212 KEMP'S GEE DEPOSITS. 



2.09.15. Park County, which lies east of Lake County and 

 embraces the South Park, has some mines on the eastern slope of 

 the Mosquito range, and in the Colorado range, to the northwest. 

 The latter are similar in their contents to the Georgetown silver 

 ores, mentioned under Clear Creek County, but the former are 

 bodies of argentiferous galena and its alteration products in lime- 

 stone and quartzite. Pyrite is also abundant, and at times a gangue 

 of barite appears. The mines are in the sedimentary series, resting 

 on the granite of the Mosquito range, and are pierced by por- 

 phyry instrusions, as at Leadville. The placer deposits at Fair- 

 play deserve mention, as it was from these that the prospectors 

 spread over the divide to the site of Leadville in I860. 1 



2.09.16. Chaffee County, on the south, contains the iron mines 

 referred to under Example 12d. There are some other gold-bearing 

 veins near Granite and Buena Vista. The lead-silver deposits of 

 the Monarch district are mentioned under Example 30ft. In 

 Huerfano County, in the Spanish Peaks, veins of galena, gray 

 copper, etc., are worked to some extent. 2 



2.09.17. Rio Grande County. In the Summit district are a 

 number of rich gold mines, of which the Little Annie is the best 

 known. The gold occurs in the native state, in quartz on the con- 

 tact between a rhyolite and trachyte breccia and andesite. The de- 

 posits are thought by R. C. Hills to be due to a silicification of the 

 rhyolite along those lines, probably by the sulphuric acid, which 

 brought the gold. Then the rocks were folded. Oxidation and 

 impoverishment of the upper parts followed, forming bonanzas 

 below. The paper has a very important bearing on the formation 

 of many replacements. 3 



2.09.18. Conejos County. Some deposits of ruby silver ores 

 have recently been developed in this county, near the town of 

 Platoro. The county lies near the middle of the southern tier. 



2.09.19. Custer County affords some of the most interesting 

 deposits in the West. Rosita and Silver Cliff are the principal 

 towns and are situated in the Wet Mountain Valley, between the 

 Colorado range on the north and the Sangre de Cristo on the 



1 J. L. Jernegan, "Whale Lode of Park County," M. E., III. 352. 



2 R. C. Hills, "On the Eruption of the Spanish Peaks," Proc. Colo. 

 Sci. Soc., III., pp. 24, 224. 



8 R. C. Hills,. Proc. Colo. Sci. Soc., March, 1883. Abstract by S. F. 

 Emmons in the Engineering and Mining Journal, June 9, 1883, p. 332. 



