Metallogenesis and Tectonics of the Russian Far East, Alaska, and ...

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Tln Creek Cu-Pb-Zn Sknn Deposit
The Tin Creek Cu-Pb-Zn skarn deposit (fig. 1 15) (Szurnigala, 1987; Newberry and others, 1997a) consi* of pyroxenerich
skm with abundnpl sphalerite and minor chalcopyrite, and garnet skarn with chalcopyrite and minor qhaletile; and locally
abundant cpibte and amphble. The pyroxene skarn is distal, and the garnet skarn is proximal to an extensive Tertiary &cite to
andesite poprhyry dike swam thar intnrdes polydeformed, middle Paleozoic contact metamorphosed, claslic a d carbwak mck.
The skam hms small. discontinuous bodies up to 3 m wide along dikes, as manto replacement in marble, and as irrephrbadies
along along thrust and high-angle faults. The skams are zoned, w~th garnet-chalcopyrite-rich skarn proximal to the dike swam
cenler, a& pyroxem-awerite-richskam distal to the dike swarm. Garnet-rich skam grades 0.5- 1% Cu and 1-2 ozti A& and
neghgible Zn and Pb. Pyroxene-rich sharn generally contains 5-20% Zn, 0.1-3% Pb, 0.5-2% Cu, and 2-9 oalt Ag. In a aingle
oulcrop, skarn proxcne bccom mare Fe-rich, and sulfides increase towards marble. Sulfide veins occw locally in dikes md
I w d rocks. Many dikes are lacking associated skarn, and many dikes possess skarn only along one contect.'lhe deposit has a
resource of an estimated 230,000 tonnes with 16% combined Pb and Zn.
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The Kijik River porphyry Cuckposit consists of a large area of low-grade, disseminated chalcopyrite, pyrite, d minor
molybdenite which o m in and @amnt to an early Tertiary dacite porphyry (Eakins and others, 1978; Nelson and others, 1985;
T.K. &adken, writtea commun., 1984). The deposit contains a distinctive orange gossan which extends over a 3 k d area. The
gossan contains an exiensive sbckwork, and zones of sericite and silicic alteration and sulfides. The stockwart varies from weak
I to intense, cansuts mainly of quartz a d sulfide minerals, and is developed both in the dacite porphyry and in overlying vdcanic
rocks. Evlensive propylitic and silicic alteration occurs in the dacite porphyry. The deposit conlains a possiMe r m e af 90
d o n tomes and some samples containing up to 0.25% Cu and 0.17% Mo (T.K. Bundtzen, written wrnmun, 1984).
Gdden Zone Deposit
The Golden h e deposit exhibits features common to polymetallic vein, Au-Ag breccia pipe, and porphyry Cu deposits.
The sulfide mineralogy consists ~f auriferous arsenopyrite and minor chalcopyrite, sphalerite, and pyritc in a quam gangue which
fills open spaces in a breccia pipe (Hawley and Clark, 1974; Swainbank and others, 1978; C.C. Hawley. wrilSeR commun., 1985,
1990). The brecia pipe occurs in the highly-fractured central part of an Late Cretaceous early Tertiary quartz diorib porphyry.
The are zone is about 125 m in diameter. At the surface, high-grade mineralization occurs in a breccia pipe whicb is
approximately 75 m wide. Abundant polymetallic veins occur adjacent to the porphyry. The breccia pipe coatains an estimated 8.9
million toones gradmg 3.2 g/t Au and minor Cu and Ag. The deposit contains an inferred reserve of 1.6 inision tomes grading 5.2
glt Au, and 0.5% Cu. An dd mine at the deposit produced 50 kg Au, 267 kg Ag, and 19 tonnes Cu. The dioritc porphyry has been
dated at 68 Ma (Swainbank ad others, 1978) and intrudes Permian to Jurassic sedimentary rocks of the Chulitna (opbiolite)
terranc, a faull-bounded Fragment within the highly-deformed Kahiltna overlap assemblage.
Nabesna Glecisr polymeWHc veln(7) deposit
The Nabesna Gkier polyrnetallic vein(?) deposit (Richter, 1975) occurs in three contiguous areas whicb contain: (1)
quartz veins and veinlets containing pyrite and minor chalcopyrite and sphalerite; (2) a zone of disseminarad malachite and
azurite; and (3) a zone of iateme ahralion and breccia cemented by quartz, pyrite, chalcopyrite, and galena. The w i t occw in
late Paleozoic melavolcanic porphyry and rnetabasalt flows of the Tetelna Volcanics and may be related to nearby Late Cretaceous
and carly Tertiary granihid plutons and dikes.
Sn and Mo Lode Deposits Hosted by
Granitoid plutons o.f McKinley Sequence
A distinctive group of Sn-greisen, polymetallic vein, and porphyry Mo deposits occur in part of the southem Alaska
metallogenic belt at Boulder Creek, Ohio Creek, Coal Creek, and Treasure Creek (Nokleberg and oihen, 1987, 1988,1993).
These d other lesser deposits occur in ar near the early Tertiary McKinley sequence of grade and granodhite plulms, which
exhibit a narrow age rage of 55 to 60 Ma (Reed and Lanphere, 1973; Lanphere and Reed, 1985). Many of the McKdey
sequence plubons arc peraluminous granites having high initial Sr ratios, suggesting incorporation of Large amounts of cwtd
material (Reed and Jspkere, 1973; Lanphere and Reed, 1985). The plutons of the McKinley sequence iatrude the the Wrangellh
sequence of the Wrangcllia supterterrane and the Kahiltna overlap assemblage (Jones and others, 1987). Lanphere and Reed
(1985) interpreted these graniloid rocks as forming during early Tertiary collision of the Wrangellia composite termne with
various parts of the passive continental-mgin Central composite terrane to the north. However, because more recent leclonic
analyses suggest this collision occurred in the mid-Cretaceous (Nokleberg and others, 1985, 1994d; Plafker and others, 198%;
Phfker a d Bwg, 1994)., tbe McKinley sequence granitoid plutons are herein interpreted as forming dwing tbe crustal
conlamhitian d magmas Born early Tertiary subduction along the southern margin of Alaska.