190 KEMPS ORE DEPOSITS. 



To the north the mines at Woody are on a great fissure, according 

 to W. E. Newberry (private communication), which carries ore 

 where not filled "by a porphyry dike. They are of recent develop- 

 ment, but promise to be rich. Although further systematic study 

 is needed, it is quite clear that the ore bodies of Aspen Mountain 

 have originated by replacement of the blue limestone and by coat- 

 ing the fragments of brown dolomite. The solutions doubtless 

 came up along the fault fissures and selected the contact for the 

 chief point of deposition. The United States Geological Survey 

 has had a party in the region. 1 



2.08.16. Example 306. Rico, Dolores County. Contact de- 

 posits of lead-silver ores, in Carboniferous limestones, along intru- 

 sive porphyries. Considerable base bullion has been shipped. 

 There are coals in the vicinity, but the operation of the smelter 

 has been somewhat intermittent. The Newman Hill mines are 

 mentioned under " Silver." 2 



NOTE. Example 30f will be found after Example 31, which 

 has been inserted for geographical reasons. 



2.08.17. Example 31. Red Mountain, Ouray County. Oxi- 

 dized lead-silver ores passing in depth into sulphides, in large and 

 small cavities, in knobs of silicified andesite. The cavities have 

 a close resemblance to caves, but differ from ordinary caves in not 

 being in limestone. They permeate the mountain in an irregular 

 way, and mark the courses of old hot spring conduits. The ande- 

 site is generally altered to a mass of quartz, but the process is 

 thought by Mr. Emmons to have taken place at a considerable 

 depth, and that the quartz is a residual deposit left by the re- 

 moval of more soluble elements of the andesite. T. B. Comstock 

 regards them as hot spring deposits. 3 



1 D. W. Brunton, "Aspen Mountain: Its Ores and Mode of Occur- 

 rence," Engineering and Mining Journal, July 14 and 21, 1888, pp. 22, 42. 

 S. F. Emmons, "Preliminary Notes on Aspen," Proc. Colo. Sci. Soc., Vol. 

 II., Part III., p. 251. Rec. C. Henrich, "Notes on the Geology and on 

 Some of the Mines of Aspen Mountain," M. E., XVII. 156. A. Lakes, 

 " Geology of the Aspen Mining Region," Ann. Rep. Colo. School of Mines, 

 1886 W. E. Newberry, " Notes on the Geology of the Aspen Mining Dis. 

 trict," M. E., June, 1889. Rec. L. D. Silver, "Geology of the Aspen 

 (Colo.) Ore Deposits," Engineering and Mining Journal, March 17 and 24, 

 1888. 



2 M. C. Ihlseng, "Review of the Mining Regions of the San Juan, ' 

 Ann. Rep. Colo. School of Mines, 1885, p. 43. 



8 T. B. Comstock, " Hot Spring Deposits in Red Mountain, Colorado." 



