20 RESURVEY OF CRIPPLE CREEK DISTRICT. [BULL. 254. 



deep. Nothing of permanent value is recorded from Mineral Hill, 

 though fairly productive placers have been worked at its southwestern 

 base, almost in the town of Cripple Creek. 



On Carbonate Hill the Elkhorn has been a small producer; on Ten- 

 derfoot Hill the Friday, Hoosier, Black Diamond, and Mollie Kathleen 

 contribute their parts to the production. Two miles north-northwest of 

 Cripple Creek is the Galena mine, the vein of which follows, for a part 

 of its course, a phonolite dike in granite and has a small output to its 

 credit. About the same distance north of the city is the small volcanic 

 center of Copper and Rhyolite mountains. At the former the Fluorine 

 mine has produced $160,000, and low-grade ore is now being cyanided. 

 Prospects are found on Rhyolite Mountain, and in fact all over the flat 

 granite country between it and Trachyte Mountain. The Lincoln mine, 

 near Gillette, and several other prospects farther south, along a belt 

 of phonolite dikes, have produced a little ore. It is claimed that there 

 are low-grade veins on both sides of Bernard Creek, northwest of 

 Gillette, in a region of granite with occasional dikes and masses of 

 phonolite. Trachyte Mountain, southeast of Gillette, is covered by 

 phonolite, and a little ore is occasionally found in veins at its southern 

 foot. Some work has also been done on Cow Mountain, about 4 miles 

 northeast of Bull Hill. 



The eastern margin of the central volcanic area, east of Victor Pass 

 and extending southward across Big Bull Mountain to Brind Mountain, 

 has thus far failed to produce anything of importance, though well 

 covered by prospects. A survey of 'these outlying parts of the district 

 serves to emphasize strongly the remarkable concentration of deposits 

 within the narrow limits of the central volcanic area. 



CHARACTER OF THE ORES. 



The characteristic feature of the Cripple Creek ores is the occurrence 

 of the gold in combination with tellurium, chiefly as calaverite, but 

 partly also as the more argentiferous sylvanite, 05 and probably to a 

 minor extent as other gold, silver, and lead tellurides. The tellurides 

 are frequently associated with auriferous and highly argentiferous 

 tetrahedrite, with molybdenite, and occasionally with stibnite. While 

 these minerals have not yet been closely studied, preliminary examina- 

 tion indicates that their contents in gold are due to an intimate mechan- 

 ical mixture of tellurides. Pyrite, while widely disseminated through 

 the country rock and of common occurrence in the fissures, is rarely 

 sufficiently auriferous to constitute ore. Such of the pyritic ores as 

 have been tested reveal the presence of tellurium, indicating that the 

 ore is a mixture of pyrite and gold-silver tellurides. Galena and 



a Calaverite ( AuAg) Te2: tellurium, 57.4 per cent; gold, 39.5 per cent; silver, 3.1 per cent. Sylvanitc 

 (AuAg) Te 2 : tellurium, 62.1 per cent; gold, 24.5 per cent; silver, 13.4 per cent. 



