166 



UNITED STATES MINERAL RESOURCES 



"1 — r 



"1 — \ — I — \ — 



Economic boom- 



01 01 



Figure 21. — U.S. primary copper production, 1850-1970. 

 Notes indicate major new sources, developments, or events. 



Average annual price 



in cents per pound Average grade of 

 Year Quoted refinery Equivalent ore mined 



1970 dollars (percent copper) 



1900 16.19 63.5 4.0 



1910 12.73 43.5 1.88 



1920 17.45 30.0 1.63 



1930 12.98 32.5 1.43 



1940 11.29 29.5 1.20 



1950 21.32 30.0 .89 



1955 37.49 41.0 .83 



1960 32.05 36.5 .73 



1965 35.02 39.9 .70 



1970 58.20 58.2 .60 



Copper ores also contain other valuable recover- 

 able metals, and many ores mined chiefly for other 

 metals also contain recoverable copper. The 

 coproduct-byproduct recovery of copper and associ- 

 ated metals from ores depends upon the quantity of 

 metals present (grade) and the processes used in 

 recovering the principal values. Copper production 

 yields significant quantities of gold, silver, molyb- 

 denum, cobalt, zinc, lead, nickel, sulfur, tellurium, 

 selenium, rhenium, palladium, platinum, arsenic, 

 and iron. Selenium is an essential byproduct of cop- 

 per production, and rhenium is obtained from the 



molybdenum in porphyry deposits. Cobalt is derived 

 mainly from copper ores mined in Zaire. 



Several problems of major concern to copper pro- 

 ducers relate to protecting environmental qualities 

 while maintaining competitive costs. Copper smelt- 

 ers are under severe new or proposed restrictions 

 on sulfur emission, requiring major capital invest- 

 ment for control equipment. This stress may result 

 in the closing of some smelters and a shift to new 

 methods of hydrometallurgy. Surface restoration is 

 particularly difficult in copper mining because of 

 the finely powdered state of mill tailings and the 

 very high ratio of waste to produced metal. Water 

 pollution by mine and mill waste is a problem, and 

 particularly as many of the big copper deposits are 

 in arid regions, obtaining adequate water supplies 

 for mining and milling becomes more difficult. 



Several porphyry copper deposits in Arizona are 

 now being worked by in-place leaching methods 

 which greatly decrease the effect of copper extrac- 

 tion on the environment. The deposits are first cut 

 by a system of tunnels, then fractured by explosive 

 or hydraulic methods, and then leached by sulfuric 

 acid introduced through pipes to the upper part of 

 the deposit. The copper-rich fluids are withdrawn 

 from the lowest levels of mine workings, pumped 

 to the surface and the copper removed electro- 

 lytically. The main disadvantages of this method 

 are that only 50-60 percent of the copper in the ore 

 deposit can be recovered under present techniques, 

 and that all of the byproduct metals, such as molyb- 

 denum, gold, and selenium, are left in the rock dur- 

 ing the leaching process. 



GEOLOGIC ENVIRONMENT 



GEOCHEMISTRY AND ABUNDANCE 



Copper is a chemical element of group II-B of the 

 periodic table ; it has atomic number 29 and atomic 

 weight 63.546, consisting of the isotopes ''^Cu (69.09 

 percent) and '''^Cu (30.91 percent). It occurs in na- 

 ture as the native element, as compounds of Cu+^ 

 (ionic radius 0.54 A) and Cu+'- (ionic radius 0.81 A 

 for sixfold coordination). In the Cu+- state, as 

 shown particularly by naturally occurring sulfates 

 and phosphates, it is isomorphous with Zn (0.83 A), 

 Mg (0.80 A), and Fe+= (0.69 A). In sulfides, Cu+^ 

 is isomorphous with zinc (as in tetrahedrite), and 

 Cu+' with silver. Copper is a strongly sulfur-seeking 

 (chalcophile) element, and it tends to be concen- 

 trated in sulfide deposits ; in igneous rocks it occurs 

 mainly as finely divided sulfides, principally chalco- 

 pyrite and bornite. 



Estimates of the abundance of copper in the con- 



