Mineral Resources of the San Juan Primitive Area, Colorado By T. A. STEVEN and L. J. SCHMITT, JR., U.S. GEOLOGICAL SURVEY, and M. J. SHERIDAN and F. E. WILLIAMS, U.S. BUREAU of MINES With a section on IRON RESOURCES IN THE IRVING FORMATION By JACOB E. GAIR and HARRY KLEMIC, U.S. GEOLOGICAL SURVEY STUDIES RELATED TO WILDERNESS PRIMITIVE AREAS GEOLOGICAL SURVEY BULLETIN 1261-F An evaluation of the mineral potential of the area UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director 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 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 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 San Juan and the Upper Rio Grande primitive areas, Colorado. The area discussed in the report corresponds to the area under consideration for wilderness status. It is not identical with the San Juan and the Upper Rio Grande Primitive Areas as defined because modifications of the boundary have been proposed for the area to be considered for wilderness status. The area that was studied is referred to in this report as the San Juan primitive area. This bulletin is one of a series of similar reports on primitive areas. CONTENTS Page Summary _ ______________________________________________________ Fl Introduction._____________________________________________________ 2 Previous investigations.________________________________________ 4 Present investigation...._.________.____.___________.___._-___.- 5 Acknowledgments. _ ___________________________________________ 7 Geologic appraisal, by T. A. Steven and L. J. Schmitt, Jr______________ 8 Precambrian rocks.____________________________________________ 8 Sedimentary rocks.____________________________________________ 10 Volcanic rocks________________________________________________ 14 Source areas______________________________________________ 14 Volcanic succession._______________________________-------- 15 Mineral resources__.____ _ ____________________________^__-___- 25 Sampling and analytical techniques.__________________---_--- 27 R6sum6 of stream-sediment sampling program________-__----- 29 Crystal Valley-Missouri Gulch area (table 3-A)______-_--- 30 Needle Creek drainage (table 3-B)_________-_--------_- 31 Johnson Creek-Grizzly Gulch area (table 3-C)__________ 32 Ruby Creek drainage (table 3-D)_____-__---_----------- 33 Noname Creek drainage (table 3-E)_____________^______- 33 Leviathan Gulch and Sunlight Creek (table 3-F)__:______. 34 Tenmile Creek drainage (table 3-G)__________-_-_---__-- 34 Elk Creek drainage (table 3-H)___-__.___---------------- 35 Whitehead Gulch drainage (table 3-1)_________-_-____--- 35 Vallecito Creek drainage (table 3-J)____________-_-_--__- 36 Rock Creek, Lake Creek, and Flint Creek drainages (table 3-K, L, and M)______._._ ._._____.___ ..-__.-_..-_- 37 Los Pinos River drainage (table 3-N)______________-_--_- 37 Ute Creek drainage (table 3-0)________._....-_--------- 38 Stream drainages in the central part of the primitive area (table 3-P through T)_____._________.,_-------------- 38 Streams draining the eastern part of the primitive area (table 3-U through Z, and AA through CC).__..._._.__ 39 Mineral resources of Precambrian age._______________________ 39 Placer gold potential in Precambrian conglomerates.-_-___- 40 Sulfide deposits in older Precambrian rocks ________________ 41 Iron resources in the Irving Formation, by Jacob E. Gair and Harry Klemic.____________________-__-----_----- 43 D escription of the Irving Formation __________________ 44 Iron-formation and similar laminated ferruginous rock.. 45 Analytical data.__________________________________ 47 Pyritic black slates.___________________________________ 50 VI CONTENTS Geologic appraisal Continued Mineral resources Continued1 Page Coal, oil, and gas potential._____-_--__-__---__-____________ F51 Deposits of unknown age.__________________________________ 52 Uranium deposits west of the Animas River._____________ 52 Runlett Park-Cave Basin area....______________________ 53 Mineralized fault near Milk Creek_______________________ 53 Possible mineral deposits of Late Cretaceous or early Tertiary age.___________________________________________________ 54 Mineralized areas associated with Tertiary volcanic activity.... 54 Needle Mountains mining district.______________________ 55 Hydrothermal alteration..._________________________ 57 Disseminated molybdenite in the intrusive center.____ 59 Vein deposits.______---____-_______-_-_____-____._ 62 Beartown mining district.________________N______________ 67 Whitehead Gulch area.________________________________ 72 Altered rocks along Ute Creek._________________________ 73 Native sulfur deposits..-------------------------------- 75 Central San Juan cauldron complex____________________ 77 Fault block mosaic._______________________________ 77 Rocks altered after eruption of the Carpenter Ridge TuflL._________________________________________ 79 Piedra Peak-Red Mountain area._____.--__.________ 79 Possible ore deposits at depth..-__._._._.______.________ 81 Economic appraisal, by M. J. Sheridan and F. E. Williams. ____________ 83 Claim coverage___-_-__________----------_-___________________- 84 Patented claims.__________________________________________ 84 Unpatented claims____-__-------_--_-__--_.______________ 84 Molas Lake and Deer Park-Whitehead Gulch areas._____________ 88 Elk Park area________________---_____--.__________________ 88 Beartown mining district._____-_---___-___-__-_--_-____.__---_- 89 Noname-Tenmile Creek area____-_-__-_-_-_____-_-_-__-___--__ 90 Needle Mountains mining district.______________________________ 90 Description of workings.___________________________________ 94 Vallecito Creek-Emerald Lake area._____________________________ 109 Cave Basin area_______________________________________________ 113 Rio Grande Reservoir area._________-___-_______-_-_-_-___-_-_- 113 Trout Creek-Middle Fork Piedra River area._____________________ 114 Piedra Peak area_________-___-_-------------------_--___------ 118 References cited.-________________-___-____-_____---__----_____--_- 118 Index. ............................................................ 179 CONTENTS VII ILLUSTRATIONS Page PLATE 1. Geologic map of the San Juan primitive area.___________ In pocket 2. Map showing U.S. Geological Survey sample localities in the San Juan primitive area.__.___-__--_____-____-___-_ In pocket FIGURE 1. Index map of Colorado, showing area of this report_______-_. F3 2-11. Maps showing: 2. Relation of the San Juan primitive area to nearby areas with numerous mines and prospects_--____- 4 3. Relation of the San Juan primitive area to main mineralized areas.-..-_________________________ 26 4. Geology of the Irving Peak-Emerald Lake area.____ 44 5. Alteration minerals in rocks of the Chicago Basin area, ____,___________-___-___-__--__--__-___-_ 58 6. Distribution of major veins and fissure zones in the Needle Mountains mining district.._-__________-- 64 7. Distribution of geologic units in the Beartown mining district. --___-___-__-__--__-__.____---_--__-__ 68 8. Mineral areas studied in relation to the San Juan primitive area._________________________________ 85 9. Claims in the Molas Lake, Deer Park-Whitehead Gulch, and Elk Park areas, and the Beartown mining district_______________________________ 86 10. Claims in the Noname-Tenmile Creek area and the Needle Mountains mining district._________....___. 87 11. Location of mine workings, Needle Mountains mining district._-_____-_._____________,_____-_____--- 91 12-16. Photographs: 12. Chicago Basin (eastward view, toward Columbine Pass)-----__--_-____----_----___---_---------- 93 13. Intrusive in Chicago Basin_-----____--___-_---__-- 100 14. Aetna mine on the Aztec vein____________________ 101 15. Part of Pittsburg mine, showing vein extending over the crest_____________________________-_-_---_- 106 16. Pittsburg shaft, showing vein structure.___________ 108 17-19. Maps showing: 17. Claims in the Vallecito Creek-Emerald Lake and Cave Basin areas_____________-__--___-__._________ 110 18. Claims in the Rio Grande Reservoir area____._--_ 114 19. Claims in the Trout Creek-Middle Fork Piedra River and Piedra Peak areas.________.__--__--_-_-___- 115 20. Photograph of Arizona-Colorado Cattle Co. drill site.------- 116 VIII CONTENTS TABLES Page TABLE 1. Stratigraphic succession in the San Juan Basin near the San Juan primitive area.___________________________________ Fll 2. Volcanic succession in the San Juan primitive area.._-._--- 16 3. Analyses of stream-sediment samples._____________________ 122 4. Abundance of major oxides in samples of magnetite iron- formation, amphibolitic schist, and greenstone of the Irving Formation, Hinsdale and La Plata Counties, Colo.,