Copper Deposits of Arizona

Abstract

A VERY complete and highly interesting monograph on the copper deposits of Ray and Miami, Arizona, by Mr. F. L. Ransome has just been issued by "the United States Geological Survey as Professional Paper 115. These ore-bodies have rapidly attained first-class importance among the great copper producers of the United States. For a good many years, dating back to 1880, work had been carried on in this district, the small richer veins being worked and a fair amount of copper won, but these deposits were not of a permanent character. About 1905 the attention of mining men was directed to the low-grade disseminated ore of the region, and work on this commenced about 1911. Up to 1918 nearly 46,000,000 tons of this ore had been mined and 490,000 tons of copper produced. The reserves in one group of these mines, that of the Ray Consolidated Copper Co., were estimated in 1916 as more than 93,000,000 tons, averaging 2.03 per cent, of copper; those in the Miami mines at 50,000,000 tons, averaging 1.6 per cent.; and those in the Inspiration mine at 97,000,000 tons, carrying 1.63 per cent. The ore-bodies are large, irregular, flat-lying masses, and consist partly of Final schist and partly of granite and monzonite porphyry, carrying disseminated copper-ore, some being more or less uniformly distributed through the rock and some concentrated in threads or veinlets. The copper occurs principally as chalco-cite, Aough chalcopyrite is also met with. The ore-deposits have apparently been formed by a process of secondary enrichment upon rock that contained relatively little copper. The latter is termed by the author “protore,” and apparently contained from 0.4 to 0.8 per cent, of copper. This “protore”appears to have been formed by the action of thermal alkaline sulphide waters carrying copper in solution, and there is considerable evidence that the presence of great bodies of monzonite porphyry lying far deeper than the present ore-bodies were in some way connected with the presence of these hypogene solutions.