COPPER 



185 



copper-bearing manganese nodules of the ocean 

 basins and brine-associated metal-rich bottom sedi- 

 ments of the Red Sea. On the basis of Mero's (1965) 

 estimates of copper content and abundance of ocean 

 floor manganese nodules (see also "Manganese"), 

 we estimate that 40-60 million tons of copper may 

 be available from this source. Development of these 

 resources depends on the accurate determination of 

 their size, research and development on economical 

 mining and metallurgical methods, and settlement 

 of the international-legal problems of ovs^nership. 



Elsewhere in the world, reasonable assumptions 

 on which to base estimates of presumed resources 

 become increasingly difficult to make. In the Andes, 

 where porphyry copper deposits are large and are 

 mined at much higher grade than those in the 

 United States and Canada, there must exist very 

 large subeconomic resources. The sedimentary de- 

 posits of Zaire and Zambia probably also contain 

 very large amounts of copper in thin or deeply 

 buried beds. A doubling of the copper reserves of 

 these areas is not difficult to imagine when modern 

 low-cost mining methods are established and (or) 

 world copper prices rise. 



Wedepohl (1971) gave 30-100 million tons as the 

 probable copper content of the Kupferschiefer in 

 Germany. Economic deposits are largely depleted, 

 and this resource lies in thin or deeply buried beds. 



PROSPECTING TECHNIQUES 



We must assume that most easy-to-find copper 

 deposits in the populated regions of the world have 

 now been discovered. For all except some remote 

 areas, new discoveries are more difficult to make 

 and indirect methods of prospecting are being used 

 increasingly to find copper and other metals. From 

 now on, our success in finding new and especially 

 hidden deposits will greatly depend on our ability 

 to develop new methods of detecting concealed ores. 



Some prospecting techniques can be applied to a 

 wide variety of ores, but others are only for specific 

 targets. Geochemical reconnaissance is often the first 

 step in prospecting and usually seeks several metals 

 that may be dispersed from any kind of ore deposit. 

 Stream sediment sampling, described by Hawkes 

 and Webb (1962), is the most effective reconnais- 

 sance method in many terranes. Refinements of this 

 method, such as improved statistical analysis of 

 data and sampling of certain mineral species (for 

 example, magnetite), have had some success. De- 

 tailed study of anomalous areas and outlining of 

 drilling targets are usually accomplished by soil 

 sampling and analysis. In tropical areas copper can 

 be mostly leached from soils overlying the deposits, 



but Learned and Boissen (1972) showed that over 

 porphyry copper deposits, traces of gold associated 

 with chalcopyrite remain in the soil and that the 

 deposit may be outlined by the gold anomaly over 

 it. In glaciated regions, ore fragments in boulder 

 trains have been studied in hope of tracing them to 

 their source; sulfide fragments were followed for 

 50 km in the discovery of the Outokumpu ores of 

 eastern Finland. 



Rocks containing widely disseminated pyrite as- 

 sociated with copper porphyry deposits, in com- 

 bination with other effects of hydrothermal altera- 

 tion, weather in the desert environment to produce 

 a large color anomaly, "distinguished by brownish 

 to greenish coloration, bleaching and variegated 

 iron staining" (Jerome, 1966, p. 82-83). In some 

 localities large red-brown areas ("red thumbs") 

 have developed near the ore bodies as at Bisbee, 

 San Manuel, and Banner-Pima-Mission, all in Ari- 

 zona. Recognition of the "red thumb" area from an 

 aircraft played an important part in the exploration 

 of the La Caridad deposit, Mexico. The areas of 

 color anomaly may be hundreds of meters to several 

 kilometers in size and might be recognizable on 

 colored aerial photography (Schmidt, 1968, p. 60). 

 They also form target areas large enough to be 

 sought from instrumented satellites; tests of the 

 detection of a porphyry ore body in a desert area 

 are planned for the Earth Resources Technology 

 Satellite A. 



Preliminary experiments have been made to com- 

 pare the spectral reflectance from trees in soil over 

 a sulfide mineral deposit with reflectance from trees 

 of the same species on nearby unminerahzed soil 

 (Canney, 1970). Early results of tests made on a 

 disseminated copper-molybdenum deposit in Maine 

 have been encouraging. 



Geophysical methods of many types are suitable 

 for copper prospecting, but they are much more 

 specific for certain types of ore. Aeromagnetic sur- 

 veys are used to outline bodies of mafic rocks which 

 may contain massive sulfide or magmatic-segrega- 

 tion deposits or to indicate areas of weakly magnetic 

 hydrothermal alteration or highly magnetic skarn 

 mineralization associated with porphyry deposits. 

 The use of geophysical methods in the search for 

 copper porphyry deposits was discussed by Brant 

 (1966) and Sumner (1970). The potassic altera- 

 tion that accompanies porphyry copper deposits can, 

 theoretically, be detectable by modern airborne 

 gamma-radiation surveys (Moxham and others, 

 1965). Electromagnetic surveys by ground or air 

 are used in outlining massive sulfide deposits; 

 induced-potential surveys are effective in locating 



