136 KEMP'S ORE DEPOSITS. 



2.04.04. Example IGb. Spenceviile, Cal. Beds of pyrites 

 with considerable chalcopyrite, in Jurassic slates, on the western 

 slopes of the Sierra Nevada. The Jurassic slates along the western 

 Sierras contain, in the gold belt, some interbedded deposits of py- 

 rite with considerable chalcopyrite intermingled. The most im- 

 portant are at Newton, Amador County, Copperopolis and Campo 

 Seco, Calaveras County, and Spenceviile, Nevada County. At the 

 first named there is a body of sulphides 7 to 8 feet wide and 

 proved about 400 feet. In the adjoining county of Calaveras, the 

 Union mine, at Copperopolis, is on a very large body of sulphides, 

 which impregnate the slates on each side without forming a very 

 sharp foot or hanging wall. The Campo Seco deposits are on the 

 same general line as the Copperopolis. The extension passes also 

 through those at Newton. A long distance north are the mines in 

 Spenceviile, Nevada County. The general geology is similar, and 

 the ore body large. It affords from 3.50 to 5.50# copper. All these 

 ores are worked by wet methods. 1 



NOTE. For Examples IQc and IQd see under "Nickel." 



2.04.05. Example 17. Butte, Mont. Veins originally fissures, 

 or shear zones, but greatly enlarged by replacement of the walls 

 with ore, filled with copper sulphides, bornite, chalcopyrite, etc., in 

 a siliceous gangue. Much silver is associated with the copper. At 

 Butte there is a north and south valley six miles wide between high 

 granite ridges on the east and lower rhyolite ridges on the west. 

 The bounding heights north and south are still farther distant. 

 Near the middle of this valley the butte of rhyolite arises which 

 gives the town its name. Silver Bow Creek, which gives the name 

 to the county, flows south along the eastern ridge and then bends 

 westward at a point south of the butte, and, after flowing directly 

 across the valley, leaves it through the western ridge. In the half 

 of the valley east of the meridian of the butte is a very dark basic 

 granite, and also in the extreme west. It consists of quartz, 

 orthoclase, plagioclase, and an unusual amount of mica, augite, and 

 hornblende. In the part west and south of the butte is a highly 



1 J. E. Ellis, "On the Spenceviile Mines," Mineral Resources U. S., 

 1884, p. 340. H. G. Hanks, Rep. California State Mineralogist, 1884, p. 

 148. J. B. Hobson, "On Spenceviile," Rep. California State Mineral- 

 ogist, 1890, p. 392. William Irelan, Jr., "On Calaveras County Mines," 

 Rep. California State Mineralogist, 1888, pp. 150-153. " On the Newton 

 Mines," ibid., p. 106. 



