Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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LODE DEPOSITS – The distribution of small- to medium-sized, historic mines and numerous small prospects are shown on the geologic map (plate 1). A total of 44 mine adits, 12 mine shafts, 14 cat cuts/trenches, and about 100 prospect pits were located during this study (appendix 1). The distribution of these mines and prospects indicates the most likely areas of potential exploration and development in the Maysville quadrangle. Most of the significant mines and potential areas for mineral exploration are located in the Proterozoic terrane in the southwest quadrant of the quadrangle. In addition, three areas have small- to medium-sized historic mines in the northwest quadrant of the quadrangle. The majority of mineralization in the Maysville quadrangle consists of base metals and precious metals associated with calc-silicate zones (Xcs) in sequences of amphibolite and hornblende gneiss (Xag and Xhig). On the basis of limited studies of deposits in the Maysville quadrangle and similar deposits in the region, the deposits have been previously interpreted as Proterozoic skarn deposits (Heinrich, 1981) or metamorphosed Proterozoic massive-sulfide deposits (Knight, 1981; Sheridan and Raymond, 1984; Alers and Shallow, 1996; and Heimann and others, 2005). Since most of the deposits exhibit features that are associated with both of these deposits types, the distinction between them is not clear cut and classification of the deposits is controversial. The interpretation of the deposit types is further complicated by the common association of younger Proterozoic intrusions, specifically abundant pegmatites related to the Berthoud Plutonic Suite, and locally Tertiary andesite dikes (Ta) and epithermal-style veins with the mineralization. Twelve samples of representative mineralization from mine waste dumps were selected for commercial multi-element geochemical analyses (table 8; UTM coordinates for samples are given in appendix 1). Some of the samples are composites from groups and clusters of mines and prospects. The geochemistry shows the overall copper-leadzinc-silver character of the mineralization hosted in the Proterozoic rocks in the Maysville quadrangle. Some samples have anomalous to sub-ore grade gold and anomalous bismuth. Also of note are the very low values (below detection) of arsenic and antimony. Two principal mining areas are present in the northwest part of the Maysville 192
quadrangle. The first area is a cluster of caved shafts and an adit located about 3,000 ft south of the summit of Mount Shavano in the SW 1 / 4 , Section 6, T50N, R7E. The caved shafts are on a flat saddle at about 13,400 ft elevation and the caved adit is located at about 12,880 ft on the west side of the ridge. The mines are associated with the Alaska group of patented claims that include 11 claims patented in 1904. The mineralization is associated with a sliver of amphibolite gneiss that is localized along a north-northwesttrending fault. The fault sliver of amphibolite gneiss is hosted in the Proterozoic foliated granodiorite (Xgdf). Mineralization includes minor Cu-oxides associated with epidoteactinolite-garnet calc-silicates, Fe- and Mn-oxides and gossan, and minor vuggy quartz veins. A grab sample of mineralized material, oxides and calc-silicates (sample 05-265, table 8) indicates anomalous silver (21 ppm) and gold (0.889 ppm), weakly anomalous copper (950 ppm), and slightly anomalous zinc and lead. The style of mineralization is the same as the mineralization in the southwest quadrant of the quadrangle. It is not clear why these claims made it to patent. The extremely remote location, the limited size of the mineralized area (that is, hosted in narrow fault slice of amphibolite gneiss), and relatively weak copper and precious-metal signature make it highly unlikely that future exploration and development activities would be conducted on these claims. The other principal area of mining and exploration activity in the northwest part of the quadrangle is associated with the northeast-trending Shavano fault zone along the range-front area. The most significant mine is the Blank mine, located in the SE 1 / 4 , Section 8, T50N, R7E. The main workings include an upper caved shaft with a large waste dump and a lower caved adit with a large waste dump that has been spread out over a large area. The lower adit has a significant spring issuing from it, indicating that the adit probably undercuts the surface shaft and intersected the main Shavano fault zone. Relatively abundant rhyolite porphyry and fault-brecciated Proterozoic rock on the adit dump suggests that the adit intersected a rhyolite dike and the Shavano fault. There are no outcrops in the mine workings or in the area. The upper shaft dump has mostly Proterozoic rocks and abundant fault-brecciated gneisses with a small component of light-gray limestone and brecciated limestone. The limestone was previously interpreted 193
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OPEN-FILE REPORT 06-10 Geologic Map
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TABLE OF CONTENTS Introduction…
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mylonitic, augen textures………
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INTRODUCTION LOCATION AND ACCESS Th
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SAWATCH RANGE RIFT-SHOULDER UPLIFT
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of the South Arkansas River (subseq
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EXPLANATION Rio Grande Rift Neogene
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in descriptions of the geologic uni
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During the Early and Middle Paleozo
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Mountains, and White River uplifts
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field are the largest remnants of t
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Figure 5. Detailed geologic-structu
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with the Colorado mineral belt (Boo
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Shannon, 2005). Widmann and others
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the Upper Arkansas graben (fig. 5)
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15-minute quadrangle, which is adja
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etween the northern and southern se
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on U.S. Forest Service color aerial
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We use fractional map units on the
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Qpt Pinedale till, undivided (late
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weathered, but Mount Princeton quar
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stratified, matrix-supported, bould
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as rockfalls, rock avalanches, rock
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stream-channel deposits of all pere
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Figure 10. View west up South Arkan
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Figure 11. View west up South Arkan
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valley near the eastern map boundar
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lithologies are variable and depend
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Arkansas River in parts of Redman C
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angular to subangular. Deposits gen
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elations, age constraints from foss
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elated to the inferred Squaw Creek
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Figure 14. Crude bedding in coarse
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microcline, and muscovite. The latt
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Volcanic Ash Figure 17. View of eas
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Figure 18. Close-up view of intense
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The western zone of brecciated Pale
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Tr Rhyolite dikes (early to late Ol
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as the overall N47°E trend of the
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One age determination on the rhyoli
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northwest-trending fault. Thus, fie
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on the North Fork leucogranite intr
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A small 400 by 400 foot body of Nor
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N12°E, 62°NW (about 6,000 ft sout
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The age of the quartz latite porphy
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Tma Mount Aetna quartz monzonite po
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of the Maysville quadrangle and the
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Mount Aetna ring dikes (Tma), one i
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the margins of the pluton, includin
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Shannon (1988). The average of seve
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indicating a granite b composition
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analysis by Crawford (1913), two an
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locally tanish to pinkish gray. It
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quadrangle (tables 1 and 3) were fr
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slices of Paleozoic sedimentary roc
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south-southwest of Maysville is a 9
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There is one additional Paleozoic s
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near the southwest margin of the qu
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eastern contact of the diorite intr
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endoskarn zones. The two widely sep
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Xhig) along the southeastern contac
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Xgd Granodiorite (Early Proterozoic
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Hybrid granodiorite is locally deve
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Xcs Calc-silicate gneiss (Early Pro
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Many of the calc-silicate gneiss zo
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typically expressed by intermittent
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The field relations and characteris
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the north side of all three segment
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eplaced by muscovite. The western m
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sillimanite-quartz-muscovite that a
Page 141 and 142: sillimanite gneiss (Xmsg) and the m
Page 143 and 144: Figure 35. Outcrop of Proterozoic h
Page 145 and 146: samples) indicates they are compose
Page 147 and 148: Xal Lineated amphibolite (Early Pro
Page 149 and 150: of the Proterozoic metamorphic rock
Page 151 and 152: that the present structural configu
Page 153 and 154: elated to rotation of domain blocks
Page 155 and 156: sometimes terminate at a cross stru
Page 157 and 158: limestone that is exposed in a wind
Page 159 and 160: quadrangle are intimately associate
Page 161 and 162: of the quadrangle. The north-northw
Page 163 and 164: quartz monzonite ring dikes (Tma).
Page 165 and 166: that truncates the Upper Arkansas g
Page 167 and 168: as at the mouth of Squaw Creek. How
Page 169 and 170: adjacent to the southwestern edge o
Page 171 and 172: graben and the Upper Arkansas Valle
Page 173 and 174: GEOLOGIC HAZARDS Potential geologic
Page 175 and 176: In addition, older landslides may h
Page 177 and 178: sparse vegetation. One such area is
Page 179 and 180: Table 7. Historical (pre-instrument
Page 181 and 182: 4262272N. ECONOMIC GEOLOGY Currentl
Page 183 and 184: A number of the larger pegmatite bo
Page 185 and 186: River placers near Buena Vista (Van
Page 187 and 188: The small mines and prospects along
Page 189 and 190: elatively recent (post-1970) explor
Page 191: contact of two Quaternary gravels (
Page 195 and 196: y Sharp (1976) to be a fault slice
Page 197 and 198: quadrant of the Maysville quadrangl
Page 199 and 200: the large Paleozoic rock outlier) i
Page 201 and 202: WATER RESOURCES Water resources on
Page 203 and 204: water near Maysville is being produ
Page 205 and 206: to Rudy C. Epis: Colorado School of
Page 207 and 208: University, M.Sc. thesis, 50 p. Din
Page 209 and 210: Hutchinson, R.M., and Hedge, C.E.,
Page 211 and 212: Litsey, L.R., 1958, Stratigraphy an
Page 213 and 214: County, Colorado, in Berg, R.R., an
Page 215 and 216: Stark, J.T., and Barnes, F.F., 1935
Page 217 and 218: Tweto, O., 1987, Rock units of the
Page 219 and 220: quadrangle, Colorado: U.S. Geologic
Page 221 and 222: 94A 391996 4263422 Prospect YXp;Xbf
Page 223 and 224: 336A 396189 4274961 Prospect Xgdf B
Page 225: 854 391849 4268852 42 Adit; Geochem
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Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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