Compositional Variations in Chromites from Sukinda Orissa, India

The chromite-bearing ultramafic pluton in Sukinda, Orissa, was emplaced in two horizons in the Iron Ore Series rocks which were subjected to shearing deformation and hydrothermal activity, followed by silicification. These processes in most cases completely transformed the early silicates to chlorites and produced, in some cases, compositional zoning in the periphery of chromite grains. The chromite grains and samples from different horizons show variations in composition, reflectivity and latticeparameter. Eight analyses of separated chromite samples are presented along with spot microprobe analyses for Cr, Mg, Fe and Al; these reveal not only marked compositional differences among discrete grains but also show distinct compositional zoning in individual grains.