COPPER 



175 



origin for the copper (Harrison, 1972) . Later re- 

 crystallization and metamorphism to the biotite 

 zone reduced rock permeability and precludes the 

 possibility of late epigenetic mineralization. 



Rocks of the Belt Supergroup, including the Re- 

 vett Formation, may contain as much as 1 billion 

 tons of ore with an average grade of 0.5-1.0 percent 

 copper. Submarginal grade rocks with anomalous 

 copper may be 10-100 times more abundant. Silver 

 will be a valuable byproduct of the Belt ores when 

 commercial exploitation begins. 



PRECAMBRIAN SEDIMENTARY COPPER DEPOSITS 

 IN THE U.S.S.R. 



With an estimated reserve of at least 10 million 

 tons of metallic copper (Sutulov, 1972, p. 10), the 

 undeveloped sedimentary ores of Udokan in eastern 

 Siberia (near 57° N., 117° E.) form one of the 

 world's largest sedimentary copper deposits ; Shank 

 (1972, p. 88) reported that it may be the largest. 

 The ores are mainly sedimentary and related to 

 lithology, and the greatest ore concentrations occur 

 in the 1,800-2,500-meter-thick Sakukan Formation 

 within the 10,000-12,000 m Udokan Group of fine 

 sandstone and siltstone and some thin lenses of 

 carbonate (Bakun and others, 1958). The main layer 

 within which ore masses occur is about 300 m thick, 

 its top 250 m below the top of the Sakukan Forma- 

 tion. The top of a lesser ore-bearing layer is 1,250- 

 1,950 m stratigraphically beneath the main one. 

 Despite the great thickness of the Udokan Series, 

 deposition was in shallow water, or in a littoral 

 and deltaic environment. 



The Udokan Series is considered by most geolo- 

 gists to be of Precambrian X age, but some geolo- 

 gists think it as young as Precambrian Z. Copper 

 minerals were deposited with the sedimentary ma- 

 terial or were diagenetic (Bogdanov, 1968). The 

 copper is believed to have come from a Precambrian 

 W shield area located to the northeast, containing 

 anomalous quantities of copper. Part is believed to 

 have been transported as fine clastic particles. 



The Udokan Series is folded into a big synclinal 

 basin, irregularly oval in plan; the southwest limb 

 is overturned, but folding is not complex. The en- 

 tire series is slightly metamorphosed, and some of 

 the rocks are now quartzites and phyllites. 



The main ores are disseminated chalcocite and 

 bornite; there are also some chalcopyrite ores that 

 are not associated with the preceding. Malachite, 

 brochantite, and other secondary minerals are pres- 

 ent in a restricted oxidized zone. Sphalerite, native 

 silver, and molybdenite are rare in the deposit. Ore 

 has been traced to depths of more than 1,500 m. 



Lyubimov (1966, p. 231) described the remote 

 location and problems that face development in the 

 Udokan Series. The region has severe climate, per- 

 mafrost, and seismicity and an elevation of more 

 than 1,000 m above sea level, but the high metal 

 content of the ore and the possibility of open-pit 

 mining probably will compensate for the high capi- 

 tal expenditures needed. 



RED-BED COPPER DEPOSITS 



Numerous deposits of copper are associated with 

 red sandstone strata of late Paleozoic or early 

 Mesozoic age, as described by Lindgren (1911). In 

 the Southwestern United States, only a few of the 

 deposits are large enough to be mined economically. 

 Host rock strata, interbedded with red strata, are 

 generally light gray to dark gray and may weather 

 yellowish gray. Nonmarine feldspathic or arkosic 

 sandstones containing carbonaceous matter are the 

 most common host rocks. Such copper deposits are 

 similar in size and shape to some of the well-known 

 deposits of uranium and vanadium in sandstone, and 

 transitional deposits containing all three metals 

 exist. The copper deposits generally contain some 

 silver, and at Silver Reef, Utah, silver values ex- 

 ceed those for copper. 



Near Cuba, N. Mex., the Nacimiento copper de- 

 posit, which occurs in the Agua Zarca Sandstone 

 Member of the Chinle Formation, is a typical large 

 red-bed copper deposit (Kaufman and others, 1972). 

 Rich ore occurs as chalcocite, bornite, covellite, and 

 secondary copper minerals, replacing fossil wood 

 and forming halos around the wood. The deposit is 

 clearly epigenetic, but appears to predate the major 

 structural features of the area. In past years selec- 

 tive mining of rich chalcocite replacements of logs 

 left much disseminated ore in the ground. The re- 

 maining disseminated and rich copper ore may be 

 as much as several million tons in this area alone. 

 The total speculative resources of copper in red- 

 bed copper deposits of the United States may be 

 several hundreds of millions of tons of mineralized 

 material. 



A second type of copper deposit generally in- 

 cluded with red-bed copper deposits is represented 

 by disseminated copper sulfide minerals currently 

 mined from thin beds of gray shale in the Flower- 

 pot Shale of Permian age in southern Kansas and 

 western Oklahoma (Ham and Johnson, 1963; John- 

 son and Ham, 1972). The copper-bearing shales oc- 

 cur in a sequence that includes red sandstone, dolo- 

 mite, gypsum, and shale and are facies equivalents 

 of evaporite deposits including salt in western Kan- 

 sas and in the Midland and Delaware basins of 



