Thermodynamics and Oxygen-Sulpbur Fugacity Variations of Mosaboni Sulphide Mineralisation, Singhbhum, Bibar

The thermodynamical calculations for the oxygen and sulphur fugacities of Mosaboni mineralisation have been made based on the equilibrium reactions for various mineralogical associations like, (a) bornite-pyrite-chalcopyrite. (b) pyrite-pyrrhotite. (c) pyrite-magnetite, (d) pyrrhotite-magnetite and (e) pyrite-pyrrhotite-magnetite and the temperatures determined by fluid inclusion studies. The association of pyrite-pyrrhotite-magnetite indicates that oxygen fugacity was 10^-24.3 atmosphere at 450°C and this got reduced to 10^-32.5 atmosphere at 300°C. Presence of bornite in place of magnetite shows that there was fluctuation in the fugacity of sulphur. This might be varying from 10^-6.3 to ^-1.6 atmosphere at 450°C and from 10^-11.6 to 10^-6.4 atmosphere at 300°C.