588 



UNITED STATES MINERAL RESOURCES 



constitute important new silver sources in the 

 future. 



Few poi-phyry copper deposits are known in Asia 

 and Africa, and none are known or developed in 

 Europe. Extensive low-grade porphyry copper de- 

 posits in the Balkhash-Kourmadskiy area of the 

 eastern part of the U.S.S.R. contain silver, but only 

 the shallow enriched zones are productive at pres- 

 ent. A small but rich porphyry-type copper deposit 

 is being mined in syenitic rocks and carbonatite at 

 Palabora, northeast Transvaal, Republic of South 

 Africa. 



COPPER-ZINC-LEAD REPLACEMENT DEPOSITS 

 AND VEIN CLUSTERS 



Silver is an important byproduct or coproduct of 

 some copper-zinc-lead replacement deposits such as 

 at Butte, Mont., and in the Johnson Camp, Turquoise, 

 Banner, and Superior districts, Arizona. In these, 

 the copper generally is in a central zone which is 

 surrounded by low-temperature zones of galena and 

 sphalerite. At Butte, a peripheral zone contains 

 manganese. Silver is enriched in the peripheral zones 

 compared with the central copper zone. The ore 

 bodies may be veins; irregular, pipe-shaped, or 

 bedded replacements; or stockworks. The predomi- 

 nant primary copper mineral is chalcopyrite, al- 

 though bornite, chalcocite, covellite, djurleite, and 

 enargite are important minerals at Butte. 



Butte yielded more than 644 million ounces of 

 silver between 1880 and 1964 — the second largest 

 producer of silver, after Coeur d'Alene, in the United 

 States. The ore occurs in veins within the Boulder 

 batholith, with a central zone of copper deposits, an 

 intermediate zone of copper-zinc deposits, and a 

 peripheral zone with zinc, lead, silver, and man- 

 ganese deposits (Meyer and others, 1968). Total 

 production of silver at Butte has averaged about 2 

 ounces per ton of ore mined, about half of which is 

 from the central Berkeley Copper Pit, the remainder 

 from the outer part of the intermediate zone or 

 from the silver-rich copper-zinc-lead peripheral zone. 

 Total production at Butte has averaged about 1 

 ounce of silver for each percent copper, and current 

 production is about 0.3 of an ounce of silver for 

 each percent copper (Meyer and others, 1968, p. 

 1376). 



The copper and copper-zinc replacement deposits 

 in Arizona are mainly in limestone or altered lime- 

 stone host rock near granitic intrusive bodies. The 

 Magma mine has consistently produced 300,000 to 

 1 million ounces of silver annually from ore that 

 has averaged 1.93 ounces per ton (Hammer and 

 Peterson, 1968, p. 1286), largely from the steep, 



east-striking Magma vein. This vein has been de- 

 veloped over a strike length of 10,000 feet and to a 

 depth of 4,900 feet. 



The Kennecott copper mine in the Copper River 

 region, Alaska, produced about 12 million ounces of 

 silver during almost continuous operation from 1911 

 to 1938. The copper ores, which contained 14 to 16 

 ounces of silver per ton, occurred in replacement 

 veins, in irregular massive replacements, and in 

 stockworks in partly dolomitic beds in the Chitistone 

 Limestone of Triassic age, which overlies thick 

 copper-bearing basalts. The copper and silver was 

 mainly in chalcocite and covellite (Bateman and 

 McLaughlin, 1932). 



At Oilman, Colo., copper-silver-gold ores fill frac- 

 tures, coat vugs, and replace early massive pyrite 

 bodies in chimneys at the lower end of mantos. The 

 ores average 3.5 percent copper, 18.7 ounces of 

 silver, 0.08 of an ounce of gold per ton. 



In the southern part of the Tintic district in 

 Utah, copper-silver-zinc-lead deposits include fissure 

 veins and wallrock replacements of enargite, spha- 

 lerite, and silver minerals near Silver City, and the 

 great replacement pipes and mantos of copper- 

 arsenic-silver ores in the southern parts of the 

 Mammoth mine. 



In the Eastern United States, ores of this type 

 are uncommon, and but few are known. The Barrett 

 prospect. East Pembroke, Maine, is a stockwork of 

 copper-zinc-silver ore in metavolcanic rocks. In the 

 Linganore district of the Maryland Piedmont, chal- 

 copyrite and bornite containing some silver, and 

 locally argentian galena and sphalerite, are in veins 

 and replace marble along contacts with metavol- 

 canics. 



MASSIVE SUFIDE DEPOSITS 



The term "massive sulfide" as used here follows 

 the definition of Anderson and Creasey (1958, p. 

 96) : " * * * deposits consisting of a granular aggre- 

 gate of sulfide minerals such as pyrite, chalcopyrite, 

 sphalerite, and galena, with little or no visible 

 gangue minerals." Many contain pyrrhotite, mag- 

 netite, arsenopyrite, tetrahedrite, and barite, and 

 many contain silver and gold as important byprod- 

 ucts. The geology and genesis of massive sulfides 

 related to volcanic belts has been discussed by An- 

 derson (1969), and is summarized in the "Copper" 

 chapter of this volume. 



Massive sulfide deposits are of tremendous world- 

 wide commercial importance as sources of silver and 

 base metals in Canada, Japan, Ireland, Cyprus, Au- 

 stralia, U.S.S.R., Spain, Sweden, Philippines, Turkey, 

 West Germany, and Norway. Some of the largest 



