Cobalt is one of the least familiar metals and with a crustal abundance of only 25 ppm it is also one of the rarest. With the exception of the Bou Azzer mine current production is entirely a secondary product of copper and nickel mining. Thirty-four cobalt minerals have been recognized - principally sulphides, selenides, arsenides, sulpharsenides, carbonates, sulphates and arsenates. The main ore minerals of cobalt are the sulphides cobaltite, linnaeite and carrollite and the hydrated oxide asbolane. Cobaltiferous pyrite is a further source.Workable deposits generally contain 0.1-0.4 percent Co and belong to one of four geologically distinct types: (1) sediment-hosted - largely Precambrian - typified by the copperbelts of Congo Democratic Republic and Zambia, which since the 1970s have contributed between 25 and 50 percent of the world's mine production; (2) mid-Tertiary to Recent nickel-rich lateritic deposits generated by tropical and subtropical weathering of peridotitic rocks, most notably in New Caledonia, Cuba and Australia; (3) primary magmatic Ni-Cu sulphide concentrations, such as Sudbury, Noril'sk, Voisey's Bay and Bushveld; and (4) a more diverse group attributable to hydrothermal and volcanogenic processes, the most important of which in terms of current and future production are the ophiolites-hosted Co-As deposit at Bou Azzer, Morocco, and the epigenetic Cu-Au-Co concentrations of the Idaho Cobalt Belt, U.S.A. The last group also includes the formerly important Outokumpu-type massive sulphide and five-element (Ni-Co-Ag-As-Bi), vein-type deposits.The currently quoted figure for global cobalt reserves of 4 500 000 t may be overstated since it does not take into account the effects of political uncertainty in the Congo Democratic Republic. However, even at proposed increased levels of production (70 000 t/year, against the current figure of 28 300 t/year) reserves have a life of at least 60 years. Some potential exists in the longer term for cobalt extraction from offshore reserves of manganese nodules.
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