Physico-chemical conditions of ore deposition in Malanjkhand copper sulphide deposit

Abstract

Heating and freezing studies on fluid inclusions in quartz from mineralized quartzfeldspar reef reveal the presence of type A CO₂-H₂O (H₂O>50% by volume), type B CO₂-H₂O (H₂O<50% by volume), type C pure CO₂ and type D pure aqueous inclusions. Types A, B and C are primary and/or psuedo-secondary inclusions while type D are secondary. Types A and B homogenize on heating into different phases at similar temperatures ranging between 307 and 476°C, indicating entrapment from boiling hydrothermal solutions. Type D inclusions homogenize into a liquid phase at temperatures between 88 and 196°C. Boiling of hydrothermal solutions led to the formation of a CO₂-rich phase of low density and salinity that coexisted with another dense and saline aqueous phase with very little CO₂ dissolved in it. Ore and gangue mineral assemblage of primary ores indicate that ore deposition was characterized by logf _{O 2}=−34.4 to −30.2 atm, logf _{S 2}=−11.6 to −8.8 atm and pH=4.5 to 6.5.