COPPER ORE IN DIFFERENT PARTS OF 

 THE COUNTRY. 



BY ARTHUR LAKES. 



[Arthur Lakes, geologist; late professor of geology at the Colorado state school of 

 mines ; he has made; exhaustive studies of gold and silver ores and is one of the leading 

 authorities on western ore deposits; he has written much for the technical and sci- 

 entific press, and is the author of Prospecting for Gold and Silver in North America, 

 Geology of the Colorado Coal Fields, Geology of Western Ore Deposits, etc.] 



In the granites and schists of the Atlantic coast, although 

 the range is generally mineralized and copper is distributed 

 here and there, only in a few places is it sufficiently concen- 

 trated to be of working value. In the northern region the 

 original unoxidized copper pyrites reach almost to the grass 

 roots and there is but little oxidized ore. But from Virginia 

 to Tennessee, where oxidation is great, decomposition, ac- 

 companied by a natural smelting and concentration of copper 

 ores, extends to considerable depths. Here we find a zone 

 of barren iron oxide derived from P5rrite, the leaching of 

 which furnished the copper to enrich the lower zone. 

 The vein resumes its true unaltered character as yellow cop- 

 per pyrites carrying a very small amount of copper, viz. 3 to 

 5 per cent, out of all proportion to the great expectations de- 

 rived from the rich copper concentrations in the oxidized zones 

 near the surface. 



In the Lake Superior region the ore occurs in beds in 

 trap and conglomerate. In Michigan the copper is in a 

 native state, probably derived from solution from oxidation 

 of copper sulphides in the underlying Huronian rocks. 



In the Keweenaw peninsula there are three classes of 

 deposits : (1) Well defined veins. (2) Copper in amygdaloidal 

 dikes. (3) Beds of conglomerate, the pebbles cemented to- 

 gether with copper. 



In considering the mode of occurrence of copper, the 

 main point to be kept in view is the change in character and 

 value of the ores as depth is attained, and as the oxidized 

 surface ores pass down into their unoxidized, normal, and 

 original condition. 



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