Thermodynamic model for hydrothermal sulfide deposition in the paleoproterozoic granite ore system at Malanjkhand, India

Abstract

Malanjkhand fossil hydrothermal deposit is a Paleoproterozoic metallogeny associated with the Malanjkhand Granitoid represents an ideal granite ore system. It is formed by mixing of two distinct compositions of hydrothermal fluids in variable proportion derived from two different sources and results in the deposition of primary sulfide ores which comprises of chalcopyrite + pyrite ± bornite. Primary sulfide ores alters to secondary sulfides (chalcocite + chovellite) and oxides (cuprite + tenorite) ores because of extensive hydrothermal activities. Occurrence of two distinct varieties of ore assemblages (primary and secondary ores) indicates broadly two stages of sulfide deposition. Thermodynamic modeling suggests that hydrothermal alteration brings change in the physico-chemical environment from reduced to oxidized zone in the Malanjkhand granite ore system. The primary sulfide ores occurs in reduction zone whereas secondary ores found in the oxidation zone which forms of a cap on the primary ores. Change in the physico-chemical environment caused change in the composition of the ore minerals which favors enrichment in Cu along with the depletion of Fe and S content.