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.