Cobaltoan pyrite in a lamprophyre from the Sidhi Gneissic complex, Mahakoshal belt, Central India

Abstract

Pyrite containing appreciable content of cobalt (up to 5.61 wt%) and minor amounts of nickel (up to 0.70 wt%) is being reported from electron microprobe studies in a lamprophyre dyke from the Sidhi complex, Mahakoshal belt, Central India. However, cobalt and nickel are conspicuously absent from the associated chalcopyrite reflecting that in a pyrite-chalcopyrite association these elements are preferentially sequestered in pyrite. The microprobe analysis of pyrite grains reveal that their Fe content is variable (40.62 to 46.02 wt%) and reciprocally related to cobalt and nickel concentrations implying the presence of latter as solid solution in the structure of pyrite. The cobalt contents of the pyrite are comparable to those (up to 3.21 wt%) reported from the cobaltbearing pyrites of the Kalyadi copper deposits of Dharwar craton of southern India. Co:Ni (16.05 average) in the studied pyrite appears to be more consistent with a magmatic, rather than a hydrothermal, origin. However, further studies are in progess. This study highlights that besides gold and diamond, lamprophyres are also important carriers of cobalt when available in the magmatic system.