PGE, Au, Ni, Cr and Cu variations in the Komatiites from the Mahakoshal Greenstone Belt, central India

Komatiites are rare ultramafic volcanic rocks containing more than 18 wt % MgO (Arndt and Niusbet, 1982) that erupted mainly during the Archean and Early Proterozoic and less frequently in the Phanerozoic. The more recent examples tend to have lower MgO content than their Archean equivalents. Komatiites are also characterised by their low incompatiable element content which is consistent with their generation by high degrees of partial melting (30–50%). Komatiites are the hottest lavas erupted on earth (eruption temperatures 1400–1600°C), and therefore they provide important constraints on the composition and thermal structure of the Archean mantle (Sproule et al., 2002). The economic importance of komatiites was first widely recognised in the early 1960s with the discovery of massive nickel sulphide mineralisation at Kambalda, western Australia. Komatiite hosted nickel-copper sulphide mineralisation today accounts for about 14% of world's nickel production, mostly from Australia, Canada and South Africa. The Late Archean Mahakoshal greenstone belt (MGB) in central India is an intracontinental rift (~500 km long) filled with a thick metavolcano-sedimentary sequence. The rocks have undergone greenschist facies metamorphism and polyphase deformation. Komatiites occur in the central part of the MGB near Katni. They are cumulate rocks and are composed mainly of olivine associated with clinopyroxene and orthopyroxene.