Geology and Ore Deposits of the Upper Blue River Area Summit County Colorado • By QUENTIN D. SINGEWALD . GEOLOGICAL SURVEY BULLETIN 970 Prepared in cooperation with the Colorado Geological Survey Board and the Colorado Metal Mining Fund UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1951 UNITED STATES DEPARTMENT OF THE INTERIOR Oscar L. •chapman, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director F.~r sale by the Superintendent of Documep.ts, U. S. Government Printigg Office · . Washin~ton 25, D. C. - Price $1.75 (paper-cover)" · CONTENTS Page­ Abstract ____ .. ______ ... _ .. _______________________ .. __ .. _ .. ______________ _ l Introduction .. ______ ... - _______________________________ ··- _____________ _ z Unconsolidated depm::itH ______________________________ .. ______________ _ 4 Bedrock ____ .. ______ .. _ ... ___ .. ________________________ .. ______________ _ 5 Pre-Cambrian rockk __ ···- ________________ ------ -··· ___________ --- _ 5 Idaho Springs formation ____________________ .. ______________ _ 5 Grantie _________________________________________________ _ 7 P'eg1natite_ ... _ .... ____________________________ .. ______________ _ 8 Pre-Pennsylvan:inn Bedimentary rocks ____________ -··· ______________ _ 8 Pennsylvanian nnd Permian sedimentary rocks. ___ ... _ .. ____________ _ 10 Southwest of Boreas Pass fault_ _____________ ·--------------- 10 Northeast of BJreas Pass fault _______________ ·--------------- 13 Mesozoic sedimentary rocks ______________________ ... ______________ _ 13 Late Cretaceous or early Tertiary igneous rocks .. __ ... __ .. ___________ _ 14 F'orm ·and c:lassification ______________________ ... ______________ _ 14 Monzonite porphyry_-· ________________ .. __ -·_ ... _______ - _- _- __ _ 15 Q~uartz momwnite porphyry ______________ --·- ... _______ - __ --- __ 15 L,ineoln porphyry-~ ___________________ ··---·_ ... -·- __ ---- ______ _ 15 Granodiorite __ .. ______________________ .. ____ ... ______________ _ 16 White porphyry _____ -· ________________ .. _· ___ ... _ .. _________ - __ _ 16 Contact met.au.orphism _____________________ . ______________ _ 16 Structure __________ -·_-· ________________________ .. __ .. _ ... _ .. ____________ _ 17 Pre-Cambrian stmcture __ -· ________________ ··- ___ ... ______________ _ 17 Laramide structure .. _____ -· ________________ .. __ .. _. ______________ _ 18 General features _____ -· __________ .:. _____ ··- ___ .. _________ -_---- 18 Structure of Hoosier Pass area _________ .. ____ . _____ - _- _---- __ 19 Boreas Pass fault and associated transverse faults ____________ _ 21 Major faults north of Breckenridge ___________ ,_______________ _ 23 Transverse heli. of major faults _______________ ---------------- 24 Minor faults_ .. ______ .. ___________________ .. _ . ______________ _ 26 Theoretical ana.lysis ____________________ .. ____ ... ______ -.- __ - _- __ 26 Ore deposi t.s _________ .. ____________________________ .. ______________ _ 27 Output and his tory. ________________________ ·- __ ... _.... ____ - _---- __ 27 Geographic distribution. __________________ . _ ·- __ .. _.... ___________ _ 28 Western min ernlized area___ ~ _____________ .. _ ... ___ ·- ______ - ____ _ 28 Structural controL ________________ .. ____ .. _______________ _ 28. Zonal pa, tt1~rn ____________________ .. _____ ... _ ·- .. _________ ~ __ 29 lVIegaseopb mineralogy of ores __________________________ _ 30 Form nnd stratigraphic relations of ores_. _______________ .: __ _ 31 Eastern min 1~ralized area. _____________ .. ____ ... _.... ____ - _ - --- __ 32 Structural control ________________ .. ____ ... _.. ·- __ - __ _ --.:- __ 32 Megascopi 3 mineralogy and zonal pattern____ .. ___________ _ 33 Form nnd 'ltratigraphic relations of ores ___ -···------------- 34 Suggestions for proE'pecting ________________ .. __ .. _ .. _ .. __ _ ------..:-_- 35 General arell1.s __ .. ______________________ .. ____ .. - .... - ---- - - - -·- -- 35 Western minenLlized area ______________ .. ____ .. _.... ________ --- _ 35 Eastern minmalized area ______________ .. ____ ... _ .. _____ ------- _ 36 III IV CONTENTS Page ~ine descriptions-------------------------------------------------- 37. ~onte Cristo Gulch ___ ---------------------------------------- 37 Lingmine------------------------------------------------ 37 Arctic mine ______________________________________________ _ 38 Senator mine _____________________________________________ _ 40 Vanderbilt mine __________________________________________ _ 42 El Dorado mine ______________________ • ..: __________________ _ 45 Monte Cristo mine __________ ------________ -----__________ _ 46 Bemrose mine ____________________________________________ _ 47 Adit located three-quarters of a mile north-northeast of Hoosier Pass----------------------------------------------~---- 49 ~cCullough, Spruce, and Carter Gulches ________________________ _ 50 Briar Rose mine ___________________ -----__________________ _ 50 Solitary and Big Bonanza mines ________ _; ___________________ _ 52 Last Dollar mine_------ ___ ------_________________ -----___ _ 52 Diamond Jack mine ____________ -----________ --------______ _ 53 Little Fool property __________________ ----_________ -----__ _ 54 Governor mine ___________________________________________ _ 55 East side of Blue River ValleY---------------------------------- 56 Fredonia mine ___________ ------_____ -----______ ------____ _ 56 Location, output, and character of ore __________________ _ 56 Geologic setting __________________ ---- ___ --------_____ _ 57 Rocks cut by mine workings---------------------------- 58 Geologic structure ____ ------______ --------__ ----______ _ 59 Ore bodies ___________________________________________ _ 60 Derilla and Hunter Boy workings---------------------------- 60 Indiana Gulch ________________ .________________________________ _ 61 Warrior's Mark mine ______________________________________ _ 61 Seven-Thirty mine ______________________ ------------------_ 63 Twin Sisters mine __ --------------------------------------- 65 Mountain Pride mine _____ .._ _________________ -----~- ___ ----_ 67 Shock Hill---------------------------------------------------­ 70 Iron Mask mine------------------------------------------- 70 Brooks-Snider mine _____ ----________________ -------------__ 70 Literature cited _______ ---------------________________ -----------__ 72 Index •• ---------------------------------------------------------- 73 ILLUSTRATIONS PLATE 1. Geologic map and sections of the upper Blue River area, Summit County, Colo ______________________________ In pocket 2. Map showing major faults, main veins, and general character of ores in upper Blue River area _____________________ In pocket 3. Map and section of part of the workings of the Ling mine__ In pocket · 4. Plan and section of Senator mine---------------------- In pocket 5. Plan of Last Dollar mine ______________________________ In pocket 6. Plan and sections of Predonia mine ___________________ "".. In pocket 7. Map of Warrior's Mark mine __________________________ In pocket CONTENTS V Page FIGURE 1. Index map showing position of upper Blue River area________ 3 2. Diagrammatic sketch of area between Alma and Breckenridge, showing alternative possible location of the postulated fault that explains reverse dips and areal distribution of strata along Hoosier Pass structure ________ --·-------------- ___ _ 20 3. Plan and section of Arctic mine _____ -··-··-- __ --------- ____ _ 39 4. Plan of workings of Vanderbilt mine--··-··------------------ 43 5. Plan of :E:l Dorado tunneL ________ --·--··----- _____ ----- __ _ 45 6. Plan of llO-foot level, Bemrose shaft _____________________ _ 48 ,,. 7. Plan of adit located 0.73 mile N. 36° W. of U. S. L. M. Hoosier _________________________ .. _.. _________________ _ 49 8. A1·eal geology at Briar Rose mine __________________________ _ 50 9. Plan and section of Briar Rose mine __ ,____________________ _ 51 10. Map of Solitary and Big Bonanza mines at upper lake in Crystal Gulch ______________________ ·-- ______ -------- __ _ 53 11. Plan of upper adit at Little Fool property _________________ _ 54 12. Plan of north (main) tunnel of Governor mine _____________ _ 56 13. Plan of Derilla and Hunter Boy workings __________________ _ 61 14. Plan and section of part of Seven-Thirty mine _____________ _ 64 15. Plan of Twin Sisters mine------------·-·------------------- 66 16. Map and section of Mountain Pride mine _________________ _ 68 17. Map of lower (main) tunnel of Iron M.ask mine ____________ _ 69 .. GEOLOGY AND ORE DEPOSITS OF THE UPPER BLUE RIVER AREA, SUMMIT COUNTY, COLORADO BY QUENTIN D. SINGEWALD ABSTRACT The upper Blue River area includes 85 square miles in Summit County. It is partly surrounded by the Breckenridge, Kokomo, Climax, Alma, and Beaver­ Tarryall mining districts of central Colorado. It has yielded more than a million dollars' worth of metals, chiefly gold and silver. This area was studied during 5 months of 1940 and 1941 as one of the cooperative projects of the United States Geological Survey, the Colorado Geological Survey Board, and the Colorado Metal Mining Fund. Unconsolidated deposits are widespread. 'l"hough locally rich in placer gold, they conceal many stratigraphic and structural featm·es of the bedrock that might leacl to discovery of ore bodies. Terrace gravel, moraine, and alluvium have been mapped, but talus and slide rock have not been mapped. The bedrock comprises five main groups of rocks-pre-Cambrian, pre­ Pennsylvanian sedimentary, Pennsylvanian and Permian sedimentary,