Wall rock alteration in Cu-Zn-Au bearing volcanogenic massive sulphide deposit at Danva, District Sirohi, Rajasthan

The Upper Proterozoic mafic volcanic suite of the Delhi Supergroup between Nanna and Deri sectors of Rajasthan host several volcanogenic massive sulphide prospects. The massive sulphide ore body at Danva is enveloped by hydrothermally altered volcanic rocks containing sulphide-bearing stock work mineralization. Geochemistry of the unaltered metavolcanics indicate that they are basalts with calc-alkaline affinity. The main types of hydrothermally altered rocks are quartz-biotite schist, quartz-biotite-sericite schist and quartz-sericite schist. Mass balance studies indicate marginal and significant gains of SiO2, H2O and K2O during the processes of biotitization and sericitization. Na and Ca show strong depletion. The iron oxides, in general, record marginal to heavy depletion whereas sulphur is significantly added during the hydrothermal activity. It is suggested that Au has largely I,een mobilized during sulphidation process.