Re-Os isotopic evidence for genesis of Archaean nickel ores from uncontaminated komatlites

Abstract

THE late Archaean greenstone terranes of Western Australia contain abundant komatlites (high-MgO lavas) hosting magmatic sulphide deposits rich in nickel, copper and platinum-group elements. Thermal erosion and assimilation of sulphidic sea-floor sediments has been proposed as a mechanism by which the komatiites were brought to sulphide saturation. Such models have important implications not only for the genesis of these sulphide ores, but also for interpreting the magnitude and extent of isotopic heterogeneity in the Archaean mantle. Here we report that massive, matrix and disseminated sulphide ores and a komatiite from Western Australia yield a magmatic Re-Os isochron age of 2,706 ± 36 Myr..