Vol. 4] 



Knopf. — Foothill Copper Belt. 



415 



ing schists, is reported from here. Amphibolite schist is the pre- 

 vailing country rock, but numerous lenses of quartz porphyry 

 schist occur in the immediate vicinity. 



Valley View Mine. — The gossan deposit here has been worked 

 for gold during many years.* At greater depth chalcopyrite and 

 covellite were struck. Development is in active progress. 



The gossan occurs in a quartz porphyry schist lens, some three 

 hundred feet wide and nearly a thousand feet long, intercalated 

 in the prevailing amphibolite schists. 



Cedar Mine, near Wolf Creek. — The country rock is meta- 

 andesite and augite porphyry tuff, roughly schistose N. 60° 

 W. The ore is chalcopyrite in a gangue of quartz and calcite. 

 The vein is a strong fissure vein, about 20 feet wide, breaking 

 at right angles across the country. Inclusions of country rock 

 omir in the gangue. The property is at present idle. 



Two miles south of this is the Ace Mine, also idle. The shafts 

 are sunk upon a mineralized shear zone in the otherwise massive 

 meta-andesite. 



CAMPO SECO, CALAVERAS COUNTY. 



Just west of the Campo Seco copper mines is a belt of black 

 clay slates (Upper Jurassic aget). Passing eastward across the 

 strike these graduate by an easy transition, as seen at the old 

 engine house, into tuffs and coarse breccias, more or less schistose. 

 A typical specimen of these greenstone schists examined micro- 

 scopically showed a large abundance of chlorite and epidote, 

 especially the latter, and a few small plagioclase feldspars. Inter- 

 calated with these breccias are some green glossy slates, well 

 exposed along the Mokelumne Kiver. In this section they are 

 found to be irregularly layered, consisting of calcite and chlorite. 

 A little quartz was noted, as also some clouds of magnetite dust. 

 These rocks, therefore, represent metamorphosed calcareous tuffs. 

 The breccias are frequently quartz-bearing, and are probably the 

 ejectments of a dacitic magma. Their thickness is 1000 feet. 



These are succeeded by quartz porphyry flows, which in turn 

 are succeeded by schistose greenstone breccias. To the eastward 



* W. Lindgren, Sacramento Folio, 

 t H. W. Turner, Jackson Folio. 



