Abstract ........................................................ 1
Introduction .................................................... 2
History and Production .......................................... 5
Stratigraphy ................................................... 10
Proterozoic Metamorphic Rocks ............................... 10
Uncompahgre Formation .................................... 10
Paleozoic Sedimentary Rocks ................................. 11
Elbert Formation ......................................... 11
Ouray Limestone .......................................... 14
Leadville Limestone ...................................... 14
Molas Formation .......................................... 15
Hermosa Formation ........................................ 16
Cutler Formation ......................................... 16
Mesozoic Sedimentary Rocks .................................. 17
Dolores Formation ........................................ 18
Entrada Sandstone ........................................ 18
Wanakah Formation ........................................ 18
Pony Express Limestone Member ......................... 19
Bilk Creek Sandstone Member ........................... 19
Unnamed Upper Member .................................. 19
Morrison Formation ....................................... 19
Tidwell Member ........................................ 20
Salt Wash Member ...................................... 21
Brushy Basin Member ................................... 21
Dakota Sandstone ......................................... 21
Mancos Shale ............................................. 23
Tertiary Rocks .............................................. 23
Telluride Conglomerate ................................... 23
San Juan Formation ....................................... 23
Quaternary Deposits ......................................... 26
Intrusive Rocks ................................................ 27
Diabase ..................................................... 27
Porphyritic Granodiorite .................................... 28
Altered Porphyritic Rocks ................................... 32
Clastic Dikes ............................................... 33
Porphyritic Andesite and Quartz Latite ...................... 34
Structure ...................................................... 36
Proterozoic Structure ....................................... 36
Paleozoic Structure ......................................... 39
Southern Block ........................................... 40
Northern Block ........................................... 41
Mesozoic Structure .......................................... 43
Folding and Tilting ...................................... 44
Faulting and Fracturing .................................. 44
Structure of Intrusive Bodies ............................ 46
Dikes and Sills ....................................... 46
Stocks and Plugs ...................................... 47
Laccoliths ............................................ 49
Ore Deposits ................................................... 50
Distribution and General Relations .......................... 50
Late Cretaceous to Early Tertiary Ore Deposits .............. 51
Structural Classification and Control .................... 54
Northern Sector ....................................... 56
Western Sector ........................................ 58
Southern Sector ....................................... 59
Eastern Sector ........................................ 61
Late Tertiary Ore Deposits .................................. 61
Rock Alteration ................................................ 62
Alteration of Sedimentary Rocks ............................. 63
Alteration of Igneous Rocks ................................. 64
Wall-Rock Alteration of High-Temperature Veins .............. 65
Wall-Rock Alteration of Other Ore Deposits .................. 66
Source of Altering Fluids ................................... 67
Rock Alteration Compared With Late-Stage Igneous-Rock
Crystallization .......................................... 68
Rock Alteration Compared With Clastic Dike Formation ..... 70
General Conclusions ......................................... 70
Paragenesis of Primary Ores .................................... 71
Normal Mineral Sequence ..................................... 71
Hydrothermal Leaching ....................................... 72
Open-Space Filling .......................................... 74
Sulfide Paragenesis ......................................... 75
Carbonate Paragenesis ....................................... 77
Descriptions of Mines .......................................... 77
Mineral Farm Mine ........................................... 77
Location, History, and Development ....................... 77
Production ............................................... 79
Geology .................................................. 80
Mineralogy and Origin of the Orebodies ................... 82
Source of Mineralizing Solutions and Zoning Along the
Ore Channel in Depth ..................................... 83
American Nettie Group of Mines .............................. 83
Location, History, and Development ....................... 83
Geology .................................................. 86
Structure ................................................ 86
Form and Origin of the Orebodies ......................... 88
Extension of the Ore Channel at Depth .................... 91
Bachelor Group of Mines ..................................... 92
Location, History, and Development ....................... 92
Production and Grade ..................................... 94
Geology .................................................. 94
Sequence of Vein Formation ............................... 96
Localization and Form of Ore Shoots ...................... 97
Calliope Mine ............................................... 98
Location, History, and Development ....................... 98
Geology .................................................. 98
Localization and Form of Ore Shoots ...................... 99
Mineralogy of the Vein ................................... 99
Newsboy Mine ............................................... 100
Location, History, and Development ...................... 100
Production .............................................. 100
Geology ................................................. 101
Mineralogy .............................................. 101
Señorita Mine .............................................. 101
Location, History, and Development ...................... 101
Production .............................................. 102
Geology ................................................. 102
Mineralogy .............................................. 102
References Cited .............................................. 103
Plates
[in pocket]
1. Geologic sections in Uncompahgre mining district
2. Plan maps and sections of American Nettie group of mines
3. Plan and structure contour maps of American Nettie group
of mines
4. Plan map and sections of Bachelor group of mines
5. Maps and sections of Calliope mine
6. Plan maps and sections of Newsboy mine
7. Plan map and sections of Señorita mine
Figures
1. Index map of southwestern Colorado ........................ 3
2. Photograph showing environs of town of Ouray .............. 4
3. Graph of metal-production values ......................... 10
4. Generalized geologic map of area ......................... 12
5-6. Photographs showing-
5. Angular unconformity on Proterozoic rocks ................ 13
6. Angular unconformity in The Amphitheater ................. 17
7. Sketch showing gypsum in Pony Express Limestone Member
of Wanakah Formation ..................................... 20
8. Lithologic profiles of Dakota Sandstone .................. 22
9. Photograph of sawn slab of San Juan Formation ............ 24
10. Total alkali-silica variation diagram .................... 26
11. Photograph of The Amphitheater ........................... 27
12. Outcrop distribution map of intrusive rocks in area ...... 30
13. Ternary plot of intrusive-rock analyses .................. 32
14. Generalized cross section of Dexter Creek laccolith ...... 32
15. Photographs of sawn slabs of intrusive clastic dikes ..... 35
16. Section showing probable direction of Bachelor clastic
dike injection ........................................... 36
17. Photograph looking along Calliope dike in Dexter Creek
valley ................................................... 37
18. Generalized structural features map of area .............. 38
19. Cross sections in southern part of district .............. 40
20. Photograph of west wall of Uncompahgre canyon ............ 43
21. Location map of mines, prospects, mills, and hot spring
in the district .......................................... 52
22. Section showing structural control of ore deposition
in American Nettie-Wanakah flexure ....................... 56
23. Sections showing ore deposition in veins south of
Dexter Creek ............................................. 58
24. Plan and section of the Rock of Ages mine ................ 60
25. Photographs of sawn slabs of mineralized rock in Dexter
Creek area ............................................... 67
26. Diagram showing paragenetic relations of minerals in
porphyritic granodiorite ................................. 69
27. Camera lucida drawing of polished section ................ 76
28. Plan and section of Mineral Farm mine and orebody ........ 78
29. Section through Mineral Farm mine ore channel ............ 80
30. Plan of Mineral Farm mine ore channel .................... 81
31. Sketch of American Nettie mine on canyon wall ............ 83
32. Generalized section of cliff face at American Nettie
mine ..................................................... 84
33. Diagrammatic sketch of splitting of Calliope vein ........ 98
Tables
1. Ouray County production ................................... 6
2. Uncompahgre district production ........................... 9
3. Chemical analyses of carbonate rocks ..................... 13
4. Partial chemical analyses of carbonate rocks ............. 14
5. Chemical analyses of volcanic rocks from the San Juan
Formation ................................................ 25
6. Analyses of hot-spring deposits and water ................ 28
7. Chemical analyses of granodiorite ........................ 31
8. Calculated mineralogical analyses of granodiorite ........ 32
9. Chemical analyses of altered porphyritic rocks ........... 33
10. Chemical and spectrographic analyses of Tertiary dikes ... 37
11. Late Cretaceous to early Tertiary principal ore and
gangue minerals .......................................... 53
12. Late Tertiary principal ore and gangue minerals .......... 62
13. Carbonate mineral analyses ............................... 77
10. Early production values at Mineral Farm mine ............. 79
15. Early production values at American Nettie mine .......... 84
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