186 KEMP'S ORE DEPOSITS. 



of argentiferous galena, pyrite, and blende, in beds of Upper Car- 

 boniferous limestone, on their contact with overlying, micaceous 

 sandstones, or with sheets and dikes of porphyry. The Carbonif- 

 erous limestones that contain the ores at Leadville extend both 

 north and south, and their equivalents occur also on the west 

 flank of the Sawatch range. Ten Mile is another productive por- 

 tion, north of Leadville and at a higher altitude. The strata are 

 enormously disturbed, and pierced even more than at Leadville 

 by sheets and dikes of porphyry. The ores are less oxidized and 

 more rebellious. The Robinson is the principal mine. 1 



2.08.10. Example 30#. Monarch District, Chaffee County. 

 Oxidized lead-silver ores in limestone. The .belt of limestones 

 south from Leadville contains some notable ore bodies in Chaffee 

 County. The Monarch district is the most important. It is situ- 

 ated at the head waters of a branch of the South Arkansas River. 

 The ore lies in limestones whose age is not yet accurately deter- 

 mined. The Madonna mine is the best known and has shipped 

 much ore to Pueblo. 2 



2.08.11. Example 30c. Eagle River, Eagle County. Galena 

 -and its alteration product, anglesite, in Carboniferous limestone, 

 on the contact between it and quartzite or porphyry. The mines 

 lie in the valley of Eagle River, on the western slope of the Con- 

 tinental Divide. The galena has changed to the sulphate, instead 

 of carbonate, probably having been less completely oxidized than 

 at Leadville, and marking the intermediate stage in the process. 

 The wall rocks lie quite undisturbed, having a low dip of 15 

 north, and not being faulted. Lying lower than the lead-silver 

 deposits, and in Cambrian quartzite, on the contact with an 

 overlying sandstone are found chutes carrying gold in talcose 

 clay. 3 



2.08.12. Example 3Qd. Aspen, Pitkin County. Bodies of 



1 S. F. Emmons, Tenth Census, Vol. XIII., p. 73 ; also a forthcoming 

 monograph of the U. S. Geol. Survey. 



2 S. F. Emmons, Tenth Census, Vol. XIII., p. 79. Rep. Director of 

 the Mint, 1884, p. 191. 



8 S. F. Emmons, " Notes on Some Colorado Ore Deposits," Colo. Sci. 

 Soc., Vol. IL, Part II., p. 100. E. E. Olcott, "Battle Mountain Mining 

 District, Eagle County, Colorado," Engineering and Mining Journal, 

 June 11, 1887, pp. 417, 436; Ibid., May 21, 1892, p. 545. G. C. Tilden, 

 "Mining Notes from Eagle County," Ann. Rep. Colo. State School of 

 Mines, 1886, p. 129. 



