feldspar-eontaininglaminae that in places are conformable and interlayeredwith amphibolite. The feldspar-containing laminae havebeen altered mostly to various phyllosilicate and epidote·group minerals. Metachert also is associated spatially withseveral other lithologies, including complexly scrambledcalc-silicate rocks, amphibolitic calc-silicate rocks, andmarble, Chemical analysis of a grab sample of a slightlypinkish micaceous or argillaceous metachert gives an Si02content of 79.5 weight percent (table 10, analysis 1). Examinationof a thin section of this metachert shows aquartz-biotite-cordierite-plagioclase prograde assemblagethat has been replaced intensely during the retrograderegional metamorphic event. The retrograde assemblageincludes chlorite, white mica, albite, and rutile. These thinsequences of metachert grade locally into iron formation,which consists ofalternating hematite- and magnetite-richlaminae and finely crystalline quartz-rich laminae. Chern·ical analysis ofa ferruginous sample which is intermediatebetween metachert and typical iron formation shows acontent ofabout 14 weight percent total iron as FeO (table10, analysis 2). In addition, this particular sample contains100 ppm copper and 200 ppm zinc. Quartz, magnetite, andhematite are the dominant minerals in the rock, and theiron oxide-rich laminae include a composite assemblageof clinopyroxene, amphibole, apatite, white mica, andabundant paragenetically late needles of probable minnesotaite,an iron analog of talc (see Deer and others,1962c). These samples (table 9, analyses 1, 2) are interbeddedwith a metaquartzite most likely derived from apebbly, limy siltstone. Under the microscope the metaquartziteshows l.O-cm elongate. clasts of monocrystallineto polycrystalline quartz set in an equigranular 0.08- tol.O-mm-size matrix of mostly quartz and epidote. Theclasts ofquartz are tightly sutured into the matrix acrosssever.d.1 millimeters of intergrown quartz and epidote.Well-developed oxide-facies banded iron formation ispresent in at least five localities in the districts (table 11,lacs. 216, 303, 664, 973, and 1086). All five of theseoccurrences ofiron formation are associated closely withat least some metabasites, including amphibolite, se·quences ofamphibolitic gneiss, and mafic schist. The bestdeveloped iron formation probably crops out at locality303 (table] 1). Here, a 60- to 90·em·thick sequence oflaminated hematitic but highly magnetic iron fonnation(fig. 22) strikes approximately N. 30° W. and dips about50° SW. It can be traced more than 200 m along strikeprimarily by using float. Further, the iron formation atTABLE 1O.-Analy»es ofWiw.dlert, bandedironftnmaticn, WilamyoliIR,and calc-'lilfuate TtUlrbJ.e in oorWus Early Proterowic llwtmlwrphicuniUfrwn the Gold Basin-lAst Basin mining districtM(Cherni

44 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN·LOST BASIN MINING DISTRICTS, ARIZONAlocality 303 has been prospected by use of an approximately20-m-deep vertical shaft. Near the shaft. the ironformation is very closely associated with laminated finegrainedamphibolite. Approximately 100 m to the westnorthwest.an exposed sequence of banded amphiboliteand quartzofeldspathic gneiss is heavily stained by variousiron oxides. However, these iron oxides are associatedwith highly manganiferous gossanlike stringers in brecciatedquartz and highly altered granitoid pegmatite. Themajor minerals in these oxide-facies iron formations aremaghemite (magnetic hematite derived from magnetite)and quartz, which are present in alternating bands. Granoblasticquartz typically shows complexly sutured boundariesand may have long dimensions of about 4 mm insome quartz-rich bands about 5 mm thick. However, suchgrains ofquartz include swarms of extremely fine grainedaligned crystals of maghemite that parallel the trace ofthe maghemite-quartz bands. Therefore. recrystallizationof these rocks must have involved a tremendous increasein grain size as has been reported in metamorphosedbedded iron formations elsewhere (see James, 1981). Weinfer that these thinly banded maghemite-quartz rocks inthe Gold Basin-Lost Basin districts were initially depositedas chemical precipitates related to sporadic volcanicactivity during the largely epiclastic deposition of theprotoliths of the surrounding metamorphic rocks.Kimberley (1983) reported that approximately 85 percentof Early Proterozoic iron fonnations examined containmore than 5 volume percent chert and thus would beclassified as cherty in his scheme. However. a more usefulclassification is one that relates the iron formation to atectonic or depositional environment. Gross (1980) proposedthat iron fonnations may be classed as epeirogenic(Superior type) or orogenic (Algoma type). The depositionalenvironment of the iron fonnation in the Gold Basinand Lost Basin mining districts is probably more closelyrelated to the Algoma type because of the association ofthe iron formation here with a presumably arc-related.graywacke-rich protolith. Indeed, some of the nearby ironformation enclosing rocks in the Gold Basin·Lost Basindistricts also include detrital magnetite (Deaderick. 1980,p. 16-19). Chemical analysis of a representative samplefrom the iron formation shows a content of about 43weight percent total iron as FeO and an Si02 content of45.8 weight percent (table 10, analysis 3). However, thehigh content of hematite in this sample is reflected in itshigh ratio of Fe:103 to FeO, about 9 to 1 (table 10).Porphyritic to seriate, foliated metarhyolite also cropsout in the general area of the iron formation at locality303 (table 11). Phenocrysts and crystal fragments ofalbite-oligoclase (AntO) and quartz make up about 20 to25 volume percent of the rock. These phenocrysts andcrystal fragments range from 0.3 to 3.5 mm in size andprobably average about 1.5 mm in their largest dimension.Some of the albite-oligoclase is present in glomeroporphyriticaggregates, some of which include small ovoidlithic clots of very fine grained granulose quartz pluschlorite. About one-third of the phenocrysts are quartz.Many of the quartz crystals are embayed, and several ofthem are obviously bipyramids. In addition, they arehighly strained, showing a ribbon-type extinction undercrossed nicols. Where the originally monocrystallinequartz phenocrysts have recrystallized, the newly growncrystals of quartz are associated with recrystallization ofchlorite, which is moderately abWldant throughout thematrix. The matrix is poorly but nonetheless distinctJyfoliated, a textural relation that is one of the mostdiagnostic features of the rock. The laths of albite havepoorly defined crystal boundaries with the surroWldingmatrix and are aggregated with quartz, chlorite, biotite,and additional granoblastic albite. Light- to mediumbrown(Z axis) biotite is paragenetically earlier thanchlorite. Minor accessories include apatite, zircon, andfine·grained granules of epidote. Chemical analysis of agrab sample from the metarhyolite shows an Si02 contentof 71.4 weight percent and an Na20 plus K20 contentof 4.7 weight percent (table 10, analysis 4), whichplots in the rhyolite field using the chemical classificationof Middlemost (1980).MARBLE, CALC·SILICATE MARBLE, AND SKARN~'32,2 MllUN£T£~SFIGURE 22.-0xide facies, banded iron fonnation. Q. quartz; M. mag.hemite. Plane-polarized light. Sample GM·303, NWV. sec. 16, T. 29N.• R. 17 W.Beds generally less than 2 m thick of marble, calcsilicatemarble. and skarn crop out sporadically throughoutmuch of the gneiss and feldspathic gneiss units (fig.2). In detail, many individual beds of these carbonate orreplaced carbonate beds are also spatially associated veryclosely with amphibolite. Most of the marble is impure and

PETROCHEMISTRY OF CRYSTALLINE ROCKS 45in places it is squeezed into the cores of very tightly appressedrecumbent and overturned folds that measure asmuch as 1 to 2 m across. Typically, wide-ranging overallproportions of silicate minerals are present in these rocksboth along individual beds and among different nearbybeds. The best replacement phenomena between carbonateand silicate minerals are recorded in some of themost calcite-rich calc-silicate marble, as exemplified bysample GM-290b (table 10, analysis 5). A relatively silicadeficient calc-silicate marble (17.8 weight percent Si0 2 )contains a composite assemblage of actinolite, diopsidesalite(trace), quartz, and sphene, which shows excellenttextural relations documenting multiple crystallizationevents. The earliest assemblage probably consisted ofcalcite, and diopside-salite. Then, medium-grained calcitecrystals, approximately 2.0 mm across, show incipientpatchy replacement by early pale-apple-green (Z axis)actinolite. Reaction fronts between unreplaced calcite andpartially replaced calcite are exceptionally sharp and seemto be confined to select crystals of calcite scatteredthrough the rock rather than defining planes cuttingacross the calcite's crystal boundaries. Further, alignedfine-grained crystals of less strongly pleochroic actinolite(and thus probably more magnesian, see Deer and others,1963) define foliations through the calc-silicate marble bytheir strong preferred dimensional orientation. Increasedabundances of the fine-grained crystals of actinolite areconcentrated mostly peripheral to lensoid clots of finelycrystalline quartz. In addition, there is some dimensionalorientation of calcite in these domains. In some of themore heavily retrograded calc-silicate marbles, and alsomore siliceous than sample GM-290b, carbonate has beencompletely replaced by an assemblage of zoisite andclinozoisite, chlorite, white mica (possibly chloritoid),sphene, and quartz, and including relict plagioclase andvarious opaque minerals in trace amounts.Some calc-silicate marble contains garnet as one of itsdiagnostic minerals. Isotropic garnet, probably rich in thegrossular molecular end member, in these calc-silicatemarbles typically includes medium-grained crystals ofdiopside-salite, a relation suggesting crystallization ofdiopside-salite preceded crystallization of garnet. Wherefoliated, the schistosity is confined primarily to the quartzandcalcite-rich domains of the rock. Minor accessoriesinclude sphene and slightly rounded crystals of zircon.Some pods of calc-silicate minerals in generallymigmatitic-gneiss sequences of rock show the developmentof zoned reaction rims with an adjoining peliticschist. These reaction rims are millimeter sized and probablydeveloped by a predominantly diffusion-dominantprocess (for discussion of diffusion phenomena, see Vidale,1969; Hewitt, 1973; Vidale and Hewitt, 1973). Where thepelitic schist has not apparently reacted with the enclosedcarbonate-rich pods, it contains a typical biotite-quartzplagioclase(about An45)-apatite-opaque mineral assemblage(fig. 23, zone I). However, within about 13 mm ofthe approximate original boundary between the peliticschist and the carbonate-rich rock, the first mineralogicalchanges are present. These changes are (1) the sporadicnucleation of newly crystallized clinozoisite that eitherenvelopes an opaque mineral (probably magnetite) or isvery close to an opaque mineral, (2) a marked decreasein the average maximum dimension of biotite from about0.5 mm in zone I to about 0.12 mm in zone II, and (3) aprogressive decrease in the grain size ofbiotite and a concomitantincrease in the modal abundance of largely untwinnedplagioclase (approximately An50)' The boundaryof zone II on the side of the calc-silicate pod is placed atthe point of final disappearance of biotite. However, abladed opaque mineral, which is most likely ilmenite, appearsinitially about two-thirds of the way into zone II andcontinues through zone III; the ilmenite disappears finallyabout one-quarter of the way through zone IV (fig. 23).A weakly pleochroic amphibole in zone III, probablytremolite-actinolite, is present as stubby crystals that havean overall shredded aspect and make up about 10 to 15volume percent of the zone. From the specific mineralassemblage and modal composition of zone III, we inferit as having the lowest K 2 0 content of the three reactionzones (II-IV) developed in rock that formerly had thesame overall bulk composition as the unreacted peliticschist. Relative to zones III and VI, the phyllosilicatesbiotite (now mostly retrograded to chlorite) and whitemica are more abundant in zones IV and V. This increasein abundance is confined mostly to a domain near theoriginal approximate boundary between pelitic rock andcarbonate-rich rock. The modal concentration of spheneis highest in zone I, on the carbonate side of the originalboundary between the carbonate and pelitic rocks. Thus,all these relations above suggest that the followingchemical changes occurred across the pelitic-carbonatecontact during metamorphism: (1) a depletion of potassiumin the pelitic rocks immediately adjacent to thecarbonate, (2) a concomitant flow of calcium from the carbonateout into the pelitic rock, (3) possibly a fixation ofsome of the potassium released from the pelitic rock intobiotite and white mica along the original boundary betweenpelite and carbonate, and (4) a possible flow oftitanium from the breakdown of biotite into the recrystallizingcarbonate. Vidale (1969) documented experimentallythe differential movement of potassium, calcium, andmagnesium across juxtaposed pelite and carbonateassemblages. In her experiments, however, potassium andcalcium moved away from the carbonate. Thus, thenucleation of newly grown biotite and white mica in zonesIV and V (fig. 23) most likely reflects circulation of asecond pulse of fluids primarily along the former peliticschist and calc-silicate contact.

46 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAZone VI contains a relatively simple composite assemblageconsisting of isotropic garnet, zoisite or epidote,sparse apatite, and an opaque mineral in trace amounts(fig. 23). The garnet apparently replaced mostly the finegrainedintergrowths of c1inozoisite, calcite, and chloriteof zone V. Further, the crystallization of garnet appearsto have overstepped that of zoisite because crystals ofzoisite typically have been enveloped by a primarily grainboundary-controlledgrowth ofgarnet. The garnet-zoisiteassemblage in zone VI is similar to assemblages in zonedcalc-silicate rocks in kyanite-grade regionally metamorphosedrocks described by Vidale (1969).Small bodies of skarn, measuring several meters across,crop out sporadically in many of the Proterozoic metamorphicand igneous units of figure 2. Generally, the skarnconsists of discontinuous layers of coarse intergrowths ofgarnet, dark fibrous amphibole, and quartz; or garnet,epidote, and quartz with or without pyrite and calcite.Locally, some skarn has been prospected for scheelite(tungsten), which is present as crystals as coarse as 2.5cm in maximum dimension in podlike masses of skarnrelated probably to nearby thin pegmatite dikes (table 11,loco 25).PROTEROZOIC IGNEOUS AND METAIGNEOUS ROCKSEarly Proterozoic igneous and metaigneous rocks in thedistricts range greatly in size and include leucogranite(unit Xl), gneissic granodiorite (Xgg), feldspathic gneiss(Xfg), biotite monzogranite (Xm), leucocratic monzogranite(XIm), porphyritic monzogranite (Xpm), and granodiorite(Xgd, fig. 2). In addition, varying proportions ofigneous and metasedimentary rocks combine to yield avariety of migmatitic rocks in the exposed basement ofthe districts. The most widely exposed migmatitic rocksare along the lower west flanks of Garnet Mountain. Furthermore,another igneous rock in the districts, presumablyMiddle Proterozoic in age, is present as scatteredundeformed diabase dikes, sills, and small intrusivemasses. In addition to small bodies of all of these Pro-Reaction zones developed in pelitic schistIIIII IV V VIMedium-grainedFine-grainedpelitic schist Fine grained Fine grained Medium grained calc-silicate rockQ Q Q Q cc grpI (An,,) pi ("'An,o) pI' (>An 6o) pi' (>An 6o) cz zo±epibi bi cz cz chi apop Op2 trem-act sph (Tr) bi' op (Tr)ap cz ap Wm sphwm' (Tr) ap Op2 op Q (sparse)zr (Tr) bi' pi (An ,) 7chI'wm..ilm.. biApproximate original boundarybetween pelitic schist andcarbonate-rich pod'Retrograde.2Includes both bladed and equant varieties; probably ilmenite and mostly magnetite. respectively.'Mostly untwinned plagioclase.'Altered mostly to chlorite.FIGURE 23.-Schematic diagram of sequence of mineral assemblagesdeveloped in zones nearcontact between medium-grained pelitic schistand fine-grained calc-silicate rock. Q, quartz; pI, plagioclase; bi, biotite;chI, chlorite; op, opaque mineral; ap, apatite; wm, white mica; zr, zircon;Tr, trace; cz, c1inozoisite; trem-act, tremolite-actinolite; sph,sphene; cc, carbonate, mostly calcite; gr, garnet, completely isotropic;zo, zoisite; epi, epidote; Hm, opaque mineral, bladed habit, probablyilmenite; --, not found.

PETROCHEMISTRY OF CRYSTALLINE ROCKS 47terozoic igneous rocks, the gneiss also includes locallysome conspicuously exposed hornblende-biotite orthogneissthat has the composition of monzonite (fig. 24).LEUCOGRANITEMasses of gneissic leucogranite (unit al of Blacet, 1975)range in size from several-centimeter-wide stringersparallel to compositional layering in the gneiss to theI-km-Iong sill that crops out about 3 km northeast of theCyclopic mine. This sill strikes north-south and dips to thewest, approximately conformable with foliation in the surroundinggneiss (unit Xl, fig. 2). On the south, the sill ofleucogranite appears to be truncated by the large massof gneissic granodiorite that crops out in the Gold Basindistrict. Throughout the gneiss, the fabrics of individualbodies ofleucogranite texturally may grade from coarsegrainedgranitoid to pegmatitic, containing potassiumfeldspar phenocrysts as much as 8 cm wide. In addition,leucogranite ranges from relatively undeformed tointensely mylonitized rock. Although mylonitized coarsegrainedleucogranite is generally conformable with its surroundingrocks, locally it cuts amphibolite and garnetiferousgneiss. Nonetheless, the two diagnostic overallfeatures of the Early Proterozoic leucogranite are (1) itssill-like concordant relation with the gneiss and (2) its commonlygneissic to intensely mylonitic fabric. In addition,many ofthese leucogranite sills contain bluish-gray, highlyQuartzEXPLANATION• Orthogneiss~ Leucogranite• Gneissic granodioriteI!l@Porphyritic monzograniteof Garnet MountainSmall igneous bodies includedwith gneissby Blacet 119751 andthat intrude gneiss...........~ I!l'I!l I!l"'-...@~I!l ~. •I!l@I!lQuartz monzonIteQuartz monzodioritePotassium feldspar•MonzodioritePlagioclaseFIGURE 24.-Modes of Proterozoic igneous and metaigneous rocks from Gold Basin-Lost Basin mining districts. Data from table 12. Compositionalfields from Streckeisen and others (1973). Dashed line, visually estimated regression line.

48 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAvitreous quartz, which is found in wispy segregationlenses. Northeast of the Gold Hill mine, large sills ofpegmatitic leucogranite increase in abundance and eventuallygrade into complexes ofhighly deformed migmatiticleucogranite (unit mal of Blacet, 1975). These complexesinclude swarms of leucogranite, aplite, and pegmatitedikes, together with pegmatoid quartz veins, all cuttinggneiss. All of the relations indicate that initial emplacementof leucogranite into gneiss occurred during the intenseductile deformation ofthe gneiss. Although we inferthat the mapped body of leucogranite is older than allother Proterozoic igneous rocks, some leucogranite in theProterozoic terrane probably was emplaced synchronouslywith all other Early Proterozoic igneous rocks here.Garnetiferous gneissic leucogranite, which ranges widelyin grain size, locally becomes very strongly foliated andmylonitic near some minor tungsten (scheelite) prospects.This tungsten mineralization may be Proterozoic in age.In addition, the pink garnet in some of the leucograniteis concentrated near the walls of the leucogranite, especiallywhere the leucogranite is in contact with biotite- orgarnet-rich gneiss. Plots of modal data (table 12) for fivesamples of leucogranite show that four samples fall withinthe compositional field of granite (fig. 24). The other sampleplots within the compositional field for tonalite.GNEISSIC GRANODIORITEAn elongate body trending N. 25° E. of Early Proterozoicmedium-grained gneissic granodiorite crops outacross approximately 10 km 2 in the Gold Basin district(fig. 2; unit ggd of Blacet, 1975). The southernmost exposuresof the gneissic granodiorite body crop out about2 km northeast ofthe Cyclopic mine. The gneissic granodioriteapparently intrudes gneiss and some leucograniteand is in turn intruded by Early Proterozoic porphyriticmonzogranite ofGarnet Mountain and Middle Proterozoicdiabase, and presumably even younger pegmatitic leucograniteand gold-bearing veins. Some samples of typicalgneissic granodiorite contain approximately 25 to 30volume percent quartz and plot in the compositional fieldfor granodiorite (fig. 24). However, other samples showwide-ranging alkali feldspar to plagioclase proportionsyielding modal compositions that fall in the granite andtonalite compositional fields. Mafic minerals, mostlybiotite, make up about 20 volume percent of the rocks.Plagioclase (approximately An20) generally is altered intenselyto white mica± carbonate± clinozoisite assemblages,whereas the potassium feldspar is remarkablyfresh and includes both microcline and perthitic varieties.Accessory minerals are sphene, apatite, and opaqueminerals. Gneissic granodiorite may be a mafic, lesssiliceous variety of igneous rock more or less isochronouswith feldspathic gneiss (Xfg, fig. 2).Numerous shallow prospect pits and mine workings arescattered throughout the gneissic granodiorite. However,the east contact between the gneissic granodiorite andthe surrounding gneiss appears to have acted as a veryimportant conduit for the circulation of fluids associatedwith gold mineralization. Prospects and productive mines,including the Malco mine in the SElf4 sec. 21, T. 28 N.,R. 18 W., are especially concentrated along the strike ofthis contact for approximately 2 km.TABLE 12.-Modal data for Proterozoic igneous and metaigneous rocks from, the Gold Basin-Lost Basin mining districtsSampleTotal pointscountedQuartz(volumepercent)Potassiumfeldspar(volumepercent)38.438.222.233.438.424.916.221.121..241.628.517.5.428.5Plagioclase(volumepercent)22.720.434.54021.449.840.732.735.128.239.242.261.927.835.148.136.8Maficminerals(volumepercent)1.62.623.624.4CommentsFoliated leucogranite dike in mixed granodioriticcomplexPorphyritic leucogranite inclusion in sample 98,showing 3-Cm crystals of potassium feldsparBiotite-hornblende granite of unit XgnOrthogneiss included in gneiss unit Xgnof Gold Hill mine, T. 29 .N., R. 18 w.Garnet-bearing pegmatoid leucogranite in gneissunit XgnAplite dike, shallow dipping, presumablycogt'!netic with Xpm unitBiotite granodiorite, slightly porphyritic,locally gneissic, in gneiss (Xgn)Gneissic granite in gneiss (Xgn); presumablycorrelative with gneissic granodiorite (Xgd)Granite in gneiss (}{gn)Leucogranite dike, 10 m thick, cutting gneiss (Xgn)Gneissic granite in gneiss (Xgn)Gneissic granodiorite (Xgd)Gneissic tonalite variant of gneissic granodiorite(Xgd)Porphyritic biotite granite of porphyriticmonzogranite (Xpm)Granite in gneiss (Xgo)Undeformed garnet-bearing leucogranite dike cuttinggneiss (Xgn)Porphyritic granite from migmatite terrane(unit Km)LocationNEI/4 sec. 15, T. 28 N., R. 16 w.NEl/4 sec. 15, T. 28 N., R. 16 w.NWI/4 sec. 24, T. 28 N., R. 16 W.Approximately 1.7 km west-northwestof Gold Hill MineSWI/4 sec. 4, T. 27 N., R. 18 W.NWI/4 sec. 4, T. 27 N., R. 18 w.NWI/4 sec. 3, T. 27 N., R. 18 W.NEI/4 sec 23. T. 30 N., R. 19 w.NWI/4 sec. 29, T. 28 N., R. 18 w.SWI/4 sec. 29, T. 28 N., R.NEI/4 sec. 17, T. 28 N., R.18 w.18 w.8El/4 sec. 21, T. 28 N., R. 18 W.NEI/4 sec. 21, T. 28 N., R. 18 w.NEI/4 sec. 16, T. 30 N., R. 18 w.SEI/4 sec. IS, T. 29 N., R. 19 w.NEl/4 sec. 3, T. 28 N., R. 16 w.SWl/4 sec. 33, T. 29 N., R. 17 w.GM-98 -------- 1,468GH-98a ------- 1,609GH-126a ------ 3,535GM-638z ------ 1,798GM-824 ------- 1,479GM-830 ------- 1,344GM-848 ------- 1,726GM-a 74 ------- 1,790GM-893 ------- 1,338GH-894 ------- 1,660GM-927 ------- 1,767GM-94Sa ------ 1,850GM-IOOO ------ 1,427GM-I027 ------ 1,086GM-I0S1 ---..-- 1,425GM-I063 ------ 1,398GM-I081 ------ 1,60237.338.819.62.239.121.424.322.621.128.928.620.720.732.733.644.627.232.83.918.823.722.61.33.819.61/112./3.43.1

PETROCHEMISTRY OF CRYSTALLINE ROCKS 49FELDSPATHIC GNEISSEarly Proterozoic feldspathic gneiss crops out in an approximately5-km-Iong and 0.8-km-wide sliver bounded byfaults in the southern part of the Lost Basin Range (fig.2; unit fgn of Blacet, 1975). These faults include both deepseatedmylonitic structures and shallow-seated structuresmarked by gouge. Generally, the feldspathic gneiss is lightgray to light pinkish gray, fine to medium grained, andhas a compositionally homogeneous and strongly lineatedfabric. The feldspathic gneiss contains few mafic schlierenand inclusions. Locally, foliation in the feldspathic gneissis highly contorted, and near the northern margins of thesliver, the attitude of foliation gradually converges withthe mylonitic rock that is present along its contact withthe surrounding gneiss. The gneiss just west of the westboundary fault of the feldspathic gneiss contains abundantslickensides and short discontinuous shear zones, aswell as iron oxide staining and increased abundances ofchlorite.The feldspathic gneiss is cut by quartz-feldspar veins,some of which are gold bearing, and sparse occurrencesof syenitic aplite. Prospect pits and abandoned shafts andadits are especially abundant near the north end of thefeldspathic gneiss. Generally, these workings follow copper(chalcopyrite, chrysocolla, malachite), lead (galena),and native gold shows along quartz plus yellow-brown carbonateveins. In places, the veins are about 0.5 m thickand attenuate downdip to stringers of about 1 to 2 cmthick. No indications of copper, lead, or gold mineralizationwere found to be associated with the syenitic aplite(P.M. Blacet, unpub. data, 1967-72), although the pits dugon some of the outcrops of syenitic aplite include quartzand orange-brown carbonate vein material and clearcrystalline calcite.BIafITE MONZOGRANITEThree bodies of equigranular to sparsely porphyriticEarly Proterozoic biotite monzogranite are mapped in theGarnet Mountain quadrangle: (1) an approximately 1-km2west-trending mass near Rattlesnake Spring, which isabout 5 km southeast of Garnet Mountain; (2) an approximately0.1-km 2 body, about 2 km southwest of RattlesnakeSpring; and (3) a north-trending dikelike masswhich has been traced discontinuously for about 4.5 kmin the southern part of the Gold Basin district (fig. 2; unitqm of Blacet, 1975). The biotite monzogranite is in contactmostly with porphyritic monzogranite of GarnetMountain. Age relations between the biotite monzograniteand porphyritic monzogranite of Garnet Mountain cannotbe established conclusively because their contacttypically is not exposed and can be located only withinabout 10 m. Nonetheless, the porphyritic monzograniteofGarnet Mountain near the contact is altered more thanthe biotite monzogranite and also contains narrow discontinuouscataclastic or protoclastic zones. Near RattlesnakeSpring, however, the biotite monzogranite is associatedspatially with moderately abundant rose quartz-bearingpegmatite and other pegmatite. Some similar pegmatitesare present definitely as inclusions in the adjoining porphyriticmonzogranite of Garnet Mountain (P.M. Blacet,unpub. data, 1967-72), relations from which we infer thatthe biotite monzogranite may be older than the porphyriticmonzogranite of Garnet Mountain. In addition, the biotitemonzogranite is intruded by small numbers of diabasedikes, some of which also include leucocratic differentiates.The biotite monzogranite, which crops out in the southernpart of the Gold Basin district, is a rather homogeneouslight-gray body and shows only minor variationsin overall composition and in igneous fabric. The biotitemonzogranite is mostly a fine-grained rock, rangingtypically between 0.5 and 1.0 mm in average grain size.Regardless, some facies of this rock in places becomemedium grained and contain euhedral potassium-feldsparphenocrysts as much as 8 cm in their long dimension andsparse quartz phenocrysts as much as 1.5 cm wide. Otherrocks are foliated. Thin sections of six representativesamples of fine-grained biotite quartz monzonite showpredominantly equigranular hypidiomorphic-granular texturesand minor porphyritic, seriate, and glomeroporphyritictextures. Modally, these rocks would plot in thecompositional field of granite, using the classification ofStreckeisen and others (1973). Some phenocrystic quartz,perhaps 1 to 2 percent by volume, is aggregated into approximately2.5-mm-wide clots. Primary biotite (darkbrown, Z axis) makes up typically about 5 to 10 volumepercent and has been altered sparingly to chlorite withor without epidote. Plagioclase (mostly An15-20) showsvarying degrees of replacement by white mica andepidote. The intensity of replacement is highest adjacentto Cretaceous(?) episyenitic rocks which largely developedfrom the biotite monzogranite. Potassium feldspar, mostlymicrocline but including also some untwinned but perthiticvarieties, is generally quite fresh. Minor accessories includeapatite, sphene, and opaque minerals. Locally, pyriteis disseminated in the biotite monzogranite where it isintergrown with coarsely crystalline anhedral fluorite.The biotite monzogranite, which crops out in thesouthern Gold Basin district, hosts numerous fluoritebearingquartz-carbonate veins, some of which containvisible gold. In addition, this body of biotite monzograniteis also cut by several very small masses of Cretaceous(?)episyenite, one of which near the east edge of the biotitequartzmonzonite contains fluorite and disseminated gold(Blacet, 1969; see below).Chemical data on three representative samples ofbiotitemonzogranite from the Gold Basin district are presented

50 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAin table 13. The major-element analyses are generallysimilar to the average granite of Le Maitre (1976), alsolisted in table 13 for comparison. However, these threesamples of biotite monzogranite are richer in KzO thanthe average granite of Le Maitre (1976), and the samplesare also lower in NazO. The average of total alkalis (sumof KzO and NazO) in the three samples is 8.3 weight percent,which is close to the 7.75 value for total alkalis inthe average granite of Le Maitre (1976). Minor elementsin the three samples of biotite monzogranite are typicalof those commonly associated with granitic rocks, withTABLE 13.-Analytical data ofEarly Proterozoic biotite monzogranite[Chemical analyses of 1 and 2 by rapid-rock methods; analysts, P.L.D. Elmore and S. Botts.Methods used are those described in Shapiro and Brannock (1962), supplemented by atomicabsorption (Shapiro, 1967). Spectrographic analyses of 1 and 2 by Chris Heropoulos. Resultsare reported to the nearest number in the serles 1, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1, 0.07, andso forth, which represent approximate midpoints of interval data on a geometric scale. Theprecision of a reported value is approximately plus or minus one series interval at 68-percentconfiden~e or two in~rvals at 95-percent confidence. Looked for but not fOmId: Ag, As,Au, BhBl, Cd, Mo, Nl, Pd, Pt, Sb, Sn, Te, D, W, Zn, Hf, In, Li, Re, Ta, Th, Tl Pr SmEu. C emical analysis of sample 3: major oxides by X-ray spectroscopy; J.B. Wahlberg:J. Taggart, and J. Baker, analysts; partial chemical analyses by standard methods; P.R.Klock and J. Riviello, analysts. Spectrographic analyses of sample 3 by Judith Kent. Lookedfor but not found:. Ag, As, Au, Bi, Cd, Sb, Sc, W, Ge, In, Re, TI, and Hg; --, not detected;N.D., not determmea]Analysis ---------- 1Sample ----------- GM-19Si02 ----------- 72.9A1 2 0 3-------------- 14Fe203 ----------- 1.4FeO --------------- 1.4MgO --------------CaO ---------------.101.2~l~~ i:j!~~~5-=:=--=:::::::::: :~~CO2 ---------------

PETROCHEMISTRY OF CRYSTALLINE ROCKS 51The leucocratic monzogranite probably has a total outcroparea of about 5 to 6 km 2 and normally is within the morewidespread porphyritic monzogranite of Garnet Mountain.Contacts between leucocratic monzogranite and theporphyritic monzogranite of Garnet Mountain locally arequite sharp, but the transition between the two rock typescan also be gradational across 8 to 10 cm or as much as0.5 m. Further, the abundance of potassium feldsparphenocrysts increases in the leucocratic monzogranitenearest the porphyritic monzogranite. Although the actualcontact between these two rocks may be highly irregularin detail at the scale of a single outcrop, the overall attitudeof the contact maintains a generally northwest strike.In addition, the potassium feldspar phenocrysts, which areconcentrated on the leucocratic monzogranite side of thecontact with porphyritic monzogranite of Garnet Mountain,also are commonly oriented with their long dimensionstrending northwesterly. Locally, where the contactbetween these rocks is well exposed, offshooting dikes ofporphyritic monzogranite of Garnet Mountain definitelycut leucocratic monzogranite, and in places both rocks arecut in turn by fine-grained dikes of granite. On the otherhand, some exposures of the contact between leucocraticmonzogranite and porphyritic monzogranite of GarnetMountain show complexly mixed flowage structures involvingboth rocks. These relations suggest that initialemplacement of the leucocratic monzogranite to the levelscurrently exposed was followed very closely by intrusionof the porphyritic monzogranite of Garnet Mountain-soclosely that the leucocratic monzogranite in places probablywas only partially crystalline.·We infer that initialemplacement ofthe leucocratic monzogranite predates thebiotite monzogranite.In outcrop, the leucocratic monzogranite is typically alight-yellowish-gray rock, which most commonly ismedium-grained hypidiomorphic granular in overall texture.Compositionally, these rocks are granite and generallyare nonporphyritic although they can grade intoslightly porphyritic micropegmatitic varieties. Partlychloritized dark-red-brown (Z axis) biotite makes up lessthan 5 volume percent of the equigranular varieties. Inaddition, very fine granules of opaque mineral(s) are concentratedin chlorite which replaces the earlier primarybiotite, whereas granules of primary opaque mineral(s)(probably magnetite mostly) are relatively sparse andsomewhat coarser grained than the secondary opaquemineral(s). Plagioclase (An15-25) makes up 30 to 40volume percent of the rocks and is moderately cloudedby a dense intergrowth of clay mineral(s), white mica, andsparse epidote. Potassium feldspar is relatively fresh andcontains patches of microcline twinning, which is concentratedusually in the cores of the potassium feldsparcrystals. The potassium feldspar also includes irregularlydeveloped bead perthite. Myrmekite is developedsparsely along potassium feldspar-plagioclase grainboundaries. Primary quartz makes up about 20 to 25volume percent of the leucocratic monzogranite and insome samples the primary quartz hosts relatively abundantand conspicuous fluid inclusions. These fluid inclusionsare concentrated along secondary and pseudosecondaryannealed microfractures through the primaryquartz. At room temperature, the fluid-inclusion populationconsists of a two-phase liquid-rich type, a three-phasetype containing liquid carbon dioxide, and a third typewhich contains from one to three nonopaque daughterminerals. One of these daughter minerals is undoubtedlyhalite and another is probably sylvite. The third daughtermineral is highly birefringent and shows equant torod-shaped habits. Heating and freezing tests were notperformed on these samples from the leucocratic monzogranite.However, the relative proportions of thedaughter minerals in many of the inclusions suggest thathighly saline carbon dioxide-rich fluids containing as muchas 60 weight percent NaCI equivalent at some timemust have circulated through some of the leucocraticmonzogranite.The leucocratic monzogranite contains locally some narrow1- to 2-m-wide zones of very well foliated gneissic rockof nearly the same composition as the nonfoliated equigranularleucocratic monzogranite. These zones crop outnear contacts between leucocratic monzogranite and porphyriticmonzogranite of Garnet Mountain and haveattitudes that parallel closely the attitude of the contactbetween the two rocks. The foliation is defined principallyby (1) a preferred concentration of stubby crystals ofdark-brown (Z axis) biotite into highly discontinuous0.2-mm-wide lepidoblastic domains and by (2) a preferreddimensional orientation of highly strained ribbonedquartz. The extreme freshness of these zones (the biotiteis not chloritized, and the plagioclase is not clouded) suggeststhat they may have been generated protoclastically.Pegmatite in the leucocratic monzogranite previouslyhas been prospected for sheet mica, as exemplified by theM.P. Mica mine, which is in the SE1J4 sec. 26, T. 28 N.,R. 17 W. (table 11, see locs. 138, 139). At several placesin the general area of the M.P. Mica mine, muscovitebooks are present in approximately N. 10° W.-strikingdiscontinuous pegmatite dikes and lenses. These dikes andlenses range from 2 to 5 m in width. The pegmatite showswell-developed quartz cores and includes some sparse concentrationsof red-brown garnet near its margins with theleucocratic monzogranite.PORPHYRITIC MONZOGRANITE OF GARNET MOUNTAINThe porphyritic monzogranite of Garnet Mountain (unitpqm of Blacet, 1975) crops out in three main areas in thedistricts: (1) east of Hualapai Valley and east of Grapevine

52 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAMesa, near the Grand Wash Cliffs, (2) near the northwestcorner of the area, in the White Hills, and (3) in thesouthern White Hills near the southwest corner of thearea where it hosts several of the gold-bearing quartzveins (fig. 2). The largest exposed body of the porphyriticmonzogranite crops out east of Hualapai Valley, nearlycentered on Garnet Mountain itself. Here the porphyriticmonzogranite is the principal rock unit exposed in an areaof about 60 km 2 . Several northwest-striking dikes and irregularlyshaped small bodies of diabase intrude the porphyriticmonzogranite in this general area. About 4 kmeast of Garnet Mountain, the porphyritic monzograniteis overlain unconformably by the Cambrian Tapeats Sandstone,and at Iron Mountain, about 5 km northeast ofGarnet Mountain, the porphyritic monzogranite and thediabase are capped unconformably by flat-lying rocksincluding the Tapeats Sandstone, Tertiary gravel, andTertiary basalt. From Garnet Mountain, the porphyriticmonzogranite can be traced to the north fairly continuouslycropping out in progressively smaller areas east ofGrapevine Mesa and in the low hills leading to the GrandWash Cliffs. Near the northwest corner of the area, theporphyritic monzogranite crops out in three irregularlyshaped bodies which total approximately 5 km 2 in area.Fanglomeratic sequences of the Tertiary Muddy CreekFormation, the upper Miocene Hualapai Limestone Memberof the Muddy Creek Formation, Tertiary ancestralColorado River deposits (not delineated separately on fig.2), and various types of Quaternary unconsolidateddeposits all rest unconformably on some part of thesethree bodies of porphyritic monzogranite. As mapped inthe southern White Hills, the porphyritic monzogranitecrops out in an approximately triangular area of about10 km 2 . Its maximum inferred dimension at the surfaceis about 6 km in an approximately N. 40° E. direction.The age of emplacement of the porphyritic monzogranitewas established by Wasserburg and Lanphere(1965) to be about 1,660 Ma using the potassium-argonand rubidium-strontium techniques. Samples of porphyriticmonzogranite and pegmatite were obtained bythem from several localities in the SW1/4 sec. 27, T. 28N., R. 16 W., near the Boyd Tenney Ranch in the QuartermasterCanyon SW 7 1 /z-minute quadrangle. These localitiesare approximately 3.2 km north-northeast of thesoutheast corner of the Garnet Mountain quadrangle, andfrom them, the porphyritic monzogranite can be tracedcontinuously to Garnet Mountain itself. Hornblende froma sample of porphyritic monzogranite, described byWasserburg and Lanphere (1965, p. 746) as "coarsegrainedbiotite-hornblende quartz monzonite characterizedby abundant microcline phenocrysts," yielded a K-Arage of 1,630 Ma. The initial 87Sr/86Sr ratio for the porphyriticmonzogranite is 0.702. Abundant dikes ofpegmatitecut the porphyritic monzogranite and the metamorphicrocks, which include garnet-biotite-potassiumfeldspar gneiss and diopside-hornblende gneiss, at theselocalities. Comprehensive analytical results on variousminerals from these pegmatites plot on a well-definedisochron of 1,660 Ma showing an initial 87Sr/86Sr ratioequal to 0.704 (Wasserburg and Lanphere, 1965). Apparently,plutonism here forms part of a northeasttrendingmagmatic arc that ranges in age from 1,610 to1,700 Ma (Silver and others, 1977). Such plutonism in thedistricts occurred well within a broad Proterozoic provinceof 1,720- to 1,800-Ma apparently supracrustal rock andmay reflect magmatism associated with the accretion ofanother 1,650- to 1,720-Ma terrane outboard to thesoutheast (Condie, 1982).Large, abundant, conspicuous potassium feldsparphenocrysts are the most characteristic feature of the porphyriticmonzogranite of Garnet Mountain. The phenocrystsare typically pinkish gray to pale pinkish cream andare set in a light-pinkish-gray, coarse-grained, hypidiomorphic-granulargroundmass. Many exposures of porphyriticmonzogranite show tabular phenocrysts as longas 10 em. Textures elsewhere in the porphyritic monzograniteare predominantly subporphyritic seriate, andsuch rocks show an almost continual gradation in size ofeuhedral potassium feldspar phenocrysts from about 1.5em to 10 em in their long dimension (fig. 25A). In addition,some of the potassium feldspar phenocrysts showevidence of partial rounding. Generally in the porphyriticmonzogranite, near its contact with the leucocratic monzogranite,tablets of phenocrystic potassium feldspar showa well-developed preferred orientation. Where oriented,the phenocrysts are aligned with their long axes parallelto the general strike of the contact. In addition, thephenocrysts are subparallel to dimensionally orientedschlieren and inclusions of leucocratic monzogranite.However, the border zone of the porphyritic monzograniteis not everywhere typified by aligned phenocrysts ofpotassium feldspar. Locally, in the Gold Basin district thisborder zone between porphyritic monzogranite and gneissis marked by a conspicuous display of randomly orientedblocks of included biotite-rich and garnet-bearing schistand gneiss. Nonetheless, the contact between gneiss andporphyritic monzogranite is conformable generally withthe trend of foliation in the gneiss as exemplified by relationsin sec. 29, T. 28 N., R. 18 W. Yet on a scale of alarge outcrop, the contact between porphyritic monzograniteand gneiss cuts the schistosity in the gneiss at ahigh angle, and there is no evidence for shearing alongthe contact. In places, the contact can be located to withinabout 1 em. Elsewhere in the Gold Basin district, the porphyriticmonzogranite becomes very distinctly porphyriticas its contact with the surrounding schist and gneiss isapproached. In such border areas, the porphyritic monzograniteincludes both euhedral and ovoid phenocrysts thatmay be mantled by plagioclase. However, such rapakivitextures are not restricted exclusively to widespread exposuresof the porphyritic monzogranite. In the GoldBasin mining district (fig. 2), the porphyritic monzogranite

PETROCHEMISTRY OF CRYSTALLINE ROCKS 53FIGURE 25.-Porphyritic monzogranite of Garnet Mountain. A, Largemierocline phenocrysts in somewhat seriate-textured, porphyriticmonzogranite in southern White Hills; NW't. see. 34, T. 28 N., R. 18W. H, Microcline mantled by rims of myrmekite (note relations at headof arrow) in rapakivi dikelike mass thatruts pendant of mostly biotitegneiss within porphyritic monzogranite in southern White Hills.Feldspars crystalli~ largely in matrix of gneiss. (See fig. 26.4, H forlarger scale view of microcline·myrmekite relations.) Scale is 18 emlong. C, Pegmatite-cored pod as inclusion in porphyritic monzogranitein SW'/. see. 20, T. 28 N., R. 16 W. Note rock hammer in center ofphotograph for scale.also includes some irregularly shaped areas approximately0.1 to 0.2 km2 in size, too small to show on the map,which consist of mixtures ofporphyritic monzogranite andgneiss. In some exposures within these areas, largecrystals apparently ofcompletely mantled microcline arevery common (fig. 25B) and define irregularly boundeddikelike masses of rock that. have a matrix of mostlybiotite-epidote gneiss. In addition, these areas of mixedrock, which undoubtedly are very close to a local roof ofthe porphyritic monzogranite, also contain quartz-cored.graphic-granite pegmatite, probably associated genetical·Iy with the porphyritic monzogranite. However, relativelydeep seated parts of the porphyritic monzogranite in t.hegeneral area ofGarnet Mountain also contain pegmatite.Some of this pegmatite is earlier than porphyritic monzogranite,owing to the presence of pegmatite as pods totallyengulfed by subsequently crystallized porphyritic monzo·granite (fig. 25C).In thin section, the large porphyroblastic crystals ofmantled potassium feldspar are seen to consist of twinnedmicrocline, which is mantled by approximately 0.2- to2.0-mm-wide rims of oligoclase-dominant myrrnekite (fig.26A). The rims of these microcline porphyroblasts alsohost some crystals of albite. In places. optically continuousmicrocline extends through the rims and is in contact. withthe biotite-epidote gneiss. Further, such microcline alsoengulfs very small fragments of biotite-epidote gneiss andshows no development ofa rim of myrmekite between thefragment and the microcline. Although myrmekite andrapakivi textures are difficult to interpret (see Smith.1974), textural relations in these samples (fig. 2M, B) suggestthat the mantles are a postmicrocline phenomenonand thus possibly reflect a simultaneous coupling of (1)calcium migration toward the microcline and (2) subsolidusexsolution of sodium·rich plagioclase.In thin section, the porphyritic monzogranite ofGarnetMountain shows an extremely varied fabric (fig. 26C-F).Although most of the groundmass of fresh porphyriticmonzogranite is hypidiomorphic granular, even the leastdeformed hornblende-biotite porphyritic facies (fig. 26C)and biotite equigranular facies (fig. 26D) of this unit showminor amounts of postcrystalline strain exemplified bymildly bent biotite cleavage lamellae and by undulosequartz. Nonetheless, plagioclase, generally in the rangeAn35 to An40, in much of the porphyritic monzograniteis quite fTesh, showing only slight alteration to white mica.Some plagioclase is zoned normally and includes rims assadic as oligoclase, An2G-25' In addition, hornblende,typically blue green (Z axis), and biotite are remarkablyfresh locally, especially in the porphyritic monzogranitecropping out in the general area of Garnet Mountain.Although the most conspicuous potassium feldspar inthese rocks is perthitic microcline, the range in size ofthese crystals is quite wide. The size of perthitic microclinein the groundmass of much of the porphyritic monzograniteseems to decrease with decreasing abundance of

54 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN·LOST BASIN MINING DISTRICfS, ARIZONAA',-, Jl~ MU...UEflS D" 1 IIIIIILLIM£TEIlSL._~,8E',-,.:;8 Ml.LlMEfEIl$c .,, -"1,,2 MLlJMETEflSF, ,• MILUtUlEllS

PETROCHEMISTRY OF CRYSTALLINE ROCKS 55microcline in the rock. Accessory minerals in the porphyriticmonzogranite include zircon, apatite, allanite,sphene, and various opaque minerals. Pyrite and rutileare very minor accessory minerals that are presentsporadically in the porphyritic monzogranite.Although the exposed levels of the porphyritic monzograniteof Garnet Mountain were not deformed syntectonicallywith the early upper-amphibolite-facies metamorphismof the area, some of the porphyritic monzogranitehas been deformed intensely during the retrogradegreenschist event. Porphyritic monzogranite, for example,which crops out about 1 km north of Iron Mountain,shows an intensely crushed and chlorite-rich metamorphicoverprint (fig. 26E, F). The intense deformation of thesegreenish-gray rocks is indicated by their bent kink-bandedplagioclase (oligoclase-andesine, about An30) and thereplacement of all primary biotite by chlorite and secondarysphene. These folia in turn show neocrystallizationof even later minute undeformed porphyroblasts ofgreenish biotite, which have grown with their {001}cleavage lamella traces at high angles to the foliationdefined by chlorite. Large crystals of primary sphene inthe rocks are broken, veined, and altered to leucoxene.FIGURE Z6.-Textural relations in gneiss immediately adjacent to porphyriticmonzogranite and in porphyritic monzogranite itself. Crossednicols. A, Microcline (M) mantled by myrmekite (myr), showing porphyroblasticdevelopment in matrix ofbiotite-epidote gneiss (gn). Frompendant engulfed by porphyritic monzogranite in southern White Hills.H, hole in thin section. Sample GM-813. B, Myrmekite microveiningmicrocline (M) across and along twin planes in microcline. SampleGM-813. C, Porphyritic monzogranite showing only slight evidenceof deformation, including bent biotite crystals and a slight ribboningand undulation of quartz (Q). Plagioclase (P) is andesine (An4o) andpartly altered to white mica. Mafic minerals are clustered tightly intomostly hornblende-biotite aggregates (bb). Optically unzoned microclinephenocrysts (M) include flakes of biotite (B) and possiblytitaniferous magnetite (mag). Sample GM-50, same as analysis 6, table14. D, Equigranular biotite monzogranite facies of porphyritic monzogranite.K, perthitic microcline; P, plagioclase (An35)' Includesaccessory allanite, sphene, magnetite, apatite, zircon, and sparsesecondary white mica. Sample GM-70, same as analysis 7, table 14.E, Porphyritic monzogranite deformed during greenschist metamorphismof area. Plagioclase (P) is partly altered to epidote and whitemica. All primary biotite is partly altered to epidote and white micaand is replaced by chlorite (C). Perthitic potassium feldspar (K) is rricroveinedby chlorite and epidote (C + E) and by other veins showingquartz-chlorite-white mica-epidote assemblages. Large crystals ofsphene (8) are broken, veined, and altered partly to leucoxene. Accessoryminerals in rock include relatively large crystals of allanite(A). Sample GM-Z9 from approximately 1 km north of Iron Mountain.F, Intensely deformed porphyritic monzogranite. Crosshatch-twinnedpotassium feldspar (K) is veined by white mica, epidote, and quartz.Epidote-rich groundmass (G) also contains chlorite, white mica, andquartz. Fairly large crystals of sphene (S) are altered heavily to leucoxeneand are veined by chlorite, quartz, epidote (trace), and whitemica. Sparse plagioclase (P) in rock is altered partly to white mica.Allanite (A) is accessory. Sample GM-Z9a, locality same as E.The large crystals, as long as 2 cm, ofperthitic potassiumfeldspar are brecciated, are cut by microveinlets of quartz,epidote, chlorite, and white mica, and are replaced bypatches of deformation-related albite.As revealed by petrographic studies, the modal compositionsof unmetamorphosed porphyritic monzograniterange from monzogranite to granodiorite (fig. 24). Mostof these modally analyzed samples, however, plot in thecompositional field of monzogranite; only two of thesamples plot in the field ofgranodiorite, very close to thefield of monzogranite. The color index of the porphyriticmonzogranite ranges from about 5 to about 24 (tables 12,14).Modal content of potassium feldspar in the samples ofporphyritic monzogranite is among the highest of theEarly Proterozoic igneous rocks in the districts (fig. 24).This relation may be interpreted to be the result of differentiation.Projection of this trendline toward thequartz-plagioclase sideline suggests differentiation awayfrom a region close to the plagioclase corner ofthe ternarydiagram. In addition, most of the analyzed samples ofEarly Proterozoic leucogranite plot near the potassiumfeldspar-rich domain of the trendline, whereas samplesofgneissic granodiorite plot near the plagioclase-rich partsof the trendline. However, these modes may not be accuratebecause of the relatively large size of the potassiumfeldspar phenocrysts. Also, many phenocrysts may havecrystallized initially from a magma that was differentfrom that represented by the matrix of the rocks (seeWilcox, 1979).Chemical analyses of eight rock samples from the porphyriticmonzogranite of Garnet Mountain suggest thatthe rocks are chemically quite uniform (table 14). Theseanalyses include a sample from a medium-grained maficpod (table 14, analysis 4) hosted by the porphyritic monzogranite.Contents of SiOz in the eight samples are between64.4 and 71.9 weight percent and average 69.5weight percent. The KzO contents range from 3.3 to 6.1weight percent, and the NazO contents are remarkablyconsistent, ranging from 2.5 to 2.9 weight percent. Theratio of KzO to NazO ranges from 1.3 to 2.4; the contentof KzO is lowest (table 14, 3.3 weight percent, analysis6) in the sample containing the most CaO (4.0 weight percent).This sample (table 14, analysis 6) includes significantamounts of hornblende, and the analysis shows thehighest ferrous- to ferric-iron ratio determined and thelowest content of SiOz. Relatively mafic phases of theporphyritic monzogranite, exemplified by analysis 8 (table14), which is of a rock determined to have a color indexof 18, only differ slightly from leucocratic phases (table14, analysis 2, color index 4.7). These differences consistprimarily of less SiOz and KzO, but more total Fe, CaO,and TiOz. Much of the increased content of TiOz reflectsprobably an increase in the amount of sphene in the rock.

56 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONATABLE 14.-Analytical datafrom the Early Proterozoic porphyritic monzogranite ofGarnet Mountain[Chemical analyses by rapid-rock methods; analysts, P.L.D. Elmore and S. Botts. Methods used are those described in Shapiro and Brannock (1962), supplementedhy atomic absorption (Shapiro, 1967). Spectrographic analyses by Chris Heropoulos. Results are reported to the nearest number in the series 1, 0.7, 0.5, 0.3, 0.2,0.15,0.1, 0.07, and so forth, which represent approximate midpoints of interval data on a geometric scale. The precision of a reported value is approximately plusor minus one series interval at 6~·percentconfidence or two intervals at 95.pe~entconfidence. L?oked for but not found: Ag, As, Au, B, Bi, Cd, Mo, Ni, Pd, Pt,Sb, Sn, Te, D, W, Zn, ill, In, Li, Re, Ta. Th, 11, Pr, Sm, Eu. '-, not detected, N.D., not determmed]Analysis ---- _Sample -------- _1GM-342GM-5533GM-5624GM-5665GM-5736GM-5G7GM-7G8GM-12010 11Chemical analyses (weight percent)3102 -------------~:~~i ===========MgO --------------CaO ------------~i~~f~~~~~~~~=P205 ------------­MnO ---------------­CO 2 -----------­F --------------Subtotal_Less a = F -----71.614.11.42.2.601.92.55.2.84.06.60.23.00.08• 12101.43.0571.914.31.71.2.4012.56.11.4.04.39.11.00.15.06101.31.0369.813.82.32.1.802.22.84.91.7.62.28.09.11.14101.01•0669.414.22.42.4.802.62.84.61.02.74.30.08

Five of the samples of porphyritic monzogranite wereanalyzed for fluorine; the average content of fluorine is0.12 weight percent (table 14). Also, a slight correlationmay exist between the cerium contents of these samplesand their differentiation indices (fig. 27). Generally theanalyses of porphyritic monzogranite are very like theaverage granite of Le Maitre (1976), listed in table 14 asanalysis 10 for comparison. Similarly, the analyses of porphyriticmonzogranite are not much different from theanalyses of biotite monzogranite (table 13), the averageof which is also listed in table 14 (analysis 11). The "degreeof alkalinity" of this suite of rocks from the porphyriticmonzogranite and biotite monzogranite, as indicated usingthe alkali-lime index of Peacock (1931), is calc-alkalic(fig. 28).The limited number of available analyses of the porphyriticmonzogranite preclude our establishing welldocumentedvariation trends. In the AlkFM diagram (fig.29A), the trend appears to be away from a region nearthe F corner to a point along the AlkF sideline, approximatelyone-third of the distance from the Alk corner.However, the two analyzed samples of biotite monzogranite,which apparently is older than the porphyriticmonzogranite, plot near the terminus of such a variationtrend. The ACF diagram (fig. 29B) also shows a poorlydeveloped variation trend projected toward the A cornerofthe diagram. The AKF diagram (fig. 29C) shows morescatter than the two preceding diagrams and suggests avariation trend projected away from the midpoint of the10,000 ,--------r------.-----.---------r-----,EXPLANATIONPorphyritic monzograniteo Fluorine concentrationCerium concentration••ZBiotite monzogranite0 /). Fluorine concentration:::;...JCerium concentration::!a:waa..(fJ 0f- aa:« 1000 -a..~...:z wf-Z0u• •• • ••• •10065 70 75 80 85DIFFERENTIATION INDEX, L(Q + Or + Ab)FIGURE 27.-Fluorine and cerium contents versus differentiation index,!(Q+Or +Ab), of analyzed samples of Early Proterozoic porphyriticmonzogranite of Garnet Mountain and Early Proterozoic biotitemonzogranite.PETROCHEMISTRY OF CRYSTALLINE ROCKS 57IaIa••-AK sideline. Figure 29D shows normative proportions ofquartz, orthoclase, and albite in the analyzed samples fromthe porphyritic monzogranite and the biotite monzogranite.All these samples contain greater than 80 percentAb +Or+An +Q; and all but one of the analyses (table14, analysis 6-a hornblende-rich facies of the porphyriticmonzogranite) contain greater than 75 percent Ab+Or+ Q. The An contents of all analyzed samples of porphyriticmonzogranite and biotite monzogranite, normalizedto 100 percent Q+Or+Ab+An, range from 2.8 to19.2 percent. However, if analysis 6 (table 14) is excluded,the range is 2.8 to 13.2 percent, and the average valueofthe normalized An contents is 8.2 percent. The normativeproportions ofquartz, orthoclase, and albite in all butone ofthe analyzed rocks cluster tightly in an area showingeither an increased K20/Na20 ratio relative to atrendline connecting the ternary minimum at PH 20=Ptotal = 100 MPa for contents of An varying from 3 to 7.5,or decreased ratios of Q/(Ab + Or) relative to these minimums(fig. 29D). However, this cluster of normative proportionsof quartz, orthoclase, and albite coincides with,and apparently is elongate along, the ternary minimumfor PH 20 =Ptotal= 2,000 kg/cm 2 projected onto the anhydrousbase of the Ab-Or-Q-H20 tetrahedron determinedby Tuttle and Bowen (1958). The plot of these data fromthe porphyritic monzogranite and biotite monzogranitethus suggests that the rocks are highly differentiated andthat they may have crystallized from a magma at PH 20 =Ptotal= about 200 MPa, assuming that (1) the samplesanalyzed reflect minimum melt compositions (see above,and Anderson and Cullers, 1978) and (2) the magma(s) wassaturated with respect to H20 (Steiner and others, 1975).The abundance of aplite dikes and pegmatites associatedwith the porphyritic monzogranite and biotite monzogranitesuggests their magma(s) was saturated withrespect to H20 (see Luth, 1969), at least during the finalstages of their primary crystallization.Analytical data based on the chemical composition ofthe Early Proterozoic porphyritic monzogranite of GarnetMountain and Early Proterozoic biotite monzogranite inthe districts appear to have the characteristics ascribedby Petro and others (1979) to continental magmatic arcsgenerated at compressional plate boundaries. This relationis especially true when the data from the districtsare compared with that for the central Sierra Nevadabatholith. The data from table 14 include (1) a nearlyunimodal distribution of differentiation indices (totalrange 67.9 to 88.3), (2) unimodal distributions of norma-90 tive anorthite (average 28 weight percent), and (3) acaldalkali index, which is defmed as the value of Si02 forwhich CaO/(Na20+K20) equals 1.00 (Christiansen andLipman, 1972), greater than 60 (actually 60.5 from fig.28). The alkali-lime index of Peacock (1931) for the cen·tral Sierra Nevada batholith is 60 (Kistler, 1974). Further,

58 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAthe high K20INa20 ratios and the high ratio of (FeO +Fe203)/MgO in these rocks from the Gold Basin-LostBasin districts suggest the rocks have continental ratherthan island-arc affinities (see Jakes and White, 1972). Ifthese analytical data were to be interpreted using the K-h(K20 versus depth to the top of a seismic zone) techniquesof Dickinson and Hatherton (1967), Hatherton and Dickinson(1969), and Dickinson (1975), a plot of percent K20at a projected 57.5 percent Si02 for these data wouldshow that the depth inferred to the top of an inclinedseismic zone would be anywhere from 160 to 270 km. Suchvalues result from the data for continental margin arcsas modified from Dickinson (1975) by Keith (1978). However,the average dip of seismic zones or subducted slabsassociated with compressional continental margins isperhaps 40° (Dickinson, 1975, p. 56). In addition to thepossibility of variably dipping seismic zones (Coney andReynolds, 1977; Keith, 1978), a significant unknown inthe region is the position of the paleotrench approximately1,660 Ma (see Condie, 1982). Further, Wyllie (1981) notesthat the composition of magma becomes depleted in Si02with increasing depth and that high-Si02 graniticmagmas cannot be generated by anatexis of crustal rocksat depths greater than about 30 km, and Glazner (1983)points out several additional problems in relations derivedbetween slab dip and convergence rates.The porphyritic monzogranite of Garnet Mountain,which crops out in the southern White Hills of the GoldBasin district, hosts several gold-bearing quartz veins. Thebulk of these veins strike north-northeast and nearlyparallel the trend of the mapped bodies of gneissicgranodiorite and the biotite monzogranite, which crop outnorth and east, respectively, of the main mass of porphyriticmonzogranite (fig. 2). However, a few goldbearingquartz veins in the porphyritic monzogranite havenorthwesterly strikes. One ofthese veins crops out about1.5 km south-southeast of the Malco mine. Another consistsof the swarm of veins that made up the deposit atthe Cyclopic mine. At the Cyclopic mine, one of theearliest discoveries and the largest overall producer oflode gold in the districts (see above), the ore is found ina northwest-striking zone of gold-bearing, brecciatedALKALI-LIME INDEX AFTER PEACOCK (1931)ALKALIC ALKALI- CALCIC CALC-ALKALICCALCIC15t----...L--------.L---------I---------- -1I-zEXPLANATIONUJU Porphyritic monzogranitea:o NazO+KzOUJQ.l-:I: 10QUJ• CaO3:Biotite monzogranite~,..:6. NazO + KzOo 6.--­L6--- oZUJ .. CaOI- Z0oUUJ 5eX0O'----=':------=- L..:.- ---L ...l...- ----I50 55 60 65 70 75SILICA CONTENT, IN WEIGHT PERCENTFIGURE 28.-Total alkalis (Nl\:lO plus K20) and CaO plotted against Si0 2 for analyzed samples of Early Proterozoic porphyritic monzograniteand Early Proterozoic biotite monzogranite in general area ofGold Basin-Lost Basin districts. Solid lines, visually estimated regression linesthrough Na20 + K20 and CaO data points used to establish an estimated silica content of 60.5 for the igneous suite at the point whereNl\:lO + K20 equals CaO. Thus, the suite is calc-alkalic (dashed line) after Peacock (1931).

PETROCHEMISTRY OF' CRYSTALLINE ROCKS 59quartz veins. most of which probably were emplaced tectonicallynear a contact between porphyritic monzograniteand metamorphic rocks older than the porphyritic monzo.granite. The dips of these veins are mostly to the northeastand range from shallow angles (15° to 25°) to steep(GO''''70')(p.M. B1ace~ unpub. data, 1967-72). The bulkof the ore at the Cyclopic mine consisted of quartz-veinmaterial and not the unconsolidated gouge associated withthe major Tertiary detachment fault which cuts the porphyriticmonzogranite in the general areaofthe Cyclopicmine (see below). Some minor amountsofgold mineraliza·tion may be associated with localized intense ferric andargillic alteration along the detachment fault (Myers andSmith. 1984). This Tertiary fault dips gently to the southwest.Crushed and brecciated porphyritic monzogranitecrops outextensively near the Cyclopic mine. and locallythe porphyritic monzogranite is highly stained by ironoxides. The porphyritic monzogranite near here is alsoseric:itized and even strongly silicified in those areas whereit is flooded by numerous veins and veinlets. The unconsolidatedgouge, which reflects movements along the Tertiaryfault, also locally includes several large blocks of veinquartz. In addition, striations and tectonic polish arepresenton many blocks of porphyritic monzogranite andcc.o..' ".., •° o~ •••K

60 GEOLOGY MD GOLD MINERALlZATION OF TIlE GOLD BASIN·LOST BASIN MINING DISTRICT'S, ARIWNAvein quartz in the fault zone, thus documenting the ageof the bulk of the mineralization at t1le Cyclopic mine aspredating movement(s) along the Tertiary faulLCRAl\ODIORITEGray granodiorite (unit gd of Blacet, 1975) crops outalong the western and southwestern flanks of GarnetMountain as a mafic border facies of the porphyriticmonzogranite of Gamet Mountain (fig. 2). The granodioriteis present both as rather homogeneous discretebodies and in a unit termed by Blacet (1975) "a mixedgranodioritic complex" which includes mosUy granodioriteand lesser amounts ofporphyritic granodiorite andporphyritic monzogranite. All of these rocks are approximatelycoeval and comagmatic with ooe another. Contactsbetween granodiorite and porphyritic monzograniteare gradational. However, the mixed granodioritic complexalso includes some of the leucocratic monzogranite,which is definitely older than the granodiorite as indicatedby crosscutting relations. Locally, the granodiorite iscoarse grc.ined and sparsely porphyritic, with perhaps 20phenocrysts of potassium feldspar scattered across an exposureof about 0.1 m2. Mostly, these phenocrysts are setin a coarse-grained, hornblende-biotite hypidiomorphicgranularmatrix that is rich in magnetite. Magnetite clotsas much as 1.5 cm wide are quite common in the gran0­diorite, and magnetite-rich sands are very characteristicof present-day arroyo bottoms that drain areas underlainby outcrops of granodiorite.In thin section, samples of the granodiorite are seen toconsist ofsomewhat varying proportions of biotite, hornblende,quartz, plagioclase, and potassium feldspar, andthe minor accessory minerals magnetite, apatite, and zircon.Plagioclase is more abundant than potassium feldspar.The major overall texture of some of the mediumgrainedfacies of this unit is hypidiomorphic granular, yetsubporphyritic, seriate, and slighUy gneissic fabrics arepresent locally. Fabric of a representative sample ofmedium-grained granodiorite is shown in figure 3OA. Thecolor index of the granodiorite ranges from ahout10 toabout 25 and probably averages about 20. Plagioclase inthe equigranular varieties of the granodiorite probably hasan anorthite percentage of about 30 to 35, whereas earlycrystallized plagioclase, which is included within some 2­to 3-em-wide equant and euhedral phenocrysts of p0tassiumfeldspar, has anorthite percentages of about 40. Inaddition, plagioclase in Ole granodiorite generally issparsely altered to white mica. Nevertheless, parts ofsome crystals of plagioclase are almost completely replacedby sheathlike aggregates of white mica and claymineral(s), with or without traces ofclinozoisite and carbonate.Blue-green (Z axis) hornblende ranges from 0 toperhaps 15 volume percent of the granodiorite. In thosefacies ofthe granodiorite that include botil hornblende andbiotile, the biotite is red-brown (Z axis), whereas thehornblende-free facies show biotites that are dark brown(Z axis). Mafic minerals tend to form clusters in thegranodiorite, which in places contain very abundant COIlcentrationsof apatite (fig. 308). Some samples ofgranodiorite show sparse concentrations of 4· to 5·mmwideovoid aggregates of highly strained, polycrystallinequartz, possibly reflecting incorporation ofsome materialfrom the gneiss.8FIGURE 30.-Textural relatiorul in Early Proterozoic gnmodiorite bordetphlUleor the porphyritic monwgrnnite or Gamet Mountain. SampleGM·1131, Stv. st>

PETROCHEMISTRY OF CRYSTALLINE ROCKS 61Fluid inclusions are abundant in some of the primaryquartz crystals. Isolated. approximately 6- to IQ-j.£m-Iongfluid inclusions are concentrated in subhedral to ovoidcrystals ofquartz hosted by essentially unaltered phenocrystsof potassium feldspar. Some of these fluid inclusionsare rich in carbon dioxide becau..

62 GEOUX;V AND GOLD MINERAUZAI'ION at' THE GOLD BASIN-LOST BASIN l'oUNUm D1STRICI'S, ARIZONA''0· ,,,..,..,.".. .,,-,,~,,-"-"~e::,~r'(I:~~ ..e-.._..._..1.. 0(! \I 10 0 -';'-1'-"-"~. ," UV eo "I~~~ ~'e • ~@ ~ 0iii1-.._ ..-\"\EXPLANATIONSIz~ of oc;curr~nc~>1000 10mOo 2100-1000 10m!o10-99 km lAg~ of occur~nce• >90MiIe 45-90 Milo

PETROCHEMISTRY OF CRYSTALLINE ROCKS 63exhibit pervasive cataclastic or mylonitic fBbrics. The twomicamonwgranite, which is fine to medium grained,shows locally sharp contacts with surrounding amphibol·itic gneiss. In the vicinity of these contacts, tbe grain sizeof the two-mica monzogranite does not progressivelydecrease, the overall abundance of mafic minerals doesnot increase, and inclusions of wall rock are absent. Thetwo-mica monzogranite generally has an equigranularfabric, and overall its area of outcrop is remarkablyhomogeneous lithologically, showing a strong affinity tothe compositionally restricted granite series of Pitcher(1979). In some localities, however, the two-mica monzograniteis porphyritic or slightly foliated. The prophyriticvariants contain as much as 5 percent quartz phenocryststhat reach sizes of about 5 cm wide. The foliated aspectis imparted by a weakly defined primary layering ofdimensionally oriented potassium feldspar and biotite,probably reflecting a flow fabric. Within the main bodyof the two-mica monzogranite, locally sharp contacts arepresent between a fine-grained, sparsely porphyriticbiotite monzogranite facies and a muscovite-biotitemonzogranite facies. Close examination of these relationssuggests that this muscovite-rich facies of the monzograniteis not a metasomatic replacement of biotite-richmonzogranite.The two-mica monzogranite contains some syeniticzones. This syenitic rock probably reflects subsolidus episyenitizationor fenitization, judging from the associatedenrichments in muscovite, fluorite, and potassium feldsparand depletion of primary quartz adjacent to local swarmsofquartz-, pyrite-, and muscovite-bearing veins. In places,such veins also include some carbonate and fluorite andappear genetically related to the two-mica monzogranite,because the veins cutthe two-mica monzogranite and arein places cut by the two-mica monzogranite. Sparse concentrationsof chalcopyrite and specular hematite alsowere noted by Blacet (unpub. data, 1967-72) to be ass0­ciated witll some of the veins which cut the two-micamonzogranite.Veins and irregular quartz segregations also appear tobe concentrated in gneiss in the general vicinity of tlletwo-mica monzogranite. The irregular quartz segregationsare associated spatially witll aplite and muscovitebearingpegmatite, an association giving the appearancethat the quartz segregations are also related geneticallyto the two-mica monzogranite.The two-mica monzogranite shows fairly clear-cut contactrelations with two other lithologies. The two-micamonzogranite is cut by some unmapped Tertiary dikes,one of which is shown in figure 32. Most such dikes arepartly chIoritized, porphyrit1c biotite dacite, probablyrelated to the Mount Davis Volcanics. On the southwest,the largest body of two-mka monzogranite (fig. 2) is infault contact with Tertiary(?) fanglomeratic rock of theMuddy Creek Formation. Crude striae are developed onthe topmost. surfaces of unweathered two-mica monzogranitewhere it was excavated by B1acet (unpub. data,1967-72) along the trace of the fault. The trend of thesestriae is approximately N. GO° W. Further, immediatelyabove the poorly striated pavement of two-mica monzogranite,a highly comminuted 10- to 15-cm-thick zone ofred sandy-clay gouge contains clasts less than 1 em indiameter. P.M. Blacet traced this low-angle fault to thesoutheast where it crops outin the immediate area oftheCyclopic mine and to other nearby areas where it juxtaposesTertiary(?) fanglomerate and Early Proterozoicporphyritic monzogranite of Garnet Mountain (fig. 2).Examinations of 10 thin sections of the Cretaceous twomicamonzogranite reveal a wide range of textures andcompositions. Modal compositions of nine samples rangefrom a biotite-free felsic muscovite granodiorite tomuscovite-biotite monzogranite (fig. 33). The samples ofF1ct!RE 32.-Tertiary (1) ~te. partly chIoritized, porphyritic biotitedacite dike containing • 8eptum oC Late Ctet8C«JU!l t ....,o-mic:a Il'JOnlOgranite.Note rock hammer in central part or pbotognapb ror scale.

64 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAmuscovite granodiorite are typified by approximately2.0-mm grain si7..es and well-developed hypidiomorphic·granular textures. The muscovite granodiorite includesas much as 47 percent by volume euhedral, tabular crystalsof normally zoned plagioclase (oligoclase, An I 5-20)'The plagioclase typically is extremely fresh and showsonly sparse dusting by minute crystals of white mica.Some samples, however, show crystallization of 0.2- to0.4·mm·long books of white mica demonstrably subsequentto crystallization of plagioclase. Biotite in the morecommon two-mica monzogranite facies of this body of rockis generally dark brown (Z axis), showing slight tints ofgreen under the microscope, and is present in very wideranging proportions (from 0 to about 10 percent byvolume). Quartz is aJso highly varied in the two-micamonzogranite, both texturally and modaJly. Rare quartzbipyramids were noted in some rocks, but more commonlythe quartz is present in 2- to 3-mm-wide ovoid aggregatesof polycrystailine quartz. Such quartz generally is interstitialto plagioclase and potassium feldspar. Potassiumfeldspar, making up 25 to 35 volume percentof the rocksstudied, is extremely fresh and shows the well-developedcrosshatch twinning of microcline. Some potassiumfeldspar crystals poikilitically include numerous orientedcrystals of oligoclase (fig. 34A). Minor accessory mineralsinclude zircon, opaque minerals (both equant and prismaticvarieties), rutile (in places clustered in books ofwhite mica, and elsewhere as needles in quartz), and raregarnet. Some extremely sparse relatively large crystalsofapatite show euhedral O.8-mm-wide basal sections containingeuhedral laths of biotite.Potessium leldspe.G.eni,e•• e" '"_Gre""-ifi'eT.,....~teFiGURE 33.-Modes of Late Cretaceous two-mica monzogranite in GoldBasin mining district. Compol;itionai flcldll from Stred.eisen and oth

PETROCHEMISTRY OF CRYSTALLINE ROCKS 65altered samples of the two-mica monzogranite show SiOzcontents that range from 70.9 to 71.9 weight percent,Alz0 3 contents that range from 14.9 to 15.5 weight percent,and total alkalis (KzO plus N&20) that range from8.03 to 8.96 weight percent. The mean ratio of N&20 toKi) in weight percent is 1.00 for the five samples. A plotshowing the ratio of Alz0 3:(KzO+NazO+CaO) inmolecular percent versus SiOz in weight percent for theanalyzed samples of the two-mica monzogranite revealsthe extent of alumina saturation in these rocks (fig. 35).For comparative purposes, we show also on this figurea field for selected Late Cretaceous to Eocene two-micagranitoids from elsewhere within the cordillera, compiledby Keith and Reynolds (1980). The two samples ofalteredtwo-mica monzogranite (fig. 35, analyses 5, 7) plot significantlyaway from the field of two-mica granitoids,whereas the samples of Wlaltered two-mica monzogranitecompare favorably with the field.The two-mica monzogranite from the Gold Basin districtis peraluminous. Five samples of unaltered monzograniteshow values for Alz03:(KzO+NazO+CaO) in molecularpercent that range from 1.09 to 1.21 (fig. 35). Althoughfour of these five values of Alz03:(KzO+N&20+CaO) plotin the strongly peraluminous field (>1.10), two-mica,A',-,__-,',;4 "lUlMETER., .. 'I .'c".,•...BD',-,'o? ....U..ETERFiGURE 34.-Textural relations in Late Cretaceous two-mica monzogranite.A, Subhedral crystalsofoscillatory·zoned, perthitic JXltassiumfeldspar (Ids) showing inclusion ofnumerous, small, oriented, euhedralto subhedral crystals of partly sericitized oligoclase (Anl~a». In addi·tion, crystal of included primary biotite (B) shows marginal developmentof secondary white mica (M). Sample GM-t09Oa. B, Coan;el~'crystalline white mica. (M) filling interstices among framework·SUpJXlrted network of euhedral plagioclase (P). Sample GM-917c. C,Knife-edge contact between muscovite (1'.1) and biotite (B) showing noalteration effccl1l in either mineral. Q, quartz; kfs, JXltassium feldspar.Sample GM-I089. D, Biotite (B) cut by muscovite(M) that has in turnbeen cut by subscquentJy crystallized, somewhat finer grained generationof biotite. All biotite is greenish brown (Z axis). H, hole in thinsection; kfs, potassium feldspar. Sample GM·I089.

66 GEOLOGY AND GOLD MINERALIZATION 0 ... THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIWNAAnalysis ___ , 2 , • , 6 1Sample GK-1089a GH-1089b G.....O G~1068 GM-811 G~ll0] G11-92]bAChetllical analyses (weiiht percent)S171.5 11.5 10.9 11.6 62.1 11.9 ".0Al 2 15.3 IS.] 15.5 111.9 20.5 15 11.]~:SOJ,., 1.19 1.]] 1.] I I." 1.06••.2 .21 .S' .15 .28." ."",,0 .20." .,. .26 .22 .n."'"" I." , .50 .26." .., 1.18 .565.69"(.., '1.21II."] ].12 ,... II.]]11.96.... '> ---- '-', 11.19 ,.60 5.2" 6."",0. .., ... .,. ...- ." ."~.,..-- •1 ., .06 .0' ... .0'T O 2 .21 .2 .25 .11 .16."'2"---- .06 .06 ... .06 ., .05.0' .02;"> .".12 .,. .".n.01 .06 .06 • 12.' ... .01Gl ______S .025 .018 .012 .026 .005SUbtotal __ ".26 98.6198.6 "...96.95 96.8]Less ~f __ .0, .0' .0' .05 .1' .02 .0'"Total ___ 99.2] 98.M 98.91 98.55 98.95 98.93 96.6se.1quant1tat1ve spectroSr8ph1C analyses (wdiht percent)B .000] .0003 .0003 .0002 .0002B. • 1 .15 .15 ., .15 ., .015.. ----- .0003 .0003 .000] .0003 .0005 .0005 .0005C. .0002 .0002 .000' .0002 .0002 .0002Cu _______ .0002 .0002 .00015 .0002 .0002 .0002 .0002" L. ______ .0005 .0005 .0005 .0005 .00' .0007 .000'Hn ________.00' .005 .0> .005 .001 .001.015 .02 .015 .02 .., .02 .02,.------ .0005Hb --____.0001 .0001 .0001 .0001 .0015 .0001 .005So eo------ _________ .003 .00] .003 .002 .005 .005 .00'.000] .000] .0002 .0003 .000]Sn --_____S, _______ .0001.0' .01 . 1 .02 .., .01 .001HI -------- .0001 .0001 .00015 .000] .0001 .00001 .000'•------- .002 .002 .00] .0015 .002 .0015 .0001, --------- .00' .0001 .0001 .0001 .001 .001 .0001" C. ------- ______ .0> .0> .015 .001 .001 .001 .0015G. ______ .001 .007 .015 .0> .015 .0>.003 .00, .00] .00' .005 .00' .001G. ------- .0001Yb-----_ .00001 .000' .00001 .00001 .0001Chemical analyses (parts per mUllon).06 .05"B------ '".CO .0> .0> •0>." ....------ 2 1 , 2,. 53 ., 61monzogranite from the Gold Basin district is significantlyless peraluminous than many other peraluminousgranites (Keith, 1986). In addition, a plot of Na20+ K20in molecular percent versus AI203 in molecular percent"12 52shows a strong clustering of the five samples of unalteredtwo-mica monzogranite in the peraluminous field, approximatelyat 10 molecular percent AJ~ (fig. 36). Suchvalues ofalumina saturation are similar to values reported"

PETROCHEMISTRY OF CRYSTALLINE ROCKS67TABLE 15.-Analytical data from the Late Cretaceous two-mica monzogranite-ContinuedAnalysis ----- 1 2 3Sample -------- GM-1089a GM-1089b GM-8804GM-10885GM-8776GM-11037GM-923bCIPW norms (weight percent)Q ------------- 28.5C --------------or ------------2.325.3ab ------------- 36.7an ------------ 3.8en -----------mt -----------.58hm ------------- 1.3il ------------ .36ru ------------- .03ap -------------fr -------------.14.13pr ------------- .06cc ------------ .30mg ------------29.32.428.3225.1 21.536.24.237.96.5.51 .91.10 .951.1 .69.39 .48.14 .22.11 .11.0430.1 4.7 29.2 16.63.2 4.3 1.9 2.331.4 37.9 24.4 29.732 48.7 37.1 48.74.4 .9.41 .1 .55 .28.04 .33 .451.3 1.3 .84 .09.3 .44 .31.02.14 .24 .12.24 .61 .08 .14.02 .06 .02.02 .12 .44 .39.22 .59Total ------- 99.5Salic ----- 96.6Femic ----- 2.999.697.22.499.696.23.499.4 99.0 99.6 99.796.7 95.6 97. 98.22.7 3.4 2.6 1.5l D•I • ----------- 90.690.687.793.5 91,3 90.6 95lDifferentiation index of Thornton and Tuttle (1960), defined as the total of normativequartz plus normative orthoclase plus normative albite.1-4. Two-mica monzogranite.5. Episyenite facies of two-mica monzogranite; NE1/4 sec. 24, T. 28 N., R. 19 W.6. Two-mica monzogranite.7. Two-mica monzogranite, partly altered by nearby quartz-fluorite-white mica veins;NW1/4 sec. 10, T. 28 N., R. 18 W.for the Australian S-type granites by Chappell and White(1974) and Hine and others (1978). The two-mica monzogranitein the district shows CIPW normative corundumto be generally more than two weight percent (fig. 37;table 15) and in this regard corresponds to an S-typegranite according to some of the criteria used by Chappelland White (1974). However, the two-mica monzogranitein the Gold Basin district shows some majorelementchemistry that is significantly different from theAustralian S-type granites. The alumina saturation in thetwo-mica monzogranite is largely a reflection of its depletionin CaO. In this regard, the two-mica monzogranitediffers from the Australian S-type granites because theiralumina saturation results apparently from a depletion inNll20 during weathering of the source rocks of the S-typegranites (Chappell and White, 1974). The two-mica monzograniteis not depleted in Na20 (table 15) as are mostother well-studied suites of two-mica granitoids in thesouthern cordillera (fig. 38; see also Keith and Reynolds,1980). In fact, relative to S-type granites in Australia,most peraluminous granites in southwestern NorthAmerica are notably enriched in sodium and some haverelatively high concentrations of strontium (White andothers, 1986). White and others (1986) have concludedfrom their studies that S-type granites, that is, graniteswhose chemical characteristics primarily reflect theircrustal sedimentary or metasedimentary protolith(s), donot exist in southwestern North America. As shown onfigure 38, the five samples ofunaltered two-mica monzogranitefrom Gold Basin straddle the mutual boundarybetween the compositional fields defined by majorelementdata obtained from the Paleocene two-mica PanTak Granite of southern Arizona (see Wright and Haxel,1982) and Late Cretaceous two-mica granitoids from theWhipple Mountains, Calif. (Anderson and Rowley, 1981).Data from the Pan Tak Granite, the Whipple Mountains,and the two-mica monzogranite in the Gold Basin districtplot on the albite-orthoclase side of the quartz-feldsparjoin at 500 kg/cm 2 , a relation which also clearly contrastswith that ofthe Australian S-type granites (fig. 38). Further,in the Australian S-type granites, Na20 is generallyless than 3.2 weight percent for rocks showing K20contents of about 5 weight percent (Chappell and White,1974), whereas the minimum content of Na20 in the twomicamonzogranite from Gold Basin is 3.72 weight percent(table 15). Haxel and others (1984) have proposed anelegant model to account for the genesis ofearly Tertiarytwo-mica granites (their compositionally restricted, silica-

68 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONArich, crustal-anatectic granites) in southernmost centralArizona. Their model includes anomalous heat flux fromthe mantle together with an upper crustal buildup of heatowing to the thermal blanketing effects of a tectonicallyoverthrust, regionally extensive sheet of rocks. The applicabilityof such a model to the rocks in the Gold Basinf- 1.4z wuffi0- 1.3a::

PETROCHEMISTRY OF CRYSTALLINE ROCKS 696I I I1---EXPLANATlON2UJCretaceous two-mica monzograniteI-201- _5 ~1 Outer limit of granitic complexU2UJ 4 Old Woman-Paiute Range-::a:U Queried where uncertain-/~a::-,-QUJ2 c..~Ia::IO~2,UUj_7UJ~ 2:=:2-7'I- -

70 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONATABLE 16.-0ccurrences of episyenitic and syenitic rocks known in the Gold Basin-Lost Basin mining districts[Modified from P.M. Blacet, unpub. data. 1967-72]DescriptionLocality(from pl. 1)CODllloditiespresentCoDlllentsSeries of four nearby coarse- and fine-grained,fluorite-bearing potassium feldspar episyeniticbodies. Locally abundant pyrite; some carbonate.Probably reflects alteration of Proterozoicrock during the Cretaceous.Medium- to coarse-grained episyenitic body.Contains fluffy, orange carbonate andsome iron oxide.Syenitic aplite dike. Abundant quartzand red-brown carbonate associatedwith this pyrite-bearing dike.Episyenitic aplite. Some disseminatedpyrite. Sparse carbonate.Muscovite episyenite facies of Late Cretaceoustwo-mica monzogranite. Abundant quartz,muscovite, and colorless fluoriteveins are associated spatially.19 Au, F800 Au?297 Cu stain (trace)308 Au?811 FMuscovite yields K-Ar ages of 128 and129 Ma. The episyenite bodies areovoid shaped, have maximum individualoutcrop dimensiOnS of about 10 m,and crop out for approximately 10 malong a N. 50 0 w. trendline.Episyenitic body measures approximately55 by 20 m and is elongate in aN. 60 0 E. direction. Ringed by anapparently genetically associatedzone made up of stringers of quartz.A N. 35 0 E.-striking dike, apprOXimately8 to 10 m thick, poorlyexposed.Exposed in area approximately 3 m longOn south slope of small hill.VeinS associated with episyenite areas much as 8 cm thick. Sparsequartz fills cavities and selectivelyreplaces potassium feldspar. Quartzencloses abundant fluid inclusionscontaining high proportions of liquidcarbon dioxide.Indeed, because of the genetic and possibly economic importanceof this occurrence, we include its petrographicdetails and chemistry in the section "Gold Deposits andOccurrences." Primarily because the Late Cretaceoustwo-mica monzogranite includes some episyenitic facies,we infer that episyenite distant from the Late Cretaceoustwo-mica monzogranite to be Cretaceous in age also.GOLD DEPOSITS AND OCCURRENCESLode and placer gold deposits and occurrences are widespreadthroughout the Gold Basin-Lost Basin miningdistricts (table 11). These reported lode deposits and occurrencesinclude numerous veins, one occurrence ofdisseminated gold, and veins caught up along the Miocenedetachment fault. The most productive placers occuralong the east flank of the Lost Basin Range. Relativelyminor placer deposits were worked along the west flankof the Lost Basin Range and south-southeast of theGolden Rule Peak in the Gold Basin district. In addition,relatively significant shows of secondary copper mineralsare present in the general area oflocality 1357 (pI. 1; table11). This area was geochemically studied in detail by Krish(1974), who concluded that the geochemical associationsin rock there most likely reflect those to be found veryhigh in a buried porphyry copper system, beyond even theoutermost extent ofthe dispersed propylitic or advancedargillic halo. However, a careful review of available evidencefor and against the presence of a porphyry-coppersystem at depth led Deaderick (1980) to conclude that itspresence could not be substantiated.The gold-bearing vein deposits and occurrences in theGold Basin-Lost Basin mining districts appear to havebeen emplaced episodically over a very long timespan thatranges from the Early Proterozoic to the Late Cretaceousand (or) Paleocene. Indeed, Schrader (1909) recognizedthat the veins in the Gold Basin-Lost Basin districts contrastedsharply with those in the Black Mountains volcanicprovince (fig. 39). He grouped the veins in these districtswith those of the Cerbat Mountains, about 50 km southofGold Basin, and noted that they appeared to be associatedwith "post-Cambrian intrusions ofgranite porphyry"(Schrader, 1909, p. 48). Schrader further noted that thefissure veins ofthe Black Mountains cut Tertiary volcanicrocks and probably formed at depths shallower than thoseof the Cerbat Mountains. Blacet (1975, and unpub. data,1967-72) documented the presence of visible gold or theinferred presence ofgold at more than 100 sites throughoutthe crystalline terranes of the Gold Basin-Lost Basindistricts (table 11). Emplacement ofthese veins took placeduring at least three periods. First, hydrothermal emplacementapparently occurred rarely sometime duringthe Early Proterozoic, most likely concurrently with theregional greenschist metamorphism. Some of the veinsin the districts may have been emplaced synchronouslywith the apparently Middle Proterozoic mineralization inthe southern Virgin Mountains. In the southern VirginMountains, 50 km north of Lake Mead, vein-type goldmineralization is probably related to the emplacement ofthe Middle Proterozoic Gold Butte Granite of Longwell(1936) (Longwell and others, 1965). After a long gap inthe mineralization record, the emplacement of gold-

GQW DEPOSITS AND OCCURRENCES 71bearing veins 0CCWTed most likely during the Late Cretaceousand early Tertiary (Laramide). The most widespreadintroduction ofgold-bearing veins was during thisperiod; many ofthese veins were localized along both highandlow-angle faults and fractures within the Early Proterozoicmetamorphic and igneous rocks. Finally, soltleof this vein·type mineralization also has been localized tectonicaJlyalong the trace of the regionally extensiveMiocene detachment fault where it crops out near thesouthwestern partof the Gold Basin district. The detachmentfault in this part of the district produced low-anglegouge zones that locally contain fault blocks of goldbearingquartz veins.Gold mineralization in the Gold Basin-Lost, Basin miningdistricts thus contrasts strongly with gold mineralizationin much of the surrounding region_ The bulk of theprecious metal mineralization in the Black Mountainsvolcanic province of Ligget and Childs (1977) appears tobe related with spatially associated Cenozoic volcaniccenters; this relation is probably best exemplified bymineralization in the Searchlight district, Nevada~.115""" •NEVADACAliFORNIA114"•EXPlANATION113"• Gold.......oingdlo"kbBlade Moun.......~..nk""00.'1..,,,.O, •• ARIZONA... •"l• ••.') ..~ •• ••FtCURE 39.-ArellS reported by Liggett and others (1974) to containgold mincraliU\tion in general area of Ule Black Mountains volcanicprovinoe of Li~ttand QUlds (1977). Only prominent mining districts""""".(Callaghan, 1939) and in the Oatman district, Arizona(Lausen, 1931; Clifton and others, 1980). Gold mineralizationin the Oatman district. is probably younger than about10 Ma (Thorson, 1971). Some other nearby areas outsidethe Black Mountains volcanic province also have beendescribed recenUy as hosting significant gold mineralizationolder than the volcanism in the province. A goldbearingbrecciapipe in the Clark Mountain mining district,72 km southwest of Las Vegas, Nev., has been dated at100 Ma (Sharp, 1980). In addition, the copper-nickeloobaJt-platinumores associated with hornblendite intru·sions at the Key West mine in the Bunkerville miningdistrict, northern Virgin Mountains. Nevada, containedlocally as much as 0.25 m per ton gold (Bea1, 1965, p_ 69).Most early workers in the district(see Lindgren and Davy,1924) believed the mineralization there to be Proterozoicin age. However, BeaI (1965) suggested that hypogenecopper (chalcopyrite) there may have been superpo6ed ona nickel-eobalt-platinum metal association during the LateCretaceous and (or) early Tertiary. The unquestionablyEarly Proterozoic massive-sulfide deposits at Jerome,Ariz., produced substantial amounts of copper ore containingbyproduct gold and silver (Anderson, 1968). TheUnited Verde deposit is reported to have produced 34million tons of ore grading 5 percent copper, 1.7 ouncesper ton silver, and 0.045 ounces per ton gold (Andersonand Guilbert, 1979, p. 42).PROTEROZOIC VEINSAt least two occurrences of gold-bearing quartz veinsare believed to be Proterozoic in age. One consists ofirregular centimeter-size stringersofquartz together withmuch less abundant calcite, chlorite, galena, chalcopyrite,and pyrite, and trace amounts of gold visible along theassociated iron oxide-stained fractures through the quartzstringers. Secondary minerals along the veins includecerussite, wulfenite, and some green and blue secondarycopper minerals. These veins. concentrated in a zoneseveral meters across, have unquestionably been involvedin the ductile deformation that has affected the enclosingmafic gneiss. In outcrop, individual veins appear tosubparallel the local schistosity. However, thin-section examinationof vein-wall rock relations shows that someveins here locally crosscut the schistose fabric of theirwaDs as they pinch and swell through the gneiss (fig. 40A).In addition, quartz in these veins has a recrystallizedgranoblastic texture wherein the [0001] axes of quartz appearto have a fabric similar to the fabric ofquartz in theenclosing gneiss. Furthermore, quartz in the veins isrelatively free of fluid inclusions, and quartz-quartz crystalboundaries typically fonn 120 0 angles. The minoramounts of chJorite in the veins are concentrated alongthe medial portions of many individual veins, whereas

72 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING D1STRICI'S, ARIWNAbiotite immediately adjacent to the veins has not beenaltered to chlorite. Calcite is a paragenetically late mineralin the veins and is present interstitially with the tightlyinterlocking quartz crystals.The second 0CCl.IIT'el'lCe of gold-bearing quartz veins thatmay be Proterozoic in age is in the general area of SaltSpring Wash, near the northeast corner of the SenatorMountain H>-minute quadrangte (pl. I,loc. 735; table 11).Gold mineralization here, however, is only provisionallyassigned to the Proterozoic on the basis of two Proterozoicages (712 and 822 Ma) obtained from white mica separatesA'tY-'?i ..1I.UO«lUl1ifrom a vein at this locality. In contrast to the welldevelopedmetamorphic fabric of the veins at the firstlocality of Proterozoic veins. these goJd-bearing veins fromthe general area of Salt Springs Wash apparently havenot been involved in the regional metamorphism of thearea and may have been emplaced sometime during themiddle Proterozoic, penecontemporaneous with the GoldButte Granite_ Altered amphibolite makes up the wallsof the veins, and the rocks show some evidence of shear·ing and brecciation along both the footwall and the hangingwall of the most persistent of the veins. In fact, theveins at this locality appear to have been broken into aseries of pods and segmented quartz veins along a steeplydipping shear Wile, which strikes about N. ]0° W. (p.M.Blacet, unpub. data, 1967-72). 1'he primary assemblagein the veins at this locality includes milky-white quartz,carbonate, galena, chalcopyrite, white mica(?), and gold.The carbonate is distributed sparsely and erraticallythrough the quartz as grayish-brown irregularly shapedmasses of ferroan("!) calcite (fig. 40B). Pyrite, some cubesreaching dimensions as much as 2.5 cm wide, is typicallyreplaced by coarsely to finely cellular boxworks that arevery siliceous. The bulk of the gold appears to have beendeposited very lateduring the overall paragenesis of theveins and is present mostly as approximately O.5-mmflakes at the interface between milky-white quartz andvery lateclear quartz, which lines some vugs and cavitiestogether with drosy quartz. In addition, the pyrite hereis possibly auriferous. Traces of very delicate flowerlikeclusters of gold are present in some of the siliceous boxworksthat replace pyrite. Indeed, our collections fromthese veins, together with Blacet's earlier sampling,yielded a suite of samples showing generally nodularmasses of paragenetica.Uy very late gold, some possiblyeven supergene, in various textural relations with earlierand subsequently crystallized quartz (fig. 41A-F).BF'IGtlRE 40.-MiI:~ and megaaropic relations in apparently Pr0­terozoic \.t'\ns. A, Vein defomwd along with biotite-dominant lIChistosC'fabric of its encloSng gneiM.. Prinwy assemblage of \'ein includesquartz (0. c:akite. c::hIorite,~ dJalcopyrite, and pyrite. Gold wasfound along iron oxXle-ltained fractun.>s. Secondary \~ minenJlS includecerrositeand wulfenite. Plaoe-polamed lighL Sample GM·911.B, Ferroar(!)gt"3y-brown calcite (C) in goId.bearing quartz: (Q) lit locality735 (table II). Note coin lit lower left corner of photograph for""",.f'lGtlRE 41.-Scanningelecll'Otl microgJ'aphlS showing relations orgoldin apparently Proterozoic mll$at klatlity 735(p1. I) in Senator MoontainIS-minute quadrangle. Au, gold; Q, quartl. A. Blebby nodulargokI depo!;ited OIl euhedraUy tenninated cpmrtz pro~ into an opencavity. Sample GM-73&-1. S, C1ustet" of smaB noduJesof gold perched011 quartz. (7)"stallS depOOted~ ....-aIb; orctDcmold infetTed to rdIectp9.I'tlgl!:oeticaily earlier aystaI or pyrite. Sample GM-735-Ic. C,Relath'ely Ialge massof rKN.l.J1ar gold on and intergrollm with quartz..RectaJlgUiararea shovo'll in D. Sampk! number GM-735-4. D, Oo6eupview or nodule or gold rrom ~anguIar area outlined in C 6howingrepeated tvtinning on {llll and poorly pr8leryed~f~Sample GM-735-4. E. Panlgenetieally late, doubly tenninated Cf)'Stalof quartz on a surface of gold. Sample GM-73&-lb. F, Quartz 0')'lStaIat head of 2lTOW associated with nodules ofgold. all of which rest 00matrix of gold. Sample GM-735-ld.

GOLD DEPOSITS AND OCCURRENCES 73A ',-, -.e,3f MICROMETERSD o 3 MICROMETERS~B ',-, -.e,3,OMICROMETERS E o 10 MICROMETERS~'-~'c o 30 MICROMETERS~'-~'F o 10 MICROMETERS~'-~'

74 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN·LOST BASIN MIl\'lNG DISTRICI'S, ARIZONALATE CRETACEOUS AND (OR) EARLY TERTIARY VEINSThe vast majority of the gold-bearing veins in the GoldBasin-Lost Basin mining districts presumably are LateCretaceous and (or) early Tertiary in age. These veins fillfissures and display sharply defined contacts with thecountry rock. Furthermore, they are locally quite persistentandin places have been traced for approximately 0.25km by surface and underground workings (fig. 42A). Thegreatest concentrations of veins are in the southern partof the Gold Basin district and in the central part of theLost Basin Range (fig. 2). Generally, in both of these areasmany veins crop out individually and have northerlystrikes, although a few have east-west strikes, their attitudesare controlled mostly by the attitudes of the surrOWldingschist and gneiss. Previously, Schrader (1917)FiGURE 42.-Sele

GOLO DEPOSITS AND OCCURRENCES 75suggested that most of the gold-bearing veins in the LostBasin Range strike north, whereas the copper-bearingveins strike northwest. However, the preferred orientationof the strike ofthe bulk of the veins measured in bothdistricts is northeasterly. Orientation of325 veins in theGold Basin-Lost Basin districts is shown in projection infigure 43. Poles to veins in this diagram show double maximumsthat plunge to approximately N. 25 0 W. and N.65 0 W. at concentrations greater than 3 and 4 percentper l·percent area. The orientation of these maximumsis compatible with the bulk of the veins in the districtshaving been emplaced into a regional stressfield whereincrustal extension during the Late Cretaceous and earlyTertiary was oriented north-northwest to south-southeast.As such, crustal extension in the districts during the LateCretaceous and early Tertiary appears to have beenoriented similar to that prevailing across much of theBasin and Range province of Arizona (Rehrig andHeidrick, 1976), with some notable exceptions, however.Late Cretaceous and early Tertiary veins in the Wallapaimining district, which includes the Mineral Park porphyrycopper deposit approximately 16 km northwest ofKingman, Ariz., show strong preferred concentrations oftheir strikes in a northwest direction (Thomas, 1949).The predominant association of gold in the quartz veinsof the Gold Basin-Lost Basin districts is with ferroancalcite, pyrite, and lesser amounts of galena and chalcopyritein varying proportions. Free gold also is presentN. 650 W.N. 25° W.,o(]oFiGURE 43.-0rientation of poles to veins in Gold Basin-Lost Basindistricts. Lower hemisphere, equal-area projection. Contours: 1.2,3. and 4 percent per I·percent area. Data modifed from P.M. B1acet(unpub. data, 1967-72).in two of the fluorite-bearing veins in the Gold Basindistrict and was noted to be present elsewhere in thedistricts in veins that include minor amounts of chlorite,topaz, and albite. An association between gold and albitewas reported by Gallagher (1940) for many other districts.However, the apparent diversity in mineralogy is largelya reflection of gradual transitions in mineralogy as theveins and their cogenetic pegmatites evolved. For example,many veins in the districts show concentrations ofcoarsely crystalline albite and pyrite along their walls,along with increased abundances of ferruginous calcitein their central portions (fig. 428). However, the overwhelmingbulk of these veins most likely reflects the finalstages of a mineralization event initiated by the emplacementof Late Cretaceous and (or) early Tertiary pegmatitesand two·mica monzogranite into the Proterozoicrocks. Pegmatites having quartz cores (fig. 42C) arerelatively abundant throughout the districts. Although thepegmatites may crosscut the metamorphic fabric of theProterozoic rocks at high angles, the clusters of pegmatiteslocally appear to give way across a distance ofaboutseveral hundred meters to quartz-dominant veins thatclosely parallel the schistosity in the surroundingmetamorphic rocks. The overall dips of these veins varywidely in the districts from shallow to steep (fig. 44A-C).The cogenetic association between the quartz-coredpegmatites and the gold-bearing quartz-ferroan calciteveins was established at several localities where criticalrelations are well exposed and well developed (P.M.Blacet, unpub. data, 1967-72). At these outcrops, 1- to2-m-thick quartz-microcline-muscovite pegmatites giveway internally to a well-defined central portion consistingofquartz, ferroan calcite, and some blades of white mica.However, in a few of these pegmatites small stringers ofquartz plus orange-brown ferroan calcite project outfromthe pegmatite's quartz core and into the surrounding Proterozoicgneiss. The quartz plus ferroan calcite stringersalso pinch out away from the pegmatite. These relationsstrongly suggest that the fluids associated with the quartzferroancalcite veins are related genetically to the quartzcoredpegmatites. Pyrite is not present in these wellexposedpegmatites but rather in the quartz-ferroancalcite stringers where they cut the Proterozoic gneiss.Alteration to a chlorite-carbonate assemblage in thegneiss parallels both the pegmatite and the quartz-ferroancalcite stringers. Last, the alteration is confined tightlyto rocks in the very immediate area of the pegmatite.Elsewhere, however, the relations between quartzcoredpegmatites and quartz-ferroan calcite veins suggesta somewhat greater time span between emplacement ofpegmatites and the spatially separate veins. Pegmatiteslocally fill jointlike fractures in gneiss, and somewhat laterquartz-ferroan calcite-pyrite-gold veins were emplacedalong the same joint system. The veins locally crosscut

76 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOS!' BASIN MINING DIS!'RICTS, ARIZONAFICURE 44.-Typical veins in Gold Basin-Lost Basin mining districts.A, Unbrecciated, shallow·dipping, quartz-ga.lcna·pyrite-gold-

GOLD DEPOSITS AND OCCURRENCES 77of small wedge-shaped stubby crystals containing signifi·cant amounts of vanadium, lead, and copper, and traceamounts of iron (fig. 46F). This unknown mineral maybe a copper-rich mottramite, which ideally has the fonnulaPb(Cu.Zn)(VO.J(OIl) (Roberts and othe.... 1974). Themottramite(?) obviously crystallized subsequent to thebulk of the gold in the sample studied. SEM studies ofother gold-bearing samples showed that gold crystallizedin them prior to the deposition of cerussite (PbCOa),which was found by Blacet (unpub. data, 1967-72) tobe a fairly common secondary mineral throughout thedistricts.Bo~.'.;.• -""O"U'5FlCURE 45.-RelationsbetWeftl QUal'tz-ferroan calcite \-ems and seriO·~ Proterozoic granitic gneisa. Q. quartz; Ii, limonite replacing fer­I"08Il eaJcite and pyrik(!); G, &ericitized granitic gneiss. SampleGM-637. A. GeneTal O'OUl:Utting relatiorls bet_-een \-eirllS and gneiss.Note rnicroGtreaks of limonite concentrated in granobIastic domaillllofgneissaway from large vein and roughly paraIIeI with vein. Planepolarizedlight. B, C1or;eup view showing textural relations \\ithinquartt·femlQfl calcite vein oontaining minor amounts oftoptU (T). Notsoown are minor amounu of albite that \-ery locally are found alongwalls of this particular vein. Crossed nicols.,oWulfenite (PbMo04), another secondary mineral, wasfound in 19 veins in the districts, and 9 of these veins alsocontain visible gold, thereby emphasizing the strongassociation between lead, molytxlenum, and gold there.Approximately two-thirds of the wulfenite occurrencesare in the southern part of the Gold Basin district; thebulk of the remaining occurrences are clustered about 1.5km east-northeastofthe Golden Gate mine (table II). Onthe other hand, none of the veins was noted to containmolytxlenite (see also Deaderick, 1980. fig. 22), thus suggestinga supergene cumulative derivation of molytxlenumin the wulfenite from many relatively widespread and dig..tant sources. Williams (1963) noted that wulfenite is abundantin many mining districts in the southwestern UnitedStates, but only rarely can it be related to hypogenesulfides. He further showed that molybdenum can be extractedfairly easily from wall rocks by oxidizing meteoricfluids. Furthermore, Wilt (1980) and Wilt and Keith (1980)have shown that molytxlenite in porphyry copper systemsand wulfenite in Pb-Ag-Zn deposits are almost mutuallyexclusive.The very strong association between lead (galena) andgold in the primary assemblages of 49 veins shown to eontainvisible gold in the districts is reflected in the followingbreakdown of speciflC, primary assemblages in theseveins:........C""", Igold"""'"±ferroan ealcite±

78 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN·LOST BASIN MINING DISTRICTS, ARIWNAA :' ::;1~ MICROM£HRS D ,? -'~ MICIlOMHERSB'c.-'6 MICROMU£RS£'~. ~'1' MICROMU£RSc'~. ---.:30 MICROMU£RS F,? ,'1' Ml(:ROMU£RS

GOLD DEPOSITS AND OCCURRENCES 79albite-rich types and include a feldspar-dominant earlystage in the evolution of these pegmatite-vein systems.The feldspar-dominant part of these systems is reflectedprimarily by the feldspar-rich border zones ofthe quartzcoredpegmatites. These border zones also include varyingbut generally minor amounts of quartz, carbonate(usually iron rich), barite, apatite, pyrite, white mica,galena, and chalcopyrite. Barite locally is quite abundantin some of these pegmatite veins, whereas galena andchalcopyrite are present sparsely in and near somefeldspar-dominant border zones. This latter relation suggestsminor deposition of these minerals (together withtraces of gold, as in the group III gold-bearing assemblageslisted above) early in the overall evolution ofsomeofthe pegmatite-vein systems. Quartz typically is presentin concentrations ofabout one-third to one-fourth ofthatof the feldspar (potassium feldspar and (or) albite) in theborder zones. Further, as the pegmatite-vein systemsevolved there appears to be a general decrease in the ratiopyrite:(galena+chalcopyrite) reflected primarily by a substantialincrease in the amounts ofgalena and chalcopyritelate in the paragenesis. This change coincides with theincrease in the amount oflargely ferroan calcite depositedand with a cessation in the crystallization offeldspar. Aswe discussed briefly above, fluorite locally is a very importantaccessory mineral during this predominantlyquartz-sulfide-carbonate stage of the pegmatite-veinsystems, especially in the southern partof the Gold Basindistrict. Therefore, for descriptive purposes, we use a twofoldclassification of the veins: (1) a feldspar-dominanttype (group ill, above) and (2) • mostly quartz-sulfidecarbonatetype (groups I and 11), which includes themajority ofthe occurrences of visible gold known throughoutthe districts.FieURE 46.-&anningelect.ron micrographs oflode gold collected fromGokIen Gate mine in Garnet Mountain la-minute quad~ Au, gold;Q, quarU. A, Fillifonn gold in cavity lined by drusy quarU tenninatedmostly by rhombohedrona.. Rectangular area shown in B. SampleGM·II. B, Enlargement of aTea cncbied by rectangle in A. At headofarrow an extrcrnety small, doubly terminated ttylital of quart% resl8on surface of gold. Striatiorul on surface of gold probably reflectn>peatai l'o\~on11111. C, Dendritiegokl assrialed ....ith prismaticcrystahI or quarU, whieh line a cavity in l-em ~ Qualitaw,'eana/ysisofgold usiTc energy~l"e X·ray~ indicatesthat gokI eontainz detedabIe amounts of silver and iron. SampleGM-Ilh. D. Nodule of gold in quartz cavity. Gok1 shows moderatelywell developed dodecahedral fllCft and contains detectable amountsofSlver and iron. SampleGM·lld. E, Irregularly shaped, roughJy teJi;.Lured JBrlieIes of gold associated with partially oxidized cubes of pyrite(py). Sample GM·lI·l. F, Unknown mineral (l1) showing a wedgeshapedhabit and containing detectable amounts of vanadium, lead,copper, and iron (in trace amounls). Unknown mincrnl may be cowerric:hmottramite, which ideally has formula Pb(CU,Zn)(VO.)(OH)(Roberts and others, 1974). Sample GM·I1-Ia.'The intensity, type(s), and lateral extent of alterationrelated to the emplacement of most veins are mostly afunction of the chemistry of the surrounding country rttkand the chemistry of the fluids involved_ A typical approximatelyO.5-m-thick vein, which includes a well-developedfeldspar (albite) stage, will show alteration phenomenavisible in outcrop for about 1 m away from its generallysharp walls. Alteration ofamphibolite adjacent to one suchwell-studied vein clearly reveals the potassic character ofsome of the early fluids associated with vein emplacement(fig. 47). The effects of alteration were studied in a suiteofsamples ofamphibolite collected 6 m, slightly over 1 m,0.6 m, 8 cm, and 3 cm from the vein.Amphibolite 6 m from the vein shows only crystallizationand recrystallization effects related to the EarlyProterozoic metamorphic events. 'The amphibolite herecontains a generally granobIastic fOOn: consisting ofcl0selypacked crystals of blue-green (Z axis) hornblende thatshow marginal recrystallization to epidote ±carbonate,chIorite+quartz, and actinolite+chloriteassemblages. Allof these latter, superposed assemblages presumablyreflect the Early Proterozoic retrograde metamorphicevent.Just beyond the alteration halo visible in outcrop, at adistance barely over I m from the vein's wall, thin-sectionstudy of amphibolite reveals a marked increase in theabundance ofchlorite, actinolite, epidote, and quartz, andthe first appearance of sphene in the matrix. Here thehornblende takes on a ragged crystal outline and a generallyrounded aspect when viewed under the microscope.We suggest that this increased growth of a chloriteactinoI.iteassemblage centralized in the preexisting matrixreflects a narrow subtle propylitic halo superposed on theearlier greenschist assemblages, and this halo thus marksthe outer limit ofalteration related to vein emplacement.At a distance ofabout 0.6 m, the blue-green hornblendehas been replaced almost totally by greenish·brown (Zaxis) biotite in a rock showing a suite of superposedassemblages. Only the former crystal outlines of hornblenderemain. These outlines are well defined by granoblasticclusters ofequant crystals ofbiotite, some of whichshow traces of th

80 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING D1STRIcrs, ARIZONAdomains in the rock show incipient development of theapparently stable assemblage white mica-epidote·dllorite(fig. 48, ill). Both of these latter two assemblages alsoinclude quartz. The very sparse presence of albite in thematrix of the rock may reflect incipient development ofassemblage IV. which is the same as the early assemblage~". ",.-wd'at"'"'''''.,"''-- -'> ,~__C-=-=~-==_ •~_v~~='-( 1- L C- ....,..,·"".,.",-,. ).()o....U·..,_o;alc;,.·b ·pyt,.., "'1I'lI'tll__________cAO'CmC"O','"'""60""'m"-- .. ,'"Iloo"•• 1~1e ."". )( '~IS;to 1I".n b'own. Z.."I. Almost

GOLD DEPOSITS AND OCCURRENCES 81in the vein itself. Thus, the parageneses of these assemblages(fig. 48, I-IV) apparently reflect an initial potassiummetasomatism, probably fissure controlled, that wasin turn followed by a complex suite of assemblages relatedto final emplacement of the sodium (albite)-rich vein.These relations imply that an early buildup in the ratio(K +)/(H +) of the first fluids to circulate along the fissurewas followed by a decrease in this ratio, an increase in(Ca 2 +)/(2H+), and then the actual emplacement of thevein was accompanied by fluids having a relatively high(Na+)/(H+) ratio.Amphibolite collected 8 cm from the vein shows a wispymicrofolded fabric defined by schistose domains of a relictgreenish-brown (Z axis) biotite assemblage (I) heavilyaltered to a chlorite-ferroan carbonate-pyrite assemblagewhich includes some quartz. The rock shows an increasedabundance of chlorite and disseminated ferroan carbonaterelative to the previously described samples and alsomarks the first appearance of sulfide in the wall rock.Some plagioclase remains in the rock relict from the Proterozoicmetamorphism(s). Furthermore, the amount ofquartz in the rock is significantly greater than that inaltered amphibolite farther out in the alteration envelope.This increase in the content of quartz and pyrite mayresult from a release of Si02 from biotite during sulfidationreaction(s) to yield a chlorite-dominant assemblage.White mica is the dominant silicate gangue mineral approximately3 cm from the vein. A white mica-ferroancalcite-quartz-pyrite assemblage is superposed here on asuite of minerals including chlorite, biotite (partly alteredto chlorite), oligoclase, and opaque minerals-all relictfrom earlier recrystallization reactions related to passageoffluids associated with the emplacement ofthe vein. Weenvision the white mica assemblage adjacent to the veinto be the end product ofa complex series of coupled reactionsin the country rock controlled primarily by a concomitantdecline toward the vein in at least two cationactivity ratios of the associated fluid(s). A simultaneousdecline in the (Mg2+)/(2H+) and (K+)/(H+) activity ratiosof the fluid(s) may explain the relations observed amongassemblages in this potassium- and magnesium-bearingalteration envelope (fig. 49; see Beane and Titley, 1981).The absence of talc from the biotite-bearing assemblage,which apparently was the earliest prograde assemblageto develop, suggests that initial values of (Mg2+)/(2H+)in the fluid(s) were less than those required to form talc.Finally, the absence of potassium feldspar from any ofthe observed assemblages suggests that the cation activityratios of (Mg2+)/(2H+) and (K+)/(H+) in the fluids remainedoutside the field of potassium feldspar.Three samples of Early Proterozoic quartzofeldspathicgneiss were collected approximately 1.1 m, 0.5 m, and 5cm from the vein to compare their alteration assemblageswith those in the adjacent amphibolite just described. Theprograde regional metamorphic assemblage in the gneissprobably consisted of quartz, oligoclase (An15), garnet,biotite, apatite, and opaque mineral(s). However, garnetand biotite are extremely rare in these samples becausethe rocks show moderate to heavy partial replacement byan assemblage of chlorite, epidote, white mica, carbonate,quartz, and opaque mineral. This chlorite- and epidoterichassemblage is concentrated mostly in domainsoriginally including abundant oligoclase. Indeed, as thevein is approached across this approximately 1-m distance,the quartzofeldspathic gneiss shows a progressive increasein the concentrations of white mica and epidotein the plagioclase. Very close to the vein, in the samplecollected at a distance of 5 cm, a very well developedphyllonitic or ribboned texture in the quartz-rich domainssuggests some ductile flow in the country rock accompaniedvein emplacement. This ductile flow may resultfrom a hydrolytic weakening of quartz (see Griggs andBlacic, 1965). In addition, the country rock as much as5 cm from the vein shows (1) fresh albitic overgrowthson the white mica- and epidote-altered plagioclase and (2)rutile as a common minor accessory. Thus, our petrologicstudies of the quartzofeldspathic gneiss failed to documenta strong early potassic alteration stage comparable to thatfound in the amphibolite. However, the few shreds ofbiotite relict now in the white mica- and (or) chloritedominantrocks might be interpreted to reflect such apotassic stage during the process of alteration, althoughthis does not seem probable. Instead, potassium feldsparis a more likely product in rocks of this overall chemistryas a result of an increase in the cation activity ratio of.iN I.. I+:;;; N

82 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONA(K +)/(H +) of the associated fluids. For some reason suchearly K+-enriched fluids did not circulate through thelayer of quartzofeldspathic gneiss. However, the predominanttype of alteration associated with the majority ofveins throughout the districts appears to be propylitic.Examination in the field (P.M. Blacet, unpub. data,1967-72) and in thin section shows that the propyliticalteration associated with these veins includes severalspecific assemblages together with wide-ranging intensitiesof development and depths of penetration into thesurrounding country rock. Some quartz-albite veinsmeasuring 0.5 to 1.0 m in thickness show visible pyritecarbonateimpregnations as much as 8 to 10 cm from thevein wall. As we described above, the ferroan carbonatetogether with some quartz in places fills tightly spacedirregular microfractures at high angles to the foliation inthe country rock. Generally, the ferroan carbonate-filledmicrofractures are discontinuously confined mostly to thegranoblastic parts of the gneiss. Other feldspathic veinsabout 15 cm thick show in outcrop an inner alteration zoneof orange-brown carbonate as much as 10 cm thick in turnmantled by an outer 15-cm-thick zone of well-developedchloritization, which may include epidote and white micawith or without clinozoisite as specific assemblages.However, visible ferroan carbonate plus pyrite alterationin outcrop is only several millimeters thick locally adjacentto some veins, whereas elsewhere along the samevein the alteration may expand markedly into widespreadzones of chloritization and flooding by ferroan carbonate.Feldspathic veins that include variable amounts of baritemay also show some albite disseminated in the adjacentcountry rock. Quartz-fluorite veins including either feldspar,or muscovite, or sulfides and gold, generally arecharacterized by white mica-dominant assemblages intheir alteration envelopes.The mineralogy of a small number of other veins in thedistricts appears to have been controlled significantly bythe adjoining wall rocks. Where such veins cut quartzofeldspathicgneiss, the mineralogy of the vein consists ofalmost 100 percent quartz. However, where the same veincuts hydrothermally altered amphibolite, the mineralogyof the vein includes abundant irregularly shaped knots offerroan calcite. The hydrothermal alteration in the amphiboliteadjacent to such veins is predominantly propyliticand shows mostly a chlorite-carbonate assemblage.The mineralized quartz veins in the districts mostlypredate emplacement of thin, presumably Tertiary, biotitelamprophyre dikes which crop out sporadically throughoutthe crystalline terranes (P.M. Blacet, unpub. data,1967-72). In many prospects, pits, and undergroundworkings, such as those at the Eldorado mine (table 11,loco 17), biotite lamprophyre is consistently fine grainedalong its margins because of rapid chilling against themineralized veins. In addition, at several other localitiesthe biotite lamprophyre was found by P.M. Blacet to actuallycut quartz-pyrite-muscovite veins. However, not allof the mafic dikes postdate the mineralized veins in thedistricts. Some mafic dikes clearly were intruded, contorted,and sheared during a postmetamorphic sheardeformation (Laramide?) that involved local crumplingand shear folding of the Early Proterozoic metamorphicrocks. Furthermore, an at least 1-m-thick biotite lamprophyreat the L.P.M. mine (table 11, loco 12) containsa ferroan calcite alteration assemblage possibly relatedto emplacement ofthe quartz-pyrite-gold vein there. Thisrelation again suggests that the biotite lamprophyre atthe L.P.M. mine may have been present before emplacementof the veins.DISSEMINATED GOLD IN EPISYENITEAn occurrence of visible gold disseminated in severalsmall alteration pipes was recognized by P.M. Blacet duringthe initial stages of his regional mapping studies inthe districts (table 11, loco 19). Blacet (1969) described thisoccurrence as follows:The second type oflode deposit consists of small intrusive bodies ofgoldbearingmedium-grained, porphyritic leucosyenite containing severalpercent ofinterstitial fluorite. Miarolitic cavities in this leucosyenite containsmall euhedral crystals of parisite [(Ce, La)2Ca(COg)gF21. Megascopicallyvisible gold is disseminated throughout the leucosyenite andappears to be primary. The leucosyenite is tentatively considered to havecrystallized in small pipelike conduits during late magmatic escape ofhighly potassic residual liquids that were enriched in H 2 0, HF, CO2,S02, Zr, Au, and rare earths***.The largest of the pipes measures at the surface about8 m across in its longest dimension (fig. 50), but only threepipes of episyenitic (see Leroy, 1978) rock are shown.However, another very small episyenitic body, approximately3 m in longest dimension, crops out about 40 msoutheast of section lineA-A'(fig. 50). The alteration pipesconsist of coarse-grained and fine-grained episyeniticrocks that cut across Early Proterozoic fine-grainedbiotite monzogranite and a coarse-grained dike of EarlyProterozoic (?) monzogranite. Apparently, the coarsegrainedmonzogranite dike acted as a structural conduitto funnel fluids that generated the episyenitic rock. Theepisyenitic rock contains unevenly distributed concentrationsof pyrite that is now oxidized to limonite andspecular hematite. In places, the original pyrite contentof the episyenitic rock probably was as high as 5 to 10volume percent. Undoubtedly, the resulting color anomalyon the pipes first attracted prospectors, who explored theoccurrence with two shallow prospect pits. The prospectpits are on the northernmost and the southernmost of thethree pipes shown.In outcrop, the coarse-grained facies of the gold-bearingepisyenitic rock locally shows a quartz-poor igneous rock

GOLD DEPOSITS AND OCCURRENCES 83fabric that contains well-developed potassium feldsparmegacrysts and that shows relatively sharp contact relationswith its enclosing quartz-rich host (fig. 51). Theserelatively large megacrysts of potassium feldspar probablyare relict from initial crystallization at magmatic conditionsduring Early Proterozoic time. Significant removalof silica and potassium metasomatism accompanied bysubsolidus crystallization and (or) reequilibration of themegacrysts occurred during Late Cretaceous and (or)early Tertiary. Late-stage fluids associated with this episyenitizationfinally deposited the gold. The interstitialmatrix among the large potassium feldspar megacrystsis mostly potassium feldspar, but also includes rare secondaryquartz, fluffy orange and red-brown limonite andspecular hematite (both replacing pyrite), purple fluorite,sparse carbonate, unevenly distributed flakes offree gold,and somewhat sporadic concentrations of white mica. Aswe described previously, study of two white mica separatesfrom the gold-bearing episyenite pipes yielded agesof 127 and 130 Ma, undoubtedly reflecting the presenceof excess radiogenic argon derived from the Early Proterozoichost for the episyenite or minor contaminant ofNGeology modified '.om lapeaM compass mapping byP.M. Blaeet. 1961_121o 10 20 J() fEEl'~__L'__~,__-",EXPLANATION---? CO

84 GEOUXY AND GOLD MlNERAUZATlON OF' THE GOLD BASIN-LOST BASIN MINING DISTRICTS. ARIZONAProterozoic muscovite or Proterozoic feldspar in themineral separate. These episyenite pipes also oould betermed feldspalhic fenite in Ute classification of SuUterland(l965b) or microclinite as used by Hanekom andothers (1965).PETROGRAPHYThe episyenitic pipes include very sparse quartz andsignificant concentrations (generally more than 90 per·cent) of modal potassium feldspar, which decreasessharply through the approximately I-m-wide contact zonesurroWlding the pipes. The variation in modal potassiumfeldspar and quartz across one of the pipes is shown infigure 52. Quartz in the central part of this studied episyeniticpipe makes up about 4 volume percent of the rock,but decreases to much less than 1 volume percent nearthe outer limit of the episyenitic rock (see table 17 for Utecomplete modal analyses of Utese samples). In contrast,quartz occurs in concentrations of about 35 volume percentin a representative sample from the silicified andsericiticaUy altered. halo which surrounds the episyeniticrock. Potassium feldspar in the episyenilic rock rangesfrom about 84 to 92 volume percent and makes up about42 volume percent of altered biotite monzogranite approximately4 m from the episyenitic contact (fig. 52 and table17, analysis 6).Thin sections from approximately 20 rocks were studiedfrom the immediate area of the gold-bearing episyeniticalteration pipes. Fresh complexly twinned potassiumfeldspar, which makes up typically 85 to 90 volume percentof the centrnl parts of the episyenitic pipes, showswide-ranging textures. The bulk of these rocks haveseriate textures and contain many zoned potassium feldsparmegacrysts whose margins are completely sutured.Some megacrysts of potassium feldspar consist of nonturbidcrosshatch-twinned potassium feldspar ovoid ooresthat are mantled by thin, approximately 0.4- to O.5-mmwide,borders of additional potassium feldspar. Theseborders comprise an inner zone of very complexly suturedpotassium feldspar that appears to be developing at theexpense of the crosshatch·twinned oore and an outer zoneof potassium feldspar that (1) is very turbid (largelybecause of the presence of numerous minute crystals ofopaque mineral(s» and that (2) forms a crustified liningfor definitely paragenetically very late quartz and (or)fluorite. We presume the borders of potassium feldspargrew in a predominantly hydrothermal postmagmaticF'tCURE 61.-GoId-bearing epis)'eIlitic rock. A, Medium- to ~nedepisyenitic: rock containing probable mixed phenocrystic and porphyroblasticmegacrysts of potassium feldspar. B, Contacl relationsbetween episyenitic rock and it/:l mantle of silicified and IlericitizedEarly Proterozoic biotite monwgranite."z~ 90zou '0N" ~ ~ 70o'-u_o' -z ~< - ..• >< ,::; 0400>" ~ i!: JO,oo"-~ ,,'0.! ~.-'

S~ple ______GOLD DEPOSITS AND OCCURRENCES 85environment. However, such turbid versus nonturbid texturalrelations in the megacrysts do not persist throughoutthe episyenitic rocks. Other samples include microclinemegacrysts showing ovoid turbid cores that are mantledby wide nonturbid borders. All of these specific texturalrelations impart an overall granoblastic fabric to therocks. Other episyenitic rocks that formed from rmegrainedEarly Proterozoic biotite monzogranite show, inplaces, wispy irregularly shaped comminuted domains ofapproximately O.OS-mm highly strained crystalsof potassiumfeldspar. These fine-grained discontinuous domainsare interstitial among fairly equant 0.4-mm crystals ofpotassium feldspar whose crystal boundaries initially werecomplexly subned. In many of the episyenitic rocksstudied, broken angular fragments oC potassium feldspar,approximately 0.1 mm in their longest dimension, havebeen tom from some oC the larger potassium Celdsparmegacrysts and are now included within secondary strainfreequartz which rills cavities. Elsewhere, rocks alteredto episyenite are commonly reported as showing cataclasticphenomena (see Viladkar, 1980). In other samplesat Gold Basin, some megacrysts of potassium Celdspar arepresent as isolated crystals set in a fine-grained mesostasisoC mostly potassium feldspar. Such megacrysts arelargely strain free and show evidence of interruptedcrystal growth wherein euhedral outer growth zonesmantle ovoid cores (fig. 53A). Hairline microveinlets ofcarbonate and white mica cut the megacryst, and openspaces at the edge oC the megacryst are filled locally byiron oxide that has replaced earlier pyrite. High-magnificationexamination of the edgesof the megacrysts revealsthat they are complexly intergrown with the groundmass.In addition, many megacrysts show no compelling systematictextural relations with the groundmass from whichtheir relative ages might be established confidently.Two generations of quartz are apparently presentin theepisyenitic rocks. An early stage consists of very sparserounded possibly resorbed inclusions ofquartz that occuronly in potassium feldspar crystals. The rounded quartzcrystals generally are about 0.1 mm in their longestdimension and are set in equant potassium Celdspar, someof which measure approximately 0.7 to 0.9 mm wide. Inaddition, some oC the megacrysts of potassium Celdsparlarger than this include rounded quartz crystals togetherwith other extremely small unidentifiable crystals alldistributed unevenly around the periphery of formergrowth zones of the megacrysts. The most common texturalrelation between early-stage quartz and potassiumfeldspar is for the central parts of the feldspar to poikiliticallyhost clustersof rounded quartz. These clusters arerelict from a much earlier, presumably Early Proterozoic,weakly developed graphic texture in the biotite monzo-TABLE J7.-Modal (I71alyllt!$, i71 1."Oht~ ~, of tAift stdiom from 1'tlt'Q i71 1M geIIf:r(ll (ITl!U of 1MocntrMICC of viIible, diMemi7lt1Ud gold croppilIg Old in IAt! 1OUl~ pari of tAt Gold Banft miningditltrict'nd~eh' - _____ , , , • , ,GH-1136d GH-113~h Ql-113~k CH-113U GH-11311.. GH-1l3~Q.PohSllilml reldllp.r _ 91.1 ~0.3 83.8 90.2 ~7".,,6Qusrt.z _______ , .., .'., 35.9 125 .5Piegio

86 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN·LOST BASIN MINING DISTRICTS, ARIZONAgranite. Furthermore, relatively stout cryst.als of rutileare conspicuous in some of this early quartz. Relativelyabundant rutile is present in some of these early-stagequartz crystals. A mass of rutile crystals remained in theresidue from episyenitic rock digested in hydrofluoric acid(fig. 53B). Primary medium-grained quartz in the biotitemonzogranite that surrounds the episyenite also containsabundant rutile. The presence of rutile may be used todifferentiate between primary and secondary quartz inthe contact zone of the episyenite.Most of the quartz in the episyenite is a late mineralwhich partly fills the spaces between euhedrally terminatedpotassium feldspar crystals. Other minerals in thesespaces which are paragenetically about the same age asthe late quartz include white mica, apatite, fluorite, pyrite(now altered mostly to limonite and (or) l>']l€Cularhematite), and native gold. Typically in the episyenite,white mica and carbonate are intergrown with each otherinterstitial to fresh potassium feldspar. A cavity filledmostly by fluorite is shown in figure 53C. Many of theAo10 MU....£TERS~--~,8o,---,-~,. D20 M~lTI'ltSFIGURE 63.-Photomicrograp,. and liCllf\1Iing electron micrognl.ph ofrelations in epis}'enitic roclt. A, Megacryst of CI'OQlhatch·twinnedpotassium feldt;par (kfs) set in rme-grained (average sire 0.4 mm)mesoat.IIsis (M) of mostly potal;l;ium feldspar, but including sparseamounta of carbonate, iron oxide(s), and white mica. Megacrysl con·tains ovoid core (dashed outline) that ill mantled by euhednLI potassiumfeldspar, Parllycl'066ed nicols. Sample GM·28(i) (I). B, Scanningelectronmicrograph showing mst of rutile n~ell in residue rell"lll.iningalter decomposing episyenitk rocks in hydrofluoric acid. Sampleo I~U'l",---,----~,GM·280-5I. C. Cavity in episyenitie roclt filled by fluorite (F) and IlplIl'lI\!amountaofwhite mica(wm). kfs, pot.allI>ium feldspar. Croesed nicob.Sample GM-28Ob. D, CatllOdoluminel:lC\!nt zonations in potal;l;iumfeldspar (Hs) from episyenitic rock. Crystal of potassium feldspar ismantled partJy by spe

GOLD DEPOSITS AND OCCURRENCES 87potassium feldspar crystals in direct contact with theminerals in the spaces, mostly quartz, show no visiblesigns ofalteration when examined in onlinary light underthe microscope. However, when such boundaries were examinedusing cath

88 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN·LOST BASIN MINING DISTRICTS, ARIZONA(1961, 1975). Residue from these procedures containedsome intergrown purple fluorite and gold (fig. 56), thusdocumenting their penecontemporaneous, late-stage emplacementin the episyenite. Fluorite in the episyenite fillscavities most likely creat.ed during the leaching of primaryquartz and plagioclase from biotite monzogranite.CHEMISI·RYAChemical analyses are available for four fist-size sam·pies of episyenite (table 18, analyses 1-4), three adjoiningsamples of the contact zone surrounding one of thepipes (table 18, analyses 5-7), and, as a comparison, a sam·pIe offine-grained Early Proterozoic biotite monzogranite(table 18, analysis 8) collected about 15 m southwest ofthe westernmost episyenite pipe (fig. 50). One of thesamples of episyenite (table 18, analysis 1) is from thewesternmost pipe. The three remaining samples of episyenite(table 18, analyses 2-4) and the three samplesanaIyt.ed from the contact zone are all from the episyeniticpipe on the east (fig. 50). Precise quantitative values ofmetasomatic additions and subtractions of all elementsinvolved during the entire process of episyenitization aredifficult to calculate because of the dynamic chemistry andnumerous stagesof the event. However, the early stagesofepisyenitization involved (1) addition of potassium andprobably barium and removal of silica. sodium, mag.nesium, and calcium and (2) an overall increase of theporosity of the rock. The samples of episyenite containmore than 14 weight percent K20 and approximately 0.4weight percent Na20. The content of normative potassiumfeldspar in the four samples ofanalyzed episyeniteis in the range 83 to 91 weight percent; normative albiteis in the range 1.7 to4.3 weight percent(table 18). Thesevalues of nonnative potassium feldspar are quite similarto the modal contents of 84 to 92 volume percent foundin the episyenite (table 17). Silica contents in the fouranalyzed samples ofepisyenite are in the range 56 to 65weight percent. These values contrast significantly withthe I-m-wide contact zone of silicification and sericitizationsurrounding the episyenitic pipes and with nearbycFIGuRE 54.-Scanningelectron micrographIl showing golddisaeminatedin epis3!enitic rock from Gold Ba..-in miningdistrict(loc. 19, tlINe II).A, Small nodule of gold (Au) containing some sil\'C!r and itofl resting00 potasl;ium fek\spaT (K·spar).Upper SUl'face of gold nodWe apparentlywas Bbraded when rock was fractured before mounting sample inmicl'(lllC(lpe. B, Small ma.tllI of gold (Au) resting a.gainst gTOundmllSl>of secondary quartz (Q) that is prellCnl loeaUy in minor 1LlI'IOUl11l1 inepisyenitic rock. Gold is featul'('\ess and shows no apparent el)"SlaIfonn. C, Small mass of gold (Au) obtained from heavy-mfneral conoentn.1eco8eeted from epis)·enite. Gold appears to ha\-e been fonnedagainst cubM: mineral, moll probably pyrite. Sih-er ....-as detected ingold using X-ray anal)'Z('r.

GOLD DEPOSITS AI\'D OCCURREKCES 89."AB.,•" -.o0,3 ....UMUU~'-~'..': .~.' .Early Proterozoic biotite monzogranite (table 18) thatforms the protolith of much of the episyenite. A graphiccomparison of normative potassium feldspar, normativealbite, and normative quartz among the episyenite, thecontact zone, and the biotite monzogranite is shown infigure 57. Initially, episyenitization involved leaching ofprimary quartz, simultaneous breakdown and removal ofmany chemical constituents composing plagioclase andbiotite, and metasomatic addition of potassium. Total iron(as F€203) makes up about 1 weight percentofthe threesamples of episyenite most deficient in ~ (table 18,analyses 1, 2, 4), whereas F€203 makes up almost 2_8weight percent of the sample (table 18, analysis 2) ofepi·syenite which has the highest content of CO2 (3.6 weightpercent). Most of the Feih in this particular sample mustbe in late-stage ferroan carbonate, which fills vugs. Someiron also may have been fixed fmally as limonite orspecular hematite Olat replaced an early epigenetic stageof pyrite_ More realistic estimates of the overall distributionof iron in the episyenitic pipes may be inferred fromtable 17, which shows modal opaque mineral(s) in episyeniteto range from about 3 to 11 percent by volume.Apparently no major metasomatic addition of aluminaoccurred to the pipes during episyenitization. The analyzedsample (table 18, analysis 8) from the biotite monzo.granite is peraluminous and shows a 1.09 value forAI203:(K20 +N320+ CaO) in molecular percent. The sam·pie is also corundum normative (1.5 weight percent C,table 18). This degree ofalumina saturation may reflectremoval ofsome calcium accompanying partial alterationof plagioclase during the Proterozoic greenschist metamorphicevent. Such alumina saturation seemingly hasbeen preserved during the Late Cretaeeousand (or) early,"'ICURE !l5.-Coone-grained cpis)'cnile containing visible gt.Ild. SampleGM·28Ob. Plane-polarized ref1acted light of polished section. A,TextunLI relatiOllll ofgold (Au), carbonate(C), potassium fcldspllr(kf),specu.Iar hematite (bm). and limonite (b). B, Closeup view r.howingdetails of relationll among gold (Au). carbcnate(C), speeuJar hematite(hm). and limonite (Ii) in A. C, Slightly oxidit.ed cube of P}'l'ite (PY).potaasium feklllplU" (\d), speroIar hematite (bm). and limonite Oi)..~. -'~ "L!6otrHIlSF'ICURE 56.-Morphologic relation. ofintergrown fluorite (I') and gold(Au), whidl an! reUduea ~ted from amaU (about 9 g) IIlllpie orepi.ayenite by deeat!'lJlO'ing epis~te in h)"drofloonc acid (see text).

90 GEOLOGY AND GOLD MIl-.'ERAUZATlON OF TIlE GOLD BASIN·LOST BASIN MJNING D1STRIC1S, ARIZONAAnal ysis __ •S-ple ....""2 3 _ S 6 7Citl-280b Citl-ll}llk Citl-113U ~11}l1. CK-IljlIn CK-113_oU>ell1cd andyses (~ilht percent)879Ct112SiD 62.2 61l._ 58 •• 60.8 15.' 76.9 76.0 72.9Al2~-- 17.7 18._ 16.7 17 .6 10.9 10.1 9.91l 13._F:6D3 .90 , '.77 .57 2.31 1.78 2.63 2. IS, --- .12." .OJ .OJ." .n .70 ,."'oO ___.00 .00 .70 .0003 .0003'" .000' .00' .0019.""'".000' .0005 .0007 .0008 .000'" .000' .0015 .002ll .0016 .000l .0061 .0037 .000>... '".".OJ .OJ .032 .0097 .016 .023 .02_... .00" .00' .003 .0007 .0009 .0009 .0009 .0003.0015 .005 .007' .005' .0038 .0038 .006' .005'".0003 .0003 .0002 .0003• .-.0012,,----- .003." ." .0," .03' .005' ."", .005880----- .00".0011 .000' .0005 .0007 .00111 .0008,,---- '".0> .015.".008 .0058 .0073 .0072 .0093.0007 .00' .0023 .00112 .0036 .0018 .0033 .0015,.00' .0012 .0069 .0075 .013 .012.".0036.018'"."', .0011l .0022 .0031 .00'.0> •OJ".", .... .011 .0> ."..0>.0> .07 .C6' .011 .0>7 .0_1."."'7'".00' .0015 .0016 .0012 .0017 .0012 .0016 .0019,. '" .000' .00' .0005 .000' .0005 .0007 .0003"'----- .007 .0> Ol.ical analYHs (perts per .UUon).. - 0.8• ., I .6••••11.0. 1.0.I.D. 1.0.'"Tertiary emplacement of the episyenite pipes. The meanof those three analyzed samples of episyenite havingminimal contents of CO2 (table 19, analysis 1) shows thatthe episyenite is saturated. similarly with respect toalumina. 'The value of AlA:(K:P+N3.20+CaO) in molecularpercent for the average analysis ofepisyenite is 0.95.However, ifthe contentofCaO is adjusted to account forthe late-stage fluorine and carbonate in the rock, then theaverage of the episyenite samples analyzed has a 1.04value for AlA:(K20 + Na:p + CaO) in molecular percent.

GOLD DEPOSITS AND OCCURRENCES 91TABLE 18.-Analytical data ofLate Cretaceous episyenite, ofthe contact zone ofthe episyenite, and ofthe adjoininghost Early Proterozoic biotite monzogranite-ContinuedAnalysis ---- 1 2 3 4 5 6 7 8Sample ------- GM-280 GM-280b GM-1134k GM-11341 GM-1134m GM-1134n GM-11340 79GM12CIPW norms (weight percent)Q ---------- 3.7 7.3 0.98 1.1 43.9 46.5 47.4 32.8C ----------- 1.1 2.2 1.1 •71 2• 1.4 1.8 1.5or ----------- 86.3 83.9 83.8 91 47 46.5 43.5 35.7ab ----------- 4.3 3.4 1.7 2.3 2.4 1.3 1.3 21.4an ----------- .37 .03 3hl ----------- .02 .02en ---------- .33 .13 .37 .89mt ----------.69 2hm -----------.91 .99 2.8 .98 2.3 1.8 2.2 .76il ----------- .3 .99 .17 .11 .55 .33 1 .59ru ---------- .29 .14 .48 .53 .05 .16ap ---------- .28 .29 .12 .22 .22 .31 .14fr ---------- 2.3 .10 .29 1.1 .33 .25 .31 .13pr ---------- .04 .06 .04 .32cc ---------- .18 .11 7.3 1.8 .76 .18 .14mg ----------- .42 .02 .23 .25 .41Total 99.7 99.4 99.4 99.8 99.4 99.7 99.5 """"99."4Salic ----- 95.6 96.8 87.6 95.1 95.3 95.7 94. 94.4Femic ----- 4.1 2.6 11.8 4.7 4.1 4 5.5 5l D• I. 94.3 94.6 86.5. 94.4 93.3 94.3 92.2 89.9lDifferentiation index of Thornton and Tuttle (1960), defined as the total of normative quartzplus normative orthoclase plus normative albite.1. Episyenite, loco 19, table 11 and plate 1; obtained from the westernmost pipeshown on figure 50.2. Episyenite, loco 19, table 11 and plate 1; obtained from the easternmost pipeshown on figure 50.3. Episyenite, loco 19, table 11 and plate 1; obtained from the westernmost pipeshown on figure 50.4. Episyenite, loco 19" table 11 and plate 1; obtained from the westernmost pipeshown on figure 50.5-7. Contact zone surrounding easternmost episyenite pipe (see fig. 50).8. Fine-grained Early Proterozoic biotite monzogranite collected 15 m southwest of westernmostpipe on figure 50.DISCUSSIONThe mineral assemblages, chemistry, and geneticallyassociated two-mica monzogranite of the episyenite pipesin the Gold Basin district closely resemble similar rockselsewhere hosted by an assortment of geologic environments.Uranium-bearing episyenite and unmineralizedepisyenite are present in upper Paleozoic two-mica graniteof the Central France Massif (Moreau and Ranchin, 1973).Emplacement of the mineralized episyenite there included(1) an almost total removal of primary plagioclase andprimary quartz from the two-mica granite, (2) conversionof primary biotite to chlorite, (3) subsolidus crystallizationof additional white mica, and (4) an increased porosityofthe rock. Viladkar (1980) also found a substantialreduction in silica during the development of the fenitizedor episyenitized aureole around the Newmania carbonatite,Rajasthan, India. The final stages of mineralizationin the episyenite pipes in the Central France Massif..:z wf-Z f-a ZU w..Ju« a:a: WW 0-100Zf- 50- J::2 r..:IW W~:s:~~:2 a:aZ0~2Or34 5ANALYSISBiotitemonzo­Contact zone ----+- graniteFIGURE 57.-Normative potassium feldspar (or), normative albite (ab),and normative quartz (Q) in analyzed samples of Late Cretaceous andearly Tertiary episyenite, contact zone ofepisyenite, and nearby sampleof Early Proterozoic biotite monzogranite. Data from table 18.678

92 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAresulted in the partial filling of the leached cavities by carbonate(s),hematite, pitchblende, and some secondaryquartz (Moreau and Ranchin, 1973). The chemistry ofother episyenitic alteration zones or fenites associatedwith some carbonatite complexes is very similar to thechemical makeup of the episyenites at Gold Basin. Thisrelation is shown in the analyses of selected samples ofpotash trachyte and fenitized granitic rock from an areaof carbonatites at Toror Hills, Uganda, feldspar-rockxenoliths in carbonatite from Amba Dongar, India, andmicroclinite from the Palabora, South Africa, carbonatitearea listed in table 19 (compare analysis 1 with analyses4-7). These latter analyses show K20 contents that rangefrom about 10 to 15 weight percent and extremely highK20 to Na20 ratios. The partial analysis for Si02, Na20,and K20 of a sample of fenitized granitic basement (table19, analysis 4) and the average sample of episyeniteanalyzed from the Gold Basin district are similar. In addition,fluorite, apatite, and pyrite are common late-stageaccessory minerals in many episyenitic rocks or feniticrocks associated with carbonatite complexes (Smirnov,1976), and fluorite even is present in economically importanttonnages and grades in some of them (Deans andothers, 1972). Parisite, a mineral ideally having the composition(Ce,La)2Ca(C03hF2 (Roberts and others, 1974),also was reported by Blacet (1969) to be present rarelyin these episyenitic rocks in the Gold Basin district.Parisite is considered by Smirnov (1976) to be one of theaccessory minerals typically developed in carbonatite complexes,but important concentrations of gold are notgenerally known to be associated with such complexes (seeSmirnov, 1976; Boyle, 1979). Some carbonatites, however,contain measurable amounts of gold. Copper concentratefrom the Palabora, South Africa, carbonatite is reportedto contain 0.05 troy ounces gold and 24.5 troy ouncessilver per ton (Hanekom and others, 1965, p. 158). Furthermore,Rubie and Gunter (1983) report that potassicepisyenite, as opposed to sodic episyenite, is only foundto be associated with carbonatite. Owing largely to thefact that we have not recognized any carbonatite of LateCretaceous and (or) early Tertiary age in the Gold Basinand Lost Basin mining districts, we conclude tentativelythat a fairly unique set of geologic circumstances mayhave contributed to the development of the goldmineralizedepisyenite there.Our study of the gold-bearing episyenitic pipes suggestsa protracted passage of potassium-charged and silicadeficientfluids initally occurred through a narrowly confinedseries of vents. This streaming of fluids eventuallyculminated in the late-stage deposition of gold there.TABLE 19.-Chemical analysis ofaverage episyenitefrom Gold Basin and chemical analysesofother syenitic and episyenitic rocks from elsewhere[----, not detected; N.D., not detennined or not listed]Analysis ----- 2 3 4 5 6Chemical analyses (weight percent)Si08 --------- 62.5 58.58 58.43 62.73 67.52 63.62A12 3 -------- 17 .9 16.64 17 .84 N.D. 13.58 18.27F:8°3 ------- .96 3.04 5.09 N.D. 4.71 1.18F --------- .20 3.13 N.D. .20 .09MgO -------- 1.87 .43 N.D. 1.03 .10CaO -------- 1.31 3.53 .80 N.D. 1.62 .80Nat ---------- .39 5.24 .38 .38 .40 .63K2 --------- 14.7 4.95 13.9 14.97 10 14.38H20+ -------- .38 .99 1.05 N.D. 1.04 .18H?O- ------- .03 .23 .11 N.D. N.D. N.D •T102 ------- •56 .84 .34 N.D. .09 .11P20 5 ------- .03 .29 .35 N.D. .33 .12MnO --------- .02 .13 .42 N.D. N.D. .02CO2 ----------.31 .28 N.D • N.D. .20 .26F ------------ •56 N.D. N.D. N.D. .30 N.D.Subtotal ---- 99.85 99.74 99.32 N.D. 100.89 99.94Less O=F --- .24 N.D. .13Total ------ 99.61 99.74 100.761. Episyenite (loc. 19, table 11). Average of analyses 1, 2, and 4(table 18).2. Syenite of LeMaitre (1976).3. Potash trachyte, Toror Hills, Uganda (Sutherland, 1965a, p. 370).4. Partial analysis, fenitized granitic basement, Toror Hills, Uganda(Sutherland, 1965a, p. 371>.5. Feldspar rock xenoliths in carbonatite, Amba Dongar, India (Deansand others, 1972, p. B5).6. Microclinite, Palabora, South Africa (Hanekom and others, 1965).

GOLD DEPOSITS AND OCCURRENCES 93These episyenitic pipes are further envisaged as reprE"­senting structurally deeper levels of mineralization thanthe veins in the districts. We infer that the early·stagefluids increased porosity and thereby enhanced permeabil·ity at the sitesof the vents primarily by leaching primaryquartz and primary plagioclase from the rocks. Thisfacilitated a continued circulation of late-stage fluid(s)associated with the introduction of gold and its accom·panying pyrite, fluorite, hematite, secondary quartz, carbonate,and white mica. Although two determinations ofthe age of white mica from the episyenite yieldedanomalously old ages (127 and 130 Ma), we nonethelessmaintain that the process of episyenitization and theintroduction of gold into the episyenitic rocks is relatedtemporally and genetically to a Late Cretaceous., two-micamagmatic event. As discussed in the section "K-ArChronology of Mineralization and 19neous Activity" theseanomalously old ages may reflect contamination of theevolving episyenite by radiogenic argon relict from theenclosing Early Proterozoic rocks or contamination of thesamples dated by Proterozoic mica and (or) feldspar. Aswill be shown in the section "Fluid-Inclusion Studies," thelate-stage fluids in the fluorite-bearing and gold-bearingepisyenitic rocks are the same chemically and approximatelythe same temperatures as those in a well-studiedfluorite-bearing vein, which cuts the Late CretacEous twomicamonzogranite north of the Cyclopic mine as well asmany other veins throughout the districts. This vein hasbeen dated at 68 Ma, and white mica from the two-micamonzogranite yields an age of 72 Ma.VEINS ALONG THE MIOCENE DETACHMENT FAULTBlocks of presumed Late Cretaceous and (or) early Tertiarymineralized quartz veins crop outalong the Miocenedetachment fault in the opencut and underground workingsat the Cyclopic mine (p.M. Blacet, unpub. data,1967-72). The workings at the Cyclopic mine, the depositshowing the largest production of lode gold from thedistricts to date, consist of a series of opencuts andshallow underground drifts along a strand of Miocenedetachment fault that has been shown to be post-MuddyCreek Formation in age (Blacet, 1975). Some displacementsalong the detachment fault may have been localizedby shallow-dipping zones of weakness dating [romLate Cretaceous or early Tertiary time. The blocks of veinquartz, which an! present sporadically in gouge of most·Iy the uppermost splay of the detachment zone, constitutethe ore in the deposit. In the general area of the Cyclopicmine, the detachment zone in pla~s consists of at leastthree stacked plates (Blacet, 1975). Here, the detachmentzone shows an approximately N. 50 0W. strike, althoughindividual splays along the zone show marked departuresfrom the general trend. Further, some of the individualsplaysat the surface crop outacross at least 40 m in someof the opencuts o[ the mine and can be traced at the surfaceas much as 1.2 Jun, as noted previously by Schrader(1909). However, the lowennost surface o[some of thesesplays locally forms a very sharp, almost planar contactwith the underlying metamorphic rocks (fig. 58A). In suchwell-exposed outcrops, the hard yellow-brown gouge zoneresting immediately on the metamorphic rocks shows veryfaint striations that trend subparallel to the northwesterlytrend of the trace of the detachment [ault. Although dipswithin the detachment fault zone generally are qUitegentle, some opencuts through individual splays revealdips of approximately 50 0 to 55 0 in varicolored gougezones that surround some of the large blocks ofbrecciatedvein quartz caught up within the zone (fig. 588). Someblocks of brecciated vein quartz an! very resistant toweathering (fig. 58C) and together with the strong ironoxide staining form excellent markers along the individualfault splays that make up the overall J\.1iocene detachmentzone. The mineralogy of these mineralized tectonicallybounded blocks o[ veins is the same as the Late Cretaceousand (or) early Tertiary veins. However, as pointedout by Schrader(1909, p. 125), the blocks of vein materialat the Cyclopic mine apparently are not continuous to anygreat depth nor do they "have any definite fissure wall,but usually at a shortdistance below the surface (instead]give way to less firm material." Although the deposit atthe Cyclopic is the only one known in the districts alongthe trace of the detachment fault, some dislocation sur­[aces elsewhere are reported to contain gold ore. Detachmentsurfaces associated with some cordilleran metamorphiccore complexes in western Arizona and easternCalifornia in places contain a chrysocoUa-ehaicopyritespecularhematite-pyrite association, together with somebarite and fluorite, that locally yielded values in gold(Reynolds, 1980; Wilkins and Heidrick, 1982).PLACER GOLD DEPOSITSPlacer gold deposits in the Gold Basin-Lost Basinmining districts are primarily present in three areas. Themost importantdeposits are within a lQ.-Jun by 3-km areaalong the east flank of the Lost Basin Range. Manyreports refer to this area as the King Tut placer area.Some placer deposits were worked also in the northernpart of the Gold Basin district when! they are clusteredin an approximately 6-km2 area, about 2 km southsoutheastofGoldenRule Peak (Blacet, 1975). In the GoldBasin district, the placers are reported to have containedgold in erratically distributed channels (U.S. GeologicalSurvey, unpub. data, 1967). Finally, a few occurrences ofplacer gold were worked from the upper reaches ofQuaternary gravel deposits along the west flank of theLost Basin Range. Although the overall areal extent of

94 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIWNAFIGURE 58.-Relationli along Miooene detacllrnent fault in~areadCydopic mine. A,~ low~faultbeRWIlProtetor:oicmeta~ rocb on north and~ along Miocene detadlment~. Hammer for 1ICllk. B, Diacootinuoua bl"ecciated and unbrecciatedbklCb and fragmenta of mineralized \-em quartzatextremeoorth",eSl end of~ opeocut... HIIl'lUl'"Ier ()fl rock for 1ICale. C, ~irdated block ofbrecciated vein~ in flal..1ying gougezone beR"leIlEarly Proterowie poI'JiIyritie ,,1OltUJglaMe in hanging wall and nUedI-:arly Proterozoic metamorphic: rock.and LateCret.aoeoua two-micamonwgrartite in footwall. Pocket COInp&Sll for scaW.the deposits and occurrences along the west side of theLost Basin Range is about the same as that along the eastside of the range, by far the largest production is creditedto the King Tut placer area on the east side of the range.Koschmann and Bergendahl (1968, p. 40) estimate thattotal minimum gold production of the Gold Basin districtwas about 15,000 oz. Most of this production was fromlode deposits. Johnson (1972, pl. 1) appraises the total pro.duction of placer gold at 1,000 oz for each district, GoldBasin and Lost Basin.The most economic concentrations of gold·bearinggravels were found in the placer deposits along the eastflank of the Lost Basin Range. The highest grade goldbearinggravels there are generally less than 1 m thickand are confined to present·day arroyo bottoms, wherethey have been concentrated above caliche-cemented falsebed rock after having been reworked primarily out of theMuddy Creek Formation (J.D. Love, written commun.,1966, 1967; P.M. Blacet, unpub. data, 1967-72). Therichest gold-bearing gravels were apparently concentratedalong the upper reaches of these arroyos (Blacet,1975). Concentrations of placer gold nuggets obtainedmostly from the King Tut placer area include coarse andangular nuggets, many showing sharp ragged edges(fig.59A), indicating that the nuggets have not traveled veryfar. In addition, some of the placer nuggets encloserounded to angular granules of vein quartz (frontispiece;fig. 59B), suggesting that some solution and reprecipitationof gold may have taken place in the environment ofthe placer gravels. Heavy minerals also are relativelyabundant in the gold-bearing alluvial sand and gravel (fig.59B). Deaderick (1980) also reports that an abundance ofblack sand is associated with the placer gold; this blacksand consists largely of partially oxidized cubes ofpyrite,magnetite, garnet, ilmenite, hematite, and limonite. Inaddition, he notes that placer operations in the late 1970'srecovered gold nuggets containing a significant amountofattached chalc€donic matrix, partly as inclusions withinsome of the nuggets.The surface morphology of selected placer nuggetscollected by a hand-operated dry washer (fig. 60) wasexamined using the SEM. A nugget from the King Tutplacer area (fig. 6IA) appears to be more worn than mostfrom that general area, and this particular nugget shows,at very high magnifications, extremely well developed surfacestriae created during transport (fig. 6lB). Such a nug·get, in contrast to the more ragged and angular nuggetsin the same general area, may have undergone majortransport during a period of £lash flooding in an otherwisegenerally arid type erosion cycle, or it may have beentransported farther than the more angular nuggets.Yeend (1975) showed experimentally that most physicalchanges in placer gold nuggets occur by exposure to a tur·bulent high-energy environment. He further documented

GOLD DEPOSITS AND OCCURRENCES 95that most physical changes reflect the effects of cobblesrather than sand and that gold is abraded faster by wetsand than by dry sand. Overall aspects of a "less wornappearing" nugget obtained from the northern Gold Basinmining district. are shown in figure GIG. Many of the nuggetsexamined by the SEM show that the gold typicallycontains numerous cubic molds, indicating the formerpresence of pyrite or galena (fig. 6W), both of which arecommon minerals in the gold·bearing veins throughoutthe districts. Spot qualitative analyses of placer nuggetsusing the energy.dispersive X-ray microanalyzer on theSEM revealed commonly detectable silver and iron. Theiron probably is a local surface coating.Some nuggets contain relicts indicating the formerpresence of carbonate in their hypogene assemblage. Alarge, irregularly shaped, 11.9-g nugget obtained fromplacer workings in the NWIJ4 see. 3, T. 29 N., R. 17 W.,approximately 2 km northeast of the main workings ofthe King Tnt placers, shows extremely well developedrhombic molds (fig. 62). Measurement of the interfacialangles of these molds suggests that the carbonate mayhave been ankerite (R.C. Erd, written commun., 1969),which is common together with siderite in the quartzcarbonate±basemetalS±gold stages of the pegmatiteveinsystems throughout the districts.Although the overall geometry and concentrations ofplacer nuggets reflect fluvial processes, some microscopicfeatures together with physical and chemical relations in·dicate limited remobiliz.ation has taken place locally in theplacer environment. A sequence of scanning electronmicrographs (fig. 63) at successively larger scales showstextural relations found between native silver and goldin a small nugget collected neat the Golden Gate mine...;cBFICURt: S9.-Placer w:>ld from Lo!>t Basin mining district (.I. David uwe,written oommun., 1966). A, Coarse angular nuggets of gold. Note27·mm pin for liC8Ie Ill. botlom ofphotograph. B, Varied sizes of concentrationsof placer gold. U.S. dime for 1ICIlle. D, ooan>est nuggetslihowing an apprmcimate1)' 1.2-em-wkle composite nugget at head oflUTOW with gold partly enclosing a rounded granule of quartz; b,mediUrn-9:t.e nuggeta; t. sma11 nuggets; d. nonmagnetie twa\')'-mineraleor'IeeI\lnlte in whid1 all large fragmenu are gold.FICl:RE 6O.-Small, han

96 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LQSf BASIN MINING DISTRICI'S, ARIZONAThese relations between native silver and native gold wereevaluated partly because Diman (1976) had determinedpreviously that the association native silver-native goldis "forbidden" because ofwidely separate stability fieldsat elevated temperatures. The two metals can occurtogether under nonequilibrium conditions or at lowtemperature(s). Furthermore, Desborough (1970) hasshown that most placer gold grains include a relativelythin rim of low silver content. Examination of this particularnugget at very high magnifications reveals thatsmall oriented triangular facets of native silver, many approximately5 ~m on a side, are present on the surfaceof the gold nugget (fig. 63B). These facets ofsilver, identifiedusing the energy-dispersive microanalyzer, areraised slightly relative to the surrounding gold and areall oriented similarly. Observation of these relations atan even greater magnification (fig. 63C) shows that someof the extremely small facets ofsilverare even nested onone another but still retain the same overall orientationof their outlines. Energy-d.ispersive analysis of the silverA o 300 MICROMETERSL'_~' co 300 MICROMETERS~B o 10 MICROMETERS~,-~, Do~'-~'900 MICROMETERSFIGuRE 61.-~ dectron micrographs ofplacwgdd nuggeta fromGoJd Basin-Lost Ballin mining di:litrict&. A, GoJd nugget from Kirw:Tut placer workings., NE'Io sec.. 9, T. 29 N., R. 17 W. Weight, 15.3mg. Small amount of iron was detected in nugget using energy·dispet'si,~analyzer. Rect.angIe indicates&lU shown in B. B, Enlargmentof area outlined in A lIhowing IIUrlaoe striae aeated duringtransport. C, GokI. nugget from workings at Old Place!'$ area (informalname), SWYo sec.. 10, T. 29 N., R. 18 W., approximately 1.5 kmnortheast ofGold Hill mine. D, Gold nugget from llite at Twin YuccaguIdI(informal name), SEY. lee. 9, T. 29 N., R. 18 W., approximate­I)' 1 km north of Gold Hill mine. Weight, 38.9 mg. NlIgg':t ahow.numerous cumc mokb indicatirW' former presen::e ofeuhelhI cryst.alaofpyrite. sman amwnt ofIllvet' was detected in nugget. using energydispersi\'eanalyzer.

eveals no detectable gold, and analysis of the gold revealsno detectable silver. We suggest that the silver mayreflect the following events in the placer environment:(1) Sedimentation of the detrital nugget of gold in theQuaternary gravel; (2) dissolution of silver from a nearbysource in the gravels, possibly galena or cerrusite, ata relatively elevated Eh and, only locally, a somewhatacidic pH (see stability relations of gold and silver in waterat25 °C and 1 atm shown by Hallbauer and Utter, 1977);(3) final deposition of the silver on the surface of the gold,controlled largely by traces of {HI} twin planes andprimarily in response to a decline in the prevailing Eh ofthe overall system. Some experimental work suggeststhat such a succession of phenomena may have occurred.Sakharova and others (1979) showed. that at room temperatureand atmospheric pressure dislocations and othersurface defects can control the actual sites where nativesilver precipitates onto placer minerals from silverchargedacid or alkaline solutions. Even ifsuch a sequenceof physical and (or) chemical events contributed towardwhat appears to be a very local and very minor accretionaryphenomenon, we do not believe that a similarchemical mechanism should be used to explain "growth"GOLD DEPOSITS AND OCCURRENCES 97o1 CENTIMETER~--~,FiGURE 62.-Relatively large placer gold nugget from Lost Basin miningdistrict showing extremely well developed rhombic molds (see text).FIGURE 63.-Scanning cleetron micrographs of silvcr·gold rolations inplacer gold nugget obtained from northern part of 1.

98 GEOLOGY AND GOLD MINERALIZATION OF' THE GOLD BASIN·LOST BASIN MINING DISTRICTS, ARIZONAof the relatively large sized nuggets in the placers from"seeds" of relativeJy small sized masses of lode goldobserved throughout the districts. In fact, such size contrastsare fairly common in many combined lode gold andplacer gold districts (see Antweiler and others, 1972;Boyle. 1979; and many others). We suggest that therelatively large placer gold nuggets were derived mostlyfrom the upper portions of the vein systems that havebeen removed by erosion. The source areas probable forthe placer gold will be discussed in this section.Minor metals in seven heavy-mineral concentrates obtainedfrom one lode site and several placer gold sites inthe Gold Basin-Lost Basin mining districts were studiedusing cursory geochemical methods (table 20). Spectrographicmethods used are those by Grimes and Marranzino(1968). An analysis (No.1) of heavy minerals concentratedfrom the site of the gold-bearing episyenitic rockis included in table 20 for comparative purposes. We werenot able to verify the site from which sample 3 wascollected by P.M. Blacet. However, the very high concentrationof tungsten (greater than 2 weight percent) in sample3 (table 20) in contrast to a maximum 0.3 weightpercent tungsten in the six other samples of placer concentratessuggests that sample 3 may be a scheeliteconcentrate handpicked from one of the seven others. Theseven remaining samples analyzed include both magneticand nonmagnetic fractions. Although the bulk of thesamples analyzed consists of nonmagnetic portions. approximatelyone-tenth to one-third by volume of the concentratesinclude a magnetite-rich fraction that may beessentially separated magnetically using a I-kg hand-heJdmagnet. In addition, all relatively large fragments of goldwere first removed by handpicking the heavy-mineral concentratesbefore the concentrates were analyzed. Thoseeight samples, now consisting of composited fragmentsofgold, were analyzed separately for palladium, platinum,and ruthenium, together with nine other gold samplessimilarly obtained from various placer workings throughoutthe districts. No palladium, platinum, or rutheniumwas detected in any of these 17 gold samples at limits ofdetermination that range between 48 and 219 ppm(Joseph Haffty and A.W. Haubert, written commun.,1978).The drainage basins contributing material to the placersample sites from which we obtained and analyzed theheavy-mineral concentrates are widespread, spanning thedistricts along their entire north-south length. As a consequence.the lode sources for these anomalous metalconcentrations must also be widespread. We have not attemptedto establish geochemical dispersion trains norhave we attempted to follow these metals back to theirspecific sources. Two analyzed samples show concentrationsof 0.3 and 0.15 weight percent uranium, and 0.5 andundetected amounts of thorium. respectively. The Th: Uratio ofabout 1.7 in analysis 4 (table 20) suggests a probablesource in detrital grains of monazite, allanite, oreuxenite derived from the Early Proterozoic metamorphicand igneous rocks. The concentration of rare-earth elementsand the values of various rare-earth ratios suggestthis relation also. Furthermore, Reyner (1954) describedsmall pods of polycrase-, euxenite-, and monazite-bearingrock associated with pegmatite in SW'/4 sec. 10 and NE'/4sec. 14, T. 28 N., R. 16 W., on the lower west flank ofGarnet Mountain. Analyses of four select samples fromthat locality range from 0.007 to 0.533 percent eUaOS.The overall abundance of rare-earth elements and thevalues of various rare-eart.h ratios in the concentratesfrom five of the six placer samples are remarkably similarto the rare-earth signature of the heavy minerals concentratedfrom the apparently Cretaceous gold-bearing episyeniticrock (table 20). The source areas of the placersamples are mostly the Early Proterozoic rocks. Theserelations suggest that the hydrothermal process of episyeniticrock development may have occurred without asignificant disruption of the rare·earth geochemicalsignature of the Proterozoic protolith of the episyenite.These inferences do not preclude the possibility that somecontamination of the heavy minerals obtained from theepisyenitic rock took place during the current erosioncycle.Gold in the King Tut placer area of the Lost Basinmining district apparently is being reworked out of theupper parts of the exposed sequences of the Muddy CreekFormation. However, these predominantly fanglomeraticdeposits have been derived from several source areas asfans were coalescing and filling the Miocene trough alongthe Grand Wash fault zone. This trough is along presentdayGrapevine Mesa (see Blacet, 1975). Detailed examina·tion by P.M. Blacet (unpuh. data, 1967-72) ofcobbles fromthe Muddy Creek Formation along the entire east flankof the Lost Basin Range revealed that granitic cobblesand boulders from the rapakivi granite of Gold Butte,which crops out north of Lake Mead, extend in the MuddyCreek Formation to approximately 1 km north of theClimax mine. Just north of the study area, granite of theGold Butte area commonly is present as 2 to 3 m bouldersthroughout an at least 200-m-thick sequence of the exposedMuddy Creek Formation. West of the Meadviewstore, I km north of the study area in the adjoiningsouthern part of the Iceberg Canyon IS-minute quadrangle.the Muddy Creek Formation also includes abundantfresh cobbles and isolated boulders of light-pinkishgrayporphyritic monzogranite that are very much likethe Early Proterozoic porphyritic monzogranite croppingout in the southeastern White Hills, just east of theCyclopic mine. In addition, suhanguJar to moderately wellrounded cobbles of medium- to coarse-grained metadiabaseare present in the Muddy Creek Formation here,

GOLD DEPOSITS AND OCCURRENCES 99whereas the adjacent Lost Basin Range includes extremelysparse abundances of this lithology generally north ofthe area of the Bluebird mine. These relations suggestthat the bulk of the debris being shed into the depositionaltrough of the Muddy Creek Formation at the northernpart of the Lost Basin district was being derived from anortherly source, but that some lesser amounts of fanglomeraticmaterial were probably coming from thesouthwest also.The lithology of clasts in the lowermost sequences ofthe Muddy Creek Formation at its southernmost exposuresin the Lost Basin district, approximately 1.5 kmwest-southwest of the junction of the Pierce Ferry Roadand the Diamond Bar Ranch Road, also suggests derivationfrom a source to the southwest (P.M. Blacet, unpub.data, 1967-72). In this general area, the Muddy CreekFormation includes scattered cobbles and small bouldersof basalt, unretrograded sparkling fresh garnet- andTABLE 20. -Semiquantitative spectrographic analyses, inweight percent, for minor metals in heavy-mineralconcentrates from a selected lode occurrence and previously worked placer deposits and oClmrrences in theGold Basi'YlrLost Basin mining districts[Spectrographic analyses by L.A. Bradley. Results are to be identified with geometric brackets whose boundaries are 1.2,0.83, 0.56, 0.38, 0.26,0.18,0.12, and so forth, butare reported arbitrarily as midpoints ofthese brackets, 1,0.7,0.5,0.3,0.2,0.15,0.1, and so forth. The precisionofa reported value is approximately plus or minus one bracket at58-percent confidence, or two brackets at 95-percent confidence. Symbolsused are: G, greater than 10 percent or value shown; N.d., not detected; L, detected but below limit of determination; ...., not lOOKed for.Looked for but not found, Pd, Pt, Sb, Te, Ge, In, Li, Re, Ta, n, Th, Tm, LuIAnalysis - 1 2 3 II 5 6 7 8Lab No. -- D1911818 D1911819 D1911820 D1911821 D1911822 D1911823 D19118211 D1911825Mn --­Ag ---As --­Au ----B---Ba --­Be--Bi -----Co ---Cr --­Cu ----La ---Mo ---­Nb ----Ni ---­Pb ---Sc ----Sn ---Sr ---­U---­V ---­W--­y---Zn--Zr ---Ce --­Ga-­Hf--Th --­Yb---Pr --­Nd ---SID ----Eu ---Gd--Dy --­Ho-­Er ---0.7.0015N.d..01N.d.•02.0003N.d.•007.02.0051.5.01•07.0015.15.003.015N.d..02N.d..15N.d..151.5.015.31.15.01.05.03.01.0150.15.03•15•05N.d..005N.d.N.d..007.015.002.7.0003N.d •.007.03.003•003•003N.d.•07.015.07.15.051.5.03N.d..5.15.7.15.01Ḷ002L0.2N.d •N.d ••003N.d •.003N.d.N.d •L.005.01.007.03•03.001.007.001•005.007N.d •.015G2.007N.d..01N.d..005N.d.N.d..0005N.d.N.d.N.d.N.d.N.d.0.15.0007N.d.N.d.Ḷ02N.d.N.d..01.015.031.002•007.007.15.002N.d •.015.3.03•3.07N.d..152N.d..5.005.31.2L.05.03.007.0150.5.0015N.d.N.d •N.d..03N.d.N.d..007.015.031.5.003N.d •.002.15N.d •.015.015L.07N.d.1G2.03.7.003.31.2L.015.0150.03.15N.d.N.d.N.d.7N.d..3.005.003.03.0151.5N.d •.003G.0007N.d •.15.15.02N.d •.003N.d..015.07N.d.N.d.N.d..02N.d.N.d.0.15.0003N.d.N.d.L.03LN.d..015.05.05.3.003.007.01.07.002•003.015N.d..05L.05N.d..07.7N.d..3.07.3.07L.03.005L.0070.15.00015N.d.N.d.Ḷ03L.003.015.03.05.3.002.007.01.07.0015N.d •.01N.d..07N.d..05N.d..07.7N.d..2.0015.07.3.07L.03.005Ḷ0051. Heavy-mineral concentrate from gold-bearing episyenite (fig. 50); SEI/ll sec. 27, T. 28N., R. 18 w.2. Drywasher concentrate. Fine gold fragments visible; SWI/ll sec. II. T. 27 N., R. 18 w.3. Drywasher concentrate. Location uncertain.II. Drywasher concentrate. SWI/ll sec. 10, T. 29 N., R. 18 W.5. Drywasher concentrate, above caliche-cemented fanglomerate. Few fine gold fragmentsvisible; NWI/ll sec. 31, T. 29 N., R. 17 w.6. Drywasher concentrate, includes barite, magnetite, limonite after pyrite, cerussite,galena, and traces of gold; SWI/ll sec. 8, T. 29 N., R. 17 w.7. Drywasher concentrate, SWI/ll sec. 31, T. 30 N., R. 17 w.8. Drywasher concentrate, SWI/ll sec. 31, T. 30 N., R. 17 w.

100 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAbiotite-bearing schists, unretrograded amphibolite,pegmatoid alaskite, and aplite. The overall proportionsof the lithologies of the Muddy Creek Formation suggestderivation from the southwest. Deaderick (1980, p. 96)analyzed the population of heavy minerals in concentratesfrom gravels along the east flank of the Lost Basin Rangeand concluded that the gold-bearing fanglomerates of theMuddy Creek Formation, out of which the gold placersare being reworked, must have been derived from somesource to the west or southwest, more distant than theadjacent Lost Basin Range. The Early Proterozoicmetamorphic complex which crops out beneath the lavasof the Table Mountain area, approximately 10 km southsoutheastof the Cyclopic mine, includes lithologies in approximatelythe same proportions as the Proterozoicclasts in the Muddy Creek Formation at the south endof the Lost Basin Range. The source area for the MuddyCreek Formation, which crops out at the south end of theLost Basin Range, could not have been from the GarnetMountain tectonic block to the southeast. This block ofEarly Proterozoic rock includes too much porphyriticmonzogranite and insufficient amounts of pegmatoidleucogranite and unretrograded metamorphic rock.Progressively increasing abundances of lithologiesderived from the Early Proterozoic terrane of the LostBasin Range make up the sequences of the Muddy CreekFormation north from about 3.5 km southeast of the LoneJack placer mine (P.M. Blacet, unpub. data, 1967-72). Aspointed out by Deaderick (1980, p. 99), apparently onlythe Early Proterozoic metamorphic-clast facies of theMuddy Creek Formation contains the gold here. Furthermore,in this general area, the Muddy Creek Formationincludes a considerable amount of 2.5- to 10.0-cm, roundedto subangular clasts of retrograded quartzofeldspathicgneiss. The clasts of quartzofeldspathic gneiss are yellowishgray and are well foliated to laminated. Sparse cobblesof pyrite-bearing vein quartz also are present herein the Muddy Creek Formation, as are minor amounts ofretrograded amphibolite. Quartzofeldspathic gneiss is thedominant clast type in the Muddy Creek Formation fromapproximately 3.5 km southeast of the Lone Jack placermine northward to several kilometers beyond the mainworkings of the King Tut placer area. The relations suggestderivation of the bulk of the gold from sources to thewest in the Lost Basin Range, but possibly including somesources farther to the west in Hualapai Valley nowcovered by alluvial deposits younger than fanglomerateand tuff of the Muddy Creek Formation. Some placer goldmay eventually have also come from the southwest. Aprobable sequence of depositional and structural eventsleading to the present-day geomorphologic relations isoutlined in figure 3.Quaternary fanglomeratic deposits which host theplacer deposits along the west flank of the Lost BasinRange are clearly dissected and incised, whereas thoseQuaternary deposits which were not worked previouslyfor their placer gold are distinctly less dissected (P.M.Blacet, unpub. data, 1967-72; Blacet, 1975). In addition,a sharp geomorphic boundary exists between the productiveQuaternary placer gold deposits and the nonproductiveQuaternary deposits. This abrupt boundary is justsouth of the major canyon leading to the Bluebird mine.South of this boundary the alluvial fans are significantlyless dissected and covered with conspicuous desertvarnish-stainedtrains of boulders and reddish-brown soil.Displacement(s) along a buried fault that is largely post­Quaternary in age may explain these relations. However,the overall strike of such a fault is not readily apparent.On the one hand, an east-striking normal fault, south sidedown, may crosscut the bajada approximately at thegeomorphic transition (P.M. Blacet, unpub. data,1967-72). Movement(s) along this hypothetical fault mayhave increased alluvial gradients on the north, therebyincreasing both the dissection of the Quaternary depositsand the concentration of the placer gold. Alternatively,the geomorphic transition may reflect the approximatefulcrum point of very late predominantly scissors-typemovements along the approximately north-south-strikingfault bounding the Lost Basin Range on the west (seeBlacet, 1975).Finally, analysis of the abundance of placer gold invarious dry-washer concentrates in the placers of the GoldBasin district suggested to P.M. Blacet (unpub. data,1967-72) that the placer gold there may not be locallyderived. Apparently, the placer gold in this general areawas concentrated by being reworked out of erosional thincaps of older Quaternary gravels resting unconformablyon the underlying Early Proterozoic gneiss. Overall productionof gold from these placer deposits in the GoldBasin district was quite small and included 19 oz of goldrecovered in 1942 by several operators (Woodward andLuff, 1943, p. 251).IMPLICATIONS OF THE COMPOSITIONS OFLODE AND PLACER GOLDBy J.C. ANTWEILER and W.L. CAMPBELLINTRODUCTIONThe purpose of this chapter is to report the results andour interpretations of about 250 compositional analyseson lode gold from 48 veins or mines in the Lost Basinmining district and from 20 mines and prospects in theGold Basin mining district and of nearly 100 compositionalanalyses on placer gold from the Lost Basin district. Samplelocalities for the two districts are shown on plate 1.Many of the analyses on placer gold were on samples from

IMPLICATIONS OF THE COMPOSITIONS OF LODE AND PLACER GOLD 101the King Tut placer mines, but some were made on placergold from other localities on the east side of the Lost BasinRange and from seven localities on the west slopes of theLost Basin Range.The compositional data are discussed with regard tohow they may be useful for (1) relating the placer golddeposits to bedrock sources, (2) determining ore-depositionconditions, and (3) suggesting the possibility ofrelating some of the gold veins to a buried porphyry copperdeposit. In previous papers (Antweiler and Sutton,1970; Antweiler and Campbell, 1977, 1982), we suggestedthat compositional analyses of gold provide informationthat can be applied to the search for undiscovered oredeposits or to studies of ore genesis; the data presentedhere are examined for those possibilities.The compositional analyses utilized mainly directcurrentemission-spectrographic techniques for quantitativedetermination of Ag and Cu in native gold (a naturalalloy composed of Au, Ag, and Cu), together with semiquantitativedetermination of other elements. The goldwas placed directly into graphite electrodes and analyzedby E.L. Mosier using a previously described procedure(Mosier, 1975). Supplementary analyses for Au, Ag, andCu by electron microprobe were made by W.L. Campbellusing methods described by Desborough (1970). Theemission-spectrographic data provide the basis for assigningsignatures (Antweiler and Campbell, 1977) to goldfrom each locality. Signatures consist of alloy proportionsof Au, Ag, and Cu together with one or more of the followingelements: Pb, Bi, Sb, As, Zn, Te, Pt, Pd, Rh, Ni, Cr,Co, V, B, Ba, and Be. Elements of high crustal abundance(Fe, Mn, Ca, Mg, Si, Ti) that are found commonly in compositionalanalyses and elements such as Zr, La, and Ythat may be found in mineral inclusions in gold grains arenot known to be useful for prospecting or ore-genesisstudies and are not included herein as part of the goldsignature. Mercury was found in extremely variedamounts in all samples but also is not included as part ofthe signature because it was found in all samples andvaried greatly from one analysis to another on replicatesamples. Gold content was estimated by subtracting from100 percent the sum of the percentages of Ag and otherelements found in the analyses. Gold fineness (parts perthousand Au in native gold) was estimated by dividing theAu content by the sum of the Au and Ag content andmultiplying by 1,000.We crushed and coarsely ground the lode samples fromveins and mines and recovered gold grains by panning andhandpicking. We avoided use of chemical, amalgamation,or roasting procedures, because those recovery proceduresalter the composition of the sample (Campbell andothers, 1973). Gold from the placer deposits was recoveredby dry placering or panning and also was obtained withoutthe use of procedures that might alter its composition.Warren Mallory, president of the Apache Oro Co.,Laramie, Wyo., which is reported to have mining claimsin the districts, collected specimens with visible gold frommany of the veins and generously donated them to us. Healso gave us gold from the King Tut placer mines and frommany of the other placer localities. Without his interestand generosity this work would not have been possible.VARIATIONS IN GOLD COMPOSITIONMany papers have been published on the compositionof native gold (for example, Warren and Thompson, 1944;Gay, 1963; Jones and Fleischer, 1969; Lantsev and others,1971). Variations in composition are present even frompoint to point within the same grain (Desborough, 1970).Native gold in oxidized zones and in associated placersgenerally contains lesser amounts of Ag and other elementscompared with the native gold in the correspondingprimary deposits; within some specific deposits singleparticles of native gold are relatively homogeneous, butin other deposits the native gold is heterogeneous (Boyle,1979). Because variations in gold composition are naturalrather than analytical, they are worthy of study, particularlyif their significance can be understood. In spiteof the variations, gold compositional data are useful in thatthey help characterize conditions of ore deposition and arecommonly areally distinctive for mines, districts, orregions.To lessen uncertainties in interpreting gold compositionaldata that are inherently subject to natural variations,replicate analyses of gold from the same samplelocality should be made if possible. As a general guide,in a district in which no prior compositional informationfor gold is available, we believe that at least five spectrochemicalanalyses of 5-mg samples of gold are desirablefor a single sample site to obtain a signature in which onecan place confidence. However, in the context of manyother analyses from the same district, a single analysisis of value. Fortunately, at many localities in both the LostBasin and Gold Basin districts, sample quantities wereavailable for several analyses. At some localities, however,limited quantites of sample precluded making more thanone or two analyses.The variations in composition of Lost Basin placer samplesare shown in table 21, where it can be seen that in46 emission-spectrographic analyses of gold from the KingTut placer mines, Ag content ranges from 2.1 to 15.0weight percent and Cu content ranges from 0.0017 to 0.07weight percent. Standard deviation for these analyses isnearly 50 percent of the mean for Ag (7.25 = 3.1 percent)and nearly 60 percent ofthe mean for Cu (0.0185 =0.0114percent). In individual analyses, Ag ranges from 2.1 to20 weight percent (0.1-22.3 for electron-microprobe analyses)and Cu from 0.001 to 0.097 weight percent.

102 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN·LOST BASIN MINING DISTRICTS, ARIZONATABLE 21.-Cc;mpilation ofsignatures ofplacer gold samples, Lost Basin mining district[N.D., not detennined]Ag (percent) Cu (percent) Au (fineness)NumberCharacteristic traceuf Standard Standard Au elements, in order ofSample analyses Range Mean deviation Range Mean deviation Mea. (Au+AgJxl,OOO AulAg Au/Cu Ag!Cu abundanceHuW-l 1 NaD. 6.8 N.D. N.D. 0.125 N.D. 93.1 932 13.7 745 54 Pb, 2nHuW-3 ----------------- 1 N.D. 7.1 N.D. N.D. .023 N.D. 92.9 929 I3.l 4,039 309 Pb. MeHuW-4 ----------------- 1 N.D. 6.5 N.D. N.D. .250 N.D. 93.4 935 14.4 374 26 PbHuW-S ----------------- 1 N.D. lZ.2 N.D. N.D. .15 N.D. 87.6 878 7.2 584 81 Pb. MoN33PC-7 1 4 4.7-8.1 5.7 1.6 .048-.08 .062 .0144 94.2 942 16.5 1,519 92 Pb, Bi, Mo, Te34pC-I ---------------- 1 N.D. 8.9 N.D. N.D. N.D. .0375 91.0 911 10.2 2,426 237 NoneLB-1 ------------------ 2 5.5-13.3 9.4 5.5 .018-.06 .039 .03 90.5 910 9.6 3,016 241 Pb. B'L8-2 ------------------1 3 18.9-19.8 19.3 .56 .038-.055 .047 .012 80.6 806 4.2 1, 715 411 Pb, Te. 2•• Bi, CdLB-3 ------------------King Tut (analyses by245*1 3 18.9-19.8 19.3 .56 .038-0.55 .047 .012 80.6 806 4.2 1, 715 411 Pb. Te, Z., Bi, Cdmicroprobe) --------- .1-22.3 11.0 5.5 89.0 890 8.1 N.D.King Tnt (ana lyses byemiss i'on spectrograph) 46 2.1-15.0 7.25 3.1 .0010-.07 .0185 .0114 92.5 926 12.8 5,000 392 Pb. Hi, Mo, Sb, Zn10PC-4 ---------------- 10 4.0-20.0 11.6 5.7 .006-.078 .029 .0216 88.5 886 7.6 3 , 051 400 Pb, HiGAS ------------------- 3 N.D. 13.2 N.D. N.D. .01 N.D. 86.7 N.D. N.D. N.D. N.D. Pb, Hi10PC-3 I N.D. 2.3 N.D. N.D. .007 N.D. 97.7 977 42.5 13,957 329 None10PC-l ---------------- 1 N.D. 10.7 N.D. N.D. • 014 N.D • 89.2 893 8.3 6,371 764 PbL8-4 ------------------ 5 3.5-6.5 4.9 2.4 .019-.097 .053 .0325 95.0 951 19.4 1,792 92 8i , Pb. Pd. Te15PC-4 ---------------- 1 N.D. 4.3 N.D. N.D. •03 N.D • 95.6 957 22.2 3,187 143 Pb14PC-2 ---------------- 1 N.D. 2.0 N.D. N.D. .0125 N.D. 98.0 980 49.0 7,840 160 Pb22PC-1 ---------------- 5 15.0-20.0 17.0 2.1 .022-.03 .03 .0021 82.9 831 4.9 2,763 567 None26PC-1 ---------------- 4 7.5-12.5 10.0 2.0 .005-.045 .022 .0168 89.9 900 9.0 4,086 455 Pbl All analyses on portions of the same nugget.245 individual grains were analyzed, each by 3-5 spot analyses which were then averaged for mean Au and Ag content. Copper waa detected only occasionally.At three localities (N33PC-7, LG-2, and LB-3) replicateemission-spectrographic analyses were made on portionsofthe same nugget. Substantial variation is evident bothin Ag content and Cu content, although such variation isgenerally not so great as in analyses made on differentgrains.The much smaller size of samples analyzed in electronmicroprobework compared with emission-spectrographicanalyses (0.05-0.10 mg compared with 5 mg) resulted ingreater standard deviation in Ag values (5.5 weight percentcompared with 3.1 weight percent). Higher meanvalues for Ag content also resulted (11.0 weight percentcompared with 7.25 weight percent). These higher meanvalues may indicate that the Ag content ofgrains analyzedby microprobe just happened to be higher than that ofsamples analyzed by spectrograph, but another explanationis that most of the microprobe analyses were madeon polished interior surfaces of individual grains, whereasspectrographic analyses were made on several wholegrains. Most of the grains that were analyzed by bothmethods were small. However, in spectrographic analysesof Lost Basin samples made earlier (Antweiler and Sutton,1970), coarse gold (nuggets) averaged lOA weightpercent Ag and 0.034 weight percent Cu, whereas finergold (minus-60 mesh) averaged 5.6 weight percent Ag and0.015 weight percent Cu. The lower Ag and Cu contentsin the smaller particle-size fraction was interpretedas havingresulted from more surface exposure with attendantgreater Ag and Cu loss through atmospheric and groundwaterleaching agents. Exterior surfaces ofgold in placerscommonly are depleted in Ag content (McConnell, 1907;Desborough, 1970). Electron-microprobe analyses areideal for determining such losses because the percentagesof Au and Ag can be determined at any spot includingexterior surfaces to which the microprobe beam isdirected. A number of spot analyses were made on exteriorsurfaces of grains by microprobe; these analysesshowed Ag content ranging from nil to 14 weight percenton exterior surfaces and generally from 2 to 5 weight percentless Ag than in the interior of the grains. The zoneof Ag depletion (and Au enrichment) varied from grainto grain, but rarely penetrated into the interior of thegrains more than a few micrometers. No attempt wasmade to compute the total percentage loss ofAg becausethe geometry of the grains varies considerably as doesthe Ag content. If the higher Ag content obtained inmicroprobe analyses is attributable to loss of Ag on grainsurfaces, the Ag content obtained by microprobe shouldmore nearly reflect the Ag content of the gold when itwas in a vein, provided, of course, that no other compositionalchanges occurred.The difficulty of identifying placer gold with a specificlode source is highlighted by the data (table 22), whichshows the extent of variation in Ag and Cu contents inlode gold from Lost Basin and Gold Basin. Only thosesamples are listed for which five or more spectrographicanalyses are available. The Cu content of Lost Basin lodesamples ranges from 0.017 percent to 0.7 weight percent,and the standard deviation at one locality, B-B1, is nearly100 percent of the mean. Ag content ranges from 6.6to 31.5 weight percent, but at most localities the standarddeviation approximates 20 percent of the mean value-agenerally smaller percentage than in the placer samples.The Gold Basin samples also show high standard devia·tions for Cu; samples from locality MAS, for example,have a Cu content ranging from 0.01 to 0.28 weight percent,resulting in a standard deviation of 0.14 percent,which is 125 percent of the mean value. The standard

IMPLICATIONS OF THE COMPOSITIONS OF LODE AND PLACER GOLD 103TABLE 22.- Variation ofsilver and copper content oflode gold samplesfrom Lost Basin and Gold Basin mining districts as shown by replicateemission-spectrographic analysesNumber As. (percent) Cu (percent)Sample of Standard Standardanalyses Range Mean deviation Range Mean deviationLost BasinS ------- 10 20.0-29.0 22 .. 3 3.0 0.004-0.014 0.0086 0.0033HW ---- 9 11.4-31.5 19.1 7.3 .03-.5 .18 .1510HET --_____5 15.9-23.9 20.7 3.8 .035-.300 .15 .11'0GG -------- 5 12.0-19.5 15.1 3.4 .04-.13 .092 .0480Climax ---- 8 7.5-14.0 10.4 2.2 .015-.025 .019 .0040Golden Mile - 6 6.6-12.5 10.7 2.5 .02-.037 .035 .0149B-J ------- 10 9.7-18.0 14.4 3.0 .0175-.50 .092 .14658-81 ------ 10 14.0-22.5 17.5 3.4 .03-.39 .17 .1624B-A ----- 8 18.0-30-0 20.8 3.8 .014-.06 .029 .0148B-B1W ---- 6 14.5-26 .0 20.9 4.2 .02-.70 .32 .2313B-C ------ 9 10.0-15.0 11.6 1.8 .028-.10 .047 .0246SUlIIIIlary -- 6.6-31.5 16.'f TI .015-.7 -:To38 .0829Gold BasinAWS-H --- 12.0-15.0 13.7 .94 .014-.0455 .0215 .0114GHH ------ 14.0-25 .0 19.3 3. I .0075-.05 .0225 .0153HAS ------- 15.0-25.0 17.4 4.3 .0100-.28 .1120 .11100ENW-2 ------ 25 .0-31.0 29.0 2.2 .003-.02 .008 .0056HWS ---- 10.0-35.0 18.0 9.8 .015-.10 .0502 .0323OLY -------- 14.0-30.0 20.3 4.8 .036-.07 .0495 .0140SUlIlllary - 10.0-35.0 T9.6 U .003-.28 :04iiO .0364deviations for most analyses of Ag in Gold Basin samples,like those in Lost Basin samples, tend to be 20 to 25 percentof the mean value, although some are less than thatand some are more.Because gold in placers could have more than one sourceand could have either a simple or a complex history inmoving from a primary source to a placer site, widervariations in composition might be in placers than in lodes.Compositional variations in placers, however, aremoderated to some extent by the natural refining that occursduring the transition from the environment of veingold in bed rock to the environment of the placer gold.Although such natural refining may affect only the surfaceof gold grains, its net effect is an overall decreasein the content of Ag, Cu, and trace elements, with a higherpercentage of Au content being the final product. If allthe grains of gold in a placer deposit are uniform in composition,the chances appear favorable that all the grainscame from one source area, which also would have goldof uniform composition. However, most of the lode goldin the Lost Basin and Gold Basin districts has a ratherheterogeneous composition.COMPARISON OF COMPOSITION OF PLACER GOLDIN LOST BASIN WITH THAT OF POSSIBLE LODE SOURCESMost of the placer gold samples obtained in the LostBasin district are not geographically relatable to a specificlode locality, but four of them are from drainages belowveins from which gold was collected and analyzed (table23). Even though this direct geographic relation does exist,gold in the placers on the eastflank of the Lost BasinRange definitely was reworked out of the Muddy CreekFormation, which locally includes the bed rock from whichthe alluvial placers were derived. On the west flank of theLost Basin Range, sample GM-G1 below the Golden Milemine must certainly have come from the Golden Mile minevein. The small volume of alluvium in the drainage wherethe placer sample was collected consists entirely of locallyderived material from the nearby Early Proterozoicrocks. Only enough placer gold was obtained for oneanalytical determination, which shows a Cu content of0.17 weight percent compared with a mean value for sixanalyses of the lode sample of0.035 weight percent. Additionof Cu to native gold during the transition from veinto placer is unlikely; therefore, the high content of Cu inthe placer sample probably reflects the presence of inclusionsof chalcopyrite or other Cu-bearing minerals in thegold sample analyzed. Decrease of Ag content from 10.7to 7.1 weight percent from lode to placer gold is reasonable,as is the loss of Bi and Mo. On the east flank of theLost Basin Range, lode-placer pair LB4-WSE2 (table 23),although geographically closely related, shows the absenceof a direct kinship. The placer sample has only 4.9 weightpercent Ag compared with 15.5 weight percent Ag forthe lode sample. If the placer sample came directly fromthe lode, its Ag content should have been at least 10weight percent, and Te should not have been present inthe placer if not in the lode. The lower Ag content couldbe explained as the addition of Au through chemical orphysical accretion, but the appearance of Te in the placerposes a mystery. A likely possibility is that some or allof the placer gold had its immediate, though secondary,source in the Muddy Creek Formation and had a moredistant primary source. Alternatively, the placer samplecould have come from a part of the vein at WSE2 (table23) that is considerably different in composition from thatwhich we analyzed.A discrepancy also exists between placer sampleN33PC7 (table 23) and the Climax vein sample (table 23).Although the Ag and trace-element contents are compatible,the greater amount of Cu in the placer sampleindicates the placer sample either came from a differentlode or from a part of the Climax vein containing a muchhigher content of Cu than that found in the part of thevein that we sampled.Placer sample LB3 (table 23) has a composition that iscompatible with derivation from lode sample BL-1 (table23) except for the placer's Zn and Cd, which could beexplained by assuming that inclusions of sphalerite containingCd were present in the particular gold sampleanalyzed. Absence of Mo and Te in the placer sample isreadily explainable as the result of loss from oxidation orleaching in the transition from vein to placer.All the lode samples from the Gold Basin and Lost Basindistricts were examined in terms oftheir Ag content andfineness as possible sources for the Lost Basin placerdeposits. Histograms showing the number of samples with

104 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONATABLE 23. -Comparison of signatures ofplacer gold and possible lode gold sourcesSampleP, placer;L, lodeNumberofanalysesAuPercent meanAg Cu FinenessAuAu/AgCharacteristic traceAu/Agelements, in orderAu/Cu Cu Ag/Cu of abundanceGMG1 (P) -­GMG1 (L) ---LB4 (P) -­WSE2 (L) ---N33PC7 (Pl ­Climax (Ll -LB3 (P) --­BL-1 (L) ---1 92.8 7.1 0.17 9296 89.2 10.7 .035 8935 95.0 4.9 .053 9512 84.4 15.5 .088 8454 94.2 5.7 .062 9438 89.5 10.4 .019 8963 80.6 19.3 .047 8072 76.6 23.0 .056 76913.1 546 77 42 Pb8.3 2,549 237 306 Pb, Bi, Mo19.4 1,792 366 92 Bi, Pb, Te5.4 959 61 176 Bi, Pb, Te, W16.5 1,519 266 92 Pb, Bi, Mo8.6 4,710 452 547 Pb, Bi, Mo4.2 1,715 89 411 Pb, Bi, Sb, Zn, Cd3.1 1,351 55 411 Pb, Bi, Mo, Sb, Tea particular level of Ag concentration (fig. 64) and thefineness of Au in Lost Basin placer samples and LostBasin and Gold Basin lode samples (fig. 65) show anabsence of strong or convincing evidence to relate thelodes to the placers. For example, no lode sample wasfound that contained less than 6.0 weight percent Ag, butseveral placer localities had gold with less than 5 weightpercent Ag, and one placer gold sample contained only2 weight percent Ag. Also, the highest mean Ag contentin any placer sample was 19.3 weight percent Ag;however, the Ag content at some lodes was as high as 38weight percent, and at 20 localities the gold samples containedmore than 20 weight percent Ag. If chemicalaccretion of dissolved Ag around detrital gold particlesoccurred, as indicated by examination of some of the nuggets(see frontispiece), the local veins presumably couldhave provided all the gold. Nearly all the placer gold isf-Z wu 320::W 8...JUi4EXPLANATION• ~~~~ :::ii~of comparatively high fineness with respect to that of thelodes (fig. 65). Therefore, although some of the placer goldprobably had its origin in Lost Basin veins (and possiblyin Gold Basin veins as well), more than half of it must haveeither had a different lode source from any of thosesampled or must have come from parts of veins no longerextant; or it represents gold that was at one time in solutionand was added to placer gold particles by chemicalaccretion or other processes. In any event, a direct sourcerelation for gold in the Lost Basin placer deposits to goldin veins in either Lost Basin or Gold Basin appears extremelydifficult, if not impossible, to determine.9809400z«90000:::l0 860:I:f-0::w 820

IMPLICATIONS OF THE COMPOSITIONS OF LODE AND PLACER GOLD 105COMPOSITION OF LODE GOLD FROM THELOST BASIN DISTRICTSignatures for lode gold samples from Lost Basin arelisted in table 24 and are arranged geographically fromwest to east and north to south (pI. 1) and grouped accordingto veins that may be related because of their proximityto one another. A crude zoning relation wasobserved in the sulfides present in the veins. At both thesouthern and northern extremities of mineralization in theLost Basin Range, galena and sphalerite were the abundantsulfides, and in some veins containing sphalerite andgalena it was not possible to obtain sufficient gold foranalysis. In the central part of the Lost Basin Range,chalcopyrite was the dominant sulfide, and some veinscontained molybdenite and arsenopyrite, with minoramounts of galena and sphalerite. The gold signaturesreflect this zoning relation only vaguely. The Climax veinsamples, the samples in the vicinity of the "Blowout"(table 24, samples B1-1, Bl-8), and the samples designated"Wall Street East" (table 24) appear to be near the centerof the district. The trace elements in the gold signaturesare dominated by Pb, Mo, and Bi, with analyses commonlyshowing the presence of As. Individual analyses could besingled out to suggest that gold of high fineness is presentin some analyses, but the gold in nearly all the veinsis extremely heterogeneous so that no convincing generalizationscan be made. The vein with lowest Ag content,the TP vein, is west of most of the veins where gold wasfound but is about midway between the northern andsouthern boundaries of mineralization. The TP vein ismore homogeneous than most of the other veins, andbeing the vein with the highest Au fineness it may representmore nearly the center of the district than any ofthe other veins.The abundance of veins in the Lost Basin district suggeststhe desirability of prospecting further, perhaps atdepth, in the Lost Basin district.COMPOSITION OF GOLD FROM MINES IN GOLD BASINSignatures of lode gold from samples taken from theGold Basin district are listed in table 25, also arrangedfrom north to south (pI. 1). Northwest of the Gold Hillmine, a group of samples is designated with the prefixAWS. Sample AWS-M (table 25), in the center of thisgroup, showed in replicate samples the least variation inAg content of any of the lode samples in either the GoldBasin or Lost Basin district. The Ag content of gold fromthis prospect was also somewhat less than most of theother prospects in the group, thus suggesting thatAWS-M may have been a local center of mineralization.The other veins in this group vary widely in composition,however; like most others in the Gold Basin and LostBasin districts they are mixed sulfide veins and aregenerally small.Pt was found in gold samples from the Excelsior mine(table 25, sample EXC), and Pd was found in gold samplesfrom the Excelsior mine as well as from sample AWS-W(table 25). No apparent significance is attached to theseoccurrences. However, minor-element analyses of amphibolitefrom the general area of the Bluebird mine inthe Lost Basin Range revealed the presence of detectablePt and Pd.A gold sample of high Ag content was found south ofthe Malco mine at locality MOK (table 25) and had thehighest Ag content found in any of the samples from bothGold Basin and Lost Basin.The average Ag content of lodes in the Gold Basindistrict is greater than that of lodes in the Lost Basindistrict, although the Ag content varies widely in bothdistricts. Cu content also varies widely in both districtsbut is generally somewhat higher in the Lost Basindistrict. These observations suggest that conditions of oredeposition were generally similar for both districts, butthe temperature and pressure of ore deposition was probablysomewhat greater in the Lost Basin district.SIMILARITY OF SIGNATURES OF GOLD SAMPLES FROMSOME LOCALITIES IN THE DISTRICTS TO THAT OFGOLD SAMPLES FROM SOME PORPHYRY COPPER DEPOSITSIn previous work (Antweiler and Campbell, 1977, 1982),we found that gold samples from some porphyry copperdeposits had an Ag content of 25 to 30 weight percent,a Cu content of 0.04 to 0.15 weight percent, and a suiteof trace elements that usually included Pb, Bi, and Sb,and sometimes one or more other elements that mightinclude Zn, As, Te, Sn, Cr, Ni, or W. Probably the mostimportant indicator in these gold-sample signatures is thequantity of Ag and Cu. Characteristically in hydrothermaldeposits, native gold includes maximum Cu and minimumAg contents at ore depositional conditions of high temperatureand pressure and minimum Cu and maximum Agcontents at low temperature and pressure (Antweiler andCampbell, 1977). Gold samples from porphyry copperdeposits, however, include an Ag content that is usuallycharacteristic of epithermal or mesothermal deposits, buta Cu content more nearly like that of hypothermaldeposits. Samples that contain or exceed 0.04 weight percentCu, and also contain at least 20 weight percent Ag,should be considered in the context of their possible relationto a porphyry copper deposit.The Lost Basin and Gold Basin gold-sample signatureswere examined to determine whether any of the signatureswere similar to those obtained on gold samples fromporphyry copper deposits (Antweiler and Campbell, 1977,

106 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONATABLE 24.-Compilation ofsignatures[N.D., notAg (percent) Cu (percent)Numberof Standard StandardSample analyses Range Mean deviation Range Mean deviationBDNI --------------------- 2 27.9-35.6 31.8 5.4 N.D. 0.075 N.D.BD ----------------------- 2 22.1-22.1 22.1 N.D. 0.042-0.085 .063 0.030BD swnmary ------------- 4 22.1-35.6 26.95 N.D. .042-.085 .069 N.D.S-HW --------------------- 2 22.6-25.1 23.9 1.3 .025-.047 .036 .016S ------------------------ 10 20.0-29.0 22.3 3.0 .004-.014 .0086 .0033S vein summary --------- 12 20.0-29.0 22.6 N.D. .004-.047 .013 N.D.WB-U --------------------- I N.D. 26.5 N.D. N.D. .019 N.D.WB-S --------------------- I N.D. 31.1 N.D. N.D. •070 N.D•WB summary ------------- 2 26.5-31.1 28.8 N.D. N.D. .0445 N.D.Ford vein ---------------- 4 20.3-25.3 23.3 2.2 .01-.07 .033 .026PB vein ------------------ I N.D. 29.8 N.D. N.D. .0125 N.D.GG (Golden Gate mine) ---- 5 12.0-19.5 15.1 3.4 .04-.13 .092 .048GGW-l -------------------- 1 N.D. 18.0 N.D. N.D. .125 N.D.Golden Gate summary ---- 6 12.0-19.5 15.6 N.D. .04-.13 .098 N.D.TP-I --------------------- 2 5.9-6.0 6.0 .07 .009-.02 .0145 .078TP-2 --------------------- 5 3.6-16.8 6.1 5.0 .01-.05 .0310 .0175TP-3 --------------------- 5 5.0-8.3 6.5 1.7 .0125-.03 .0190 .007TP-4 --------------------- 2 8.3-10.1 9.2 1.6 .005-.0125 .0088 .005TP vein summary -------- 14 3.6-16.8 6.7 N.D. • 005-.05 .021 N.D•HWW-G -------------------- 2 30.2-31.2 30.7 .7 N.D. .03 N.D.HWW ---------------------- 3 30.6-40.6 34.9 5.1 .2-.4 .27 .11HET ---------------------- 5 15.9-23.9 20.7 3.8 .035-.3 .15 .11HW ----------------------- 9 11.4-31.5 19.1 7.3 .03-.5 .18 .15HEE-l -------------------- 2 12.2-13.7 13.0 1.1 .025-.028 .027 .015Harmon veins summary --- 21 11.4-40.6 22.3 N.D. N.D. .16 N.D.el imax mine -------------- 8 7.5-14.0 10.4 2.2 .015-.025 .019 .004CBW-2 -------------------- 4 16.8-25.8 20.8 3.7 .016-.025 .02 .003CB-C --------------------- 3 10.9-19.4 15.1 4.3 .015-.03 .0225 .008Climax mine summary ---- IS 7.5-25.8 14.1 N.D. .015-.03 .02 N.D.Bl-1 --------------------- 2 22.0-24.0 23.0 1.4 .05-.065 .058 .011BI-8 --------------------- 3 19.0-39.0 29.0 10.0 .017-.025 .022 .004Blowout summary -------- 5 19.0-39.0 26.6 N.D. .017-.065 •036 N.D•Go Iden Mile mine areaGM --------------------- I N.D. 9.7 N.D. N.D. 0.0375 N.D.GIIR -------------------- 3 24.4-37.4 31.0 6.5 0.005-0.010 .007 0.0026GMGI ------------------- 6 6.6-12.5 10.7 2.5 .02-.037 .035 .0149Summary -------------- 10 6.6-37.4 16.7 N.D. .005-.0375 .027 N.D.Wall Street veinsA. West veins ----------WS-V ---------------- 2 34.0-34.0 34.0 N.D. .0235-.0335 .029 .007WS-W7 --------------- 2 1l.4-21.4 16.4 7.1 .15-.30 .225 .106Ws-w ---------------- 3 15.5-19.5 17.8 2.1 .02-.036 .0277 .008WS-HG2 -------------- 1 N.D. 8.6 N.D. N.D. .0200 N.D.WS-HG3 -------------- 3 13.9-15.9 14.9 1.0 .018-.028 .024 .007WS-HG5 -------------- I N.D. 23.9 N.D. N.D. .010 N.D.Summary West -------- 12 8.6-34.0 19.3 N.D. N.D. .058 N.D.B. East veinsWS-HVN -------------- 3 21.4-42.4 33.2 10.0 .0625-.0825 .0725 .010WS-HV --------------- 3 26.6-28.6 27.9 7.2 .023-.10 .0510 .043WS-E12 -------------- 2 13.6-18.0 15.8 3.9 .0125-.25 .1300 .168WS-CL5 -------------- 1 N.D. 9.4 N.D. N.D. •0700 N.D•WS-El --------------- 2 17.3-21.1 19.2 2.7 N.D. .1500 N.D.Summary East -------- 11 9.4-42.4 23.9 N.D. .0125-.25 •09 N.D•Summary West, East - 23 8.6-42.4 21.5 N.D. •0125-.25 .07 N.D•Bluebird veinsA. West of washB-A ---------------- 8 14.6-30.6 20.9 4.5 .014-.06 .031 .015B-BI --------------- 10 13.4-23.4 18.4 3.1 .03-.38 .17 .16B-BIW -------------- 6 15.1-26.0 21.5 4.2 .02-.7 .31 .26B-C ---------------- 9 10.3-15.3 1l.9 1.8 .02-.1 .046 .016BM-9 --------------- 2 15.3-19.8 17.6 3.3 .006-.018 .012 .008BM-8 --------------- 1 N.D. 29.2 N.D. N.D. .0075 N.D.BM-3 --------------- 2 8.7-14.2 11.5 3.9 .034-.04 .037 .004BM-3S -------------- 3 14.1-18.1 17.5 2.2 .032-.0375 .035 .003BM-1S -------------- 2 8.8-15.8 12.3 4.9 .02-.025 .0225 .004Summary ---------- 43 8.7-30.6 17.5 N.D. .02-.31 .104 N.D.B. East of washB-J ---------------- 10 9.9-18.2 14.6 2.9 .0175-.10 .0525 .032B-20L2 ------------- 2 12.9-15.4 14.2 1.8 .019-.026 .0225 .005B-JP --------------- 1 N.D. 17.3 N.D. N.D. .0250 N.D.Summary ---------- 13 12.9-18.2 14.7 N.D. N.D. .046 N.D.

of lode gold, Lost Basin mining districtdetermined]IMPLICATIONS OF THE COMPOSITIONS OF LODE AND PLACER GOLD 107Au finenessAu ~ Characteristic trace elements,Mean (Au+Ag)xl,OOO Au/Ag Au/Cu Cu Ag/Cu in order of abundance67.8 681 2.1 900 28 425 Bi, Pb, Ba73.7 769 3.3 1,170 52 351 Pb, Mo, Bi, Te, Co, Ni70.75 725 2.6 1,025 38 391 Pb, Bi, Mo, Te. Ba, Co, Ni76.0 761 3.2 2,083 89 664 Pb, Bi77.6 777 3.5 9,023 407 2.593 Pb, Mo, Bi, Ba77.3 774 3.4 5,946 263 1,738 Ph, Bi, Mo. Ba69.7 725 2.6 3.668 137 1,394 Pb, Bi63.9 694 2.1 913 30 444 Pb, Bi, Mo, Co, V, Sa66.8 710 2.4 2,291 84 919 Pb, Bi, Mo, Co, V, Ba75.8 764 3.3 2,296 100 942 Pb, Si70.2 703 2.4 5,616 2,384 192 Pb, Bi84.8 849 5.6 922 61 164 Pb, Bit Sb, As, Zn. Pd, Cr, Ni81.9 820 4.6 654 37 144 Pb, Bi, As, Zn84.3 844 5.4 860 55 159 Pb, Bi, As, Zn, Sb. Pd, Cr, Ni93.9 940 15.7 6,302 1,082 4,141 Bi, Pb. Pd, Mo90.8 909 10.0 2,929 322 294 Pb, Bi, Mo, Co. Ni, Cr93.4 935 14.4 4,916 758 342 Pb, Zn. Cd, Cr90.7 908 9.9 10.306 1,120 1,045 Pb, Bi, Zn, Cd, Cr92.2 923 13.8 4.388 655 319 Pb, Bi, Cr, Mo, Zn, Cd, Mo,Pd, Co69.1 692 2.3 2,303 75 1,023 Pb, Bit Mo, Te61.4 638 1.8 227 6.7 129 Ph, Bi, Sa79.2 793 3.8 528 26 138 Ph, Mo, Bi80.8 809 4.2 449 23 106 Ph, Bi, Mot w86.6 869 6.7 3,207 247 481 Ph, Mo, Bi77.1 776 3.5 482 22 139 Pb, Bi, Mot W, Te t Ba89.5 896 8.6 4.710 453 547 Ph, Bi, As, Mot Zn79.0 792 3.8 3.950 190 1,040 Pb, Mo84.3 848 5.6 3,750 249 671 Pb, Mo, Bi, As, Te85.7 859 6.1 4.285 305 705 Ph, Mo, Bi, As, Zn, Te76.7 769 3.3 1,400 59 411 Ph, Mo, Bi, Sb, Zn, Cr, Ba70.6 713 2.4 3,200 109 1.318 Ph, Mo, Bi, V, Ba, Sr73.0 733 2.7 2,027 76 739 Ph, Mo, Bi, Sb, Zn, Ba, V, Cr90.1 903 9.3 2,402 248 259 Pb, Bi, Ba, Cr68.8 689 2.2 9,828 317 4,428 Pb, Mo. Bi, Sa89.2 893 8.3 5,986 238 718 Pb. Bi, Cr, Ba83.1 837 5.0 3,078 185 618 Pb, Bi, Ba. Cr, Mo65.7 659 1.9 2,270 67 1,172 Pb. Bi83.0 835 5.1 370 23 73 Pb, Bi, Ba79.4 817 4.5 2,890 160 647 Ph, Bi, Mo, Ni, V, Sa91.2 914 10.6 4,560 530 430 Pb, Bi, Ba84.9 851 5.7 3,540 237 621 Pb, Bi, Te, Mo76.0 761 3.2 7,600 320 2,390 Pb, Bi, Te, Mo. Cr, V, Ba79.8 805 4.1 1,376 71 333 Pb, Bi, Mo. Ba, Te. V, Cr, Ni64.7 661 1.9 890 27 458 Pb, Bi, Mo, Sn, V, Sa71.7 720 2.6 1.405 50 558 Pb, Bi, Mo, Sn, Zn. Cr, V83.8 841 5.3 645 41 122 Pb. Bi, Te, V90.5 906 9.6 1,290 138 134 Pb, Bi, Mo, Ba79.6 806 4.1 530 28 128 Pb, Bi, As75.1 759 3.1 834 35 266 Pb, Bi, Mot V, Ba, As, Zn,Crt Ni77.6 783 3.6 1,108 51 307 Ph, Bi, Mo, Ba, V, Te, As, Zn,Crt Ni78.7 790 3.8 2,540 120 674 Pb, Bi, Ba79.6 804 4.3 470 25 108 Pb, Bi, Sb, Zn, Ba77.9 782 3.6 250 12 69 Pb, Bi, Mo87.7 881 7.4 1,900 160 259 Pb, Bi, As, Zn, Mo, Ba81.7 823 4.6 6,808 383 1,467 Pb, Bi, Te, Cr, Sa71.5 716 2.4 9,530 326 3,893 Pb, Bi, Te. V, Sa88.3 885 7.6 2,390 208 311 Pb, Te82.3 825 4.7 2,400 134 500 Pb, Bi87.3 877 7.1 3,880 315 547 Pb, Bi81.8 824 4.7 787 45 168 Pb, Bi, Te, Ba, Mo, Zn, Cr, V85.2 854 5.8 1,620 110 278 Pb, Bi85.7 859 6.0 3,800 268 631 Pb, Cr, V82.6 827 4.8 3,300 190 692 Pb, V85.1 853 5.8 1,850 126 320 Pb. V, Bi, Cr

108 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONATABLE 25.-Compilation of lode gold[N.D.• notAg (percent) Cu (percent)Numberof Standard StandardSample analyses Range Mean deviation Range Mean deviationSSM-W ------------------- N.D. 11.3 N.D. N.D. 0.0215 N.DProspects northwest ofGold Hill mine:AWS-M 7 12.0-15.0 13.7 0.94 0.014-0.0455 .0215 0.0114AWS-W -------------- 4 13-18.4 14.9 2.4 .008-.026 .0155 .007AWS-E -------------- 1 N.D. 17 N.D. N.D. .011 ·N.D.AWS-T -------------- 4 9.3-14.5 11.8 2 .02-.05 .032 .015AWS-ES ------------- 1 N.D. 7.5 N.D. N.D. .075 N.D.AWS-TS3 ------------ 2 20.5-21.5 20 .7 .028-.065 .05 .026AWS-TS2 ------------ 2 30-35 32.5 3.5 .2-.5 .35 .21Summary ---------- 21 9.3-35 15.8 N.D. .008-.5 .05 N.D.Gold Hill mine --------- 8 14.3-25.4 19.7 3.1 .0075-.05 .0225 .015Senator mine ----------- 1 N.D. 12.8 N.D. N.D. .0250 N.D.MAS -------------------- 5 15.6-25.6 18 4.3 .01-.28 .112 .14VVM -------------------- 4 6.3-15.3 12.5 4 .014-.0375 .0216 .0109ENW-2 7 25-31 29 2 .003-.02 .008 .0056ENW -------------------- 3 14.4-18.4 16.7 2.1 .05-.07 .058 .01EXC -------------------- 3 28.3-42.5 36.1 7.2 .003-.0375 .023 .018MAL-C ------------------ 3 23-30 27 3.6 .007-.014 .0117 .004MWT -------------------- 4 26.5-31.5 28.5 2.4 .003-.0125 .0075 .004MOK 3 46.2-54.2 49.5 4.2 .005-.006 .0057 .0006MWS -------------------- 5 10.5-35.5 18.5 9.8 .015-.10 .05 .0287OLY -------------------- 8 15.1-30.1 21.3 4.2 .036-.118 .058 .0311OLY-SS ----------------- 2 12.8-14.3 13.5 1 .0375-.0830 .06 .032FLU-SS ----------------- 3 23.8-26.8 25.5 1.5 .008-.012 .01 .002CUR 1 N.D. 12.5 N.D. N.D. .0375 N.D.CYE -------------------- 3 9.6-21.5 16.8 6.4 .005-.03 .021 .0125CYC -------------------- 1 N.D. 24 N.D. N.D. .0125 N.D.CYC SW ----------------- 1 N.D. 18.1 N.D. N.D. •03 N.D•MES4 ------------------- 1 N.D. 32.4 N.D. N.D. .03 N.D.1982). Samples with signatures that might qualify arelisted in table 26 together with those from four porphyrycopper deposits. The best candidates in the Lost Basindistrict are in a cluster northeast of the Golden Gate mine,samples BDN-1, BD, and S-HW; sample cluster WB-S,HW, and HET; on the Bluebird vein, samples B-B1W andB-B1; at the "Blowout", sample BL-1; and sample WSE-1on one of the "Wall Street" veins. The most similarsignatures are in the Gold Basin district near the Malcomine, sample MAS. However, of note is that no outcropsof Late Cretaceous and (or) early Tertiary I-type graniteare known to us in either of the districts. All porphyrycopper systems in North America are associated withI-type granites (Burnham, 1979).FLUID-INCLUSION STUDIESInitial fluid-inclusion studies of the precious- and basemetalvein deposits and occurrences and of samples containingdisseminated gold in the districts were carried outin 1970-72 by J.T. Nash in conjunction with the field investigationsof P.M. Blacet. These studies included quantitativetests using heating and freezing techniques, visualestimates of approximate filling temperatures of aboutone-third of the studied samples, and the examination offluid-inclusion relations in all available thin sections. Subsequentlythese investigations were supplemented by intensiveheating and freezing tests by T.G. Theodore andT.F. Lawton of a few geologically critical samples toresolve some ambiguities remaining between mineralizationand its associated fluids. About 60 doubly polishedplates, approximately 0.5 to 1 mm thick, were preparedof rock and vein samples from about 40 different localities.Three different stages were used during the course of theinvestigations. The earlier studies by Nash used a customfabricatedheating stage probably having a more than± 5 °C precision. Freezing tests were accomplished usingcooling equipment that utilized approximately 7 liters ofrapidly circulating acetone as the heat-exchange medium(see Roedder, 1962). The later investigations by Theodoreand Lawton used a commercially available Chaixmecastage described by Poty and others (1976) and modifiedusing insulation materials designed by Cunningham andCarollo (1980). The Chaixmeca stage uses dry nitrogengas passed through a liquid nitrogen bath as the refrigerant.Repeated calibrations of this stage using natural

FLUID-INCLUSION STUDIES 109signatures, Gold Basin mining districtdetermined]Au(fineness)Au ~ Characteristic trace elements,Mean (Au+Ag)xl,OOO Au!Ag Au!Cu Cu Ag!Cu in order of abundance88.6 887 7.8 4,100 390 526 Pb86.1 863 6.3 4,004 293 637 Pb, Bi, Mo, Co, Cr, Ni, Ba85 851 5.7 5,484 368 961 Bi, Pb, Pd82.9 830 4.9 7,536 445 1,545 Pb, Bi, Ba88 882 7.5 2,750 233 369 Pb, Mo, Bi, Ba92.4 925 12.3 1,232 164 2,846 Pb, Mo, Ni79.7 799 4 227 154 57 Pb, Bi, Cr67.4 675 2.1 193 6 93 Pb, Te, Mo, Bi, Co, Ni, CrN.D. N.D. N.D. N.D. N.D. N.D N.D.79.9 802 4.1 3,551 227 875 Pb, Bi86.9 872 6.8 3,480 271 512 Pb81.4 819 4.5 728 40 161 Pb, Bi, Sb, Zn, Cr, Sn, Mo87.5 878 7.2 4,050 333 578 Pb, Bi, Mo, Co70.4 708 2.4 8,850 300 3,625 Pb, Sb, Bi, Co80.8 829 4.8 1,403 83 288 Pb, Bi, As, Mo62.9 635 1.7 2,735 76 1,570 Pb, Pt, Pd, Bi, Mo, Te72.9 730 2.7 6,230 230 2,308 Pb71.3 714 2.5 9,506 333 3,800 Pb, Bi, Mo, W, Ba48.6 495 .98 8,526 172 8,684 Pb, Bi, Mo, Cr81.2 814 4.4 1,620 88 370 Pb, Bi, Mo, Cr, V, Pd78.5 787 3.7 1,570 64 367 Pb, Bi, Zn, Mo, V86. 864 6.4 1,430 107 225 Pb, Ba69 730 2.7 6,900 271 2,550 Pb, Bi, Cr, Ni87.4 875 7 2,330 187 333 Ph, Mo, V, Ba80.1 827 4.8 3,815 227 800 Pb, As, Bi, Mo, Cr74.7 757 3.1 5,975 249 1,920 Pb, Ba, Sr, Bi81.6 818 4.5 2,720 150 603 Pb, Mo, Bi, Cr67.5 676 2.1 2,250 69 1,080 Pb, Crand synthetic standards suggest temperature measurementsare less than ±0.1 °C in error in the range -56to +200 °C and approximately ± 1.0 °C in the range 200to 550 °C. Fluid inclusions rich in carbon dioxide werestudied using the methods of Collins (1979). Daughterminerals were studied using the SEM and an attachedenergy-dispersive detector following the sample-preparationtechniques of Metzger and others (1977).TYPES OF FLUID INCLUSIONSSeveral types of well-developed and relatively large fluidinclusions are present in quartz and fluorite that areassociated spatially and temporally with gold. The fluidinclusions may be classified as follows:1. Type I, moderate salinity type, consists of a liquidphase and a vapor phase (fig. 66A). The vapor phaseof this very common inclusion type typically makesup about 15 volume percent ofthe inclusion at roomtemperature. Freezing tests show these inclusionsto have salinities generally in the range 10 to 14weight percent NaCI equivalent. Very rarely thistype of fluid inclusion also contains an extremelysmall crystal of hematite. However, some sulfideminerals also have been trapped in these fluid inclusionsduring the growth oftheir host mineral, mostlyquartz. These sulfides include chalcopyrite, galena,and pyrite (fig. 66B, C) and are believed to be capturedminerals trapped during crystallization of thequartz; they apparently are not daughter minerals.Some type-I inclusions also contain significantamounts of C02 because during freezing tests liquidC02 appears at temperatures slightly below roomtemperature as a thin meniscus around the vaporbubble. The moderate salinity of the liquid in thetype-I fluid inclusions is reflected in the presence ofextremely small rounded crystals of NaCI, about0.25 fJIll wide, found near open fluid inclusions usingthe SEM and indicate dessication from the evaporationof the released fluid-inclusion waters.2. Type II, a very low density, vapor-rich type, showsmore than 50 volume percent vapor at room temperature.This type of inclusion is very rare in the GoldBasin-Lost Basin districts and may reflect eitherlocal boiling or secondary necking down.

110 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONATABLE 26.-Signatures ofgold from Lost Basin and Gold Basin mining districts that[N.D. notAg, percent Cu (percent)Numberof Standard StandardSample analyses Range Mean deviation Range Mean deviationBDN-1 ------------------ 2 27.9-35.6 31.8 5.4 N.D. 0.075 N.D.BD --------------------- 2 22.1-22.1 22.1 N.D. 0.042-0.085 .063 N.D.SHW -------------------- 2 22.6-25.1 23.9 1.3 .025-.047 .0360 0.011WB-S ------------------- 1 N.D. 31.1 N.D N.D. •07 N.D•HW --------------------- 9 11.4-31.5 19.1 7.3 .03-.5 .18 .151HET -------------------- 5 15.9-23.9 20.7 3.8 .035-.3 .15 .111B-BIW ------------------ 6 15.1-20.0 21.5 4.2 .02-.7 .31 .26B-Bl ------------------- 10 13.4-23.4 18.4 3.1 .03-.038 .17 .16BL-l ------------------- 2 22.0-24.0 23.0 1.4 .05-.065 .058 .011WSE-l ------------------ 2 17.3-21.1 19.2 2.7 N.D. .15 N.D.MAS -------------------- 5 15.6-25.6 18.0 4.3 0.01-.28 0.112 0.14ENW -------------------- 3 14.4-18.4 16.7 2.1 .05-.07 .058 .01NWS -------------------- 5 10.5-35.5 18.5 9.8 .015-.10 .05 .0287MES-4 ------------------ 1 N.D. 32.4 N.D. N.D. •03 N.D•OLY -------------------- 8 15.1-30.1 21.3 4.2 .036-.118 .058 .0311Los.GoldGold from known copperButte, Mont. ----------- 111Mineral Park, Ariz. ---- 15Cala Abajo, P. R. ------ 11Stinkingwater, Wyo. ---- 21l Antwei1er and Campbell (1977).2Antweiler and Campbell (1982).N.D. 25.9 N.D.N.D. 29.6 N.D.N.D. 25.1 N.D.N.D. 25.0 N.D.N.D. 0.05 N.D.N.D. •04 N.D•N.D. •15 N.D •N.D. .15 N.D.3. Type III, a high salinity type, includes one or morenonopaque daughter minerals at room temperature.The most common daughter mineral is NaCI (fig.66D, E). A highly birefringent mineral that hasparallel extinction and is probably anhydrite, and asparse carbonate mineral, probably calcite, are alsopresent in some ofthis type offluid inclusion. In addition,small crystals ofopaque minerals may be presentin this type of inclusion. Some type-III inclusionsalso show low concentrations of liquid C02 at roomtemperature. Although we do not recognize opticallythe presence of sylvite (KCI) in these type-III inclusions,some extremely small rounded crystals ofsylvite were found using the SEM on broken surfacesof vein quartz (fig. 66E). These crystals probablyformed during evaporation of liquid from theruptured fluid inclusions. If so, these are notdaughter minerals but do attest to some minoramounts of potassium in the fluid. The proportionof vapor in the type-III inclusions is about 15 volumepercent. Type-III inclusions are relatively rare in theexamined deposits and occurrences but seem to beconcentrated preferentially in quartz parageneticallyassociated with the feldspathic parts of the quartzcoredpegmatitic veins or with narrow micropegmatiticveins that did not evolve a significant quartzcarbonate± base- and precious-metal stage.4. Type IV comprises three-phase inclusions that at roomtemperatures contain mostly liquid H20, relativelyabundant liquid C02, and C02-rich vapor. TheseC02-rich inclusions are the preeminent signature ofthe fluid-inclusion populations associated with thegold-bearing veins and the gold-bearing episyenite(fig. 67A-D). About 70 percent of the samplesstudied contain the liquid carbon dioxide-bearingfluid inclusions. Typically, the combined liquid C02plus vapor proportion of these inclusions is in the 15­to 20-volume-percent range. A very few of theseinclusions also show extremely small opaque to partiallytranslucent minerals. The salinity of these type­IV inclusions also is moderate (3 to 9 weight percentNaCI equivalent). In addition, primary quartz in theLate Cretaceous two-mica monzogranite containsabundant concentrations of type-IV inclusions in

are 8011It'IIIhat rimiWT to tlwse ofgold from porphyry copper deposib; in other aroosfLUID-INCLUSION STUDIES 111.. (!ineneu)~ Chuacterhtic trace elementa,~.,l",,+o\g)xl,O(l() " ""flo¥, ""Ie" c, Io¥,fe" in order of ab"ndance~,,., '00 Bi, n, ~'"" .'" n,"'n, "', "". ,~, ~,'" n, Bi,'" " "'~, Bi, ""'" '"19.6 4. ,'" '" n, IIi,'" " '" '"Buin61.813.7 '" J.J 1,17016.0'"."'" J.' 2,0836].9 ,.,80.84.' 449'" '"19.2,,,17.9'" '" '"' J••19.6 "'4 4.J16.7J.J 1,400Ilaain81.480.881.261.578.5'"'"'"'"porphyry depoaita74.0'"'" '"4. , no4.' J ,4034.4 1,620,., 2,250J. , 1,35lJ.' 1,500" '"J.O "0"'"'"10.3 '04 '.4 1,800 6074.815.0J.O "0"~, ~, Bi,", ~,JO 4" ~, Bi, ~, ~, V, Ba""'", ••"n, ~, Bi, 'b. '", C" ,.~, II i,'" "" '". C" '"",n, 8i,no"', ~~. 8i, ~. ~,'."N1,080 n, ~J" ~. 8i,'"'". "'" ,>0, n, ,~~, 8i,"', '". '", C" "~, II i , 'b,'". ".~. 8i,""'", "', ..clusters (fig. 67B, C)'and in planar arrays alongsecondary annealed microfractures (fig. 67D).Thus, the CO 2 -rich fluids are probably youngerthan the initial crystallization of the two-mica monzogranitefrom a magma.Artificially broken cleavage surfaces in galena also wereexamined using the SEM to study fluid inclusions.Generally, the fluid inclusions in galena are rounded andequant in the range 1.0 to 10.0 ~m, although someelongate fluid inclusions are as long as 40 f.lm. The fluidinclusions are apparently free of daughter minerals,although this judgment is based on the examination ofonly a limited number of samples of galena. Some of theinclusions contain crystals ofquartz, potassium feldspar,iron sulfide (possibly marcasite because of apparentlyorthorhombic habit and comb structure), and an unknownsilver telluride mineral. Many of these crystals are probablyminerals captured during late crystalli7.ation stagesof the host galena. Trace amounts of silver also weredetected locally in some crystals of galena by spotqualitative analyses using the energy dispersive analyzer.HOMOGENIZATION TEMPERATURES AND SALINITIESHomogenization temperatures in the Gold Basin·LostBasin districts are in the range 150 °G to about 300 °G(table 27). However. most of the homogenization temperaturesare approximately 200 °G. Although the overwhelmingbulk of the heating tests resulted in the fluidinclusions filling to liquid, some inclusions in two samplesfrom the quartz+carbonaie+sulfide(s) vein stage (table27, mineralization stage B) homogenize to vapor. In addition,only one sample contains relatively abundant vaporrich(table 27. type II) inclusions in late-stage clear quartz,a relation which suggests either that boiling occurred onlylocally during mineralization and most likely during thefinal stages of the mineralization or that these vapor-richinclusions reflect secondary necking. A significant differencein homogenization temperatures was not apparentbetween the feldspar-dominant stage (table 27, mineralizationstage A) and the quartz-earbonate-sulfide(s) stage(table 27, mineralization B) in which the bulk of the goldwas finally deposited. However, at most only six of the

112 GEOLOGY AND GOLD MINERAUZATION OF 'fAE GOLD BASIN·LOSl' BASIN MINING DIS'fRICTS, ARiZONAA ~? -:i:J;O MICROMETERS D ~, --'~ MlCllONEnRSB '~, .::' MICROMETERS E 'L, -", MICROMfllRSc o 'MICAOMfllRS'--,-------',FIGURE OO.-Fluid inclusioru; in rocks from Gold Basin-Lost Basin miningdistricts. Photomicrograph in plane-polarized light. Q, quartz. A,Photomicrograph showing type-I fluid inclusions consisting of moo,,"ly liquid A:!l (L) and vapor (V) hosted by vein quartz. SampleGM·433. B, Scanning electron micrograph showing chalcopyrite (cp)trapped in fluid inclusion hosted by vein quartz from quar1.z..oll'tonatebarite-albite-pyritevein. Sample GM·689. C, Scanning electronmicrograph showing pyrite (py), galena (gn), and calcite (C) trappedin fluid inclusion hostOO by vein quartz from quartz.alliite-calcite-baritepyrite-galenavein. Sample GM·382. D, Scanning electron micrographshowing crystal of halite (NaCI) projecting from irregularly shapedfluid inclusion in vein quartz from quartz-earbonat.e-barite-albit.e-pyritevein. Sample GM·689. E, Scanning electron micrograph showingsomewhat rounded crystal of halite (NaCI) in fluid inclusion about 3"'" in longestdimension. Also shown on surface of artificially brokenquartz is cluster of rounded sylvite (KCI) crystals that individuallymeasure about 1.0 I'm wide.

FLUID-INCLUSION STUDIES 113studied samples are from the feldspar-dominant stage ofmineralization and probably include some quartz parageneticallylater than the feldspar (mostly albite).'The salinities of the fluid inclusions determined fromthe districts range from about 6 to about 35 weight percentNaCI equivalent. The measured temperatures offirstmelting of ice in the fluid inclusions not containing adaughter mineral of NaCI are consistently near - 24 °C,a value that is very close to the -21.1 °C expected eutectictemperature for the system NaCI-H:p. From this relationwe infer that the inclusion fluids contain sparse concentrationsofcalcium or magnesium, thereby supportingour referral of the data to the system NaCl-HzO. Thetype-I inclusions generally show salinities between 10 and14 weight percent NaCI equivalent (table 27). and theirabundance in the deposits. together with type-IV inclusions,indicates the largely nonboiling nature of themineralizing fluids. Only {our ofthe samples studied containNaCI daughter minerals, and the measured solutiontemperature (260 0c) of the NaCI in one of these samplessuggests that the saJinities very locally were as high as35 weight percent NaCI equivalent. However, within theseoverall salinity limits there is a wide range even withina singte crystal of vein quartz or fluorite, suggesting theo•.. MICJIOM£UIISA •, ,C•.. ..•• • • • • (I • •e' ~ •• •• •8 a XI MICIlOMETEIISa ~ MICII()MnE~S'----~, D'--,--'FlCURE 67.-RelatioOll among liquid carbon dioxide-bearing (type IV)fluid indusiona. Q. qUll1tz; ~ rJ\06t1)' liquid J¥>; 4::0.. mostlyliquid carbon dioxide: V. rJ\06tl)'~ \'llpor. PJane..poIarized"ligtlt. A.180lated, relativel)' large. pswdOlleOOfldary fluid inclusion containingabundant liquid carbon dioxide at room temperature. InclusiorJ ishosted by vein quartz from approximately O.6-m-thick quartz.chaIcop)Tite-galena \'('in emplaced along a shallo.....-dipping fault. SampleGM-433. B, TypicaI COfICeIltntion of t}'Jle-IV apparently serorJd·Ill')' fluid illl;luOOns in primary quartz phenocr:'!'Sts in the LateCretaooouI two-mica monzogranite. SampleGrtl·I089. C, Clo6eIIp viewshoY,ing relative proportions ~ lIV.l61Iy liquid ~, liquid carlxlrI dioxide.and mostly catboo dioxide \1lpor fouoo rommonl)' in fluid indllsioruIbolIted by primary~ in the LateCretaceous two-mica monzo.granite. Sample GM·1103. D. Abundant secondary type-IV fluid~ along annealed microCl"IloCb.Ire:5 in prirnlu)' quartz in the LateCretace

114 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN·LOST BASIN MINING D1STRICfS, ARIZONATUI.E 27.-llt1mogellizmKm tempen.tllln:'3 mtd $Olmuy dala.fromflllid-inclurion It,",;'i", lite Gold 8Mi7t-LOO Barin mining districtl-- • , ",.,.. a.~,•n.-Il__..l". epls~nlUe rc:k COl>-1A.1~1..(quart>..oI>ite2boriteUll!'i"'('h"'",","~qooortr.'~'="k:~1lluoriu~"'hore~f'.1luoriw:Q,~s.liaiI.J.d..~~_t",.a~u..f poiIlt~.-hod (1962).11, IOld•-"'-- • £Iorly-at..&__.-QtaInlnc dl..eaInM.ed &14 1_ t.4tH).".", IO.l19CslO LM.e.. -'",, 19la 5•15.' Later _en....,,-- • ••ll. ..0.~.- b. _ Eorlr-rtac" ql>8M.I",.Lat.e-.~.•• 0._ ..u....,,-- n .-250.25 \2·15.5•EMI, n .... :sc.e 11",1...1_ N" "••D. ..0. Lae n .... hleU',dr_"p.r-..ldl 1""1...1",,........ - • no.l0 ,""£arl, at.a&e, ••0. ..D. Lae It...-tori,La\.••t.ap....,,-- n ",."., ".~ .t....12_11....~-- • """ '.7_12.6twl\'-st.ap .UkJ' _,-u"'" 167sJ LM.e-SUC. cl.... ...,...-".,-- ,,,. .." ......-- -18Cl-210 '.5-1_.....,-- "••0 • .....,.. .. ,,~ ,-"'-- • -" n-... """ ". .... --- .~. ••0. ..0. •••0....... -- • ••0. '"••0. t-Ir sl.af;•190..10 7_1_ L.K••t ....,..,,,-- 205.10 1)-16...,... -- • , 171-240 10.2-16.) Conhlll11 .1s1bl. "'lei In url,_n-.:.._rt,CM-S67 __• , ... ,.,--- IIll-12O ••0. ~..st-.:... _r n ..leI 1"",1...1011".17-2)CM-51t> ~.. ..0.,.... •• 'J> ..0"" ,,~ ••0. ,~~ ••0.,.....,-- • ••D. ..D. •,,~ .~,'J>~2_5 ••D. ~CM-690 __• ,,~ ••0. 110o, o\rIh(?l £lorI, IhS•• NQO " ••• _. N.cleI...,nter .In.nh, 176-205 N.D. t..U IhS.CM-715 -- 186--197 10._ CoolUlnl .Islbl. aclelGM-735-1 -- 17&-200 N.D. Connlnl .Ialbl. ,old~Oh __• m. ..D. Mn(1)CII402D __• ,• m-~. ""NICI."•,~CIl-II2 ___• , ,,~, ~.. N.D.N.D.oWl (?)N.D.,

salinity of the fluids associated with gold mineralizationvaried widely. The overall range in salinities of the fluidsassociated with gold mineralization largely bridges theinterval in fluid compositions between many epithermalprecious-metal districts and porphyry copper deposits(fig. 68).In an attempt to bracket closely the pressure-temperature-chemicalenvironment(s) associated with Late Cretaceousand (or) early Tertiary precious- and base-metalmineralization in the districts, fluid-inclusion studies werefocused especially on (1) samples from the episyeniticalteration pipes containing disseminated gold and on (2) aquartz-fluorite-white mica vein that cuts the Late Cretaceoustwo-mica monzogranite."z~ 36~~· iJ "~ 26•~ 24• "G 20•!l; 16," Z:::J 12•"",------,----,----,----,--,--,,,M,u'sSIOOi ValleyPb·2,,·F,,,•Po,ptly,y coppe',..­7ffIIIIHOMOGENIZATION TEMPERATURE. IN DEGREES CElSIUSFLUII).INCLUSION STUDIES 115eoos;1SG""veinso1__L~~:1~~j~~;=~"";·'~·~_Jo 100 200 300 400FIGURE 68.-FllIid-inclusion homogenization temperature and salinitydata for various precious- and base-metal distrkts and deposits.Modified from Nash (1972). Data for Rochester, Nev., silver districtare from Vikre (1977, 1981) and have been corrected for inferredpl'(lSSl.lre5 of approximately 1,000 bars during mineralization. Data forGold Basin-Lost Basin districts are from this study. Lines of equaldensity (in grams per cubic centimeter) also shown; dashed wherelocated approximately.FLUID INCLUSIONS IN THE EPISYENITIC ALTERATION PIPESCONTAINING DISSEMINATED GOLDAbundant type-I and type-IV fluid inclusions are presentin hydrothermal quartz and purple fluorite that fillcavities in the episyenitic alteration pipes that containdisseminated gold. Two samples (table 27, GM-280 andGM-1134h) were collected from coarse-grained episyeniticrock in the interior portions of two of the alteration pipes.However, the generally small size of the fluid inclusionsin these rocks restricted our quantitative studies to fluidinclusions in fluorite from sample GM·280 and to fluidinclusions in quartz from sample GM·1l34h. All fluid inclusionsare trapped in the fluorite along nearly planararrays.Type-I fluid inclusions presumed to be primary, or havingformed during initial crystal growth (Roedder, 1972),are present in diffuse planar arrays that commonly containparallel linear trains ofinclusions, the effect of whichis to create a cubic network (fig. 69A). These networksare inferred to reflect the cubic habit and growth planesof the host fluorite and suggest that the fluid inclusionswere trapped on growth planes during early stages of thefluorite crystallization. The fluid inclusions are equant inshape, generally rhomblike to circular, and range fromless than 4 jJm to 14 jJm. They exhibit a consistent vaporfraction, which averages 20 volume percent at roomtemperatures. Although these early stage or primarytype-I fluid inclusions in fluorite show at magnificationsof about x 1,000 no liquid carbon dioxide at room temperature,they nonetheless may contain limited amounts ofcarbon dioxide. The solubility of carbon dioxide in H 2 0at 25°C and at a pressure of 50 bars is approximately2.1 mol percent (Greenwood and Barnes, 1966), and thelimit of detection optically is about 3 mol percent (Ypma,1963).Type-IV fluid inclusions in the fluorite are interpretedto be mostly pseudosecondary. This type of fluid inclusionis concentrated in discontinuous planar arrays thatare confined to the interiors of the fluorite crystals. Thefluid inclusions were trapped during the latter stages ofgrowth of the fluorite. Crystallization of the fluorite must. have continued after trapping of the fluids along theseplanar arrays. The type-IV inclusions consist ofsaline fluid(mostly HlP), vapor (mostly carbon dioxide), and about15 to 18 volume percent liquid carbon dioxide. In fact, oneof the diagnostic features of the pseudosecondary type­IV fluid inclusions in these gold-bearing episyenitic rocksis the high proportion ofliquid carbon dioxide in them atroom temperature (fig. 69B). The volume ratio of liquidcarbon dioxide to vapor has a value of about nine, andliquid carbon dioxide plus vapor is typically about 20

116 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAvolume percent of the inclusion. These type-IV inclusionsare somewhat larger, ranging from 16 to 35 /-1m, than theprimary type-I fluid inclusions noted above. Their habitsare equant to somewhat elongate. The type-I and type­IV fluid inclusions trapped together in the fluorite suggestthat the fluids that circulated through the episyeniticrocks at various times during the crystallization of fluoriteand thus during the introduction of gold there includedwide-ranging proportions of carbon dioxide.Secondary fluid inclusions are present in fluorite alongwell-defined planes that converge, diverge, and intersectat various angles and which do not have the generaJlyorthogonal aspect of the primary inclusions. The planescommonly are broadly arcuate and cutcrystal boundariesin the fluorite. Such secondary inclusions exhibit variedshapes, from smoothly elliptical to highly irregular, andvaried sizes, from 10 to 48 I-ffil in diameter. The secondaryinclusions are mostly type I and show varied amountsof vapor fill at room temperature, with a range from 0to 50 percent, aJthough most commonly they contain between2 to 10 volume percent vapor.Salinities of the primary and pseudosecondary fluid inclusionsin fluorite overlap significantly the salinities ofthe secondary fluid inclusions. Salinities of the primarytype-I fluid inclusions were determined using the depressionof freezing-point method (Roedder, 1962), and salinitiesof the pseudosecondary type-IV fluid inclusions weredetermined from the final melting temperature of clathrate,most likely CO 2 ·53f. H 2 0 (Roedder, 1963), formedduring the free-.dng runs (see Takenouchi and Kennedy,1965; B

FLUID-INCLUSION STUDIES 117sions. However, the salinity of the secondary fluids rangesupward to slightly more than 15 weight percent NaCIequivalent.In all, 41 filling temperatures were measured from theprimary, pseudosecondaty, and secondary inclusionstrapped in fluorite from the goId-bearingepisyenitic rocks(fig. 71). The primary type-I fluid inclusions show a veryrestricted range in filling temperatures between 251°Cand 268 °C (262°C mean). The pseudosecondary type­IV fluid inclusions contain significant proportions ofliquidcarlx>n dioxide and have a lower or first homogenizationwherein their vapor phase disappears between 26.9 and28.0 °C. The average temperature of vapor-phase disappearancefor these inclusions is 27.6 °C. Continuedheating of four of these inclusions results in their homogenizationinto a single liquid phase in the temperaturerdnge 280 to 282°C. The secondary fluid inclusions influorite all flIl to liquid at temperdtures of 130 to 167°C,significantly less than the filling temperatures of theprimary and pseudosecondary fluid inclusions (fig. 71).Limited freezing and heating tests also were performedon type-I fluid inclusions hosted by irregular patches ofsecondary quartz, that nus cavities (table 27, sampleGM·ll34h). The quartz, which contains these fluid inclusions,typically contains some needles of rutile that areconcentrated near the margins of the quartz. The fluidinclusions range in size from less than 1 to 24 Jim. Somehave elliptical shapes, but. many are irregular in outlineand confined along planar annealed microfractures, suggestingsecondary origins. Eight freezing tests yieldsalinities in the range 5.8 to 9.5 weight percent NaCIequivalent; the mean is 7.8 weight percent NaCIequivalent. Heating tests show 17 fluid inclusions to fillto liquid in the range 144 to 186°C. The filling temperaturesfor these f1ukl inclusions in quartz correspond quitewell the filling temperatures of the secondary fluid inclusionsin fluorite; the mean filling temperature of the fluidinclusions in quartz is 159°C, and the mean temperatureof the secondary fluid inclusions in fluorite is 149 °C.Thus, much of this paragenetically late quartz, sparselydistributed through the episyenitic rock, may have beenintroduced after the initial deposition of fluorite there.FLUID INCLUSIONS IN A QUARTZ·FLUORITE-WHITEMICA VEIN THAT CUTS THE LATE CRETACEOUSTWO-MICA MONZOGRANITEAdditional fluid-inclusion studies were conducted on asample of a carefully selected quartz-fluorite-white micavein (table 27, sample GM-923) that unquestionably cutsfB oLO 40 MICROMETERS-"fiGURE 69.-Continued.

118 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIWNA~"z w,w"~~

FLUID-INCLUSION STUDIES 119generally fail to show visible melting of ice at temperaturesbelow 0 °C because of the presence of clathrate. Thefirst visible evidence of a phase change occurs when theclathrate melts somewhere in the temperature rangebetween 0 and 10°C. This melting is accompanied byrapid expansion of the vapor phase and sweeping of thevapor phase across the inclusion, commonly followed bythe immediate reappearance of the third phase, liquid carbondioxide. Fluid inclusions in quartz are slightly differentfrom those in fluorite. Consequently, all inclusiontypes are described separately by host mineral.Two-phase type-I fluid inclusions observed in fluoriteoccur in planar arrays. The inclusions have regular ovoidshapes that range in length from 2 to 22 tJIll. The percentageof vapor fill in the inclusions at 22°C is fairly consistentat 5 to 7 volume percent; salinities range from 6.3to 10.1 weight percent NaCI equivalent (fig. 72A) with anaverage of 9.0 weight percent. Type-I fluid inclusionshomogenize by vapor disappearance between 149 and206°C, with an average of 177 °C (fig. 72B). The narrowrange of salinities and homogenization temperaturesfor these inclusions indicates that necking and resultantchanges in vapor percentage and salinity were not significantfollowing trapping of these inclusions. However, thepresence of the type-I fluid inclusions along intersectingplanar arrays contrasts with the mode of occurrence ofthe type-IV fluid inclusions in the fluorite, and this relationsuggests that the type-I fluid inclusions studied aresecondary.Type-IV liquid carbon dioxide-bearing inclusions in thefluorite do not appear to be constrained to planar arrays.Instead, they are present in restricted clusters in whichindividual inclusions occur along wispy rays that radiatefrom a vague center. The type-IV fluid inclusions areabout the same size as the type-I fluid inclusions, and theyalso have consistently elliptical outlines. At 22°C, about7 percent of the volume of a typical inclusion consists ofvapor plus liquid carbon dioxide; of this, 10 to 15 volumepercent is vapor. The salinity of these fluid inclusionsranges from 5.5 to 6.0 weight percent NaCI equivalentand is thus somewhat lower than many of the type-I fluidinclusions (fig. 72A). The type-IV fluid inclusionshomogenize to the liquid high-density carbon dioxidephase by vapor disappearance between 28.1 and 29.1 °C,with an average of 28.7 °C for nine measurements. Furtherincreases in temperature enhance the mutual solubilitiesof the phases, and between 203 and 207°C (average206 0c) the type-IV fluid inclusions homogenize to a singlephase (fig. 72B). The chemistry, habit, and higherhomogenization temperatures contrast the type-IV fluidinclusions with secondary type-I fluid inclusions in the veinfluorite and indicate that fluids circulating in the environmentof the vein decreased in content of carbon dioxideand increased somewhat in salinity with time.Both primary and pseudosecondary type-I and type-IVfluid inclusions in vein quartz are randomly dispersedthroughout the quartz and can be distinguished easilyfrom planar trains of obviously secondary inclusions. Thefluid inclusions tend to cluster by type, indicating that thesilica-depositing fluid varied significantly in chemistryduring the deposition of quartz. Type-I fluid inclusionshave 4 to 7 volume percent vapor at 22°C. They rangefrom about 1 to 16 j.tm in size and have regular ellipticalforms, and they show a very good correspondence oftheirsalinities to the type-IV fluid inclusions (fig. 72C). The fullrange of salinities determined for both types of fluid inclusionsis between 7.0 and 11.0 weight percent NaCIequivalent, averaging about 8.2 weight percent NaCIequivalent. However, almost all of the type-I fluid inclusionsstudied contain some carbon dioxide because theydevelop clathrates during freezing tests. The clathratespersist to temperatures in the range 4.6 to 6.4 °C. Thetype-IV fluid inclusions in quartz range in size from less10(f)f-ZU.J~U.Ja:::l(f)« 0U.J 2A~u.0a:U.Jco 10~::lzo '--'--l..-.l....L.~.a.....La_-'C 2 6 10 14SALINITY. IN WEIGHT PERCENTNaCI EQUIVALENTEXPLANATIONo Type IVlliI Type I~ Type I and type IVO'---E.:L100B250FIGURE 72.-Salinity and filling-temperature data obtained from selectedquartz-fluorite-white mica vein. Sample GM-923. A, Salinities of fluidinclusions hosted by fluorite. Salinities of type-IV primary fluid inclusionsdetermined using final melting temperature ofclathrate (seetext), and salinities of secondary type-I inclusions determined usingdepression offreezing point method. B, Filling temperatures of fluidinclusions hosted by fluorite. C, Salinities of fluid inclusions hostedby quartz. Salinities determined as in A. D, Filling temperatures offluid inclusions hosted by quartz.1010,-----r---.------,o'--_--'-_IaD 100 150TEMPERATURE. IN DEGREESCELSIUS

120 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN·LOST BASIN MINING DISTRICTS, ARIZONAthan 1 to 22 j.lm. The small size of the fluid inclusions commonlymakes it difficult or impossible to resolve the liquidcarbon dioxide meniscus even at magnifications of aboutx 1,000. For the larger of these type-IV fluid inclusions,visual estimates suggest equal volumes of liquid carbondioxide and vapor carbon dioxide at room temperatures.Typically, these fluid inclusions contain 80 to 90 volumepercent saline liquid. The type-IV fluid inclusions homogenizeby vapor disappearance between 28.3 and 30.0 DC,with an average of 29.4 DC. This indicates that the carbondioxide is somewhat less dense than in the fluoriteinclusions but still dense enough to homogenize to liquidcarbon dioxide rather than vapor upon heating (see Kennedy,1954; Koltun, 1965, fig. 5). Upon additional heating,the type-I and type-IV inclusions homogenize to a singlephase in the range 188 to 240 DC, averaging 218 DC (fig.72D). As such, these filling temperatures are slightlyhigher than those measured from the primary type-IVfluid inclusions in fluorite (compare fig. 72B with 72D).COMPARISON OF FLUIDS IN A QUARTZ-FLUORITE-WHITEMICA VEIN AND IN GOLD-BEARING EPISYENITIC PIPESSimilarities in physical and chemical properties determinedby fluid-inclusion studies of a quartz-fluorite-whitemica (table 27, sample GM-923) vein and the gold-bearingepisyenitic pipes provide an insight into the deposition offluorite and quartz and their accompanying gold mineralizationin the districts.Similarities include:1. Carbon dioxide densities of fluid inclusions from thepipes and the vein, which is clearly related to thetwo-mica monzogranite, have very similar lowdensities of about 0.61 to 0.66 g/cm 3 . The fluidsassociated with the introduction of gold into theepisyenitic pipes show a slightly greater density ofcarbon dioxide than fluids from the selected vein.Type-IV fluid inclusions in fluorite from the episyeniticpipes homogenize by vapor disappearancein the range 26.9 to 28.5 DC, which corresponds todensities of carbon dioxide of about 0.64 to 0.66g/cm 3 . Type-IV fluid inclusions in the well-studiedvein homogenize by vapor disappearance in therange 28.1 to 30.4 DC, which corresponds to densitiesof carbon dioxide of about 0.61 to 0.64 g/cm 3 • Visualestimates of the proportion of liquid carbon dioxidepresent at room temperatures in many other veinsthroughout the districts suggest that their carbondioxide contents are similar to those of sampleGM-923.2. Carbon dioxide content of fluid inclusions of both thevein and the pipes, calculated from visual volumeestimates of the amount of carbon dioxide in the fluidinclusions at room temperatures, ranges from about4 to about 8 mol percent. The proportions of carbondioxide to saline-water solution appear to be veryconsistent (see above), but precise determinationsare difficult to make (Roedder and Bodnar, 1980).3. Salinities of fluids that deposited quartz and fluorite,and presumably gold, in the gold-bearing pipes andthe vein are in the same range. Fluid salinities rangefrom 3 to 16 weight percent NaCI equivalent andcluster especially in the interval from 6 to 10 weightpercent NaCI equivalent, a range not common inmany epithermal gold-bearing hydrothermalsystems.4. The mineral assemblages and parageneses in both thelate gold-bearing stage of the pipes and the vein arevery similar. Hydrothermal minerals in both includequartz, fluorite, pyrite, white mica, ferroan carbonate(ankerite), and gold. The relative amounts ofquartz and fluorite, however, are variable in the twoenvironments; quartz dominates in the vein, andfluorite is more abundant than quartz in the pipes;together the two minerals are paragenetically lateminerals filling cavities. Both the pipes and the veinshow decreasing activity ratios of (K+)/(H+) overtime in their alteration envelopes as the systemsevolved from biotite-stable (vein) and potassiumfeldspar-stable (pipes) assemblages to white micastableassemblages.5. Homogenization temperatures of the vein and thepipes are generally similar. Temperatures of finalhomogenization to a single fluid for primary type-Iand pseudosecondary type-IV fluid inclusions influorite from the pipes are among the highest fillingtemperatures recorded throughout the miningdistricts. They range from 251 to 282 DC (table 27).Nonetheless, many of the vein occurrences areestimated to have filling temperatures close to thesevalues, and a few were measured so (table 27). Incontrast, fluid inclusions from the vein, which moreprobably was emplaced near the final stages of theLate Cretaceous and (or) early Tertiary mineralizationin the districts (exemplified by sample GM-923,which cuts the two-mica monzogranite), show fillingtemperatures 45 to 60 DC less in quartz and 70 to100 DC less in fluorite (fig. 72) than those in the pipes.ESTIMATES OF THE PRESSURE-TEMPERATURE ENVIRONMENTOF MINERALIZATIONFluid-inclusion data and phase relations provide usefullimiting estimates for the physical and chemical environmentof mineralization. Consistent proportions of salineliquid, liquid carbon dioxide, and carbon dioxide-rich vaporfor most early-stage type-IV fluid inclusions in the goldbearingepisyenitic pipes suggest that they were trappedfrom a homogeneous fluid. Furthermore, the early-stageCO 2 -rich fluids (pseudosecondary type-IV fluid inclusions

FLUID-INCLUSION STUDIES 121in fluorite, see above) in the pipes most likely include about8 mol percent C02 and are moderately saline, rangingfrom about 3 to 7 weight percent NaCl equivalent. Thesetype-IV fluid inclusions must also contain minimalamounts of calcium and magnesium as determined fromthe temperatures of first melting. Thus, we can model thebehavior of the fluids by referring to the system NaCl­H20-C02. However, the episyenitic pipes also showevidence (primary type-I fluid inclusions) for early-stagecirculation of C02-depleted fluids that range from 8 to 10weight percent NaCl equivalent in salinity. The earlystagefluid inclusions relatively rich in C02 in the episyeniticpipes homogenize to a single fluid at temperaturesof about 280 to 282 DC. From this isotherm and by assuminga fluid composition including 8 mol percent C02 and6 weight percent NaCl, we interpret pressures at thetimes of trapping were above 500 bars. In making thisinterpretation for these fluids, we have assumed that themiscibility gap for the 280 DC isotherm in the systemH20-C02, initially determined by Todheide and Franck(1963), expanded an amount similar to that found experimentallyby Takenouchi and Kennedy (1965). Takenouchiand Kennedy (1965) showed that addition of a limitedamount of salt, about 6 weight percent NaCl, to thesystem H20-C02 significantly widens the miscibility gap.Furthermore, at a fluid composition of about 8 mol percentC02, isotherms converge tightly and are extremelysensitive to slight differences in pressure (see discussionby Roedder and Bodnar, 1980).An upper pressure estimate during the development ofthe episyenitic pipes may be inferred from the experimentallydetermined solubilities of quartz in the systemSi02-H20 (Kennedy, 1950; Fournier, 1977) and from thefact that dissolution of primary quartz was an importantprocess in the evolution of the episyenitic pipes. Kennedy(1950) showed that a "solubility hump," or region of increasingsolubility ofsilica for decreasing temperature atconstant pressure, occurs in the system Si02-H20 atpressures less than 750 bars. Subsequently, Fournier(1977) refined these experimental results and determinedthe apex of the "solubility hump" is at a pressure of 715bars, and a corresponding temperature of 480 DC.The range in pressure 500-700 bars estimated respectivelyfrom data derived from the type-IV fluid inclusionsin fluorite, and the primary quartz solubility relations maybe used to establish a + 50 to + 70 DC temperature correctionfor the primary type-I fluid inclusions. Such apressure estimate for the type-I fluid inclusions appearsto be geologically reasonable because of the very closetemporal relations between the two related sets of fluidinclusiontypes in the fluorite. The type-I fluid inclusionswere trapped from a homogeneous fluid at poT conditionssomewhere along an isochore, or line of equ;:ti volume, thatoriginates at a temperature of 263 DC on the two-phaseor liquid-vapor curve for a solution approximately 9weight percent NaCl equivalent (fig. 70A). This temperatureis the average temperature of filling to a liquid of18 type-I fluid inclusions (fig. 71). Then from the isochoricdata for a 10-weight-percent NaCl solution, as compiledby Roedder and Bodnar (1980, fig. 4), our best estimateis that the type-I fluid inclusions in fluorite were trappedat temperatures of about 315 to 335 DC.Pressure corrections cannot be obtained successfullyfrom fluid-inclusion data (fig. 72) of the quartz-fluoritewhitemica vein that cuts the two-mica monzogranitebecause of lower carbon dioxide content. But these datanonetheless indicate that pressures at the time of trappingwere more than 100 bars to maintain the carbon dioxidecontent of the fluid and to retard effervescing. Fluoritefrom this vein shows an average temperature of 206 DCfor the homogenization of its type-IV fluid inclusions toa single phase. This value in a PoT diagram is then thetemperature of the isotherm that marks the boundarybetween the two-phase and one-phase regions in thesystem H20-C02-NaCl (see Roedder and Bodnar, 1980,fig. 7). Yet, for a 9-weight-percent NaCl-equivalent solutioncontaining approximately 4.5 mol percent C02(values determined from the fluid inclusions), such anisotherm essentially would parallel the pressure axis andcannot be used to establish an effectual lower boundaryfor the pressure prevailing at the time of trapping of thefluid inclusions. At best, we only can estimate thatpressures in the environment of this vein during itsemplacement were greater than the pressure along theliquid-vapor curve at the point(s) ofhomogenization of itstwo-phase type-I fluid inclusions. These pressures are lessthan 100 bars. Therefore, we have not been able to determinewell-defined limits of the pressures in the fluidsassociated with the final stages of precious-metal mineralizationin the districts.We judge the pressure-temperature conditions duringthe late-stage gold mineralization at the site of the episyeniticalteration pipes, namely more than 500 bars and315 to 335 DC, to be reasonable values for the physicalconditions prevailing during the onset of Late Cretaceousand (or) early Tertiary gold mineralization in the districts.A pressure estimate of 500 bars corresponds to a minimumdepth of about 2 km under a lithostatic load and aminimum depth of about 5 km under a hydrostatic load.Assumptions involved in the calculation of the hydrostaticload are (1) a nonstratified fluid column occurs above thesite(s) of the gold-depositing fluids and (2) the fluid columnis open to and extends to the ground surface at the timeof gold mineralization (see Roedder and Bodnar, 1980).A value somewhere between lithostatic and hydrostaticis most likely on geologic grounds; the Paleozoic formationsthat must have overlain the districts total approximately2.1 km in thickness (Peirce, 1976).

122 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONADISCUSSIONMost of the fluid, mineral, and geologic observationsrelated to gold mineralization documented during ourstudy compare well with observations in many othermesothermal (Jensen and Bateman, 1979) districts thatshow generally similar geology. For example, in theHopewell and Bromide districts of New Mexico, goldbearingfissure veins typically are associated with siderite,chlorite, pyrite, chalcopyrite, and galena (Graton, 1910).Gold vein deposits in the Grass Valley, Calif., districtyielded about $300 million (Clark, 1970). This district,about 30 km north of the northern terminus of the MotherLode but considered generally not to be part of the MotherLode (Albers, 1981), shows vein and wall-rock assemblagescontaining quartz, iron and magnesium carbonates,white mica, chlorite, epidote, arsenopyrite, pyrite, galena,chalcopyrite, and gold (Lindgren, 1896; Johnston, 1940).The wall rocks, which consist of Paleozoic and Mesozoicunits intruded by a Mesozoic granodiorite (Johnson, 1940),are variably sericitized, carbonatized, and chloritized. Thebulk ofthe gold and galena in the veins was deposited duringa quartz substage (Johnston, 1940). Further, liquidvaporrelations in fluid inclusions shown in Johnston(1940, pI. 22) suggest that the fluids associated withmineralization were trapped from homogeneous nonboilingfluids. Wall-rock alteration surrounding the goldquartzveins in the Alleghany, Calif., district, about 30km northeast of Grass Valley, includes carbonates (mainlyankerite), albite, mariposite, and white mica (Fergusonand Gannett, 1932). The occurrence of late-stage gold,preceded by a potassium-enriching and (or) silica-depletingstage, as in the episyenitic pipes at Gold Basin, may becomparable to gold associations reported elsewhere.Harris (1980a, p. B1; 1980b) described disseminated goldin the altered parts of a granodiorite in the Salave goldprospect in northwest Spain as occurring in a zone typifiedby "increased carbonatization, desilicification, sericitization,albitization, sulphidization and texture-destruction."In addition, he reports that the "introduction of CO2 ascarbonates and the loss of Si02 as quartz derived fromthe silicate-destructive alteration are petrographically obvious"(Harris, 1980b, p. Bll). Furthermore, in thesealteration facies, his "hongorock," secondary fluid inclusionsare abundant and include liquid carbon dioxidebearingtypes showing highly varied proportions of carbondioxide possibly indicative of unmixing. The silicatedestructivephenomena together with a mineralizing environmenthighly enriched in carbon dioxide are verysimilar to the gold-bearing episyenites in the Gold Basindistrict. Maclaren (1908, p. 100-101) mentions severalother occurrences ofparagenetically late gold being presentin "acidic dyke rocks." Boyle (1979, p. 296) citesseveral reports ofgold ore bodies that are hosted mostlyby syenitic rock (Dyer, 1936; Derry and others, 1948;North and Allen, 1948). At the Young-Davidson mine inthe Matachewan district of Ontario, Canada, disseminatedgold-bearing pyrite makes up about 2 volume percent ofan early-phase syenite; minor associated minerals arechalcopyrite, galena, molybdenite, scheelite, andspecularite. Subsequent fracture-controlled mineralizationthere includes quartz-carbonate veins and free gold.However, all the syenitic rocks in these latter districtsmay not be equivalent genetically to the episyenites wedescribe here. Nonetheless, Dyer (1936) and Sinclair(1984) describe some pink to brick-red, gold-bearingsyenite that apparently formed by potassic alteration ofgray porphyritic syenite in the Young-Davidson mine. Thered altered facies of these rocks includes the assemblagepotassium feldspar and hematite, both of which make upa significant proportion of the episyenite in the Gold Basindistrict. The syenite-hosted gold deposits in theMatachewan district have yielded about 800,000 troyounces gold from as much as five million tons ore (Sinclair,1984). Further, Comba and others (1981) allude to a fenite(episyenite)-gold association at the Upper Canada goldmine at Dobie, Ontario.Fluid-inclusion compositions and mineral assemblagesin the veins and wall rocks provide fairly limiting constraintson the chemistry of the ore-depositing environmentin the Gold Basin-Lost Basin districts, but mostlikely above a mass of Cretaceous two-mica monzograniteat depth. The exposed episyenitic pipes most likely reflecta mineralized level deeper than the bulk ofthe pegmatiteveinsystems throughout the districts. At the episyeniticpipes, early stages of alteration initially must have involveda tightly confined flux ofupward-streaming fluidswhose (K +)/(Na +) ratios eventually exceeded the bufferingcapabilities of potassium feldspar and plagioclase relictfrom the protolith (see discussion in Poty and others,1974). Such fluids also leached primary quartz from theEarly Proterozoic monzogranite protolith and increasedthe porosity at the sites. Generation of silica-undersaturatedfluids may reflect interaction of Early Proterozoicmafic or ultramafic rocks and fluids initiallyevolved from Late Cretaceous two-mica monzogranite(fig. 73). As pointed out by Burnham and Jahns (1962),magmas of pegmatitic granite, such as the two-micamonzogranite of the Gold Basin district probably contain8 to 12 weight percent H20. Those fluids should bedepleted significantly in silica and become quite alkalineifthey were to react at elevated pressure and temperatureconditions with mafic or ultramafic rocks (Fournier, 1985).Specific mineral assemblages resulting in mafic or ultramaficrocks from these chemical reactions would reflectlargely the mol fraction C02 in the fluid(s): fluids severelydepleted in C02 might yield serpentine-bearing assemblages,whereas fluids containing relatively abundant C02might yield anthophyllite-, talco, and (or) magnesitebearingassemblages, (Evans and Trommsdorff, 1970;

FLUID-INCLUSION STUDIES 123A".1'• EiMsvenil" locaIilV con-. ltoining 0i~1e

124 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING D1S7RIC'TS, ARIZONAWinkler, 1974). The potassium feldspar stage of episyenitizationat Gold Basin may be comparable to theearly-alkaline high-temperature (450-600 "C) stage ofmicrocline crystallization associated with many greisens(Shcherba, 1970). Further, some intragranitic veinsassociated with uranium mineralization show paragenesessimilar to the gold-episyenite relations at Gold Basin (seeNash and others, 1981). In the intragranitic Gunnaruranium deposit, Saskatchewan, Evoy (1961) showed thatalbitization there preceded ore mineralization and thatalbitization produced a so-called syenite by leachingprimary quartz from the syenite's protolith. However, wehave no fluid-inclusion data documenting the chemistryof the fluids at Gold Basin during the onset of floodingby potassium feldspar and dissolving of quartz. Earlystagefluids probably contained some fluorine and carbondioxide, although partition of fluorine toward a vapor oraqueous phase in equilibrium with a granitic magma is low(Burnham, 1967, 1979; Koster van Groos and Wyllie,1969; Cannichael and others, 1974, p. 314-316). However,with progressive differentiation of granitic rocks, thereis a tendency for coexisting very late fluids to show abuildup in their fluorine contents (see Bailey (1977) fordiscussion of such relations). The overall HF content inthese fluids must be subordinate to their HCl contentbecause of the very large partition coefficients of HCI infavor of the aqueous phase (Burnham, 1979). In such asupercritical late-magmatic environment, fluorine probablycombines into very soluble complexes, possibly including(SiF6'? - (Shcherba, 1970), which may be relatedto the early stages ofdevelopment of the episyenitic pipes.Subsolidus consumption of primary quartz and replacementof plagioclase by potassium feldspar there may haveoccurred by a coupling of reaction (1) or reaction (2) tothe alkali exchange reactions (3) and (4) proposed by Burnham(1979):12HF+6F- +3Si02(s)-3(SiF6)l- +6H20 (1)2KF+H20+Si02(s)-KSiOs+2HF (2)NaAlSis08(s)+ KC~v)-KAJSis08(s)+ NaC~v) (3)CaAI2Si208(s) + KC~v) + Si02(s)-KAISis08(s)+CaC~v)(4)Eventually, fluorite and gold were deposited in the porespaces within the episyenitic pipes at temper.atures of 315to 335 "G and at pressures between 500 and 700 bars.Solubility studies of gold (Baranova and Ryzhenko, 1981;see also Lewis, 1982) suggest that free gold has a widerangingstability field in terms of pH and temperature.Thus, oxidation resulting from the dissociation of H20may be one way to precipitate gold in a relatively deepseatedgeologic environment. As a comparison, the depthsof such an environment in the Gold Basin-Lost Basindistricts appear to be similar to that of the more deeplyseated porphyry copper deposits (Nash, 1976). At thesetemperatures, deposition of fluorite may have occurredin response to a combination of interrelated factors (seeRichardson and Holland, 1979; Holland and Malinin,1979), including a common-ion effect with NaF(aq) as thesystem evolved and possibly a decrease in salinity.However, the fluids associated with mineraJi7..ation in thedistricts show no compelling evidence requiring a salinitydecrease as an important component during deposi·tion of the ores. Early- and late-stage fluids in quartz andfluorite of the pipes and vein both are correspondinglymoderately saline in contrast to the early fluids at otherfluorite deposits, which are extremely saline (for exam·pie, see Nash and Cunningham, 1973). Furthermore, suchtrapping temperatures (315 to 335 "C) are quite commonin mesothennal environments, which led Barnes (1979)to suggest that cooling of JX)stmagmatic fluids is an importantore-depositing mechanism that must be consideredalso.The prevailing high pressures in the mesothermal environmentat the sites of the pipes and the vein duringearly and late stages of mineralization precluded boilingof the fluids with a concomitant loss of carbon dioxide.Loss of carbon dioxide can lead to a decrease in thesolubility of carbonate (Ellis, 1963; Holland and Malinin,1979). However, in the Gold Basin-Lost Basin districtsfluid-inclusion relations apparently do not suggest signifi·cant boiling of fluids occurred during the quartz, carbonate(ferroan carbonate or ankerite), white mica,fluorite, sulfide, and gold stages of miner.alization. Somerocks may contain apparently nonboiling relations.although the associated fluids were boiling (Roedder,1984). The fact that the fluids circulatingat the pipes andin the vein apparently were not boiling indicate a fairlywidespread high fugacity of carbon dioxide in the fluids.In addition, the nonboiling of these fluids must haveretarded the physical separation and removal of acid components(including mostly carbon dioxide) from the circulatingfluids and thereby enhanced the stability of whitemica during the ore-depositing stage. This relation is inmarked contrast to the preceding potassium feldsparstablestage in the episyenitic pipes. The increased abundanceof white mica both later.ally toward the so-calledpegmatitic-vein systems and temporally as they and theepisyenitic pipes evolved demonstmtes a transition fromhigh (K+)I(H+) fluids to ones with lower (K+)I(H+)(Remley and Jones, 1964) and probably somewhat moreacidic conditions. Seward (1982) has shown experimentallythat at 300 "C the solubility of gold increases withincreasing alkalinity of a fluid in the stability field of pyriteand chalcopyrite. Thus, deposition of gold may reflectpartly a response in the change from an alkaline to anacidic chemical environment.

SUGGESTIONS FOR EXPLORATORY PROGRAMS 125The association in the Gold Basin-Lost Basin districtsof Late Cretaceous and (or) early Tertiary gold mineralizationwith fluids related to two-mica magmatism is apparentlymore widespread in the southern cordillera thanmost geologists previously realized (Keith, 1986). Manytwo-mica peraluminous granites of Arizona and Californiaare not associated with any significant ore deposits,although a few commercial tungsten deposits are presentlocally in wall rocks adjacent to some two-mica plutons(Reynolds and others, 1982), gold mineralization in theCargo Muchacho Mountains, California, may be associatedwith two-mica magmatism, and 19 districts in Arizona andadjacent regions show production of gold, silver, copper,lead, and zinc from mines associated apparently with twomicaplutons (Keith, 1986). Furthermore, Reynolds andothers (1982) note that all two-mica peraluminousgranitoids must incorporate significant crustal componentsbecause of their uniformly high initial 87Sr/86Srisotopic ratios. Therefore, we suggest that the gold andbase metals and possibly fluorine in the districts may alsohave a crustal source and may have been recycled fromEarly Proterozoic rocks. These crustal sources may includesome near-surface Proterozoic rocks in the districts,possibly including some of the Early Proterozoic metabasitesdescribed above (fig. 73; see also Moiseenko andFatyanov, 1972). However, some of the gold in the LateCretaceous and (or) early Tertiary occurrences also mayhave been incorporated in the magmatic stages of the twomicamonzogranite and thus reflect anatexis of deepcrustal rocks.The Proterozoic rocks in the districts and elsewhere inthe region include some gold and fluorine that may be consideredas potential sources for the Late Cretaceous and(or) early Tertiary occurrences and deposits. In thisreport, we have described mineralized veins in Proterozoicrocks that have a fabric and mineral assemblage that seemto date from the Proterozoic greenschist metamorphicevent. In addition, some of the gold-bearing veins of thedistricts may have been emplaced at about the same timeas the copper, lead, and gold veining in the Gold Buttedistrict, which apparently is Proterozoic in age (Wasserburgand Lanphere, 1965). Early Proterozoic gold ispresent elsewhere in the southwest, as exemplified by anoccurrence of stratiform gold in Early Proterozoic rocksof Yavapai County, Ariz. (Swan and others, 1981).Fluorine in the veins and episyenitic pipes in the GoldBasin-Lost Basin districts also may have been recycledfrom a Proterozoic protolith. Our analyses, for example,of the Early Proterozoic porphyritic monzogranite ofGarnet Mountain in the districts show contents offluorinein the range of 0.06 to 0.17 weight percent (table 14).Remobilization of fluorite from Proterozoic igneous rocksinto Late Cretaceous and (or) early Tertiary veins hasbeen postulated by Snyder (1978) at the Park Range,Colorado; Antweiler and others (1972) suggestedsomewhat similar relations for gold at Han's Peak, Colorado.Furthermore, Stephenson and Ehmann (1971)showed the depletion of gold from hydrothermally alteredcountry rock and the apparent migration of gold into veinsat the Rice Lake-Beresford Lake area, southeasternManitoba, Canada. On the other hand, metal ratios in LateCretaceous and (or) early Tertiary and Tertiary oredeposits in Yavapai County, Ariz., apparently do notreflect the metal ratios of the Proterozoic crust (DeWitt,1982). Nonetheless, Boyle (1979, p. 65) maintains thattransport and, by implication, remobilization of gold asgold-sulfide complexes by near-neutral to moderatelyalkaline carbonate-depositing fluids must occur. Many experimentalstudies have confirmed the transport of goldas a sulfide complex in a largely reducing environmentshowing relatively high contents of total sulfur (Baranovaand Ryzhenko, 1981; Seward, 1982). Deposition of goldwould most likely occur by a chemical reaction(s) thatresults in an increase of the oxidation potential of thefluids. On the other hand, the experimental studies ofHenley (1973) also reveal an inflection or solubility humpfor gold that culminates in the range 300 to 350°C in 3Mpotassium chloride solution (approximately 18 weight percentKCI) at pressures less than 1,000 bars. Certainly theearly-stage fluids at the episyenite pipes and at many ofthe veins in the Gold Basin-Lost Basin districts must havehad high KINa ratios because of their associated potassicalteration. We suggest that such fluids may have beenprimarily responsible for the remobilization and extractionduring the Cretaceous of the bulk of the known goldfrom shallow Proterozoic, possibly metabasite, sources,whereas some of the gold probably was emplaced duringthe Cretaceous after having been incorporated into themagmas of the two-mica monzogranite. Experimentalstudies suggest that the gold-carrying capacity of thefluids associated with the final crystallization of theCretaceous two-mica monzogranite would be more thanadequate to account for all the known gold in the districts.Ten cubic kilometers of such monzogranite (equivalent tothe exposed two-mica monzogranite extending to a depthof about 0.5 km) would have the capacity to deposit orextract about 64 t (70 tons) of gold, on the basis of experimentaldata of Ryabchikov (1981). Further, Korobeynikov(1976) reported a significant amount of gold tobe soluble in the fluid-inclusion waters of mineralsassociated with skarn- and vein-type gold deposits.SUGGESTIONS FOR EXPLORATORY PROGRAMSThe known and inferred relations of gold mineralizationin the Gold Basin-Lost Basin districts suggest severalgeologic environments that should be evaluated carefullyin exploratory programs. Certainly the most obvious

126 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONAwould be any remaining high-grade ore shoots in the veinsthemselves. However, such occurrences most likely wouldnot yield the relatively large tonnages of ore needed fora commercial mining operation. Five environments shouldbe considered. (1) Sequences of rock that might formfavorable replacement zones adjacent to or near any ofthe gold-bearing veins that crop out should be evaluated.Such sequences might include Early Proterozoic carbonate,amphibolite, or any zones of porous rock that occurredbefore mineralization. Such favorable zones couldinclude any rocks shattered tectonically prior to the majormineralizing event in the Late Cretaceous. (2) If the occurrenceof disseminated free gold in the fluorite-bearingepisyenitic alteration pipes in the Gold Basin districtevolved as we described above, then such an environmentmust reflect a mineralized level geologically deeper thanthe bulk of the veins that crop out elsewhere in thedistricts. Thus, all quartz-fluorite-bearing veins should beevaluated as to whether or not they reflect the upperquartz-depositing parts of a system which at depth includesearly quartz-dissolving and late gold-depositingparageneses. Similarly, the two-mica monzogranite thatcrops out in the Gold Basin district might include somedisseminated gold-bearing episyenitic facies at depth (fig.73). (3) The entire trace of the low-angle detachment surfaceor glide surface should be evaluated for the occurrenceof Cyclopic-type deposits (see fig. 2). Much of thetrace or inferred trace ofthis structure as mapped by P.M.Blacet along the west flank of the White Hills is poorlyexposed, partly because it is locally covered by Quaternarysand and gravel. However, the increased abundanceof tectonically polished or striated vein quartz along someof the poorly exposed parts ofits trace might be indicativeof gold-bearing Cretaceous veins caught up tectonicallyalong the detachment surface. Furthermore, detailedgeologic mapping along the general trace of the detachmentsurface might reveal other fault strands that shouldbe evaluated similarly. (4) The Early Proterozoic metamorphicrocks in the districts should be considered aspotential hosts for syngenetic, stratiform deposits. Certainly,as we described above, some indications in therocks suggest that boron-enriched fluids were importantin the paragenesis of tourmaline-bearing schists. Suchrocks might reflect emanations of boron-bearing fluids expelledfrom exhalative centers in the protolith of themetamorphic rocks. Tourmalinite makes up the major partof the ore in the gold deposit of Passagem de Mariana,Brazil, and this deposit yielded more than 60 tons of gold(Fleischer and Routhier, 1973). The exploration implicationsof tourmalinite horizons are exceptionally welldescribed by Slack (1980, 1981, 1982) and Nicholson(1980). In fact, Nicholson (1980, fig. 1) shows a strikingcorrelation between tourmalinite horizons and golddeposits. However, in the Early Proterozoic metamorphicrocks of the Gold Basin-Lost Basin districts, somehorizons of tourmalinite may be mistaken for amphibolite.Nonetheless, detailed mapping of all tourmalinite horizonsin the Proterozoic might yield some additional targetsworthy of further exploratory efforts. 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134 GEOLOGY AND GOLD MINERALIZATION OF THE GOLD BASIN-LOST BASIN MINING DISTRICTS, ARIZONADeWitt, E., 1985, Mine index for metallic mineral districts ofArizona: Arizona Bureau ofGeology and Mineral Technology Bulletin196,92 p.Wenk, Eduard, 1954, Berechnung von Stoffaustauschvorgangen[Calculation of matter-exchange reactions]: Schweizerische Mineralogischeund Petrographische Mitteilungen, v. 34, no. 2, p. 309-318.White, A.J.R., Clemens, J.D., Holloway, J.R., Silver, L.T., Chappell,B.W., and Wall, V.J., 1986, S-type granites and their probableabsence in southwestern North America: Geology, v. 14, p. 115-118.White, A.J.R., Williams, 1.S., and Chappell, B.W., 1977, Geology oftheBerridale 1:100,000 sheet 8625: New South Wales [Australia]Geological Survey, 138 p.Wilcox, R.E., 1979, The liquid line of descent and variation diagrams,in Yoder, H.S., Jr., ed., The evolution ofthe igneous rocks, fiftiethanniversary perspectives: Princeton, N.J., Princeton UniversityPress, p. 205-232.Wilkins, Joe, Jr., and Heidrick, T.L., 1982, Base and precious metalmineralization related to low-angle tectonic features in the WhippleMountains, California and Buckskin Mountains, Arizona [abs.]:Geological Society ofAmerica Abstracts with Programs, v. 14, no. 4,p.245.Williams, S.A., 1963, Oxidation of sulfide ores in the Mildren and Steppemining districts, Pima County, Arizona: Economic Geology, v. 58,no. 7, p. 1119-1125.Wilson, E.D., 1939, Pre-Cambrian Mazatzal revolution in centralArizona: Geological Society of America Bulletin, v. 50, no. 7, p.1113-1164.__ 1962, A resume of the geology of Arizona: Arizona Bureau ofMines Bulletin 171, 140 p.Wilson, E.D., Cunningham, J.B., and Butler, G.M., 1934, Arizona lodegoldmines and gold mining: Arizona Bureau of Mines Bulletin 137,Mining Technology series 37, 261 p.Wilt, J.C., 1980, Arizona molybdenum minerals as keys to metallogenictypes: Geological Society ofAmerica Abstracts with Programs, v. 12,no. 6, p. 309.Wilt, J.C., and Keith, S.B., 1980, Molybdenum in Arizona: ArizonaBureau ofGeology and Mineral Technology, Fieldnotes, v. 10, no. 3,p. 1-3, 7-9, 12.Winkler, H.G.F., 1974, Petrogenesis of metamorphic rocks: New York,Springer-Verlag, 320 p.Woodward, G.E., and Luff, Paul, 1943, Gold, silver, copper, lead, andzinc in Arizona, in Needham, C.E., ed., Minerals yearbook 1942:Washington, U.S. Government Printing Office, p. 231-259.Wright, J.E., and Haxel, Gordon, 1982, A garnet-two-mica granite,Coyote Mountains, southern Arizona: Geologic setting, uranium-leadisotopic systematics of zircon, and nature of the granite sourceregion: Geological Society of America Bulletin, v. 93, no. 11, p.1176-1188.Wyllie, P.J., 1981, Magma sources in cordilleran settings, in Dickinson,W.R., and Payne, W.D., eds., Relations of tectonics to oredeposits in the southern cordillera: Arizona Geological SocietyDigest, v. 14, p. 39-48.Wyman, R.V., 1974, The relationship of ore exploration targets toregional structure inthe Lake Mead metallogenic province: Tucson,University of Arizona, Ph.D. dissertation, 103 p.Yeend, Warren, 1975, Experimental abrasion of detrital gold: U.S.Geological Survey Journal of Research, v. 3, no. 2, p. 203-212.Ypma, P.J.M., 1963, Rejuvenation ofore deposits as exemplified by theBelledonne metaliferous province: Leiden, The Netherlands, Universityof Leiden, Ph.D. dissertation, 212 p.

TABLE 11

......~enTABLE n.-Notable occurrenees of commodities in the Gold Basin-Lost Basin mining districts[Modified from P.M. Blacet, unpub. data, 1967-72; 1, presence of commodity inferred]Locality(pl. 1)11121314NameGolden Gate mineL.P.M. mineRed Norse mineJunction mineApproximate location(UTM 10,bOO-m grid, zone 11)NW1/4 sec. 32, T. 30 N., R. 17 W.NW1/4 sec. 4, T. 27 N., R. 18 W.NE1/4 sec. 32, T. 28 N.,R. 18 W.SE1/4 sec. 29, T. 28 N., R. 18 W.ConunoditiespresentAu, CuCu, AuAu, Cu, Pb,MoAu, Cu, PbMoConunentsFree gold occurs in yellowish- to red-stained quartzcharacterized by empty pyrite molds and cellularhematite vugs. Gold usually is in very intricatesheaves that are so fragile that they wave in thewind. Some rather solid gold pieces as much as1 nun in diameter are present also. Veins as muchas 1 m thick, but many of the veins consist ofmassive quartz containing little sulfide.Relatively abundant free gold on the dump so earlyminers must really have high-graded the deposit.First workings probably date before 1900.Chalcopyrite, cuprite, malachite, and pyrite noted.Two shafts to approximately 15 m deep in pe~iment.Country rocks are very coarse grained, porphyriticmonzogranite, including potassium feldsparphenocrysts as much as 5 cm. Altered schist cropsout in pit 60 m northwest of old head frame. Sparsesecondary copper found. Low sulfide content andabsence of coarse vein material suggests generalalteration zone with many small quartzose seams.A zone of steeply north dipping to vertical quartzveins and veinlets have an average strike of N. 50 0E. The veins are not persistent and the majorityare stringers less than 2.5 cm, while a few are 20to 30 cm long. No chalcopyrite, galena, fluorite,or carbonate was observed. A trace of gold wasfound in fine- to medium-grained quartz. Oreprobably was hosted by silicified granite andschistose metamorphic rocks.Vein 20 cm wide at the collar of 60 0 inclinedshaft. Vein strikes N. 15 0 E., dips 60 0 E. Countryrock is Early Proterozoic porphyritic monzogranite.Free gold coarse and abundant in cellular vuggyquartz containing limonitic and hematitic cavityfills. Some secondary copper minerals and wulfenite.Quartz, galena, chalcopyrite (minor), pyrite (trace),and relatively abundant wulfenite in vein exposed inshallow opencut trending N. 30 0 E. Vein strikesapproximately N. 30 0 -35 0 E. and dips 85 0 southeast.Some masses of partially oxidized pyrite showirregularly shaped blebs of free gold~ot"'o~~8~~t'j::>:;l~.....N~~o"':l>-3:r:t':l8t"'o~00~t"'o 00>-3~00Za::~Q8~i?:lo>-3.00::.-~~

1617Cyclopic mineEldorado mineSW1/4 sec. 30, T. 28 N., R. 18 W.SW1/11 sec. 21, T. 28 N., R. 18 W.Au, Pb, Mo,Cu, Pb, Mo,Auapproximately 1 to 2 mm across. Exposed segment ofthe vein is approximately 1 m and includes 'some septa of granitic rock from the surroundingEarly Proterozoic porphyritic monzogranite.Opencut is about 30 m southwest of two shallowshafts, each 15 to 30 m deep.Series of northwest opencuts and pits along Miocenedetachment fault breccia which is exposed in placeat several localities. Free gold in at least onehand sample picked up in southern half of series ofcuts. Abundant angular fragments contain milkywhitequartz with dark-reddish-gray matrix.Considerable cellular gossan, with wulfenitecommon. Old underground workings intersected insome of the opencuts; none accessible. Numerousprospects, pits, and trenches in the lower(?) gougezone. Vein quartz is brecciated and widelyscattered in the gouge as blocks 0.6 m long andapproximately 0.3 m thick. Veins contain galena,pyrite, ferrocalcite, malachite (alteration ofchalcopyrite(?», wulfenite, gold, cerussite.Brilliant crimson mineral may be cuprite. Red,brown, and black Fe and Mn(?) oxides.The mineralized vein seems to average 1 m thick anddips 25 0 -30 0 E.-SE. on west side of workingsand shallowing to nearly horizontal at the tunnelportals on the east side of the ridge. Theworkings generally dip 20 0 E.-SE. parallel tothe vein. The country rock is intensely sheared,cataclastic medium-grained Early Proterozoicgneissic granodiorite. The mineralized vein(s)is occupying an intensely sheared zone that is ofprobable Late Cretaceous and (or) early Tertiaryage. Although the vein quartz is fractured(locally intensely), it is not brecciated.Some veins crosscut highly foliated gneissicgranodiorite, but generally they approximatelyparallel the schistosity. No red or other claygouge and no indication of notable Tertiary movement.The main vein parallels also the pegmatite, and, inpart, the 2-m thickness of quartz probably reflectsthe quartz-core stage of the pegmatite. Thequartz vein lies between a crumpled and kinkbandedschistose granodiorite and an overlying sill ofleucogranite pegmatite.Abundant chrysocolla; moderate galena; but nochalcopyrite seen. Some wulfenite and cerrusitepresent also.In the irregular surface cut 10 m northwest of theopening at the northwest end of the undergroundstopes, altered biotite lamprophyre has consistentchilled margins against the mineralized veinquartz. This indicates the mafic dikes and sillsare postmineralization. Intensely sericitizedleucogranitic sills occur below the vein here,~ b:J~.....,....CA:l-:]

TABLE ll.-Notable occurrences ofcommodities in the Gold Basin-Lost Basin mining districts-Continued....C.:l00Locality(pl. 1)17192112526138139NameEldorado mine--ContinuedUnnamed prospectFord mineUnnamed prospectBlue Bird mineUnnamed prospectM. P. Mica mineIApproximate location(UTM 10,OOo-m grid, zone \1)SE1/11 sec. 27, T. 28 N., R. 18 W.SW1/11 sec. 33, T. 30 N., R. 17 w.SElI11 sec. 19, T. 28 N., R. 16 w.NE1/11 sec. 19, T. 29 N., R. 17 w.SE1/11 sec. 26, T. 28 N., R. 17 W.SE1/11 sec. 26, T. 28 N., R. 17 W.CommoditiespresentAu, FAu, Cu, PbWAuMicaMicaCOlllllentsindicating a somewhat crosscutting relationship.Numerous veins 2 cm to 1 m thick are concentratedin an intensely sheared zone, which dips very gentlybut is undulating overall.Fluorite-gold-pyrite-bearing episyenitic rocks, whichcut fine- to medium-grained biotite monzogranite.Gold occurs in leached cavities in these episyeniticrocks (see text). In outcrop, the episyenitic rockoccurs in four small pipelike masses, the largest ofwhich measures about 8 m across (see fig. 50).Two shallow prospect pits have been dug on thepipes most likely because of the color anomalyresulting from the oxidation of pyrite.Portal initially trends N. 10 0 W., then bends toN. 15 0 E. and extends 100 to 150 m intersectingraise and winze. Winze continues 10 m below levelof main drift. Workings follow shear zone. Quartzvein as much as 1.5 m thick, exposed in back,contains thin seams of chalcopyrite OXidizing tochalcocite, cuprite, malachite, and azurite; and atrace of galena. Some fine gold seen in yellowbrownlacy quartzose gossan. Vein ends byinterfingering with altered and shearedamphibolite.Vertical shaft 30 ft deep in opencut made in garnetepidote-quartzskarn composing a small roof pendantor septum in Early Proterozoic porphyriticmonzogranite. Pendant is approximately 50 m longand trends N. 115°_55 0 W.Horizontal adit 800 m along northwest-striking shearzone dipping 65 0 SW. Damp clay gouge iscontorted and locally contains some quartz veinletswhich mushroom into quartz stringers making as muchas 0.5 m of the adit width.Two pegmatite dikes, both apparently claimed butunmined. The dikes are muscovite bearing withbooks as much as 15 cm in diameter and 5 to 8 cmthick. One dike trends approximately N. 10 0 W.and is about 3 m wide. Small prospect pit atsecond dike.A series of north-northwest-striking pegmatite lenses3 to 5 m thick with well-defined bull quartz cores.Coarse muscovite is common, transparent in thincleavage sheets, but inclusions of other minerals~ oS~§§~~~~ o~~§~ rn~~~ rnZ~~t:l~::t1a>::t1N~

2052132162172592711275Unnamed prospect NE1/11 sec. 28, T. 30 N., R. 17' w.Unnamed locality SE1/11 sec. 29, T. 29 N., R. 17 w.Valley View NW1/11 sec. 32, T. 29 N., R. 17 w.Malco mine SE1/11 sec. 21, T. 28 N., R. 18 w.Unnamed prospect SE1/11 sec. 20, T. 29 N., R. 17 w.Unnamed prospects NE1/11 sec. 20, T. 29 N., R. 17 w.Unnamed prospect SE1/11 sec. 20, T. 29 N., R. 17 w.Au?CrFeAuAu?Au?Auare common. The books are less than 10 to 15 cmacross. This series of pegmatites possibly iscontinuous with a series of several muscovitebearingpegmatites to the northwest. EarlyProterozoic.leucocratic monzogranite makes up thecountry rock. The main mine workings are opencut.prospect pit just west of contact between Muddy CreekFormation and Early Proterozoic gneiss. The pitexposes an alternating sequence of amphibolite andbiotitic quartzite and (or) quartzofeldspathicgneiss. The rocks here also show abu~dant ironoxide-stained cubic molds after pyrite. No gold orsecondary copper minerals observed. Locally,coarse-grained granitic dikes or sills are abundantirt some of the schistose sequences.Metaclinopyroxenite contains very sparseconcentrations of chromite.Banded jasper-magnetite beds associated withlaminated or foliated quartzite. Foliation strikesN. 30 0 w. and dips 65 0 _70 0 SW. Quartziteincludes vitreous white and micaceous pink types.Inclined shaft plunging 115 0 -55° (30 0 below third mainlevel) parallel to a conspicuous shear zone whichstrikes N. 115 0 E. Mineralized quartz veins areparallel to the shear zone. There are three majorlevels, about evenly spaced, from which irregularraises follow ore shoots. Overall workings areclose to a contact between Early Proterozoicgneissic granodiorite and gneiss.Prospect pit exposing compleXly intermixed quartzpyriterock and apparently genetically related andintermixed quartz-calcite-pyrite and feldsparcalcite-quartz-pyriterock very similar to theepisyenitic rocks containing visible gold in theEast White Hills (loc. 19, above). AlthoughOXidized, pyrite-rioh rocks were examinedcarefully, no free gold was seen.In one of the prospect pits, a pyrite-bearing apliticdike strikes east-northeast and dips 110 0 _115 0 S.A large amount of weathered pyrite is associatedwith the dike. In addition, nearby there is acouarse-grained magnetite-rich pegmatite. which mayhave a genetic connection with the pyrite-bearingdike. The dike is about 0.5 m wide and-has rathersharp contacts with altered and silicifiedfeldspathic gneiss.Prospect contained a very altered feldspar-quartzpyritevein several centimeters thick, judging fromrock samples on the upper "ore" pile. Generallysimilar to rocks at location 2711. The apliticfeldspar rock usually bounds the quartz vein on thenorth side, and the quartz-rich portions containmost of the sulfide. Gold was seen in theboxwork. No indications of copper were seen.S2~............t-'~co

TABLE ll.-Notable occurrences ofcommodities in the Gold Basin-Lost Basin mining districts-Continued"""" ~oLocality(pl. 1)NameApproximate location(UTH 10,000-m grid, zone 11)CODlDoditiespresentCODlDents276 Unnamed aditand prospectpit277 Unnamed adit279 Unnamed prospect284 Unnamed drywashersiteNWl/4 sec. 20, T. 29 N., R. 17 W.NWl/4 sec. 20, T. 29 N., R. 17 W.NW1/4 sec. 20, T. 29 N., R. 17 W.NW1/4 sec. 19, T. 29 N., R. 17 W.Au?Au?F, Au?AuSmall adit driven straight in for about 9 m alonga fault zone varying about 0.6 to 1.2 m wide.Slickensides are well developed with the wall rockaltered to an ochre-orange color. The slickensidesplunge westward at about 50 0 in the fault zone,which strikes N. 50 0 W., and dips about 60 0 W.An irregular vein zone of crushed- and carbonatecemented(ankeritic) white milky quartz, rangingfrom 0 to 23 cm thick can be seen locally at theback of the adit. A small prospect also is locatedalong the fault about 60 m to the southeast. Nocopper staining, sulfides, or pyrite-type boxworkspresent. A newspaper found inside suggests workwas before or during the 1920's.This adit is similar to location 276. The adit isdriven at about N. 50 0 W. along the same fault asin location 276 for about 10 to 12 m. The faultdips about 60 0 _65 0 SW., and it contains obliquemullions and slickensides plunging about 55 0 W.The fault zone, which is about 0.3 m to 0.9 m wide,is composed of highly sheared gouge and brecciatedlenses of white milky quartz. The quartz veinobserved at location 276 is not continuous throughthis adit. An orange-ochre color from weatheringankeritic calcite was also observed at thislocality. This adit also intersects a raise to thesurface about 9 m from the portal. No sulfides orcopper staining were observed.The prospect pits are along feldspathic veins whichcontain quartz, potassium feldspar, carbonate, andpyrite. The veins are about 0.6 m thick and strikeirregularly N. 55 0 W. roughly paralleling thevertical layering in the surrounding bandedgneiss. On the dump there are samples of fluoriteand topaz. Gold was not observed but may bepresent in the vuggy (pyrite molds) quartz at thepits. There is also abundant ankeritic carbonatecommonly containing large pyrite cubes about1.3 cm. The pyrite is generally altered. Nocopper staining or galena was observed.The sample was taken from above the caliche-cementedfanglomerate just west of mine road leading tothe adit and shaft at locality 285. A few finesand-sizefrosted colors were found. From their~[2~~t::l8 bis:Zt".l~......N~~o":z:j>-3::c:t".lgt::l~enZ t-< oen>-3~enZis:~~en >-3~~~No s;

285286291297300303No name opencut SW1I4 sec. 18, T. 29 N., R. 17 W.and aditUnnamed drywasher SW1/4 sec. 18, T. 29 N., R. 17 W.siteUnnamed prospects SW1/4 sec. 17, T. 29 N., R. 17 W.Unnamed prospect NE1/4 sec. 20, T. 29 N., R. 17 W.Unnamed adit SE1/4 sec. 17, T. 29 N., R. 17 w.Unnamed shaft NE1/4 sec. 17, T. 29 N., R. 17 W.Au?AuCu, Au?CuAu?Fecondition, they are probably some distance fromtheir source.The first 6 m along the adit consists of Quarternaryfanglomerate which has been faulted againstamphibolitic, banded gneis. The fault strikesnorth-south and dips 60 0 W. The brecciatedamphibolite and banded ~neiss generally have theirlayering striking N. 15 E. and dipping 50 0 W.Well-developed striations trend N. 85 0 W. andplunge 43 0 W. The fanglomerate, gravel, andbreccia generally are poorly cemented except incertain spots where they have been case-hardenedby caliche. About 50 m from the portal, the aditapparently was filled subsequently with waste rockfrom a shaft. No vein material seen in place, butthe dump contains vein material similar to that ofthe Bluebird vein.Drywasher concentrate from irregular surfaceconsisting of amphibolite bed rock about 6 mupstream from highest Quarternary fanglomerate andfault. One small color was observed with abundantgarnet.This locality consists of two prospect pitsapproximately 3 m apart along a shear zone strikingN. 30 0 E. and dipping 65 0 E. and about 1 to 1.5 mwide. Although the fault may be relativelyimportant, and somewhat like the one at the Bluebirdmine, it could not be traced because of talus- anddebris-covered slopes. In the pits, the veinsconsist of pyrite and chalcopyrite together withmilky quartz and ferruginous carbonate. Generallythe veins are thin stringers, less than 3 em wide,although one pod reached as much as 25 em across andhad a well-developed sericitic envelope.An approximately 8-m-thick syenitic micropegmatitecontains abundant quartz associated with red-brown,presumably iron-rich carbonate and pyrite. Thislocality is approximately 30 m N. 35 0 E. of the twoprospects known as the Jumbo (loc. 913, thistable). The feldspar in the micropegmatite ismicrocline, and only traces of secondary copperminerals were noted to stain the rocks.An approximately 35-m-long adit initially drivenN. 40 0 E. on a black quartz-rich lens. Exposedin the workings are a series of three northeaststrikingquartz veins or stringers that are as muchabundant yellow or reddish-brown carbonate andsparse amounts of weathered pyrite. Country rockconsists of strongly lineated feldspathic gneiss.A N. 30 0 W.-striking oxide facies, banded ironformation. An approximately 20-m deep verticalshaft has been sunk on the iron formation; theas 13 em wide. Associated with these veins areshaft probably follows a minor fault zone. Anothershaft, approximately 100 m N. 70 0 W. of this~to t"'l'=:l>-'>-',...~,...

TABLE ll.-Notable occurrences ofcommodities in the Gold Basin-Lost Basin mining districts-ContinuedI-'~Looality(pI. 1)303305307308310NameUnnamed shaft--ContinuedUnnamed shaftIdeas Lode 30Unnamed prospeotVanadinite mine(Van-Wulf)Approximate looation(UTM 10,OOO-m grid, zone 11)NE1/4 seo. 17, T. 29 N., R. 17 W.NE1/4 seo. 17, T. 29 N., R. 17 W.NE1/4 seo. 17, T. 29 N., R. 17 w.NE1/4 seo 17, T. 29 N., R. 17 w.CommoditiespresentPb, Cu, AuAu?Au?V, Pb, MO,CuCommentslooality, has been put down on dark, manganiferousgossanlike stringers in breooiated and highlyaltered granitoid pegmatite. See figure 22 (thisreport) for a photomiorograph of quartz-iron oxiderelations in the banded iron formation.Shaft along a N. 35 0 W.-striking, 55 0 NE.-dipping approximately 0.6-m-wide quartz-oarbonatevein. Downward the vein feathers into a series ofveinlets measuring from 2 to 8 om wide. Yellowbrownoarbonate fills the oenter of the veins, butmuoh of the oarbonate is intergrown with quartz.The primary minerals observed in the veins inoludegalena, ohaloopyrite, pyrite, and free gold.Seoondary minerals inolude ohrysooolla andmalaohite.Workings along nearly flat lying shear zone whiohinoludes irregularly distributed quartz-yellowbrown-oarbonateveins nearly parallel to theshallow-dipping foliation. Some evidenoe forthe flooding of nearby rook by yellow-brownoarbonate.Episyenitio aplite exposed in the prospeot pit.Disseminated pyrite, but relatively littleoarbonate and no fluorite were seen. Theepi~yenitio aplite orops out in an approximately9-m area. The upper parts of the guloh in thisgeneral area inolude many small, irregular dikesof similar episyenitio aplite.The adit is about 15 m long, driven along a faultzone striking S. 15 0 E. and dippingabout 70 0 NE. Sliokensides have a variableorientation but generally they plunge moderately(50 0 _60 0 ) to the north. Vanadinite andwulfenite are espeoially abundant in breooiatedvein material and in adjaoent wall rook justinside the portal. Rooks aoross the openoutshow at least 3 m of offset. At east end ofopenout is an 8-om-thiok quartz-earbonate vein,oontaining sporadioally distributed interstitialohlorite. Minerals observed in the vein inoludegalena, ohrysooolla, wulfenite, vanadinite, redbrownoarbonate, quartz, mottramite(?), ohlorite,minor greenish olear oaloite, and serioite.Little or no altered pyrite, no gold seen. Minorseams of episyenitio aplite were observed also.~S~~®~~N~o'%j~t':l~ t:1~~ o~g:rnZ a::2zC)t:1~.~~N~

311 Unnamed adit SE1/4 sec. 32, T. 30 N., R. 17 W. Pb, Au, Cu A lower adit follows a well-defined fault zone 15 cmthick striking N. 80 0 E. and dipping 45 0 _50 0 S.Galena is rather abundant in quartz-carbonategangue.Upper workings consist mostly of dump materialderived by stripping overburden from vein lyingalong a N. 75 0 E., 45 0 _50 0 S.-dipping fault.Vein material ranges from 0 to 30 cm thick. Novein material seen in lower workings, whichfollows the fault, and the quartz+minor carbonatevein occupied a steeply plunging mullionlikeopening along the fault which had no lateralextent. Some gold, but minor chrysocolla, alittle unoxidized pyrite, and galena. Quartz isthe major gangue together with yellow-browncarbonate. Wall rock alteration appears to be316 Unnamed drywasher NW1/4 sec. 23, T. 28 N., R. 18 W. Ausite319 Unnamed drywasher NW1/4 sec. 27, T. 28 N., R. 18 W. Ausite324 Unnamed drywasher NE1/4 sec. 24, T. 29 N., R. 18 W. Ausite325 Unnamed drywashersiteSW1/4 sec. 7, T. 29 N., R. 17 W. Au327 Golden Mile mine NW1/4 sec. 8, T. 29 N., R. 17 W. Pb, Cu, Au?mostly introduction of carbonate. One speck ofgold found in the samples.From approximately 12 hoppers processed throughthe drywasher, only a few colors wereobtainedOnly one color obtained from gravelly, reddish soilwhich overlies hard caliche-cemented false bedrock in the Quaternary fanglomerate.Moderate amount of fine gold.Moderate amount of gold.1-2-m-thick prominent quartz vein exposed in facewest of road approximately 20 m northwest ofsmall shack; vein strikes N. 70 0 W. and dips20 0 _25 0 SW. It is offset in a reverse senseapproximately 1 m by an intensely clay-alteredshear zone striking east-west and dipping40 0 N. Fe-bearing calcite occurs in coarselycrystalline irregular masses which are markedlytabular and form lenses striking N. 20 0 W. anddipping 30 0 SW. These lenticular andirregularly shaped calcite pods definitely areoriented obliquely to the plane of the vein andmay represent replacement of earlier quartzalong opened gash fractures. The bulk of thiscarbonate occurs along the central zone of thevein, but it is sporadically distributedthroughout the length of the examined vein. Apoorly developed alteration zone in the vein'swalls seems to include albite and pyrite+galenaand a little chalcopyrite. A secQnd oblique slipfault offsets the vein 1 m west of the incline.Slickensides plunge N. 65° E. at 25°.Crystals of feldspar (albite?), quartz, andcalcite commonly reach 10 to 15 cm across inoptically continuous, irregular, intergrownmasses. Galena can be seen to vein or crosscutcalcite, feldspar, and quartz--probably the~~t'"tr.J.........~c.:>

TABLE n.-Notable occurrences ofcommodities in the Gold Basin-Lost Basin mining districts-Continuedf-'oj:>.oj:>.Locality(pl. 1)NameApproximate location(UTM 10,OOO-m grid, zone 11)CommoditiespresentComments327329Golden Mile mine--ContinuedUnnamed prospectNW1/4 sec. 8, T. 29 N., R. 17 W.330 Unnamed drywasher SW1/4 sec. 31, T. 30 N., R. 17 W. Ausite(location uncertain)341 Unnamed prospect SE1/4 sec. 7, T. 29 N., R. 17 W. Au?356 Glow in the Dark SW1/4 sec. 8, T. 29 N., R. 17 W. Pb, Cu, Au?8Au?galena, pyrite, and trace of chalcopyrite aresomewhat later than the coarse crystallinematerial although all are probably related totransition pegmatite-vein processes.The vein exposed 15 m south of the portal is about1 m thick and rather clearly the extension of thevein exposed in the small inclined shaft.Numerous east-northeast or easterly faults offsetthe vein, which strikes N. 70 0 W., 25 0 SW. Nostopes in the adit. A trace of weathered pyritewas observed along the footwall in the adit.The prospect exposes approximately 2-m-thickpegmatite containing well-defined crudely tabularmasses of fine-grained green sericite in potassiumfeldspar in its 15-cm-wide alteration wall zones.A specimen found on the dump of the small cutshows a remnant of a white mica book, with cleavagefaces 1 em across. Pegmatite strikes N. 40 0 E.and dips 80 0 _85 0 SE. No sulfides except rarepyrite pseudomorphs near the walls.Gold as.much as matchhead size especially in upperreaches of small gulch.A prospect cut poorly exposing a small quartzcarbonate-feldspar-sulfidevein of the Golden Miletype. Vein strikes north-south and is vertical.Maximum width about 0.6 m.Prospects along wash about 0.8 km southeast ofGolden Mile cabins. Opencut on side exposese forabout 8 m 15- to 25-cm-wide quartz vein strikingN. 15 0 _20 0 W. and dipping 50 0 NE. in a shearzone of approximately the same attitude. Maximumdepth of vein exposed in cut is about 5 m. Theshear zone separates vertically dipping interlayeredquartzofeldspathic gneiss from amphiboliteto the east. The vein pinches and swells averaging25 to 30 em in thickness. Galena and chalcopyriteappear disseminated in knots throughout quartz;sparse carbonate. No gold seen, but a trace hasbeen reported. Another nearby prospect is oncoarse magnetite-bearing highly fracturedpegmatite containing galena and chalcopyrite (somealtered to malachite). The sulfides in thispegmatite are scattered widely in white quartzas vug fillings. Somewhat anomalousradioactivity, approximately three timesbackground.~go~tzt::I8bi5~~......N~~o"".j~t."J§~U1~S~~U1Z~ZC:lS:l~.S3~N~:>

372374375389405409436Miss Texas 2Bluebird 17-16Unnamed prospectUnnamed prospectsTwin yucca gulchUnnamed drywashersiteUnnamed prospectNE1/4 sec 17, T. 29 N., R. 17 w.NW1/4 sec 17, T. 29 N., R. 17 w.SE1I4 sec. 7, T. 29 N., R. 17 w.NE1/4 sec. 6, T. 29 N., R. 17 w.SE1/4 sec. 9, T. 29 N., R. 18 w.NW1/4 sec. 22, T. 30 N., R. 17 w.NW1/4 sec. 32, T. 30 N., R. 17 w.Au?PbAu?Au?AuAuCu, AuPyritized zone now limonitic striking N. 60 0 W.and parallel to foliation in the surroundinggneiss. Several quartz veins cut this 10- to15-m-wide altered zone which can be followedtoward the southeast for at least 0.3 km.Location of zone about 100 m S. 25 0 E. fromstone monument of the Miss Texas 2.Two veinlets generally 2 to 8 cm thick but locallyas much as 15 cm thick, striking nearly east anddipping steeply south. Abundant galena, but sparsepyrite noted. Veins cut amphibolite and gneiss.Broad open fold in amphibolite, plungingapproximately 35 0 NW. just north ofprospect. Some pyrite and altered feldspar inborder alteration zone, which measures about 2to 8 cm in thickness.A 10-m shaft along the road 300 m south-southwestof Golden Mile cabins. Barren-looking velns, littlecarbonate, pyrite, and feldspar. No galena orcopper minerals noted. The vein is about 0.6 m thick.A group of prospects near the west base of Lost BasinRange, approximately 1.5 km north-northwest of theGolden Mile mine. Intensely altered myloniticcoarse-grained granite or alaskite dike strikingN. 20 0 E. and dipping 55 0 _60 0 W. parallelsthe adjacent well-layered quartzofeldspathic gneisswhich contains abundant thin well-definedamphibolite layers. Abundant hematite with somelimonite. Pyrite molds are abundant in hematiticmasses along shear zone. An inclined shaft southof the wash is 10 m deep. A gneissoid very coarsegrained biotite granite dike forms the footwall.There is parallel layering in quartzofeldspathicgneiss which forms the hanging wall.North of Salt Springs Wash road. This general areashows evidence of old placering possibly in the1930's and much more recent scraping using a smallbulldozer. Possibly part of the early SummitMining Company work. Good placer gold as much as2 mm obtained using a drywasher. The gold is notwell concentrated on bed rock but instead isdistributed throughout 20 to 35 cm of dirt aboveearliest Proterozoic outcrop. Proterozoic rocksare quartz-mica schist and gneiss.Some fine placer gold in heavily dug gulch. Highpercentage of granitoid clasts in the general areaof this locality is distinctly out of proportionwith the amount of granitoid rocks exposed in theLost Basin Range.Prospect adit about 150 m southwest of lower dump ofthe Golden Gate mine. The adit essentially followsa well-developed, vertical, N. 50 0 E.-strikingfault. Conspicuous cross faults include an eastwestfault dipping 50 S. A little copper staining~~t':l.................01 """

TABLE ll.-Notable occurrences ofcommodities in the Gold Basin-Lost Basin mining districts-Continuedf-'.,.0')Locality(pI. 1)436442443444445NameUnnamed prospect--ContinuedUnnamed prospectUnnamed prospectUnnamed prospectClipperApproximate location(UTM 10,000-m grid, zone 11)NWl/4 sec. 32, T. 30 N., R. 17 W.NW1/4 sec. 32, T. 30 N., R. 17 W.SW1/4 sec. 29, T. 30 N., R. 17 W.SE1/4 sec. 29, T. 30 N., R. 17 W.CommoditiespresentPbCu, Au?Au?Au?~COlIDDents~ooccurs on brecciated blocks of quartz-carbonate- ~minor chalcopyrite blocks. Considerable >sericitization and carbonatization of the country Srock. No vein material observed. A short adit ~directly up the ridge to the south exposes a 0prominent fault striking north-south to N. 10 0 E. bThis fault occurs between the brecciated footwall ~of an east-dipping quartz-carbonate vein which is Zas much as 0.6 m thick. The faulting postdates the ~quartz-carbonate vein whose footwall it follows. 5:There is abundant sericitization and carbonate ~flooding of the quartzofeldspathic gneiss within a ~weathered pyrite noted. .wJoins north endline of claims at Troy prospect and >lies approximately 1 km southwest from the Scanlon ~Nmine. The quartz mass at this locality is bounded~@few meters of the vein. The brecciated vein ~material locally looks like that at the Cyclopicmine. A shaft at the top of the ridge is vertical 0and includes abundant broken-up vein quartz. Some ~free gold noted. ~Small veinlets, apprOXimately 5 to 20 cm wide, cut ~medium-grained quartzofeldspathic gneiss and minor ~amphibolite. Veins include minor galena, pyrite, ~carbonate, and chlorite. In addition, these veins 0locally develop a comb structure. ~A small prospect pit on ridge crest at bend in ~ridge. A trace of copper stain occurs on an Zapproximately 10-cm-thick vein including quartz, ~carbonate, some chlorite, pyrite, and possibly ~some gold. ~A small prospect pit along major 10-m-wide range- ~front fault between iron oxide-stained ~quartzofeldspathic gneiss and interlayeredZamphibolite and caliche-cemented fanglomerate or ~talus. Clearly quartz-carbonate vein material is broken up in the zone, suggesting the fault zone may Zhave followed locally an already emplaced vein ~system. The fault zone also shows evidence of ~having originally contained a lot of highly ~sericitized, chloritized, and carbonate-altered ~gneissic fragments. No sulfides or gold seen; little Qby two shear zones 15 em thick dipping eastapprOXimately 75 0 • The shearing has been localizedalong the steep east..dipping northeast limb of a

446453456457Troy SEl/4 seo. 29, T. 30 N., R. 17 W.Scanlon mine SWl/4 sec. 28, T. 30 N., R. 17 W.Unnamed prospects SE1I4 sec. 29, T. 30 N., R. 17 W.Eagle Nest SWl/4 sec. 28, T. 30 N., R. 17 W.Cu, AuAu, Pb, Cu,MoAu?, Cu, PbAu, Cu, Pb,Monorthwest-plunging fold. Gneissic-rock inclusionsare sericitized and altered by carbonate. Littleindication of sulfide mineralization.Lower adit contains a splendid example of a quartzcarbonatevein disrupted and sheared out by laterfaulting. Lower adit driven almost due southbeneath quartz vein outcrop; adit length is about30 m, and the vein is sheared off 15 m fromportal. Footwall bounded by fault, as is hangingwall. This ooourrenoe is a brecciated quartz veinsliver in a low-angle oblique slip fault, similarto that in the vein just west of the Golden Gate.Total vein exposed in the lower adit is about 10 mlong, and it has a maximum thickness of about 1 m.No sulfides seen in lower adit.In main adit or Troy vein, small amount of Custaining (malachite) and some ooarse anhedralpyrite oxidizing to oellular drusy boxworks. Afew small flecks of gold seen in cellular drusy"high grade." The upper prospect pit shows fourvein slivers in a nearly vertioal shear zone.Overall strike of the vein is N. 5 0 _10 0 E. anddips 65 0 -85 0 E. A little orange-browncarbonate oocurs in the mostly quartz vein.Very little stoping. Probably no production.Prospeot probably was worked in the 1930's. Veinsshow sheared margins oontaining gouge and containmilky-white quartz that is brecciated. Countryrock consists of complexly and tightly foldedquartz-feldspar gneiss. Wulfenite and anglesitenoted.Vein cutting amphibolite consists of milky quartzwith irregularly distributed orange-brown carbonatewith some granular chlorite in distinct irregularmasses. Approximately 30 to 50 m west, otherprospects show flat-lying similar veinsapproximately 0.3 m wide, containing traces ofgalena and secondary copper minerals.Workings along the same vein system as exposed at theScanlon mine (100. 453). At adit number 1,complexly layered folded quartzofeldspathio gneissis exposed direotly north of portal. In adit,quartz-eored pegmatite containing microclineorystals as muoh as 30 om across in its outer zonesorops out. No sulfides seen in rocks on the dump,but malachite oocurs as minute orystals in someboxworks showing cellular struotures. No stopes inadit.Adit number 2 is short ,and \straight and strikes N.15 0 E. Fine gold seen at several points alongvein outorop. Here. the vein apparently outs thepegmatite as does the fsult zone. Average strikeof Soanlon fault-vein in the workings is northsouthto N. 3 0 E. dipping 85 0 E. Somemalachite, galena, and wulfenite noted in sampleson dump.~t:l:l~............f-'~-::l

TABLE H.-Notable occurrences ofcommodities in the Gold Basin-Lost Basin mining districts-ContinuedI-'~00Locality(pI. 1)Name464 Unnamed adit466 Warren Lode 5(Cumberland)470 Warren Lode 10480 "BaBa" prospect("Tungstake" onone 1955 claimnotice)482 Unnamed prospectApproximate location(UTH 10,OOD-m grid, zone 11)NE1/4 sec. 32, T. 30 N., R. 17 w.NW1/4 sec. 33, T. 30 N., R. 17 W.SW1/4 sec. 28, T. 30 N., R. 17 W.SW1/4 sec. 4, T. 29 N., R. 18 W.NW1/4 sec. 33, T. 30 N., R. 17 w.CommoditiespresentAu, CuPb, CuPbW?Au, Cu, Pb,MoCommentsApproximately 15-m-long adit driven due south. Alittle highly cellular boxworks on dump ispresumed to be ore from this vein system. Goldseen in several samples. Some specular hematitemay reflect an alteration of carbonate or pyrite.Another nearby short adit driven along a steep westdippingshear zone shows sparse amounts ofchalcopyrite associated with iron-bearing calcite.Abundant galena, wulfenite, malachite in N. 15 0 W.­striking vein.Poorly exposed 1-m-thick feldspar-rich dikes(albitite?) containing sparse amounts of quartz,iron-bearing carbonate, and pyrite.Quartzofeldspathic gneiss makes up the wall rockof this dike and within about 5 to 15 m of it thewall rock shows veining by quartz and some evidenceof propylitic alteration. Numerous quartz veinletsare the range 2.5 to 10 cm wide and locally theyshow abundant amounts of galena, especiallyconcentrated in the central portions.Small 1-m-deep pit on ridge and main 6-m-across opentrench to the northeast. The prospect is inlayered amphibolite and biotite schist. Noscheelite noted. Some tourmaline seen in quartzfeldspar-biotitepegmatitic-gneiss stringer. Somequartz-carbonate-pyrite-albite(?) veinlets as muchas 8 cm thick. Euhedral tablets of albite(?) atextreme margins of vein. Main prospect is onsoutheast side of ridge 30 m northeast of smallpit. The main prospect consists of an opencut 6 mlong. Skarnlike amphibolite associated with quartzpods or stringers as much as 18 cm thick is exposedhere. Pegmatoid gneiss also occurs in crosscuttingdike as much as 8 cm thick which strikes N. 30 0 W.and dips 25 0 SW.Prospect across gulch to east-southeast contains moreskarnlike calc-silicate rock apparently owing tothe silicification of limy amphibolite or limyquartzofeldspathic gneiss. Well-layeredamghibglitic gneiss strikes north-northwest dipping30 -35 SW.An exposed feldspathic vein here is 45 to 60 cm thickand shows a well-developed quartz core. The veinstrikes N. 55 0 W. and has an almost vertical dip.§:5ot"'oQ5::t::J~t::Ja::~~ ......N~~o"':l~t'=J8t"'t::J~w.~b~~w.Z~~ZClt::J~~~~N~

483498505509513Unnamed drywashersiteClimax mineUnnamed drywashersiteUnnamed prospectUnnamed prospectSE1/4 sec. 30, T. 30 N., R. 17 w.SE1/4 sec. 33, To 30 N., R. 17 W.NE1/4 sec. 9, T. 29 N., R. 17 W.SE1/4 sec. 32, T. 30 N., R. 17 w.SE1/4 sec. 32, T. 30 N., R. 17 W.AuPbAuAu, CuAuQuartz-carbonate-pyrite-chalcopyrite stringers cutthe south end of the vein. They are as much as5 cm thick and strike north-south, dipping70 0 _75 0 E. The northeast wall of the vein isa 5-cm-thick crumbly fault gouge; whereas thesouthwest wall of the vein is healed to countryrock. A second quartz-carbonate vein strikes N.10 0 _15 0 E. approximately one-half of the wayto the top of the hill from this locality andapproximately 60 m S. 10 0 E. of the terminationof the first vein described above. The secondvein is 10 to 20 cm thick, locally brecciated,and shows no apparent copper staining or sulfides.No prospects on this second vein. Rock fragmentsincluded in the second vein are intenselysericitized. There are several pegmatites of thequartz-cored and related types which strike N.50 0 _60 0 W. and are also cut by quartzcarbonateveins.A partial list of minerals identified in the veinsincludes: galena, wulfenite, malachite,chalcoyrite, gold (fine, fernlike in quartz andoxidized chalcopyrite), ferruginous carbonate,tenorite-cuprite(?). chrysocolla. opal. specularhematite. goethite.One moderate-sized color obtained from approximately10 to 12 hoppers of gravel taken from twolocalities about 8 m apart.Vein strikes N. 18 0 E•• dips 80 0 W.-NW. and swellsto at least 2 m thick about 15 m south of theheadframe. Massive milky quartz is present withsome brecciated and recemented zones. A littlecarbonate. galena, pyrite molds, and honeycombedquartz showing cubic molds and elongate moldswere noted. The host rocks are a sequence ofgranitoid gneiss within the mapped paragneiss unit.Sample of relatively small volume. approximatelythree hoppers. of red soil. Sample was not obtainedfrom a good caliche horizon. One pinhead-sized colorobtained.Prospect pit 3 m deep on lenticular, discontinuousquartz-carbonate-chalcopyrite-pyrite-gold vein.Lenticular masses of chalcopyrite and pyrite arelargely altered to limonitic boxwork. No galenawas noted. Gneissic inclusions are sericitized.Gold occurs along boundaries of chalcopyriteboxwork and quartz.Prospect in 3-cm-thick vein. showing mullionlikestriae plunging 20 0 N.-NE. along footwall. Goldseen as fine dendritic foil in quartz. Webbedboxwork similar to that at the Golden Gate.Massive granular chlorite and sericitized quartzofeldspathicgneiss inclusions occur in the vein.Some are lined by quartz crystals and calcite.Pyrite is rather abundant but no chalcopyrite.~t:l:It"'t'ol............~tl'>o­(.0

TABLE H.-Notable occurrences ofcommodities in the Gold Basin-Lost Basin mining districts-Continuedf-'01oLocality(pl. 1)513546552604608609611623NameUnnamed prospect--ContinuedUnnamed prospectUnnamed prospectGold BarrApproximate location(UTM 10,OOO-m grid, zone 11)Unnamed drywasher UTM: 149,800 mE., 3,918,540 m N.siteUnnamed site UTM: 149,800 mE., 3,918,540 m N.Mead Tungsten UTM: 149,110 mE., 3,919,010 m N.MarihaunaSE1/4 sec. 35, T. 30 N., R. 18 W.(In Iceberg Canyon quadrangle)UTM: 152,500 mE., 3,981,610 m N.NE1/4 sec. 16, T. 29 N., R. 18 w.NE1/4 sec. 16, T. 29 N., R. 18 W.CommoditiespresentCuMnAu, Pb, CuAuPb, Cu, Au?WAu, Cu, PbCommentsgalena, or copper stain observed.A second nearby prospect contains a 45- to 60-cmthickvein including intense sericitization ofthe wall rock. Small crosscut adit.Massive anhedral pyrite is the only sulfideobserved. There was no galena, chalcopyrite, ormalachite seen at any of these largely echelonquartz veins. Numerous small quartz-carbonatestringers cut quartzofeldspathic host.Small prospect pit in chalcopyrite-quartz bodiesin coarse-grained granite pegmatite. Thechalcopyrite occurs locally in the feldspathicportion of the pegmatite, and mineralization isprobably cogenetic with the late hydrothermalstages of the pegmatite.Breccia cemented with manganese oxide and calcite.Maximum amount of vein exposed is 20 em. The veincuts Proterozoic gneiss. Prospect is approximately3 m long.Gold-bearing quartz stringers about 15 em thick,poorly exposed in prospect pit, where they areseen to occupy a shear zone in biotite gneiss.Quartz, galena, iron-bearing calcite, albite,chlorite, pyrite pseudomorphs; trace copper stain.Free gold associated with pyrite and redchalcopyrite boxwork observed in three samples.Sample collected from alluvial gravels along apresent arroyo bottom. Collected to a depth ofabout 20 em, and approximately 1 ft3 of materialput through drywasher. Few colors were obtained.Thin east-west-striking quartz vein containing finegrainedalbite along its walls, orange-brownweatheringiron-bearing calcite in knots, amoderate amount of pyrite, and some galena andsecondary copper minerals. Not prospected.Abundant scheelite in crystalline masses as much asabout 3 em across. Scheelite occurs in narrowwest-dipping skarn zones, developed as small podsless than 0.3 m thick adjacent to a 10-cm-thickgranitic pegmatite stringer.Trace of gold associated with oxidized blebs ofchalcopyrite in quartz stringers. Stringers cut afine-grained porphyritic granite dike exposed atsoutheast end of small opencut.Microcline{?)-bearing alteration assemblages are~flo~~8b~~~ N~~o"':l~I:":l~ t='~w.~S~~~~s:l~CO).~~N~

626627 Unnamed drywasher SW1/ij sec. 21, T. 29 N., R. 18 W. Ausite629 Unnamed drywasher SW1/ij sec. 20, T. 29 N., R. 18 W. Ausite635 Unnamed drywasher UTM: 7ij9,230 mE., 3,977,500 m N. Ausite636 Unnamed prospects UTM: 750,310 mE., 3,977,500 m N. Pb, Cu637639Unnamed drywasher SW1/ij sec. 21, T. 29 N., R. 18 W.siteRed Rattler or UTM: 7ij9,150 mE., 3,977,170 m N.RichmanUnnamed adit UTM: 7ij8,950 mE., 3,977,060 m N.AuAuCuapparently similar to that noted previously atlocality 19 (this table), but no fluorite wasfound here.Ferrocalcite and galena in quartz occur insurficial rubble.Over the hill from the highest cut, galena found inplace as sparsely scattered blebs and irregulargrains as much as 0.6 cm in diameter together withminor chalcopyrite. An ogen trench exposes veinapparently striking N. 10 W. that cuts gentlyeast dipping gneiss. Approximately 9 m west ofnorth end of northern prospect cut, a quartz veinis at least 12 to 15 cm thick and contains abundantgalena and chalcopyrite. Narrow alteration zonesand quartz seams cut a granite dike here strikingmost likely N. 10 0 W. and dipping 55 0 E.There is a moderate amount of surface scraping bybulldozer in this general area. Bed rock in thisplacer area consists of weathered and calicheencrustedgently dipping gneiss. The gold andsome rounded pebbles of magnetite appear to becoming off the low ridge to the northwest. Sweptbed rock at head of the gulch at this site yieldednot one single color, suggesting that the placergold that was found is not local.Rather fair showing of placer gold in concentratesfrom drywasher. Some gold is approximately 1 mmacross in longest dimension.Gold concentrated in coarse quartz gravel at scouredand winnowed head of delta in previously workedplacer gravels.Only a trace of gold, one color, obtained inconcentrate from gravels excavated from deep cracksin outcrops along main gulch. Concentrate includedabundant lavender zircon and some fresh garnet.Two veins, approximately 6 m apart, follow shearzones developed along the schistosity in thesurrounding gneiss. Quartz is the predominantmineral in the veins and only trace amounts ofsecondary copper minerals and galena were notedin one of the veins. In an incline, one of theveins pinches and swells along the shear zone.Adjacent to the veins where they cut amphibolite,there is a marked development of chlorite andcarbonate for about 1 m.Vein i~ approximately 0 to 0.6 m thick, and it hasbeen explored by a shaft approximately 15 m deep.Gold occurs in fine honeycomb and pyrite(?)boxwork. Minerals in the vein also includequartz, ferrocalcite, and chlorite. Chloritemost likely reflects altered fragments of countryrock picked up by the vein.Abundant staining by secondary copper mineralsoccurs at this adit driven approximately N.20 0 E. Another prospect approximately 20 m~I:!:![;j................

TABLE n.-Notable occurrences ofcommodities in the Gold Basin-Lost Basin mining districts-Continuedf-'01r>:lLocality(pI. 1)639640641642643Unnamed adit--ContinuedSummit NE1/4 sec. 16, T. 29 N., R. 18 W.644 Unnamed drywasher NW1/4 sec. 15, T. 29 N., R. 18 W. Ausite645 Unnamed prospectpitSW1/4 sec. 15, T. 29 N., R. 18 W. Cu646 Merrieta SW1/4 sec. 15, T. 29 N., R. 18 W. Au, Cu647NameUnnamed prospectSongbirdApproximate location(UTM 10,OOO-m grid, zone 11)UTM: 748,670 mE., 3,977,530 m N.UTM: 749,850 mE., 3,976,890 m N.Pick 'N' Pan NW1/4 sec. 16, T. 29 N., R. 18 w.Originally named:Intention toGoldUnnamed prospect NE1/4 sec. 16, T. 29 N., R. 18 W.(part of GoldHill workings)CommoditiespresentAU,CuAu, Cu, PbCuCuCu, Au?COlIIDentsnorth-northeast of this locality shows gneissicbiotite granite cut by a 0.6-m-wide vein which isin turn cut off by a N. 10 0 E.- striking fault.Prospect in gently north-dipping granite gneiss.Honeycomb quartz; trace of copper stain in quartzpyrite-chalcopyrite(?)vein. No gold observed.Late irregular patches of chalcopyrite, galena,pyrite pseudomorphs in irregular quartz vein;thickness approximately 0.3 to 0.6 m. Very minutegold specks associated with chrysocolla in latefractures.Mullion structure on footwall. Quartz veinapproximately 30 to 45 cm thick, traced laterallyabout 1 m using float. Trace of malachite,chrysocolla, and dark-red cuprite(?). Generallypoor in sulfides.Two parallel veins dip apprOXimately 45 0 to 50 0 E.,parallel to layering in surrounding gneiss. Lowervein explored by an incline sunk along the veinwhich is 0.3 to 0.45 m thick. Trace of gold occursas minute inclusions in oxidized chalcopyrite.A sheared alteration zone above and below lowervein consists of orange carbonate. A third veinis poorly exposed in upper portion of the prospectand includes very minor amounts of chalcopyrite.Very fine gold, some quite flakey, collected at thislocality.Prospect pit on 20- to 50-cm-thick quartz vein,containing minor pyrite, chalcopyrite, andcarbonate. Considerable chlorite and carbonatealteration of the gneissic diorite country rock.Sparsely scattered patches of altered chalcopyriteand pyrite are included in milky-quartz vein.Trace amounts of gold occur as minute platelikeinclusions in pyrite and possibly in chalcopyrite.Open stope along vein and inclined shaft suggestthat gold was once much more plentiful than may beinferred from samples now available. Very fewsulfides overall, however.Swarm of veins and associated altered country rockexposed in prospect cut. Overall shear zonestrikes about N. 35 0 W. dips approximately40 0 NE. Irregular main vein contains pyrite andpatches of chalcopyrite generally less than 2 emacross almost completely altered to dark-red&J§Zo~§8t""t::JE5zt.::l> t""N~o Zo"1~::I:it.::lo_ti5>~N~

648651653654657Gold Hill mine NE1/4 sec. 16, T. 29 N., R. 18 W.Smokey NW1/4 sec. 16, T. 29 N., R. 18 W.(or Highline)Unnamed prospects UTM: 749,440 mE., 3,977,060 m N.Unnamed adit UTM: 748,710 mE., 3,978,170 m N.Gold Bond UTM: 748,650 mE., 3,977,450 m N.AuCu, Au, PbAu, P, Cu,BaAu?Au, Pb, Cumineral and chrysocolla. No gold observed.Country rock is altered diorite gneiss. Inuppermost portion of prospect, a vein approximately10 to 15 em thick cuts a gently dippingleucogranite pegmatite dike. Minor amounts ofcarbonate pyrite and oxidized chalcopyrite areincluded within this vein.Intermittent production of gold from 1930 to 1942(see text, this report).Irregular and brecciated vein approximately 10 to15 cm thick, dips gently to the northeast. Sixadits are driven to intersect the vein, in total,they aggregate approximately 90 m of workings.Minor oxidized chalcopyrite occurs as late fracturefillings and irregular patches. Minor galena,mostly altered to cerussite, occurs as blebsfilling quartz-lined vugs. Gold occurs as minutegrains in oxidized pyrite and quartz.A series of pods and stringers of quartz veinsemplaced along what appears to be a N. 80 0 W.­striking and 35 0 _50 0 N.-dipping shear zone. Anearly quartz-carbonate-pyrite-galena-chalcopyritegoldassemblage in the veins has been brecciatedand cut by subsequent seams of white calcite,limonite, and barite. Bladed groups of thin baritecrystals fill vugs from which the early carbonatehas been leached. Considerable free gold foundalong pyritic seams in large quartz blocks on theeasternmost dump along these workings. Galena andchalcopyrite are also abundant. Country rockconsists of an altered granitic gneiss sequencewithin the gneiss unit.An approximately 1.5-m-long adit underlies a 4o-cmthickmilky-quartz vein. The close association ofan altered pegmatite beneath the vein may indicatethat the vein itself may be the quartz-core portionof a small pegmatite-vein system here. No sulfidesor secondary copper minerals were observed. Aquartz pod approximately 1.2 m thick is exposed30.5 m northest of the prospect; it also may berelated to the pegmatite.Massive milky-quartz veins are cut by many low-anglefaults. Along the Gold Bond incline, severalquartz veins approximately 1.7 m thick do not showsignificant alteration of the adjoining country.rock. However, seams of pyrite voids and boxworkshoneycombed by quartz are distributed throughoutthe vein parallel to its surface. Unalteredpyrite, chalcopyrite, and galena found in traceamounts. No gold was observed in place within theworkings, although chalcopyrite and associated goldwere found in an ore sample at the miner~' camp.Mine predominantly worked during 1910-20. Asecond period of occupation of the workingsoccurred during the following depression.~td~..........,.....CTIC>:l

TABLE H.-Notable occurrences ofcommodities in the Gold Basin-Lost Basin mining districts-ContinuedI-'01"""Locality(pl. 1)659 Solomon66qNameUnnamed site668 Unnamed prospect675 Unnamed site676 Unnamed site678 Unnamed prospects687 Unnamed siteApproximate location(UTH 10,000-m grid, zone 11)UTM: 7q8,590 mE., 3,976,5qO m N.SW1/q sec. q, T. 29 N., R. 18 W.UTM: 7Q9,660 mE., 3,978,160 m N.UTH: 7Q9,650 mE., 3,981,510 m N.UTM: 7Q9,560 mE., 3,981,030 m N.NW1/Q sec. 3Q, T. 30 N., R. 18 W.SE1/Q sec. 28, T. 30 N., R. 18 W.CommoditiespresentAu?FeCuWCuCu, Au?SaCOlllDentsA simple, massive, milky-quartz vein about 0.6 mthick. An approximately 3-m-deep prospect shaftpenetrates the vein at approximately 1.5 m belowthe surface. Cubic pyrite boxwork, partiallyfilled by jarosite(?), is present in outcrop.No sulfides were observed.An approximately 20-cm-thick sequence of highlymagnetic iron-formation crops out at thislocality. The iron-formation is conformable withthe surrounding amphibolite and mafic schist. Inthis general area, there are also some centimetersizedtourmaline-bearing pegmatitic dikes whichcrosscut sharply the layering in the amphiboliteand quartzofeldspathic gneiss.A 20-cm-wide quartz-ankerite-pyrite vein containstrace amounts of secondary copper, and honeycombpartings. No gold was observed.Calc-silicate rock and stringers of marble occur ina zone as much as 0.6 m thick, largely adjacent to2- to 15-cm-thick sills and pods of quartz-richleucogranitic pegmatite. Generally, the overallzone of calc-silicate rock and marble is enclosedwithin laminated amphibolite. The presence ofscheelite in the calc-silicate rocks was verifiedusing a black light. In addition, approximately30 m north of the locality there is a post-regionalmetamorphicgranite dike striking approximatelyN. 10 0 W.A 20-cm-wide quartz-ankerite (or siderite)­chalcopyrite vein crops out here. No gold orgalena found.Prospects at top of peak show quartz-ankeritesericite-pyriteveins. Trace secondary copperpresent, and some gold was observed. Theremoteness and amount of past work done at thesite suggest that some gold must have been foundhere previously.Group of approximately H. 10 0 W.-striking veinswhich dip 30 0 _35 0 HE. crop out here. Irregularstringers and elongate masses of coarselycrystalline barite are somewhat abundant in thisgeneral area as late fillings of echelon gashes.Ankerite is associated with the barite, and analbite-pyrite-ankerite assemblage is common alongthe walls of individual veins.~~o~~8 b~~~~-,3::t:t.".l~t::I~UJ~S~~~~oS~~.~:>~~

689690735754800802803804810811Unnamed site NE1I4 sec. 28, T. 30 N., R. 18 w.Unnamed site NE1/4 sec. 29, T. 30 N., R. 18 w.Unnamed prospects UTM: 747,180 mE., 3,984,640 m N.Unnamed prospect UTM: 746,850 mE., 3,984,420 m N.Unnamed site 5W1/4 sec. 35, T. 28 N., R. 18 w.Unnamed site 5E1/4 sec. 34, T. 28 N., R. 18 w.Unnamed site 5E1/4 sec. 34, T. 28 N., R. 18 W.Unnamed site 5E1/4 sec. 34, T. 28 N., R. 18 w.Unnamed site 5W1/4 sec. 34, T. 28 N., R. 18 W.Unnamed site 5W1/4 sec. 34, T. 28 N., R. 18 w.BaBa, CuAuHg?Au?FF, Au?FF, PbFVeins showing an assemblage of quartz, carbonate,barite, albite, and pyrite crop out here. Thereis considerable albite along the wall zone of theveins. The main vein here measures about 20 cmthick, but several others are about 2 to 5 cmthick.A 0.6-m-thick vein here includes chalcopyrite in itsquartz-carbonate-barite-albite-pyrite assemblage.Gold was observed at five different prospects in thisgeneral area. A deep vertical shaft approximately30 m deep had the largest amount of secondary(?)gold (see fig. 41). The veins generally pinch andswell irregularly and are composed essentially ofquartz, carbonate, pyrite, and gold. They may beProterozoic in age (see text).An adit approximately 9 m long intersects a gentlysouth-dipping shear zone. Apparently, the prospectwas for mercury, as the remains of an old hearthand a stockpile of hematitic schist suggests thatthe early prospectors mistook this for cinnabar.Leucosyenitic pipe, elongate in a northeasterlydirection crops out at this locality. Its overalldimensions at the surface are about 20 by 60 m. Thepipe contains a quartz-free central zone whichalso shows fairly abundant concentrations offluffy orange iron oxide (s) replacing iron carbonate. r'lThe outer portion of the pipe shows increasing ~concentrations of quartz in irregularly ~distributed stringers and veinlets. Although ~..........this locality shows no fluorite or obvious pyrite,the pipe here is nonetheless similar to that atlocality 19 which contains visible disseminatedgold.Quartz-fluorite vein crops out here and shows anaverage thickness of about 20 cm. The quartz isintergrown with the variably colored fluorite,which ranges from colorless to deep purple.An approximately 2-cm-wide quartz-fluoritespecularite-pyritevein crops out here. Onepossible speck of free gold observed in limoniticboxworks after pyrite. Bleaching and the possibleintroduction of feldspar extends into the countryrock for about 2 cm adjacent to the vein.Fluorite occurs as coarsely crystalline knots in aquartz-fluorite-ohlorite-iron carbonate-hematitepyritevein. The vein has a maximum observedthickness of about 20 cm.A quartz-oarbonate-fluorite-chlorite-galena veinsystem cuts a mixed zone of Early Proterozoicbiotite monzogranite and porphyritic monzogranite.Most of the veinlets in the system measure about0.6 em thick, and they contain colorless fluorite.A quartz-purple fluorite veinlet parallels the localnorthwest-striking joint 'set in the porphyriticmonzogranite.I-'c:TIc:TI

TABLE ll.-Notable occurrences of commodities in the Gold Basin-Lost Basin mining districts-Continuedf-'Ol'"Locality Approximate location Commodities(pl. 1) Name (UTM 10,OOO-m grid, zone 11) present812 Unnamed site NW1/4 sec. 34, T. 28 N., R. 18 W. F815 Unnamed site NW1/4 sec. 34, T. 28 N., R. 18 W. F817 Unnamed site NW1/4 sec. 34, T. 28 N., R. 18 W. CU820 Lady Mary SW1/4 sec. 27, T. 28 N., R. 18 W. F, Pb, Cu,Au821823824828Unnamed prospect SW1/4 sec. 27, T. 28 N., R. 18 W.Unnamed site SE1/4 sec. 28, T. 28 N., R. 18 W.Unnamed drywasher SW1/4 sec. 4, T. 27 N., R. 18 W.siteUnnamed prospect NW1/4 sec. 4, T. 27 N., R. 18 W.FFAuCuCommentsQuartz-fluorite-iron carbonate-pyrite-chloriteveinlets fill northeast-striking joints.Quartz-fluorite-pyrite and quartz-pyrite veinlets asmuch as 15 cm thick fill northeast-striking steeplydipping joints.An approximately N. 15 0 E.-striking and 75 0 NW.­dipping vein includes quartz, pyrite, chlorite, andsecondary copper mineral(s).Numerous parallel veins and veinlets, less thanor equal to 15 cm thick parallel the jointing incoarse-grained porphyritic monzogranite. Palelavenderfluorite is in association with browncarbonate in quartz-lined cavities. There areabundant indications of galena and alterationproducts of chalcopyrite; numerous zones of small(less than 2 mm) pyrite molds and pseudomorphs; andminor unaltered pyrite. These veins were exploredby three small inclines, but apparently the veinspinch out with depth as they are exposed only inthe opencuts.Vein cuts coarse-grained porhyritic monzogranite.Purple fluorite occurs with pyrite along latehypogene fractures and in masses about 1.0 cmacross in milky quartz. No galena, gold, or copperstain was observed. The vein probably was emplacedalong a northeast-striking fault as suggested by anintensely altered and friable zone at least 0.6 mthick along the footwall of the vein.A quartz-fluorite-pyrite-chlorite-bearing veinstrikes approximately N. 50 0 E., and dips 35 0 ­40 0 NW. The vein is as much as 0.3 m thick andcan be traced at the surface for a distance of about30 m along strike. The fluorite in the veinconsists of coarsely crystalline masses as muchas 6 cm across.Fine particles of detrital gold are moderatelyabundant in gravel on a somewhat consolidated,reddish-brown ciay soil. This soil fillsirregularities developed in the true bed rockhere. However, the reddish-brown soil does notitself contain placer gold particles.Relatively abundant iron oxides replacingchalcopyrite in wispy quartz stringers following aN. 70 0 E.-striking and north-dipping shear zone.Considerable silicification along the zone.~ot"'o~§

831il32834835836837838856858868Unnamed siteUnnamed siteUnnamed shaftUnnamed siteUnnamed prospectUnnamed siteUnnamed siteUnnamed prospectRed CloudCyclopic 6prospectsSE 1/4 sec. 32, T. 28 N., R. 18 w.SE1/4 sec. 32, T. 28 N., R. 18 W.SW1/4 sec. 33, T. 28 N., R. 18 W.NW1/4 sec. 33, T. 28 N., R. 18 W.SE1/4 sec. 33, T. 28N., R. 18 W.SW1/4 sec. 32, T. 28 N., R. 18 W.NE1/4 sec. 32, T. 29 N., R. 18 w.SE1/4 sec. 30, T. 28 N., R. 18 W.NW1/4 sec. 31, T. 28 N., R. 18 W.NE1/4 sec. 25, T. 28 N.,· R. 19 W.FFPb, Cu, AuCU, Pb, AuF, PbFFAu?CuAu?An approximately 3-cm-thick quartz-pyrite-fluoritecutsporphyritic monzogranite atcarbonate veinthis locality. The vein strikes N. 65 0 ·E. and dips7~ ~.At this locality, two veins crop out about 1 mapart. The mineralogy of the veins includesquartz, pyrite, pale-lavender fluorite, carbonate,white mica, and possibly potassium feldspar.Quartz veins, as much as 20 cm wide, appear toparallel a strongly developed foliation in aN. 35 0 E.-striking shear zone in cataclasticallydeformed porphyritic monzogranite. The porhyriticmonzogranite contains some scattered patches ofgalena and secondary copper minerals. One smallgrain of gold was noted.Several quartz-pyrite-carbonatezchalcopyritezgalenazgold (trace) veins cut coarse-grained porphyriticmonzogranite. Gold occurs as minute grains 'in ironoxide-stained cavities possibly reflecting theformer presence of chalcopyrite. In addition, ahornblende porphyry dike crops out at this localityand strikes northeasterly.A quartz-fluorite-pyrite-galena (trace) vein strikesN. 25 0 E. and dips 80 0 NW. Fluorite in the veinis as much as 4-cm-across and varies from colorlessto dark purple.Two quartz-fluorite-white mica veins crop out hereapproximately 3 m agart. The veins strikeapproximately N. 65 E. Greisen occur in thesurrounding coarse-grained porphyritic monzograniteand includes some pyrite and feldspar. Apotassium-argon age determination of white micafrom these veins yielded an age of 65.4 Ma (seetable 3).Quartz-pyrite-fluorite veinlets in porphyriticmonzogranite strike N. 20 0 _25 0 E. and dip 70 0 NW.In addition, several mafic dikes at this localityparallel the trend of the veins, but no veins wereobserved to cut the mafic dikes.Prospect sunk on a 15- to 20-cm-thick, brecciatedquartz-carbonate-pyrite vein. Further, a nearlyflat lying shear zone is exposed throughout theprospect pit. The shear zone includes abundantsericitized and broken-up schist.Approximately 30-m-long adit and 5-m raise to surfacealong quartz-pyrite-carbonate-chalcopyrite (trace)veins cutting porphyritic monzogranite. Numerousminor faults in the workings show shallow dips.Major splay of detachment-fault zone containing redbrowngouge and comminuted monzogranite cutsthrou§h the prospects. A minor fault strikesN. 10 _15 0 E., and dips approximately 40 0 W.; it ispossibly parallel to the main fault system. Quartzcarbonate-pyriteveins and recemented quartzbreccia of the Cyclopic type occur in the gougezone.~ ttl~............f-"01-:]

TABLE H.-Notable occurrences ofcommodities in the Gold Basin-Lost Basin mining districts-ContinuedI-'

889891897900902903904Unnamed shaft SW1/4 sec. 29, T. 28 N., R. 18 W.Unnamed prospects NE1/4 sec. 30, T. 28 N., R. 18 W.Golden Rule mine NW1/4 sec. 29, T. 28 N., R. 18 W(Gold Day mine)Mountain View SE1/4 sec. 20, T. 28 N., R. 18 W.2Unnamed shaft SE1/4 sec. 20, T. 28 N., R. 18 W.Ridgetop prospect SE1/4 sec. 20, T. 28 N., R. 18 W.(Never-get-left)Unnamed prospect SW1/4 sec. 28, T. 28 N., R. 18 W.Au?PbAu, PbZn?, CU,Au, PbCU, PbCU,CU,PbPbZn?, Pb,Cu, Mo45 em thick. Immediate country rock consists of aseptum of metamorphic rocks that have been engulfedby the two-mica monzogranite.Shallow, 8-m-deep shaft is sunk in gneiss intrudedby numerous biotite minette(?) and fine-grainedandesite dikes. No obvious signs of mineralizationpresent.Series of prospects along generally east-weststrikingstructures crop out in the vicinity ofthis locality. One quartz vein (probably 15 to30 em thick) lies along a N. 85 0 E.-striking fault.Movement along the fault probably is premineralization.Abundantcerussite, minor galena, and somepyrite molds were noted locally. Numerous quartzveins and pods occur along a sericitized anddeformed contact zone between medium-grainedgneissic biotite granodiorite and leucocraticgranite-bearing metamorphic complex. Theeasternmost prospect pits were sunk on two quartzpyrite-galena-cerussiteveins 15 to 30 em thick.At top of hill, a shaft 6 m deep is sunk on a quartzvein 0.9 to 1.2 m thick, striking N. 20 0 E. anddipping 45 0 SE. Pyrite and other sulfides areconcentrated along late hypogene fractures parallelto the overall strike of the vein. Only a smallpercentage of the vein is mineralized.Downhill to the east, the vein strikes N. 35 0 E.,dips 20 0 SE. and is from 0.15 to 1.2 m thick.Here, the vein pinches and swells, cutting stronglysheared gneiss or medium-grained granodiorite, andit includes a quartz-iron carbonate-chlorite-pyritegalena-sphalerite(?)-chalcopyrite(?)assemblage.Chrysocolla is abundant; no chalcopyrite wasobserved, although it may be present. Mineralogyof the north-northeast-striking, gently tomoderately southeast dipping vein includes quartz,pyrite, galena, and cerussite. Trace amounts ofsecondary copper minerals were noted. Gold wasfound in the dump of the main shaft, approximately30 m north-northeast of the hilltop. Veinletslocally cut hydrothermally altered alaskite.A fine-grained granular quartz-galena vein includes atrace of copper stain.Incline workings have a maximum depth of about 12 m,and include a Short, approximately 7-m-long driftalong a minor fault. Traces of galena andsecondary copper minerals were noted.Uppermost working is a 9-m-long, 0.6- to 3.1-mdeepopencut; along a N. 50 0 E. striking, 75 0 SE.­dipping fault vein. The vein contains minorchalcopyrite, galena, and pyrite.The prospect pit is approximately 1.5 m deep andcuts an irregular q~artz-galena-sphalerite(?)­chalcopyrite-pyrite vein. Wulfenite is abundant;chalcopyrite and pyrite are rare. No free gold wasfound after an extensive search.~ t:l:lt"'tz:l............I-'

TABLE n.-Notable occurrences of commodities in the Gold Basin-Lost Basin mining districts-Continuedf-'0">oLocality(pI. 1)909911913913a917920921923NameUnnamed prospectUnnamed aditJumbo prospectUnnamed prospectUnnamed sitePatsy (Neglected)Unnamed prospectUnnamed siteApproximate location(UTM 10,OOO-m grid, zone 11)SW1/4 sec. 20, T. 28 N., R. 18 W.Location uncertainSW1/4 sec. 19, T. 28 N., R. 18W.SW1/4 sec. 19, To 28 N., R. 18 w.NW1/4 sec. 19, T. 28 N., R. 18 w.NW1/4 sec. 20, T. 28 N., R. 18 w.SW1/4 sec. 17, To 28 N., R. 18 W.NW1/4 sec. 19, T. 28 N., R. 18 W.CommoditiespresentCu, PbPb, Cu, Au,MoAu?FFPb, CuPb, AgFCODlllentsA 0.6-m--thick quartz-galena-ehalcopyrite vein heredips about 45 0 S. and strikes N. 85 0 E.Irregular sulfide-bearing quartz pods and stringers,parallel to foliation in sheared mafic gneiss. Theveins have been deformed by the regionalmetamorphic events (see text). Sulfides includegalena, chalcopyrite, pyrite, minor secondarycerussite, wulfenite, and green-blue copper stains.Main vein is 2.4 to 3 m thick, strikes N. 10 0 W., andhas a vertical dip. The vein crops outcontinuously for approximately 140 m and appears tobranch out into several veins at its north end. Inthe main prospect pit, which is about 3 m deep, thevein is 3.1 m thick and dips 80 0 E., cutting thegently northeast dipping gneiss.A second vein, 2 to 3 m thick, lies 30 m to the westand crops out for 30 m. The strike is N. 10 0 W.,dip vertical. Veins consist of quartz, minorpyrite, trace sericite, and trace ferrocarbonate.No copper, lead ore, fluorite, or gold wasobserved, however.Massive quartz vein appears to dip 30 0 SE. and isintimately associated with two-mica monzograniteand pegmatite. Feldspar, muscovite, fluorite, andminor pyrite occur as thin seams less than 2.5 emthick. The veins cut and are mutually cut by themonzogranite, suggesting a genetic relation.Quartz-pyrite-white mica-fluorite veinlets as much as5 em thick cut a fine-grained facies of the twomicamonzogranite.Several prospect pits on a gently southwest dippingquartz-pyrite-galena-ehalcopyrite vein, 0.9 to1.2 m thick. Also present are cerussite,chrysocolla, pyrite voids, and boxworks.Considerable galena and cerussite exposed in a smallpit. Country rock consists of quartzofeldspathicgneiss, amphibolite, and biotite sequences of theparagneiss unit.An approximately east-west-striking vertical veincuts the two-mica monzogranite and the adjoininggneiss. The vein includes quartz, pyrite, whitemica, and fluorite. Some of the fluorite cubesare 5 em on a side. A potassium-argon agedetermination on white mica from this vein yieldedan age of 68.8 Ma (see text and table 3, this report).Clt'.l~o~tzt::Igt""t::I~~::>:I~ N~ ......o Zo"%j~t'.lgf;s::00Z t-

921928 Unnamed adit929 Gold Street(also titledClimax group)931 Big Lease931a933934935935a938938aShelby mine(Harmonica)Unnamed prospectUnnamed prospectStar Extension2Morning StarSaint CharlesRound TopUnnamed aditNW1/4 sec. 11, T. 28 N., R. 18 w.SE1I4 sec. 11, T. 28 N., R. 18 w.NE1/4 sec. 11, T. 28 N., R. 18 w.NW1/4 sec. 8, T. 28 N., R. 18 w.NW1/4 sec. 8, T. 28 N., R. 18 w.NW1/4 sec. 5, T. 28 N., R. 18 w.SW1/4 sec. 16, T. 28 N., R. 18 W.SW1/4 sec. 16, T. 28 N., R. 18 W.SE1/4 sec. 16, T. 28 N., R. 18 W.NW1/4 sec. 22, T. 28 N., R. 18 W.NW1/4 sec. 22, T. 28 N., R. 18 W.Au, Pb, Cu,V, MoAu, Pb, CuPb, Cu, V,MoTrace CuAuTrace CUCu, Pb, Mo,Au?Au?Pb, trace Cu,Au?Pb, Cu, Au?Au, Pb, CuHilltop prospect pit exposes a pod of quartzchalcopyrite-galenathat is approxima~ely 1.8 mthick. Examination of mineralogy on samples fromdump revealed abundant gold approximately 1 mmin diameter; galena, minor altered chalcopyrite,pyrite, wulfenite, vanadinite, chrysocolla, copperstain.Lower adit is approximately 14 to 15 m long.Workings are along a quartz-galena-cerussite-goldalteredchalcopyrite (malachite) vein,approximately 0.9 m thick.Main shaft inaccessible but was approximately 9 mdeep. A quartz-pyrite-iron carbonate-galenachalcopyrite-chloritevein is goorly exposed.It appears to strike N. 25 0 -30 W. Somevanadinite, wulfenite, and copper stain wereobserved also.Prospect pit is approximately 3 m deep on a zone ofquartz-pyrite-chlorite-sparse chalcopyrite veins,1.5 m thick. The veins are fractured, brecciated,and recemented somewhat similar to ore at theCyclopic mine workings.A small opencut, about 3 m deep and 12 m long, liesin a zone of brecciated quartz lenses in anorthwest-striking shear zone. Float suggeststhat this system of veining is the continuationof the zone of quartz veins extending through theShelby mine (loc. 921). Vein includes quartz,pyrite, carbonate, chlorite, and gold.Pit on quartz-pyriteooQarbonate-chlorite vein,approximately 2.4 m thick. A trace of copperstain was observed on float. The vein strikesapproximately east-west and dips 35 0 N.Upper pit is on a quartz-pyrite-chalcopyrite-galenavein that ranges from 2.5 to 25 cm(?) thick. Minorchrysocolla and wulfenite present. No gold wasobserved. The vein strikes N. 25 0 E. and dips15 0 SW. A mafic dike approximately 3 m thick isin the hanging wall of the vein and has a chilledmargin against the vein.Morning Star is a shaft with a short connecting adit.Quartz-pyrite-galena-trace copper-bearing vein, 1 to25 cm thick, strikes N. 10 0 E., and dips 35 0 E.Quartz-pyrite-galena-chrysocolla vein occurs in a lensless than 0.9 m thick. Also present arecerussite and malachite.Vein and veinlets are concentrated in a shear zone.Country rock includes gneissic granodiorite belowshear zone and paragneiss above the shear zone.At this locality, a prospect pit in lower plate ofgneissic granodiorite has been dug on rocks cut bynumerous small quartz veinlets. This pit liesapproximately 15.2 m below a N. 65 0 E.; 25 0 SE.­dipping fault zone. The main quartz-pyrite-galenachalcopyrite(cerussite-malachite)-gold vein near~1:0t"'i?'Jf-'f-',.....m,.....

TABLE H.-Notable occurrences of commodities in the Gold Basin-Lost Basin mining districts-Continuedf-'0'>t-.:lLocality(pl. 1)938a911091119112911791189119NameUnnamed adit....ContinuedApproximate location(UTM 10,000-m grid, zone 11)Claude (Eastside) NW1/11 sec. 22, T. 28 N., R. 18 W.Lester 1 and 2 SW1/11 sec. 15, T. 28 N., R. 18 W.Ridge Lode SE1/11 sec. 16, T. 28 N., R. 18 W.(For Years)Unnamed prospect NW1/11 sec. 28, T. 28 N., R. 18 W.Grand View SElIl1 sec. 10, T. 28 N., R. 18 W.Valley View 2 SW1/11 sec. 10, T. 28 N., R. 18 W.CommoditiespresentAu, Cu, PbPb, AuPb, Cu, AuPb, CuAu, Cu, PbCu, Pb, Au?Commentshere, however, is less than 7.6 cm thick and lieswithin the fault zone. Adit is 1.2 m in length.Quartz-iron carbonate-pyrite-galena-chalcopyrite(minor)-gold vein is hosted by gneiss. Veinstrikes N. 75 0 E. and dips 50 0 NW.An approximately 8-m-long adit is driven along asoutheast-dipping fault zone in gneiss. The quartzvein is fragmented and recemented, and overall isnot notably mineralized except at the north endwhere galena, cerussite, pyrite, and trace goldwere observed.A quartz-pyrite-galena-carbonate-chalcopyrite-goldbearingvein is 0.3 m thick here; it strikesapproximately N. 115 0 E. and dips 110 0 SE.Galena and copper stain noted in a small prospect pitdug on the ridgeline, approximately 30 m south ofthe contact between gneissic granodiorite andporphyritic monzogranite.Prospects and opencuts lie on group of echelon veinsstriking N. 55 0 -75 0 W. and dipping 55 0 _70 0 NE.Lower adit is approximately 7 m long and includesa 7-m opencut driven on a N. 115 0 W.-striking, 65 0 W.­dipping fracture zone containing irregular quartz,iron carbonate, and pyrite veinlets. The fracturezone is 5 cm wide in the gneissic granodiorite.A second adit uphill is about 13 m long and wasdriven along a quartz vein system varying from 1to 60 cm in thickness; it occupies a N. 55 0 W.­striking, 55 0 NE.-dipping fault in the gneissicgranodiorite. The system consists mostly of a zone8 em to 0.6 m wide that is made up of branchingquartz veinlets. A third prospect here explores afracture-vein system which strikes N. 75 0 W. andincludes individual quartz veinlets as much as 8 cmwide. Sericitization of the gneissic granodioriteextends about 3 m out from the fracture-vein system.Free gold was noted in oxidized vein material on thedump. Individual veins may include variable amountsof galena, chalcopyrite, quartz, carbonate, pyrite,cerussite, and limonite.Two prospect shafts approximately 5 to 6 m deepexplore a 75-cm-wide vein of white quartzcontaining less than 1 percent overall pyrite,chalcopyrite, iron carbonate, and gold(?).~ot'"o~§gt:JE5~ :;c:;.:.~~@o":l>-3~8 b~r:Il~t'"o~~r:IlZis:Zc;Jt:JU3>-3:;co>-3.r:Il:;.:.:;cN~

952957964967968971972973973aValley View SW1/4 sec. 10, T. 28 N., R. 18 W.Unnamed placer SE1/4 sec. 28, T. 29 N., R. 18 W.workingsUnnamed placer NW1/4 sec. 29, T. 29 N., R. 18 W.workingsUnnamed prospects NE1/4 sec. 31, T. 29 N., R. 18 W.Unnamed drywasher NE1/4 sec. 32, T. 29 N., R. 18 W.siteUnnamed drywasher NW1/4 sec. 31, T. 29 N., R. 18 W.siteUnnamed drywasher NW1/4 sec. 1, T. 29 N., R. 19 W.siteOwens mine NW1/4 sec. 1, T. 28 N., R. 19 W.Hope NW1/4 sec. 1, T. 28 N., R. 19 w.Au?Au?Au?Cu, Pb, Au?AuAuAuCu, FeCuThere are two shafts near this locality. Southernshaft exposes 3-m--wide contorted gouge zonecontaining blocks of vein quartz as much as 1 mlong. The mineralogy of the veins includesquartz, carbonate, and pyrite.Gulches in this general area have been placered veryheavily during several intervals of what appears tohave been prolonged occupations.Gulches on both sides of the road in this generalarea were worked extensively for their placer goldcontent. Apparently the placer gold wasconcentrated on fractured but coherent gneissicbasement rocks.Four shallow prospect pits, the deepest of which isabout 4 m, explore a series of northeast-strikingsoutheast-dipping milky quartz veins. The veinscontain local concentrations of chalcopyrite,galena, and carbonate. The veins are lenticularand branch approximately parallel to foliation inthe paragneiss country rock.Placer gold occurs in particles approximately1 mm across. The gold is hosted widely by theslopewash debris and is associated with relativelysparse concentrations of magnetite.Several small colors and one cerussite-encrustedpebble of galena were obtained from materialcollected from a small gulley cut in Tertiaryand (or) Quaternary gravel. False bed rock is notwell-cemented by caliche but instead consists ofgravel cemented by a red clay-rich matrix.Some relatively coarse placer gold, with particlesmeasuring more than 1 mm across, was obtained froma heavily worked gulch approximately 200 mnortheast of the cabin at Owens mine.Underground workings at the mine probably measured atleast 100 m. Headframes and ladders have beenremoved. Considerable chrysocolla and malachiteoccur as staining along a narrow fault zone whichparallels the gneissic layering in its hangingwall. There is a slight discordance of the faultplane with the attitude of the layering in thefootwall gneiss. Amphibolite and biotite gneissare the main rock types in the mine area, but atleast one 0.6-m-thick bed of laminated ironformation crops out at several points southwestand west of the main shaft. Calc-silicate rockis cut locally by quartzose veins or pegmatiticalaskite. The veins inclUde fine-grained granularquartz, iron carbonate, specularite, pyrite, andsecondary copper minerals. Sericitization isintense and widespread.A shallow 3-m pit shows altered and copper-stainedschistose cataclastic gneiss. Malachite,cuprite(?), and chalcopyrite occur in veinlets as~ !:XlI:""t:rj..................0">c,.:>

TABLE ll.-Notable occurrences of commodities in the Gold Basin-Lost Basin m·ining districts-Continued......CP~Locality(pl. 1)973aNameHope--Continued974 Unnamed drywasher SEl/4 sec. 36, T. 29 N., R. 19 W.site976 Unnamed drywasher NEl/4 sec. 12, T. 28 N., R. 19 W.site980 Unnamed drywasher NWl/4 sec. 17, T. 28 N., R. 19 W.site988 Excelsior mine NW1/4 sec. 22, 1. 28 N., R. 18 w.990 0.0. 1992 Unnamed prospect1031 Unnamed drywashersiteApproximate location(UTH 10,000-m grid, zone 11)SWl/4 sec. 22, T. 28 N., R. 18 w.SWl/4 sec. 22, T. 28 N., R. 18 w.SEl/4 sec. 7, T. 29 N., R. 17 W.CommoditiespresentAuAuAuPb, Au?Pb, Cu, Au?PbAuCommentsmuch as 2.5 cm wide. They parallel foliation andlayering. Brecciated zones in the gneiss arecemented by iron and copper oxide minerals.Relatively abundant and moderately coarse fragmentsof detrital gold obtained entirely from Tertiaryand (or) Quaternary gravel. The bulk of the gold atthis locality is concentrated on caliche-cementedfalse bed rock.Very few colors were obtained from this site. Onefragment of gold measured 0.5 mm across. Inaddition, the overall abundance of magnetite inthe sand at this site is relatively low.Relatively abundant concentrations of magnetite occurin the Tertiary and (or) Quaternary gravel, but onlyone color was found.Thin quartz-carbonate veinlets parallel foliation ina highly foliated zone that strikes N. 35 0 _40 0 E.The highly foliated shear zone shows silicification,sericitization, and flooding by carbonate; the zoneoccurs between gneiss and porphyritic monzogranite.The bulk of the alteration and quartz veinlets areconcentrated in a zone approximately 7 m wide.The veins include quartz-carbonate-chlorite-pyritegalena(trace)-gold(?) assemblages.As much as 0.6 m of well-mineralized quartz occupiesa west-northwest-dipping fault zone--possibly theextension of the Excelsior vein system. Abundantcerussite after galena, local concentrations ofmalachite and chrysocolla staining, and iron oxidepseudomorphs after pyrite.Shaft 15 m deep shows stoping to that depth along a0.3- to 1.0-m-thick vertical quartz vein occupyinga N. 10 0 E.-striking sericitized shear zone. Twobiotite lamprophyre dikes are visible in mainshaft. One dike 15 cm thick crosscuts the vein,and the other, which is 40 cm thick, lies 0.6 meast of the vein. Galena and weathered pyriteoccur in the vein quartz.Considerable coarse-grained and fine-grainedfragments of gold are associated with a moderateamount of magnetite, some barite, and aconsiderable amount of cerussite-encrustedgalena. The coarse fragments of gold aremoderately rounded, whereas the fine fragmentsare angular.~ot"'o~~t:Jgt"'t:J~Z t".J~~HN~Ho Zo"':l"'l;:r::t".JQo f;g:rn?!t"'o rn "'lg:rnZe5zZQt:JU1"'l2:la.~> 2:lNo~

1036104310711086108710951096Unnamed prospects SW1/4 sec. 8, T. 29 N., R. 17 w.Unnamed prospect UTM: 756,030 mE., 3,988,780 m N.Lone Jack placer SW1/4 sec. 15, T. 29 N., R. 17 w.Unnamed prospect SW1/4 sec. 1, T. 28 N., R. 19 W.Unnamed prospects NW1/4 sec. 1, T. 28 N., R. 19 W.Senator mine NW1/4 sec. 14, T. 28 N., R. 19 W.Buena Vista SE1/4 sec. 11, T. 28 N., R. 19 W.U?, W?CuAuPb, Cu, Ba?,FeCu, Pb?Cu, Au?Au?Radioactivity is as much as seven times backgroundlocally in some hot spots. At this prospect amagnetite-bearing leucogranite pegmatite containscataclastic margins characterized by fine-grainedmagnetite. The margins of the pegmatite have thehighest counts in areas along the hanging wall.A block of skarn occurs in the wash at the prospect.Some calcite, quartz, garnet, pyrite, amphibole,and scheelite(?) were noted in the skarn.Prospect is east of Burro Springs in the IcebergCanyon quadrangle. A l-m-wide quartz vein containssome knots of brown-weathering carbonate, ratherabundant pyrite, and a trace of secondary copperstaining. The vein occupies a narrow augen gneisscataclastic zone in an otherwise fresh porphyriticcoarse-grained monzogranite.Yellow-gray distinctly foliated to laminatedquartzofeldspathic gneiss (medium grained) isthe dominant clast type. Sub angular to subroundedboulders as much as 0.6 m in diameter are common.Pyritic vein quartz is present but uncommon, andsome pyritic and feldspathic altered wall rock ofquartzofeldspathic gneiss is present. Gold andlimonite pseudomorphs after pyrite were foundnorthward. Heavily worked in the late 1950's;reportedly fragments of gold greater than 1 mmwere very common.A 0.3-m-thick quartz vein containing some ironcarbonate, albite, and some minor seams ofbarite(?) crops out here. Considerable late galenaand oxidation products of chalcopyrite also occurin the vein. The vein occupies a minor normal(?)fault in predominantly amphibolite paragneiss,which includes a lens of well-laminated ironformation, approximately 100 m north-northwestof the 2-m-deep pit at this site.These workings include approximately 10 m of verticaland inclined shafts. There is considerablechrysocolla, but very little galena, if any.Iron oxides after pyrite are rather abundant.An approximately 100-m-long adit has been drivento crosscut an approximately 0.6-m-thick brecciazone along a shallow-dipping fault zone. Thefault zone dips 5 0 _10 0 E.- NE. and has ahanging wall of brecciated gneiss and afootwall of two-mica monzogranite. Only tracesof secondary copper minerals were noted to occurin the fault zone, approximately 20 m from theportal. The fault zone in the adit also includessome vein quartz.Two quartz lenses as much as 2 m thick and 25 m alongstrike appear to lie on either side of a shear zonepoorly exposed in a small prospect pit at the northend of the lenses. Indications of mineralizationare very sparse. Faulting along the shear zone mayS2ttlfu ..........,.....~

TABLE H.-Notable occurrences ofcommodities in the Gold Basin-Lost Basin mining districts-Continued,....0)0)Locality(pl. 1)109610971100110511061107112712251356NameBuena Vista-ContinuedUnnamed siteUnnamed siteUnnamed prospectUnnamed prospectUnnamed aditUnnamed siteUnnamed prospectUnnamed prospectApproximate location(UTM 10,000-m grid, zone 11)SEl/4 sec. 11, T. 28 N., R. 19 W.NE1/4 sec. 15, T. 28 N., R. 19 W.NW1/4 sec. 14, T. 28 N., R. 19 W.NW1/4 sec. 14, T. 28 N., R. 19 W.NW1/4 sec. 14, T. 28 N., R. 19 W.NW1/4 sec. 32, T. 28 N., R. 16 W.NE1/4 sec. 26, T. 28 N., R. 20 W.NW1/4 sec. 9, T. 29 N., R. 17 W.Commodi tiespresentCuPb, CuAu?Au?Au?FAuCuConunentshave repeated a single lens. There are a fewbarren-appearing quartz veins in this general area,but no other prospects were noted.Altered amphibolite here shows silicification andflooding by carbonate. In addition, a quartzcarbonate-hematite-pyritevein crops out hereand includes some secondary copper mineral(s).Quartz-white mica-pyrite veins cutting two-micamonzogranite locally include relatively abundantconcentrations of galena and trace amounts ofsecondary copper minerals(?).Prospect exposing fanglomerate of the Muddy CreekFormation in fault contact with paragneiss. Thedeep-brick-red and red-brown gouge of the faultzone, however, is not well exposed. The rocks inthe lower plate here sporadically include tectonicblocks of crushed and recemented vein quartzsimilar to the Cyclopic-type ore.A lens of crushed quartz as much as 15 cm thick cropsout in a prospect here. The prospect exposes theseveins as gently east-dipping crosscutting bodiesenclosed in crushed, brecciated, and intricatelyfaulted Proterozoic gneiss. The brecciated ore isrestricted entirely to a tectonic sliver of gneissbetween two-mica monzogranite and fanglomerate.Horizontal adit penetrates a low-angle fault, whichis in turn offset about 1 m by a high-angle normalfault. An upper prospect nearby is an opencut 15 mlong, entirely in mangled gneiss, containingcommonly isolated blocks and lenses of crushedquartz. A trace of pyrite was found on one veinfragment.A 10-cm-thick vein of quartz, epidote, calcite, andfluorite crops out in a sheared and brecciated zonewithin the granodioritic border facies of theporphyritic monzogranite. Fluorite varies fromcolorless to purple and occurs together with whitecoarsely crystalline calcite in veinlets which cutthe quartz- and epidote-bearing vein.Gold-bearing quartz+pyrite+carbonate vein materialoccurring in a coarse, angular landslide breccia.Trace of gold visible.Two prospects occur at this locality. In the firstprospect, hematitic gossan is apparentlyassociated here with a 30-cm-wide quartz veinQt:rJot""o~§Q~ o~~~>~N~~o'"".l~t:rJQ~og;wZ t-

13571359Copper Glance 2(Copper Blowout)White Beauty(High Voltage)NW1/11 sec. 9,. T. 29 W., R. 17 w.SW1/11 sec. 9, T. 29 N., R. 17 w.CuPb, Cuoriginally carrying abundant sulfides, includingchalcopyrite. The vein dips moderately andparallels the dip of layering in the enclosinggneiss and leucogranite complex. In the secondprospect, a trace of chrysocolla was notedassociated with a 1-m-wide quartz vein occupyinga minor fault in nearly flat lying amphibolitegneiss.Gentle inclined adit exposes a 2- to 25-cm-thickzone of massive goethite-hematite lying parallelto the rounding, undulating foliation. Somemalachite and chrysocolla on dump. Another shaftis vertical and about 10 m deep; it passesthrough a flat-lying hematite+goethite+malachite+chrysocolla gossan exposed at the surface by cuts.The country rock is gently dipping amphibolequartzofeldspathicgneiss and alaskite. Thisarea seems to be dominated by a series of gentlydipping quartz+ sulfide lenses parallel to layeringin interlayered amphibole-quartzofeldspathic gneiss.Mineralization in this general area is referred toas Copper Blowout ridge in Deaderick (1980) andKrish (19711). Geochemical studies of minorelements in rocks in this area suggested to Krishthat if there is a porphyry copper system buriedhere, the exposed rocks are above the outermostpropylitic fringes of the system.A vein as much as 25 cm thick contains abundantcerussite, malachite, chrysocolla, and bornite(?).~t:dt'"t.":l....,.....0')...;J