Chromite alteration at Boula-Nausahi igneous complex, Orissa

Abstract

During Serpentinization of the ultramafic rocks, the accessory chrome spinels are altered at grain margins and/or along fractures to highly reflecting phases of ferritchromit and magnetite which occur as rims around parent chromite. Of these two altered phases, ferritchromit exhibits greater compositional variation. Electron probe microanalysis data indicate that these phases are rich in Fe and poor in Cr, Al and Mg with respect to parent chromite. Magnetite rim is characterised by extreme iron enrichment and marked depletion of Cr, Al and Mg whereas ferritchromit represents intermediate chemical composition between parent chromite and the magnetite outer rim. This compositional variation is due to solid state diffusion of elements from chromite outwards during serpentinization. Textural features, chemical composition and presence of chromiferous serpentine attest genetic relationship between serpentinization and chromite alteration.