STUDIES RELATED TO WILDERNESS PRIMITIVE AREAS GfiOIJOGF Mineral Resources of the Wilson Mountains Primitive Area, Colorado By CALVIN S. BROMFIELD, U.S. GEOLOGICAL SURVEY, and FRANK E. WILLIAMS, U.S. BUREAU OF MINES With a section on GEOPHYSICAL INTERPRETATION By PETER POPENOE, U.S. GEOLOGICAL SURVEY STUDIES RELATED TO WILDERNESS PRIMITIVE AREAS GEOLOGICAL SURVEY BULLETIN 1353-A An evaluation of the mineral potential of the area UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY W. A. RadHnski, Acting Director Library of Congress catalog-card No. 79-183754 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.G. 20402 (paper cover) Stock Number 2401-1217 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 primi­ tive areas. Areas officially designated as "wilderness," "wild," or "canoe" when the act was passed were incor­ porated into the National Wilderness Preservation Sys­ tem. 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 in­ corporation 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 Wilson Mountains Primitive Area and vicinity, Colorado. This bulletin is one of a series of similar reports on primitive areas. CONTENTS Page Summary______________________________________________________ Al Introduction ______________________________________________________ 3 Previous investigations.--_--_----______________________________ 7 Present investigation.__________________________________________ 8 Acknowledgments. ____________________________________________ 9 ___---_-_______-____________________________ 9 ____----__-_-___-_-_-_____________________--____ 9 Mesozoic rocks.___________________________________________ 10 Cenozoic rocks-__---------__-____-___-_-_____-----------_- 11 Eocene and Oligocene rocks___________________________ 11 Middle and upper Tertiary intrusive rocks______________ 13 Surficial deposits.__-____-___________________-__-_----_ 13 Structure and geologic history________________________________ 14 Mineral resource evaluation_______________________________________ 17 History and claims._____-__-____-__-______________----__----_- 17 Production__________________________________________________ 18 Methods of appraisal________________________________________ 22 Re'sume' of stream-sediment sampling__________________________ 24 Geophysical interpretation, by Peter Popenoe___________________ 27 Geologic relations of the mineral deposits.________________________ 29 Vein deposits________________________________________________ 31 Trout Lake mining district________.._____________-___-----_- 31 San Bernardo mine_______________________-_-___-_----- 34 Atlas and Clara claims___________________________--_-__ 38 Ural claim__________________________________________ 40 Sunshine, Bear, and Tiger claims------------------------ 40 Other prospects______________________-____------------ 41 Mount Wilson mining district________-----------_-_-_------- 41 Silver Pick Basin__-________________------___-___------ 43 Silver Pick mine_______________-_-__--_---------- 43 Other prospects in Silver Pick Basin_____--_--__-,--- 45 Lower Bilk Basin area.___._________________---_--__-_- 46 Morning Star mine.____________________-_---_----- 46 Magpie mine_______________-_____-_---_--------- 47 Upper Bilk Basin___________________________--_-_---- 48 Navajo Basin________________-______________-_-_-_---- 50 Rock of Ages mine.________-_______--------------- 50 Wheel of Fortune area_____________---__-_--------- 51 Other prospects in Navajo Basin.____________------- 52 Elk Creek______________________.___________.____.--_- 54 Special Session mine.___________________-_---_-_--- 54 v VI CONTENTS Mineral resource evaluation Continued Page Disseminated copper in Navajo Basin__ __________________________ A55 Vanadium-___________________________________________________ 58 Goal. ________._____._____.___._..___--___-___.-__._.___ 59 Oil and gas____________________________________________________ 60 Sand and graveL_______________-_--_-_-__-___-_---_____-_____- 61 Conclusions._-_-__________-______-___--___---___--__-_____-_______ 61 References cited____________________________________________________ 62 ILLUSTRATIONS Page PLATE 1. Geologic map and section of the Wilson Mountains Primi­ tive Area and vicinity, Colorado-._____________ In pocket 2. Map showing sample localities, Wilson Mountains Primitive Area, Colorado______-_____-_-___________--_-_ In pocket FIGURE 1. Index map showing location of Wilson Mountains study area._____________________________________________ A4 2. Photograph showing north face of the eastern San Miguel Mountains _ _ _____________________________________ 5 3-6. Maps showing: 3. Major structural features, intrusive igneous rocks, and distribution of mineralization in the western San Juan Mountains._________-_-___---______ 16 4. Approximate location of claims, Wilson Mountains Primitive Area_____________________________ 20 5. Concentration of copper in stream sediments, Wilson Mountains study area_______________ 25 6. Concentration of molybdenum in stream sediments, Wilson Mountains study area_______________ 26 7. Total intensity aeromagnetic map of the Wilson Mountains Primitive Area.____________________________________ 28 8. Photograph showing general course of the San Bernardo vein____________________________________________ 33 9. Geologic map of the main part of the Trout Lake mining district showing principal veins._____________________ 37 10. Photograph showing lonely vigil of abandoned mine cabin, Rock of Ages mine._________ ____________________. 50 11. Geologic map of the eastern part of Navajo Basin showing area with disseminated chalcopyrite_________________ 56 TABLES Page TABLE 1. Sedimentary and volcanic rocks of the San Miguel Mountains, Colo____---___----__-_--___------------ A10 CONTENTS VII Page TABLE 2. Dollar value of precious- and base-metal production from A19 mines in the Wilson Mountains Primitive Area________ 3-6. Analyses of samples from the Wilson Mountains Primitive Area: 3. Veins and mineralized rocks-___________________ 66 4. Altered rocks_______________________________ 68 5. Stream sediments and panned concentrates. ______ 72 6. Soils and miscellaneous samples_____--_____-__ 78 7. Assays of grab and chip samples from mines and claims, Wilson Mountains Primitive Area.____________________ 39 8. Partial analyses of samples from the area of disseminated copper on the north side of Navajo Basin_ ______________ 57 STUDIES RELATED TO WILDERNESS PRIMITIVE AREAS MINERAL RESOURCES OF THE WILSON MOUNTAINS PRIMITIVE AREA, COLORADO By CALVIN S. BROMFIELD, U.S. Geological Survey, and by FRANK E. WILLIAMS, U.S. Bureau of Mines SUMMARY A mineral survey of the Wilson Mountains Primitive Area and adjacent study areas in southwestern Colorado was made by the U.S. Geological Survey and U.S. Bureau of Mines. The combined area encompasses about 68 square miles of rugged terrain straddling the west-trending San Miguel Mountains, on the west­ ern edge of the San Juan Mountains region. The investigations by the U.S. Geological Survey were made during 1968, and those by the U.S. Bureau of Mines were made during 1966 and 1969. The areia is on the edge of the Ouray-Telluride- Silverton area, one of the great metal-mining regions of Colorado. The principal visible structural features in the primitive area were determined by middle Tertiary intrusion of an east-west belt of composite stocks, laccoliths, sills, and dikes into nearly flat lying Mesozoic sedimentary and overlying Tertiary sedimentary and volcanic rocks. Subsequent erosion has removed much of the Tertiary sedimentary and volcanic sequence. Base- and precious-metal fissure veins cut intrusive rocks and adjacent sedimentary rocks. iSince the discovery of gold- and silver-bearing veins in 1877, mines in the Wilson Mountains Primitive Area have yielded about $1.78 million in gold, silver, copper, lead, and zinc. About 96 percent of this total is from two mines, the Silver Pick mine in the Mount Wilson district and the San Bernardo mine in the Trout Lake district. About 43 percent of the total value is from gold, 43 percent from silver, 13 percent from lead, and only 1 percent from copper and zinc. Nearby, less than 1 mile outside the eastern boundary of the primitive area, two mines the Silver Bell and Butterfly-Terrible yielded $3.07 million in production, mainly in silver. Production from seven smaller mines in this same area was valued at about $43,000. A few miles north of the primitive area vanadium and uranium ores have been produced from sedimentary host rocks on or near the surface. One mile south of the area coal was mined from the Dakota Sandstone. 442-746 O 72 2 Al A2 STUDIES RELATED TO WILDERNESS PRIMITIVE AREAS Farther south, at Rico, limestone replacement deposits near intrusives yielded lead-zinc and precious metal ores. These same limestones probably occur near intrusive rocks beneath the surface of the Wilson Mountains area, but lie too deep to represent feasible exploration targets. The Wilson Mountains