OC1 LO STUDIES RELATED TO WILDERNESS PRIMITIVE AREAS OHIO GEOLOGICAL SURVEt OCT 2 r iQ70 GORE RANGE-EAGLES NEST AND VICINITY, COLORADO GEOLOGICAL SURVEY BULLETIN 1319-C f* MINERAL RESOURCES of the GORE RANGE-EAGLES NEST PRIMITIVE AREA and VICINITY, COLORADO Crest of Gore Range and head of middle fork of Black Creek. View is westward. Mount Powell (alt 13,534 ft) is massive peak at right of cen­ ter. Eagles Nest Mountain is at far right. Duck Lake is in right foreground. Trough above right end of lake marks fault zone of north-northwest trend. Dark area on steep front of rock glacier at left in photograph is typical "wet front" suggesting ice core in rock glacier. Mineral Resources of the Gore Range-Eagles Nest Primitive Area and Vicinity, Summit and Eagle Counties, Colorado By OGDEN TWETO and BRUCE BRYANT, U.S. GEOLOGICAL SURVEY, and by FRANK E. WILLIAMS, U.S. BUREAU OF MINES c STUDIES RELATED TO WILDERNESS PRIMITIVE AREAS GEOLOGICAL SURVEY BULLETIN 1319-C An evaluation of the mineral potential of the area UNITED STATES GOVERNMENT PRINTING OFFICE. WASHINGTON : 1970 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 78-607129 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 ^. STUDIES RELATED TO WILDERNESS PRIMITIVE AREAS The Wilderness Act (Public Law 88-577, Sept. 3, 1964) and the Conference Report on Senate bill 4, 88th Congress, direct the U.S. Geological Survey and the U.S. Bureau of Mines to make mineral surveys of wilderness and primitive areas. Areas officially desig­ nated as "wilderness," "wild," or "canoe" when the act was passed were incorporated into the National Wilderness Preservation System. Areas classed as '.'primitive" were not included in the Wilderness System, but the act provided that each primitive area should be studied for its suitability for incorporation into the Wilderness System. The mineral surveys constitute one aspect of the suitability studies. This bulletin reports the results of a mineral survey of the Gore Range-Eagles Nest Primitive Area, Colo. The area discussed in the report includes the Primitive Area as defined and bordering areas that may come under dis­ cussion when the area is considered for wilderness status or that provide geologic perspective of the area. The Primitive Area is referred to as the Gore Range Primitive Area in this report, and the total area that was studied is referred to as the Gore Range. CONTENTS Page Summary _____________________________________ Cl Introduction ___________________________________ 3 General character and access _____________ 5 Previous investigations _.-_____________ _ _ 7 Present investigation ____________________ _ 7 Acknowledgments ___________________________ 9 Geologic appraisal, by Ogden Tweto and Bruce Bryant _______ 10 Precambrian rocks _________ . - , 11 Sedimentary rocks _____ _ _ - 14 Volcanic and dike rocks ________ _ . 19 Unconsolidated deposits __-__1 __ _ 19 Structure __________ ______ _ - 22 Age of faults _______________ 23 Gore fault ____________________ 24 Frontal fault ________________ 26 Precambrian shear zones __________ - 31 Folds _______________________. 31 Aeromagnetic results ______________ 32 Mineral resources ________ _ _ 35 Mineral setting _____________________ _ 35 Sampling and analytical program _____ 37 Geochemical patterns ____________________ _ 43 Economic geology of areas _________.__ ___ 48 Eagles Nest-Cataract Creek area _____________ 48 Black Creek-Slate Creek area ___________ _ 52 Boulder-Rock-Willow Creeks area ______________ 56 Boss mine and vicinity _________________ 56 Area north of Boss mine ___________ 67 Willow Creeks-Red Peak area ______________ 68 Hammer fluorspar deposits ______________ 69 Stream sediments ___________:_________ 74 Southern area ______________ _________ 74 Gore Creek-Booth Creek area ________________ 83 Northwestern area _______________________ 90 Summary and analysis of mineralization features _______ 91 Coal, oil, and gas _____..____________. _______ 96 Nonmetallic minerals _ ______________________ 96 Conclusions _________________________________ 106 Economic appraisal, by Frank E. Williams _______________ 107 Mining claims _______________________________ 108 Economic evaluation ___________________:_______ 112 IX CONTENTS Page Economic appraisal Continued Description of deposits _____ *_______ C112 Red Peak area ______________________ 112 Bighorn Creek area _________________ 113 Keller Mountain area __ - 114 Deluge Lake area ____________ 114 Pitkin Creek area ____ 115 North Rock Creek area _ 116 Chief Mountain area _ 117 Wheeler Lakes area _____ 119 South Willow Creek area 119 Slate Mountain area ____ 120 Black Lake area _______ 121 References cited 121 Index _________ 125 ILLUSTRATIONS [Plates are in pocket] PLATE 1. Geologic and aeromagnetic map of the Gore Range-Eagles Nest Primitive Area and vicinity. 2. Map showing sample localities and claims in the Gore Range- Eagles Nest Primitive Area and vicinity. FRONTISPIECE. Photograph of crest of Gore Range and head of middle fork of Black Creek. Page FIGURE 1. Index map showing geographic setting of Gore Range study area ____________________________________ C4 2-6. Photographs: 2. Glacial topography at head of canyon of south fork of Black Creek _________ 3. Fractured rocks and notches marking faults of north-northwest trend on west side of crest of Gore Range south of Mount Powell_ 10 4. Migmatite ____________________'. 12 5. Porphyritic granodiorite _______________ 13 6. Rock glacier at head of Brush Creek _______ 21 7. Sketch map showing major structural features and mining districts in vicinity of Gore Range Primi­ tive Area _____________________________________ 22 CONTENTS XI Page FIGURES 8-11. Photographs: 8. Mount Powell from remnant of preglacial erosion surface that forms top of Dora Mountain ____ C25 9. Abrupt east front of Gore Range at Slate Creek ___________ 28 10. View northwest along scarp of Frontal fault 30 11. Typical fracture zone in Precambrian rocks __ 37 12-19. Maps of Gore Range study area showing localities of rock samples containing 12. 300 ppm or more copper _ 39 13. 600 ppm or more lead ___ 40 14. 1,000 ppm or more zinc ______ _ 41 15. 6 ppm or more silver _ 42 16. 0.05 ppm or more gold ___ __ 43 17. 15 ppm or more molybdenum 45 18. 1 ppm or more mercury __ _ _ 46 19. 300 ppm or more arsenic; 15 ppm or more bismuth; 200 ppm or more antimony _ 47 20-23. Photographs: 20. Typical quartz vein in granite ________ 115 21. Boss mine dumps _______________ 117 22. Slate Mountain _________________ 119 23. Dakota Sandstone outcrop _..____ _ 120 TABLES Page TABLE 1. Sedimentary rock formations of the Gore Range and vicinity __________________________ C15 2-7. Analyses of rock samples from the Gore Range: 2. Eagles Nest-Cataract Creek area (area A, pi. 2) ______________________ 54 3. Black Creek-Slate Creek area (area B, pi. 2) 50 4. Boulder Creek-Willow Creek area (area C, pi. 2) ______________________ 58 5. Southern area (area D, pi. 2) _________ 70 6. Gore Creek-Booth Creek area (area E, pi. 2)__ 76 7. Northwestern area (area F, pi. 2) _______ 86 8. Analyses of stream-sediment samples from the Gore Range ___________________________ 97 9. Assays of vein and dump samples and Dakota Sand­ stone samples from the Gore Range _________ 109 10. Semiquantitative spectrograph analyses of vein and dump samples and Dakota Sandstone samples from the Gore Range _____________________ 110 * STUDIES RELATED TO WILDERNESS PRIMITIVE AREAS MINERAL RESOURCES OF THE GORE RANGE-EAGLES NEST PRIMITIVE AREA AND VICINITY, SUMMIT AND EAGLE COUNTIES, COLORADO By OGDEN TWETO and BRUCE BRYANT, U.S. Geological Survey, and FRANK E. WILLIAMS, U.S. Bureau of Mines SUMMARY A mineral survey of the Gore Range-Eagles Nest Primitive Area and vicinity in central Colorado was made by the U.S. Geological Survey in 1969 and by the U.S. Bureau of Mines in 1968-69. An aeromagnetic survey was made earlier by the Geological Survey, in 1967. The Primitive Area as denned occupies about 96 square miles in the highest and roughest part of the spectacularly rugged Gore Range. Bordering areas on the flanks of the range were included in the study to obtain necessary perspective of the range as a geologic unit, and also to obtain information on areas that may come under discussion when the Primitive Area is considered for inclusion in the National Wilderness Preservation System. The total area considered herein is 215 square miles. Geologically, the Gore Range is a fault block of Precambrian rocks between the Gore fault on the west and the Frontal fault on the east. Sedimentary rocks west of the Gore fault are Paleozoic and younger, and those east of the Frontal fault are Mesozoic and younger. At the south, the range extends into the border zone of the Colorado mineral belt, which in this region in­ cludes the highly productive mining districts of Climax, Leadville, and Gilman, as well as many lesser districts. The Mosquito fault, one of the controlling features of the ore deposits at Climax and Leadville, extends into the southern part of the Gore Range and connects with both the Gore and Frontal faults. The block of Precambrian rocks that makes up the main body of the Gore Range is broken by many faults. The Gore and Frontal faults and many of the interior faults as well are old faults that were later reactivated when the range was elevated to its present height. This uplift began very late in geologic time and it continues to the present. The Frontal fault in particular shows evidence of very recent movement. The recent uplift, which began in late Tertiary time, produced a high scarp that forms the abrupt eastern front of the range, along the Frontal fault. Near Cataract Creek, Cl C2 STUDIES RELATED TO WILDERNESS PRIMITIVE AREAS the line of recent uplift turns westward, along the north base of Eagles Nest Mountain, and connects with young faults parallel to the Gore fault on the west side of Mount Powell and in the upper Piney River drainage.