Chloritization in Paleoproterozoic Granite Ore System at Malanjkhand, Central India: Mineralogical Studies and Mineral Fluid Equilibria ModellingIn the Malanjkhand Granitoid (MG), chlorite occurs in micro-domain along with mineral assemblage biotite, horn

In the Malanjkhand Granitoid (MG), chlorite occurs in micro-domain along with mineral assemblage biotite, hornblende, quartz, K-feldspar and plagioclase. Chloritization of biotite is the most dominant processes during the hydrothermal alteration in MG ore system followed by alteration of hornblende. Chlorite composition revealed two major types of substitution mechanism, i.e. couples Tschermak (TK) and di-trioctahedral (DT) which correspond to the coupled exchange of Mg and Fe for Al between end-members clinoclore-daphanite and amesite. TK substitution is more prominent than DT substitution between endmembers of chlorite solid solution during hydrothe rmal alteration in MG. Temperature estimates for chloritization using chlorite geothermometry range from 110°C to 400°C and are consistent with the temperature of hydrothermal mineralization (200-375°C) at Malanjkhand. The chloritization process incorporates K⁺ and Ca²⁺ ions in the hydrothermal fluids. Therefore, it is inferred that the chloritization in granitic plutons is due to alteration of biotite and hornblende which increases the oxygen fugacity and activities of K⁺ and Ca²⁺ ions in the hydrothermal fluid.