148 



UNITED STATES MINERAL RESOURCES 



concentrated in a pyrite-rich separate that contains 

 0.68-1.4 percent cobalt. About 75 percent of this 

 cobalt is recovered and these mines are currently the 

 major domestic source of cobalt. Some gold (1,700 oz 

 in 1953) and silver also have been recovered from 

 the pyrite concentrate at the Cornwall mine (Lap- 

 ham, 1968, p. 79). The deposits in this region are 

 large: The Cornwall mine alone has yielded nearly 

 100 million tons of ore since 1742. 



LATERITIC DEPOSITS 



Laterite, a mantle of internally weathered soil 

 from a few feet to more than 100 feet thick, is 

 formed over large areas of low relief during long 

 periods of intense weathering and erosion, chiefly in 

 humid subtropical to tropical climates. The weather- 

 ing of peridotite and serpentine bodies generally 

 yields a laterite rich in iron, nickel, cobalt, and 

 chromium. The lateritic deposits commonly underlie 

 many hundreds to many thousands of acres, and 

 individual deposits may contain millions of tons of 

 ore. Commercially valuable deposits contain 40-50 

 percent iron, 1-2 percent nickel, and 0.01-0.1 per- 

 cent cobalt. Although the cobalt content of laterites 

 is only one-tenth to one-fourteenth the nickel con- 

 tent, the cobalt can be recovered by chemical 

 processing. 



Cobaltiferous laterite deposits, many of Tertiary 

 age, are scattered over the world, and resources in- 

 clude billions of tons of ore. Lateritic ores in the 

 United States occur chiefly in California, Oregon, 

 and Washington, and probably to a lesser extent in 

 North Carolina. One of the largest deposits, near 

 Riddle, Oreg., has reserves of 16 million tons of ore 

 containing 0.05 percent cobalt (Vhay, 1969, p. 120). 

 Smaller deposits containing 0.16 percent cobalt occur 

 in the Webster district. North Carolina (Cornwall 

 and others, 1968, p. 325) . 



Major lateritic iron-nickel deposits of the world 

 occur in eastern Cuba where more than 2 billion 

 pounds of cobalt occur in ore with an average con- 

 tent of 0.1 percent cobalt, 1.39 percent nickel, 2.75 

 percent chromium, and 88 percent iron (McMillan 

 and Davis, 1955 ; Andrews, 1962, p. 149-150 ; Engi- 

 neering and Mining Journal, 1968, p. 74). Other 

 deposits of assorted sizes also occur in New Cale- 

 donia, the Solomon Islands, Indonesia, Australia, 

 Philippines, Puerto Rico, Guatemala, Colombia, 

 Venezuela, Brazil, U.S.S.R., Yugoslavia, Greece, and 

 Malagasy Republic. 



Closely allied to lateritic deposits are those chiefly 

 in the eastern and central parts of the United States 

 that have been derived from the weathering of man- 



ganiferous sedimentary rock. The deposits tend to 

 be small. The cobalt content is more variable than in 

 many nickeliferous laterites. The White Oak mine, 

 Tennessee, contains 0.37-2.28 percent cobalt; the 

 deposit at Round Mountain, Va., contains 0.12-2.24 

 percent cobalt; and the deposit at Rock Run, Ala., 

 contains 0.05-4.8 percent cobalt. About 300,000 

 pounds of cobalt occur in deposits of this type in the 

 southern Appalachian Mountains (Pierce, 1944, p. 

 270; Cornwall and others, 1968, p. 375). Manganese 

 deposits of this type in Missouri contain over 1 mil- 

 lion tons of ore in grade of 20 percent manganese 

 and 0.5 percent cobalt at the contact of the Eminence 

 and Gasconade Dolomites (Grawe, 1943). Cobalt 

 also occurs in the manganese deposits of the Bates- 

 ville district, Arkansas (Vhay, 1952). 



Pierce (1944, p. 268) reported that the greatest 

 cobalt concentrations in the manganese deposits of 

 the southeastern States occur in those deposits con- 

 taining the lowest concentrations of manganese. Ex- 

 perimental work has been done by the U.S. Bureau 

 of Mines on chemically treating these manganese 

 ores. When such beneficiation does become economi- 

 cally feasible, some cobalt and other metals present 

 in small amounts can be recovered. 



MASSIVE SULFIDE DEPOSITS IN METAMORPHIC ROCKS 



Deposits of massive sulfides consisting chiefly of 

 pyrite and pyrrhotite (some containing small 

 amounts of cobalt) occur in metamorphic rocks. The 

 host rocks commonly have andesitic composition and 

 are probably of volcano-sedimentary origin. (See 

 "Copper.") These deposits generally are mined for 

 their content of sulfur, iron, copper, and smaller 

 amounts of zinc, nickel, and cobalt. 



Large massive sulfide deposits occur in the Blue 

 Ridge and Piedmont provinces of the southeastern 

 United States (Laurence, 1968, p. 162-164). The 

 largest and best known of these deposits occur at 

 Ducktown, Tenn. (Magee, 1968), where pyrite that 

 contains 0.4-0.5 percent cobalt is reported by Corn- 

 wall, Vhay, and Frendzel (1968, p. 375). The cobalt 

 currently is not recovered. The deposit at Sykesville, 

 Md., contains base metals and some gold; the aver- 

 age content of cobalt is 0.07 percent (Heyl and 

 Pearre, 1965). The en echelon bodies of primary 

 pyrrhotite, chalcopyrite, and sphalerite along the 

 20-mile trend of the Gossan Lead, Carrol and Gray- 

 son Counties, Va., contain about 0.01 percent cobalt. 

 At least 16 other deposits believed to be of the Duck- 

 town type have been mined or explored from Carroll 

 County, Md., southward to Randolph County, Ala., 

 according to Laurence (1968, p. 164). 



