Mineralogical and chemical characteristics of the serpentinites from Boula-Nausahi igneous complex, Orissa

Abstract

The ultramafic rocks of Boula-Nausahi igneous complex have undergone extensive alteration resulting in the development of serpentinites. Petrographic and mineralogical observations have led to the recognition of two stages of mineral formation. The first stage (retrograde metamorphism) is characterised by complete transformation of magmatic olivine to lizardite and the second stage (prograde metamorphism) in the formation-of antigorite and alteration of accessory chrome spinels. Mineral assemblages indicate serpentinization to be a low temperature oxidation phenomenon. Formation of magnetite, ferritchromit and sulphide minerals is controlled by oxygen and sulphur fugacities prevalent during the process of serpentinization. Mineralogy, chemistry and geological setting of the serpentinites indicate an isochemical nature of the serpentinization process.