DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY MINERAL RESOURCES OF THE WEST ELK WILDERNESS and vicinity, Delta and Gunnison Counties, Colorado Open-file report 77-751 1977 This report is preliminary and has not been edited or reviewed for conformity with U.S. Geological Survey standards and nomenclature, Contents Page Summary . .. .. .... ..... .. ... ^ Chapter A. Geology of the West Elk Wilderness and vicinity, Delta and Gunnison Counties, Colorado Introduction 5 Previous studies 5 Present investigations and acknowledgments 8 Geologic setting 8 Sedimentary rocks 9 Volcanic rocks 9 West Elk Breccia 9 Basal cone vent facies 9 Volcaniclastic facies 11 Ash-flow tuffs 15 Intrusive rocks -< - 15 Laccoliths and sills< 15 Sheep Mountain pluton 16 Coal Mountain pluton 16 Dikes 16 Plugs and other igneous bodies 16 Unconsolidated deposits 18 Structure and geologic history 18 References cited 22 Chapter B. Geophysical surveys in the West Elk Wilderness and vicinity, Delta and Gunnison Counties, Colorado Interpretation of geophysical data 27 References cited 31 Chapter C. Geological and geochemical evaluation of the mineral resources of the West Elk Wilderness and vicinity, Delta and Gunnison Counties, Colorado Mineral setting 33 Geochemical exploration 3 3 Metallic mineral commodities 36 Manganese 36 Molybdenum 36 Gold and silver 57 Copper 57 Zinc 61 Lead 61 Uranium and vanadium 64 Other metals 66 Geochemical patterns 67 Geochemical exploration continued Page Mineralized areas of possible explorational interest 71 Sheep Mountain area 71 West Elk volcanic center 71 Sun Creek manganese deposits 73 Coal Mountain pluton and other mineralized areas 74 Nonmetallic commodities 74 References cited 75 Chapter D. Mines, prospects, and mineralized areas of the West Elk Wilderness study area, Delta and Gunnison Counties, Colorado Introduction 79 Previous studies 79 Present investigation 79 Acknowledgments 79 History and production 80 Mining claims 80 Sampling and analytical methods 81 Areas of detailed investigation 81 Ruby Anthracite Creek (Locality 1) 81 Ohio Pass (Locality 2) 86 Ohio and Castle Creeks (Locality 3) 86 Swampy Pass (Locality 4) 87 Cliff Creek (Locality 5) 87 Little Robinson Creek (Locality 6) 87 Castle Pass (Locality 7) 88 Soap Basin (Locality 8) 88 Upper Soap Creek (Locality 9) 89 Upper West Elk Creek (Locality 10) 89 Mill Creek (Locality 11) 90 Steers Gulch (Locality 12) 90 Lower Beaver Creek (Locality 13) 90 Sun Creek (Locality 14) 90 Steuben Creek (Locality 15) 92 Lower West Elk Creek (Locality 16) 92 Lower Soap Creek (Locality 17) 92 El Ray mine (Locality 18) 92 Big Soap Park (Locality 19) 93 West Soap Creek (Locality 20) 93 Sink Creek (Locality 21) 93 Lone Pine Creek (Locality 22) 94 Sheep Mountain (Locality 23) 94 North Smith Fork (Locality 24) 96 Hoodoo Creek (Locality 25) 96 Minnesota Creek (Locality 26) 96 Interocean Pass (Locality 27) 96 ii U.S. Bureau of Mines, 1953-1970, Analyses of tipple and delivered samples of coal (collected during the fiscal years 1952-1969): Repts. of Inv. 4934, 4972, 5085, 5221, 5270, 5332, 5401, 5489, 5615, 5792, 6086, 6300, 6461, 6622, 6792, 6904, 7104, 7219, 7346. Ill Areas of detailed investigation Continued Page Elk Basin Pass (Locality 28) 96 Coal Mountain (Locality 29) 97 Box Canyon (Locality 30) 97 Bell Creek (Locality 31) 97 Cottonwood Creek (Locality 32) 98 Needle Rock (Locality 33) 98 Mineral fuels 98 Coal 99 Oil and gas 104 Other mineral commodities 109 References cited 110 111 Illustrations Frontispiece. Photograph of the Castles, West Elk Wilderness, Colorado [plates are in pocket] Plate 1. Geologic map and cross sections of the West Elk Wilderness study area, Colorado 2. Aeromagnetic map of the West Elk Wilderness study area, Colorado 3. Map of the West Elk Wilderness and vicinity, showing geochemical sample localities, Colorado 4. Preliminary complete Bouguer gravity map of West Elk Wilderness study area and vicinity, Colorado 5. Map showing mining claims and U.S. Bureau of Mines sample localities in and near West Elk Wilderness study area, Colorado Figures Page Figure 1. Areas of mineral resource potential, West Elk Wilderness study area 2 2. Index map of 7 1/2-minute quadrangle maps and access roads, West Elk Wilderness study area (stippled) 6 3. Shaded relief map of the West Elk Wilderness study area and vicinity 7 4-7. Photographs: 4. Pinnacles of West Elk Breccia 12 5. Major unconformity in volcaniclastic facies of the West Elk Breccia 13 6. Angular unconformity in West Elk Breccia 14 7. Sheep Mountain and Mount Guero 17 8. Map showing some major structures in the West Elk Mountain region 21 9. Magnetic map of the region of the West Elk volcanic center 30 10-16. Maps of the West Elk Wilderness study area showing locations of samples containing; 10. Molybdenum 5 ppm or more 37 11. Gold 0.02 ppm or more 58 iv Page Figure 12. Silver 0.3 ppm or more 59 13. Copper 70 ppm or more 60 14. Zinc 200 ppm or more in stream sediments and rocks, and 300 ppm or more in panned concentrates 62 15. Lead 90 ppm or more in rock samples, and 200 ppm or more in panned concentrates 63 16. Vanadium 300 ppm or more in rocks, and 700 ppm or more in panned concentrates 65 17. Map showing localities examined in and near the West Elk Wilderness study area 85 18. Map of Sun Creek adit 91 19. Map showing extent of the coal-bearing Mesaverde Formation in the West Elk Wilderness study area, and structure contours on the base of the coal-bearing rocks 100 20. Coal ownership of the known coal resources in and near the West Elk Wilderness study area 103 21. Map showing the location of oil and gas leases in and near the West Elk Wilderness study area 108 Tables Table 1. Sedimentary rock formations of the West Elk Mountain 10 2. Threshold values of selected elements from the West Elk Wilderness study area, Colorado 35 3. Arbitrary threshold values of selected elements and metals from the West Elk Wilderness study area 38 4. Mean values of elements in unaltered rock, stream-sediment, and panned-concentrate samples from the West Elk Wilderness study area 39 5. Analyses of selected samples from stream sediments, panned concentrates, and fresh and altered rocks by drainage basin, in the West Elk Wilderness study area 40 6. Analyses of samples of rocks from the Sheep Mountain area and West Elk volcanic center hub area 68 7. Analyses of samples of soils from the Sheep Mountain area and the West Elk volcanic center hub area 70 Page Table 8. Analyses of samples of panned concentrates from the Sheep Mountain area and the West Elk volcanic center 11U.Uh« t%> a.rt -*»^L cct *+ ! ii i - _ - - - - _ _ _ - _ -__ - - ___-- - - -__«.«__. - - - - -_ ». » _ ,/ ^/ 9. Analyses of samples collected by the Bureau of Mines from the West Elk Wilderness and adjacent areas 82 10. Analyses of coal samples 21 and 22 84 11. Bituminous coal resources in the West Elk Wilderness study area 12. Classification of mineral resources vi SUMMARY A mineral survey of the West Elk Wilderness and contiguous areas, which cover about 434 mi (1,225 km )in west-central Colorado, was made by the U.S. Geological Survey and the U.S. Bureau of Mines during parts of 1971, 1972, 1973, and 1974. The results of the survey indicate that the area has large resources of good grade bituminous coal. The area may contain buried deposits of base and precious metals. The potential for oil and gas discoveries is slight, and no evidence was found to indicate a geothermal resource. The study area lies along the trend of the Colorado Mineral Belt, and it is locally transected by a major fracture zone connecting with mineralized structures in the nearby Ruby-Irwin mining district. The northern part of the area is characterized by myriad Tertiary igneous bodies that intrude as much as 8,000 ft (2,440 m) of Mesozoic and Tertiary sedimentary strata. Numerous laccolithic mountains form conspicuous topographic eminences. In contrast, the southern part of the area is a deeply dissected pile of Oligocene volcanic and intrusive rocks that includes layered volcaniclastic deposits, lava flows, plugs, plug domes, dikes, vent complexes, and at least one large, deeply eroded strato- volcano of intermediate composition (the West Elk volcanic center). The volcanics overlie an eroded surface on sedimentary strata. The sedi­ mentary rocks thin southward, and in places along the southern margin of the area, the volcanic rocks probably lie on Precambrian crystalline rocks. The mineral potential of the area was studied by examining mining and mineral production records, claims and exploratory workings, by a geochemical survey, by aeromagnetic and gravity surveys, and by the preparation of a geologic map. The area contains 117 unpatented mining claims and no patented claims. A few small exploratory workings are widely scattered throughout the study area. The only production from the area is about 1,000 tons (900 t) of coal from the Mosely Mine on the west side of Coal Creek. Small amounts of gold, silver, copper, lead, and zinc have been produced from the nearby Ruby-Irwin mining district (fig. 1). The geochemical program consisted of the collection and analyses of 1,364 rock, stream-sediment, panned-concentrate, and soil samples. None of the samples contained visible amounts of ore minerals; however, altered rocks at several localities contain anomalous amounts of base and precious metals. The results of geophysical surveys help to define two intrusive bodies of possible economic interest. One is a hypothetical intrusive body underlying altered rocks at the West Elk volcanic center; and the other, a more favorable target, is the Sheep Mountain laccolith.