176 



UNITED STATES MINERAL RESOURCES 



Texas and New Mexico. Like the Kupferschiefer of 

 Europe, these deposits have lateral persistence 

 within thin strata, which is commonly cited as evi- 

 dence for a syngenetic origin. 



Strata-bound copper-bearing sandstones that oc- 

 cur in Carboniferous rocks of Dzhezkazgan in 

 central Kazakhstan, U.S.S.R., are included here 

 even though descriptions of these deposits indicate 

 significant differences from our red-bed copper de- 

 posits. Copper sulfides with some lead occur in gray 

 sandstone horizons interbedded with barren brown 

 sandstones of shallow marine lagoonal and deltaic 

 facies. As many as 27 zones of mineralized sand- 

 stone occur in 700 m of enclosing rock. The gray 

 host rock is more calcareous and dolomitic than the 

 associated barren rock. The primary ore consists of 

 sandstone impregnated with bornite, chalcocite, 

 chalcopyrite, and galena concordant with the lami- 

 nation of the sandstone. The first stage of minerali- 

 zation is probably syngenetic or diagenetic with the 

 enclosing strata; it is cut by a second, epigenetic 

 stage of copper-lead-zinc mineralization that forms 

 intersecting veins, stockwork zones, and hydro- 

 thermal wallrock alteration. The ore-forming solu- 

 tions may have been derived from basaltic magma 

 at depth below the sea floor according to Shcherba 

 (1971). These deposits were estimated to have a 

 reserve of more than 3.5 million tons copper metal 

 in ore containing 1.6 percent copper (Sutulov, 1967, 

 p. 113). 



MODERN SEA FLOOR NODULES 



Extensive deposits of ferromanganese nodules 

 now forming on the deep-sea floor in the major 

 oceanic basins are examples of syngenetic copper- 

 bearing deposits that may become economic in the 

 near future as technology progresses. Although the 

 origin and mode of concentration of metals in these 

 nodules are the subject of intense debate, there can 

 be no question that the nodules represent syngenetic 

 deposition. The copper content of the nodules varies 

 regionally in the ocean basins; the higher concen- 

 trations are normally on the west sides of the basins 

 and between lats 10° N. and 10° S., 2,500-6,000 m 

 below the surface. The nodules in the richer areas 

 contain more than 25 percent manganese, as much 

 as about 1.5 percent copper and nickel, and 0.25 

 percent cobalt, as well as many other elements in 

 smaller quantity. The copper ions are thought to 

 be adsorbed on the manganese oxides; copper min- 

 erals have not been reported. These nodules are 

 discussd in more detail in "Manganese" ; Mero 

 (1965) reported information as to distribution and 

 quantity. 



METAL-RICH SEDIMENTS OF THE RED SEA 



In March 1964, during an oceanographic survey 

 of the Red Sea, scientists aboard the RRS Discovery 

 found hot brine in the Discovery Deep. Subsequent 

 exploration has shown that underlying the hot brine 

 are iron-rich, brine-saturated sediments at least 

 10 m thick containing anomalous amounts of copper 

 and zinc. The geology, chemistry, and physical prop- 

 erties of these sediments are discussed in detail in 

 a collection of reports edited by Degens and Ross 

 (1969). Aside from the economic potential of these 

 deposits (Bischoff and Manheim (1969) estimated 

 50 million tons of brine-free sediment averaging 

 1.3 percent copper), the greatest interest lies in the 

 theoretical implications of these deposits with re- 

 spect to the origin of sedimentary deposits else- 

 where. James (1969) suggested that deep burial of 

 deposits of this type and continued circulation of 

 hot brine through them would result in re-solution 

 of the base metals and lateral migration. He specu- 

 lated that such migration would continue until the 

 solutions reached the HaS-bearing reef limestones 

 known to be laterally continuous with the metal- 

 rich sediments, there to precipitate as sulfide min- 

 erals. Such a model provides a basis for new 

 appraisals of the theories of origin of many types 

 of sedimentary base-metal deposits. Furthermore, 

 since the hot brines which have introduced the 

 metals to the sea floor appear to be related to con- 

 tinental rifting, a tectonic control for sedimentary 

 deposits is suggested. If stratigraphic and paleotec- 

 tonic studies of a region suggest rifting and deep 

 basin filling, favorable host rocks along the flanks 

 of the rift may contain deposits of base-metal sul- 

 fides. 



HORIZONTAL TRANSPORT OF SECONDARY COPPER DEPOSITS 



A few localities are known where copper dis- 

 solved from sulfide-bearing rock as a part of the 

 conventional surficial leaching has then traveled 

 laterally and been deposited in a secondary zone that 

 is not located above the primary sulfide. Perhaps 

 this phenomenon is more common that is suspected, 

 and consideration might be given to searching for 

 such ores in the vicinity of subeconomic sulfide 

 mineralization. 



Lateral transport and secondary deposition of 

 copper has been described at the Emerald Isle mine, 

 Wallapai mining district, Arizona (Dings, 1951, p. 

 149-153), Jerome, Ariz. (Lindgren, 1926, p. 90-91), 

 Chuquicamata, Chile (Newberg, 1967), Globe- 

 Miami district, Arizona (Throop and Buseck, 1971), 

 and Ray, Ariz. (Phillips and others, 1971). The 

 transport distance at Chuquicamata was about 4 



