COPPER 



183 



exploration. 



In western Colombia, quartz diorite intrusions of 

 probable middle Tertiary age in the Sierra Occi- 

 dental (Irving, 1971) suggest a large region where 

 porphyry deposits might be found. Recent geo- 

 chemical investigations by U.S. Geological Survey 

 and Colombian government geologists have revealed 

 strong copper anomalies in one of these intrusions 

 in the north end of the Sierra (E. M. Irving, oral 

 commun., 1972). 



In Panama, recently discovered porphyry copper 

 deposits related to upper Tertiary volcanic rocks 

 (Ferencic, 1970; Dengo and others, 1969) suggest 

 a wide province with potential mineralization. 



Economically important copper deposits are un- 

 known in the Precambrian shields of South 

 America, but the region is vast, nearly unpopulated, 

 and difficult of access. In Brazil, the recent highway 

 construction and westward pioneering movement 

 and accompanying geologic and geochemical explora- 

 tion may yield copper resources of great size. Not 

 enough is known of the geology of this region to 

 do more than speculate on the possibility of major 

 sedimentary copper deposits of the Zaire-Zambia 

 type or smaller deposits of the Tsumeb type. 



In western Europe and northwest Africa, por- 

 phyry copper deposits of late Paleozoic age may be 

 preserved. These could be products of a Paleozoic 

 subduction zone resulting from the collision of the 

 European-African and the American crustal plates. 

 Goosens (1971) suggested the possibility of por- 

 phyry copper occurrences in western Africa. 



The Alborz Mountains of northern Iran, with nu- 

 merous small copper occurrences, may be a long 

 extension of the copper-molybdenum porphyry prov- 

 ince in Soviet Armenia. The areas of volcano- 

 sedimentary complex northeast of the Dasht-e-Lut 

 in eastern Iran and in the northern part of the 

 Chagai District in Pakistan, both areas of some late 

 volcanism, are favorable areas for the occurrence 

 of very young (Pliocene-Pleistocene) porphyries. 

 One untested porphyry at Saindak in the Chagai 

 District was described (Schmidt, 1968), and one 

 prospect in east-central Iran, that at Gazu, was 

 described in a way suggesting a porphyrylike de- 

 posit (Bazin and Hubner, 1969, p. 107-108). 



Mesozoic fold belts of the Soviet Far East prob- 

 ably contain large porphyry copper deposits. The 

 Koryak Peninsula would be the logical beginning 

 for the search for these because of the apparent 

 continuity of cordilleran-type structures into this 

 area. Younger deposits may occur along the Kurile- 

 Kamchatka-Aleutian arc-trench system. 



Recent discovery of porphyry copper deposits in 



the Philippines, Solomon Islands, and Borneo sug- 

 gests that all the island arc areas in the Western 

 Pacific, especially the Indonesian islands, might be 

 potential prospecting ground. 



A region of abundant felsic volcanic rocks in 

 northeastern China and eastern Mongolia would 

 seem to have potential for significant copper- 

 porphyry and massive sulfide deposits. Other ranges 

 besides the Ch'i-lien-shan, especially in northern 

 Tsinghai Province, might contain significant mas- 

 sive sulfide copper deposits. There is also consid- 

 erable potential for sedimentary copper deposits in 

 many parts of this large country. We do not know 

 enough about recent Chinese geologic literature to 

 speculate on extensions of the environment of the 

 copper porphyry of Chung-t'iao-shan in Shansi 

 Province. 



The Tasman geosynclinal belt in eastern Australia 

 contains many copper occurrences and major de- 

 posits of the massive sulfide type. Late Paleozoic 

 felsic intrusions in this belt may contain large re- 

 sources of the porphyry copper type. 



Table 40 summarizes our estimate of the amount 



Table 40. — Summary of speculative resources, in millions 

 of tons, of copper ' 



Basin and Range porphyry copper 100 



Alaska porphyry copper 10 



Other Western United States possibilities, 

 Appalachian Mountains porphyry copper, 



and Antilles porphyry copper 10 



Central America — Colombia porphyry copper 10 



Brazilian shield sedimentary copper 50 



Western Europe-northwest Africa porphyry 



copper 10 



Middle East porphyry copper 10 



U.S.S.R. Far East and Kurile-Kamchatka arc__ 100 



China (?) 



Australia 10 



Indonesia 10 



Total 320 



^ Speculative resources : Undiscovered mineral deposits, whether of re- 

 coverable or subeconomic grade, that may exist in unknown districts or 

 in unrecognized or unconventional form. Based mostly on estimates of 

 geologic favorability and extent of geologic mapping. 



of copper that might be contained in these untapped 

 districts and provinces. The figures are at best a 

 guess and may be in error by as much as 100 

 percent. 



SUBECONOMIC RESOURCES 



Lowell (1970) estimated that in the upper mile of 

 the earth's crust there are about 3x10'° tons of 

 copper. The recoverable identified, hypothetical, and 

 speculative ore deposits discussed in the previous 

 section make up a small fraction of this amount. 

 Another fraction, subeconomic resources, comprise 

 bodies of mineralized rock containing copper in 

 amounts considerably higher than crustal abun- 



