Silver Mineralisation in Early Proterozoic Rocks of Bharak Area, Near Baghera, District Bhilwara, Rajasthan

Rich silver mineralisation (up to 0.78% on the surface and O. 58% in borehole) has been discovered in siliceous dolomitic marble at the interface with stratigraphically underlying calc-silicate rocks of Bharak area (Rajpura-Dariba Group of Late Archaean/ Early Proterozoic age). The surface geochemistry over the region bas helped in delineating a 600 m x 200 m zone on the surface having sil vel' content of more than 10 ppm and ranging up to 7800 ppm. The subsurface data obtained by drilling has shown the extension of the mineralised zone beyond the limits of the surface geochemical anomaly, and the extension is caused by the continuation of folded strata below surface. Ore microscopic study has indicated that the main silver ore mineral is cerargyrite (AgCI) with minor relicts of argentite Ag₂S).

The variation diagram of Ag-Cu-Pb-Zn in the stratigraphic layering at the contact zone of siliceous dolomitic marble and the calc-silicate rocks, depicts significant patterns showing syn-sedimentary stratiform silver precipitation in a particular stratigraphic section, at the bottom of the siliceous dolostone. Two pulses of chemogenic silver precipitation within the bottom part of the siliceous dolomitic marble associated with CuPb- Zn are identified, while the effects of remobilisation and supergene enrichment are predicated by certain aberrant peaks of silver with variable relationship of associated metals such as Cu, Pb and Zn.