Copper mineralization at the Nallakonda deposit, copper-lead mineralization at the Dhukonda deposit and lead mineralization at the Bandalamottu deposit constitutes the Agnigundala Sulfide Belt of Paleoproterozoic Cuddapah basin. A sandstone-shale-carbonate association of shallow marine origin hosts the mineralization. Copper sulfide mineralizations in sandstones are stratabound and disseminated type and lead sulfide mineralizations occur as stratabound fracture filling veins and/or replacement veins within dolomite. Systematic mineralogical and sulfur, carbon and oxygen isotope studies of the three deposits indicate that the same ore-fluid that deposited copper at Nallakonda at relatively higher temperature, also deposited copper-lead at Dhukonda and lead at Bandalamottu under progressive cooling during migration through sediments. The ore-fluid was a low temperature (<200°C), oxidized fluid containing enough metal and sulfate to form sulfide mineralization in the Agnigundala Sulfide Belt. Further, the present study indicates thermochemical reduction of basinal water sulfate to account for the sulfur for sulfide ores. It is envisaged that basal red-bed and evaporite bearing rift-related continental to shallow marine sediments might have acted as the source for the metals in low temperature and oxidized ore-fluid. Rift related faults developed during sedimentation in the basin might have punctured the ore-fluid pool in the lower sedimentary succession and also acted as conduits for their upward migration. The ore-fluid, under progressive cooling, deposited the copper sulfide ores at Nallakonda, copper-lead sulfide ores at Dhukonda and lead sulfide ores at Bandalamottu. The ore bearing horizons have participated in deformations during basin inversion without any recognizable change in mineralization patterns.
