WORLD'S SUPPLY OF COPPER 



255 



At the present time the productive mines are located in 

 the conglomerate or in the diabase, the ore averaging from 

 six tenths to four per cent copper. The Calumet and 

 Hecla is the richest and largest of all the mines m this region. 

 This district has been an active producer for over fifty years 

 and still promises many years of productiveness because of 

 its favorable conditions for deep mining. 



The greatest development of the copper mining industry 

 in the United States came, however, with the opening of 

 the deposits in Arizona and Montana. The latter state now 

 produces about 43 per cent of the country's supply, Arizona 

 about 22, and the Lake Superior region 29. The following 

 table shows the share contributed by each state or territory 

 to make up the country's total: 



Montana's most productive mines are found near Butte. 

 The deposits occur as fissure veins in granite and consist of 

 bornite, chalcopyrite, chalcocite, and other sulphides. Im- 

 mense quantities of ore averaging as high as 40 per cent 

 copper have been found, but as the mines have been sunk 

 deeper there has been a gradual decrease in values. At pres- 

 ent the average is probably about 5 per cent. For several 

 years the Anaconda maintained a yearly output of over 

 100,000,000 pounds. 



Next in importance as a producing region comes Arizona, 

 with its deposits at Bisbee, Clifton and Globe. The Arizona 

 ores are carbonates, oxides and native copper. They are 

 found only in carboniferous limestone and porphjTy. The 



