154 



ECONOMIC GEOLOGY 



of copper in this western belt. The most important field is near 

 the northern end of the Sacremento Valley in Shasta County. 

 The ore occurs in Permo-Carboniferous and Triassic lavas and 

 tuffs. The ores are of the sulphide type and the lodes vary from a 

 few inches to hundreds of feet in width. 



Chalcopyrite, chalcocite and bornite occur in the Iron Moun- 

 tain district as impregnation deposits in a zone of crushed brec- 

 cias in rhyolite. Chalcopyrite, pyrite, quartz and barite occur 

 in the Bully Hill district in a sheared zone following a dike of 



Schia* 



FIG. 93. Ferris-Haggerty mine, Bonauza stope, Encampment district, 

 Wyoming, showing form of the ore body. (After A. C. Spencer, U. S. 

 Geological Survey.) 



diabase. The ore lies either in the dike or at the contact with 

 rhyolite. Chalcopyrite and pyrite occur in lens-shaped masses 

 in the metamorphic slates and schists in the foothills of the Sierra 

 Madre Mountains. 



The Bingham Disrtict, Utah: According to E. T. Hancock, 

 this field includes an oblong area of about 24 square miles. It lies 

 between the Jordon Valley on the east and the Oquirrh range of 

 mountains on the west. The terranes are Carboniferous quartz- 

 ites and limestones that have suffered extensive intrusion, intense 

 fissuring, and partial burial beneath an andesite flow. The ore 



