T. A. Gornostaeva, A. V. Mokhov, P. M. Kartashov, K. V. Lobanov
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Abstract
Native cobalt was found in amphibolite of the Kola superdeep borehole (SG-3) from a depth of 9630 m by a complex of local analytical methods (analytical scanning electron microscopy, electron backscatter diffraction). The studied amphibolite is a fine-grained melanocratic rock composed mainly of magnesioferri- hornblende and containing accessory native metal, telluride, sulphotelluride, and sulphide (Au, Ag, Pd, Bi, Cu, Pb, Zn, Sb, and Fe) mineralization.It also includes the clinopyroxene xenoclast carrying a fundamentally different set of accessories—poor in sulphides and including native cobalt. The absence of significant impurities, including iron, in native cobalt and its belonging to the hexagonal α-modification was determined. It is shown, that the metallic cobalt particles exposed during ion polishing of a compact pyroxene matrix cannot be a contaminant, introduced into the sample during drilling and sample preparation. Cobalt, obviously, was formed not only before the stage of retrograde metamorphism and subsequent hydrothermal processing of the amphibolite containing it, but probably long before the formation of the sedimentary protolith of this rock. That is, native cobalt belongs to the early high-temperature mineral phases inherited from the older Proterozoic—Archean main volcanism, while the time of formation of this layer of amphibolites dates back to the age of 2.4 billion years—the Early Karelian era of the Proterozoic.
期刊介绍：
Geology of Ore Deposits is a periodical covering the topic of metallic and nonmetallic mineral deposits, their formation conditions, and spatial and temporal distribution. The journal publishes original scientific articles and reviews on a wide range of problems in theoretical and applied geology. The journal focuses on the following problems: deep geological structure and geodynamic environment of ore formation; distribution pattern of metallogenic zones and mineral deposits; geology and formation environment of large and unique metallic and nonmetallic deposits; mineralogy of metallic and nonmetallic deposits; physicochemical and isotopic characteristics and geochemical environment of ore deposition; evolution of ore-forming systems; radiogeology and radioecology, economic problems in exploring, developing, and mining of ore commodities.
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