422 



University of California Publications. 



[Geology 



place, shearing the ehalcopyrite and plating the foliation planes 

 of the chlorite schist with yellow mineral. 



The introduction of the ore has been subsequent to the latest 

 intrusive, for the quartz monzonite is often impregnated with 

 ehalcopyrite, especially along fracture zones. The amygdules of 

 the flows west of Copperopolis occasionally show a speck of 

 ehalcopyrite in the interior of the solid filling. 



NAPOLEON MINE, CALAVERAS COUNTY. 



The Napoleon mine is six miles southwest of Copperopolis. 

 The section between them is composed largely of the meta- 

 andesites, including, however, about 5000 feet of Upper Jurassic 

 clay slates and an intrusive mass of granodiorite. 



The prevailing rock in the vicinity of the Napoleon mine is 

 a massive quartz porphyry whose characteristic feature is its 

 abundance of glassy quartzes in an aphanitic base of flinty 

 appearance. The microscopic petrography of this rock shows 

 numerous idiomorphic quartz phenocrysts, often affected by 

 magmatic corrosion, and a large number of porphyritic feldspars, 

 untwinned, turbid, opaque, and frequently containing much sec- 

 ondary epidote. Femic constituents were nearly absent, and are 

 now represented by chlorite. The groundmass is a microcrystal- 

 line assemblage of feldspar, quartz and minute spherulites. 



Two thousand feet east of the shaft the tuffs, breccias, 

 amygdaloids, and porphyries of the meta-andesite series appear in 

 great thickness. In the immediate vicinity of the mine is an 

 intercalated flow of hornblende andesite, which having a thick- 

 ness of about a hundred feet at the hoisting shaft, rapidly thick- 

 ens towards the southeast to 500 feet. The distinguishing fea- 

 tures of this rock are the presence of hornblende prisms and the 

 great abundance of calcite amygdules. Certain highly feld- 

 spathic facies are associated with the hornblende andesite. The 

 quartz porphyry where resting upon the andesite was found to 

 show a narrow chilled selvage against a scoriaceous amygdaloid. 



The lode lies along the contact of the feathering end of the 

 andesite flow with the quartz porphyry. This contact has been a 

 locus of exceptional dynamic activity, along which the horn- 

 blende andesite has been reduced to a chlorite schist, and the 



