Compositional variations of chromites in archean komatiites from gorumahisani greenstone belt, kapili area, mayurbhanj district (Orissa)

Abstract

The Kapili area is a part of the Gorumahisani greenstone belt, which is composed of the Iron Ore Group of rocks, metamorphosed upto amphibolite facies. The study area consists of serpentinized peridotites, spinifex-textured komatiites, metabasalts and intercalated metasediments. The Kapili hillock is composed of spinifex-textured komatiites that are also found in Kolidiha which is a north-east extension of the Kapili hillock. Chromites in these komatiitic rocks are mostly skeletal in shape, some less some more, and on the basis of their alteration patterns, which is found to be a function of their shape, porosity and size, are classified under three categories. The Cr# and Cr2O3 concentrations in the cores of the chromites are indicative of their high-chromian origin. Bivariate plots of TiO2, MnO, Fe3+# and V2O5 indicate their diffusion during secondary alteration events. The homogeneity of the core and rims of the chromite grains, and crystallization of tremolite and magnesite and other carbonate minerals indicate metamorphic event which is thought to have occurred after the event of alteration.