COPPER 



167 



tinental crust have been reviewed by Parker (1967) ; 

 most recent estimates are about 50 ppm (parts per 

 million). As indicated in table 37, copper is con- 



Table 37. — Copper content of various materials 



Copper content generally reported 

 Type of material Kange Average 



Igneous rocks (parts per million) 



Ultramafic rocks 15 



Basaltic and gabbroic rocks 30-160 90 



Andesites 35 



Granitic rocks 5-30 15 



Sedimentary rocks (parts per million) 



Limestones 4 



Sandstones UO-20 10(?) 



Shales and clays 18-120 '45 



Soils 2-100 20 



Phosphorites 10-100 30 



Coals 2-40 15 



Waters (parts per billion) 



Sea Water 1-15 3 



Surface waters .4-150 5(?) 



iPettijohn (1963). 



= 260 for deep-sea clays (Turekian and Wedepohl, 1961); 560 average 

 for 450 samples of deep-sea clay (Landergren and Manheim, 1963). 



centrated in the igneous cycle in basaltic and gab- 

 broic rocks. In these it is highest in the ferromag- 

 nesian minerals such as pyroxenes and biotite vi^here 

 it probably occurs mainly as minute grains of chal- 

 copyrite (Goldschmidt, 1954, p. 182). 



During the crystallization of igneous rocks, cop- 

 per and some other elements that do not fit readily 

 into the structures of silicate minerals may be con- 

 centrated to form ore deposits. If the magma con- 

 tains appreciable volatiles, copper may be dissolved 

 and transported with these into veinlets or exten- 

 sive vein systems. If, as in the case of some gab- 

 broic rocks, the volatile content is low, copper may 

 remain in the intrusion, concentrating as an im- 

 miscible copper sulfide fluid. 



The data on sea water indicate that less than 

 0.1 percent of the copper carried to the ocean re- 

 mains in solution, the remainder being precipi- 

 tated — mainly with the clays, in part with manga- 

 nese oxides, and in part removed by biota. Probably 

 much, perhaps most, of the copper reported in sur- 

 face waters is due to industrial contamination from 

 metallurgical wastes, plating work, and so forth. 



Copper is found in at least trace amounts in 

 nearly all sedimentary rocks. The averages for 

 some common rocks are shown in table 37. The cop- 

 per content of Lower Eocene nonmarine sandstones 

 in the Rocky Mountain region was found to average 

 11 ppm and, for individual basins, to range from 

 5.2 to 29 ppm (Vine and Tourtelot, 1970a). Pelitic 

 Belt rocks from the Mission Mountains Primitive 

 Area, Mont., contain an average of 14 ppm copper. 



whereas similar rocks in the Pend Oreille, Idaho, 

 area contain 6.8 ppm copper (Harrison and Grimes, 

 1970, table 11). 



Copper is readily soluble and mobilized by oxidiz- 

 ing solutions; therefore, it concentrates in certain 

 environments of deposition. Thus, marine clays and 

 other fine-grained rocks tend to have more copper 

 than coarse-grained rocks and limestones. Moreover, 

 the average black shale contains about twice as much 

 copper as the average shale, and some black shales 

 rich in organic matter contain several hundred parts 

 per million copper (Vine and Tourtelot, 1970b). 

 Pelagic sediments contain significantly greater con- 

 centrations of copper than continental rocks. Lan- 

 dergren and Manheim (1963) reported 560 ppm 

 copper as the average for 450 samples of deep-sea 

 clay. Bostrom and Peterson (1966) found more than 

 1,000 ppm copper and an enrichment of several 

 heavy metals along the crest of the East Pacific rise. 

 A metal-rich sediment associated with hot brine 

 from the Atlantis II deep in the Red Sea is reported 

 to contain 0.5 percent copper (Miller and others, 

 1966). 



GEOCHEMICAL CYCLE 



Copper is introduced into the accessible part of 

 the earth's crust from unknown deeper sources by 

 igneous intrusions and by upward migrating fluids. 

 Economic concentrations of the metal may result 

 directly from these processes and from secondary 

 effects of weathering, erosion, and sedimentation. 

 Remobilization and reconcentration by numerous 

 later stages of intrusion and by metamorphism may 

 occur, and in addition ground water and deep con- 

 nate waters may dissolve, transport, and redeposit 

 copper to form younger ore deposits. Copper in 

 oceanic basalt and copper carried to the sea in solu- 

 tion and deposited with oceanic sediments may be 

 remobilized during subduction of oceanic crustal 

 plates, and a part may ultimately be redeposited in 

 continental crustal rocks above the subduction zone. 



The weathering of chalcopyrite readily oxidizes 

 copper and releases it to ionic solution. A portion 

 of this ionic copper may be adsorbed on organic 

 matter, clay minerals, and iron oxide particles, and 

 some of it probably reaches the sea in ionic form. 

 According to Robert Ehrlich and T. A. Vogel (oral 

 commun., 1972), the absence of much potassium is 

 an important factor in the transport of copper as a 

 complex with montmorillonite. The copper in solu- 

 tion in river waters ranges widely, but 0.010-0.015 

 ppm is probably the general range for large rivers. 

 Some copper is believed to have been transported 

 to the Siberian Udokan deposits in detrital form 



