r.s'AV-V/. .I/ AT. I AN 



157 



UK nt dejM>sits of impregnations in a shear zone in slate* 



ami nr:iy\\:ickes. 



(3) The Copper River district is near Mount WrungeM- The 

 One are chaloodte and Komite associated with pyrrlmtite and 

 magnetite MS di emin:iti<.n deposits in masses of nn-rn-tnin-. 



(4) The Kotsina district is -incited some little di>t:mcc in- 

 from the coast. The chief copper mineral is chalcocite. 



Limestone Schist A Granite Copper I 



AQuartzite Greenstone 



FIG. 96. Sketch map of the Copper Mountain district. Prince of Wales 

 Island, Alaska. (After F. E. and C. W. Wright, U. S. Geological Survey.) 



The ore is found as replacement deposits in the Triassic lime- 

 stones associated with the earlier greenstones. 



The Geographical Horizon. Copper ores are not restricted 

 to the rocks of any particular age. They occur in all hori/.on- 

 up to the Tertiary, but the ores are especially abundant in the 

 older formations as the pre-Cambrian, Cambrian and Ordovician 

 terranes. 



Methods of Extraction. (1) The Reduction Process. Copper 

 is extracted from its carbonates and oxides by means of roasting 



