Native Cobalt in Deep Levels of the Kola Superdeep Borehole

Native cobalt was found in amphibolite of the Kola ultra-deep borehole (SG-3) from a depth of 9630 m by a complex of local analytical methods (analytical scanning electron microscopy, EBSD). The studied amphibolite is a fine-grained melanocratic rock composed mainly of magnesio-ferri-hornblende and containing accessory native-metal, telluride, sulphotelluride and sulphide (Au, Ag, Pd, Bi, Cu, Pb, Zn, Sb, Fe) mineralization. It includes a clinopyroxene xenoclast which poor in sulphides and including native cobalt. The absence of any significant impurity in native cobalt and its belonging to the hexagonal α-modification was determined. Native cobalt was formed probably before both the stage of retrograde metamorphism with the hydrothermal alteration of amphibolite and the formation of the volcano-sedimentary protolith of this rock. Native cobalt probably belongs to the early high-temperature mineral phases inherited from the older Proterozoic-Archean basic volcanism, while the time of formation of this layer of amphibolites is 2.4 billion years.