146 



UNITED STATES MINERAL RESOURCES 



490-3, 280 ppm in ashed petroleum (Krayushkin and 

 others, 1964), and as much as 90,000 ppm, or 9 per- 

 cent, in ashed asphalt. 



During the formation of metamorphic rocks, ap- 

 parently little movement and concentration of cobalt 

 takes place. Thus, the cobalt content of different 

 metamorphic rocks depends almost entirely on the 

 amount of cobalt in the original igneous or sedimen- 

 tary rock source. Metamorphic rocks derived from 

 ultramaiic and mafic rocks average about 100 ppm 

 Co; in contrast, gneissic granite contains only 16 

 ppm Co, and metasedimentary rocks average about 8 

 ppm. An exception to the general stability of cobalt 

 during metamorphism is involved with the proposed 

 origin of the sulfide deposits at Thompson, Manitoba, 

 described briefly in a subsequent section. 



Under oxidizing conditions, cobalt displays a 

 strong tendency to concentrate with manganese 

 (Rankama and Sahama, 1950, p. 650; Goldschmidt, 

 1954, p. 627, 632-642; Mason, 1958, p. 174; Gold- 

 berg, 1954; and Krauskopf, 1955). Mero (1965), 

 describing the widespread occurrence of manganese 

 nodules on the bottom of the Pacific Ocean, pointed 

 out that MnOa precipitates as submicroscopic col- 

 loidal particles that "scavenge" any nickel, copper, 

 cobalt, zinc, and molybdenum in the water. Cobalt is 

 also abundant in residual soils derived from the deep 

 weathering of manganiferous sedimentary rocks in 

 a number of areas, particularly in the Eastern 

 United States. 



The concentration of cobalt, particularly with 

 manganese oxides, and the separation of cobalt from 

 nickel are especially pronounced in laterite deposits 

 that occur over deeply weathered mafic and ultra- 

 mafic rocks in tropical areas where rainfall is abun- 

 dant (Engineering and Mining Journal, 1968). Dur- 

 ing the weathering process, magnesia and sihca are 

 leached downward or are removed. Nickel also mi- 

 grates downward, whereas iron, manganese, cobalt, 

 and alumina are residually enriched near the sur- 

 face (Banning and others, 1962 ; Hotz, 1961 ; McMil- 

 lan and Davis, 1955; and Pecora, 1944). In New 

 Caledonia, the cobalt occurs in nodules, lenses, and 

 small veins of cobaltiferous wad, or asbolane, com- 

 monly in a matrix of red iron-rich clay that does not 

 contain appreciable nickel (Andrews, 1962, p. 187). 

 In Cuba, both nickel and cobalt commonly occur in 

 the same ore bodies. 



COBALT MINERALS 



Cobalt is a major or important constituent of ap- 

 proximately 70 minerals (Andrews, 1962, p. 6-12), 

 and is a minor or trace constituent of several hun- 

 dred more, particularly those containing Ni, Fe^+, 



or Mn^+ (Fleischer, 1955). Minerals that are rela- 

 tively high in cobalt and have been mined or con- 

 centrated for their cobalt content are listed in table 

 31. In addition, 27 cobalt sulfides, selenides, sulfo- 



Table 31. — Cobalt minerals 



Mineral Percent cobalt 



Linnaeite, C03S1 58.0 (theoretical) 



Siegenite, (Co,Ni)3S. 20.4-26.0 



Carrollite, (C02Cu)S. 35.2-36.0 



Cobaltite, (Co,Fe)AsS 26.0-32.4 



Safflorite, CO,Fe)As, 13.0-18.6 



Glaucodot, (Co,Fe)AsS 12.0-31.6 



Skutterudite, (Co,Fe)As3 10.9-20.9 



Heterogenite, CoO(OH) 64.1 (theoretical) 



"Asbolite," (Manganese oxides + Co)_ .5—5.0 



Erythritp, (Co,Ni)3(AsO,):«8HjO 18.7-26.3 



(Jersdorffite, (Ni,Co)AsS (low) 



Pyrrhotite, (Fe,Ni,Co)._iS, 1.00 (maximum) 



Pentlandite, (Fe,Ni,Co)eS8 1.50 (maximum) 



Pyrite, (Fe,Ni,Co)S2 13.00 (maximum 



Sphalerite, Zn(Co)S .30 (maximum) 



Arsenopyrite, Fe(Co)AsS .38 (maximum) 



Manganese oxide minerals .10-1.00 (or more) 



salts, and hydrated sulfates and arsenates contain 

 relatively large amounts of cobalt, but are generally 

 of such rare occurrence as to have no commercial 

 importance. (See Fleischer, 1955; Fryklund and 

 Fletcher, 1956; and Burnham, 1959.) 



TYPES OF DEPOSITS 



Cobalt is recovered from mineral deposits both as 

 a principal product and as a byproduct. Most of the 

 world's supply of cobalt reaches the market as a by- 

 product of mining copper, nickel, and silver ores; 

 smaller amounts are byproducts of iron, chromium, 

 lead, zinc, uranium, and manganese. In this discus- 

 sion of cobalt deposits, the geology will be empha- 

 sized, but the geologic features of specific cobalt 

 deposits will be reviewed only briefly. Further infor- 

 mation and references to many deposits are avail- 

 able in works by Vhay (1952) , Andrews (1962) , and 

 Cornwall (1966), and in other chapters in this vol- 

 ume about commodities with which cobalt is 

 associated. 



Cobalt deposits may be classified geologically ac- 

 cording to their environment of genesis or occur- 

 rence: (1) hypogene deposits associated with mafic 

 intrusive igneous rocks; (2) contact metamorphic 

 deposits also associated with mafic rocks; (3) later- 

 itic (weathered) deposits; (4) massive sulfide 

 deposits in metamorphic rocks, chiefly of volcano- 

 sedimentary origin; (5) hydrothermal deposits of 

 several varieties ; (6) strata-bound deposits ; and (7) 

 deposits formed as chemical precipitates. 



HYPOGENE DEPOSITS ASSOCIATED WITH MAFIC 

 INTRUSIVE IGNEOUS ROCKS 



Commercial bodies of massive and disseminated 



