Nature of Shear-Zone Hosted Epigenetic Gold Mineralisation in BIF of C.S.halli, Chitradurga Schist Belt, Western Dharwar Craton

Gold mineralisation occurs at Chikkasiddavanahalli (C S Hall!) in Archaean volcano-Sedimentary sequence of the Ingaldhal Formation, in Chiradurga Group, Dharwar craton. The C S Hal1i ridges and low mounds are about 1 2 km long and 100 in wide with N-S strike and vertical to steep easterly dips comprising mixed sulphide/oxide facies banded iron formations (MSOBIF) and associated ferruginous phyllites, metavolcanics and minor carbonates. Several horizons of BIF's occur as parallel to subparallel linear brands and extend over a strike length of 20-40 km with widths ranging from 2-25 m. These BIF s are highly sheared, deformed and metamorphosed to upper greenschist facies. The shears in BIF's are occupied by several syn-Tectonic quartz carbonate veins of various dimensions and found to be favourable loci for Gold-Sulphide mineralisation. Petrological studies show major mineral constituents with pyrite, arsenopyrite and subordinate grunerite, hornblende, chlorite, muscovite, ankerite, calcite, magnesian siderite and quartz. Most gold deposits world over are hosted in second order and subsidiary shear zones. The primary gold in BIFs is enriched with intense fracturing controlled by major shear systems extending from Gadag in the north and Doduguni in the south Active convergent margin settings related to accretionary processes and fluid activity are suggested to have led to Epigenetic gold mineralisation in BIFs at C S Halli area with an average gold grade of 2 08 g/t.