Morphology and Analysis of Gold Grains Associated with Auriferous Quartz Veins, Gopur, Keonjhar District, Orissa

At Gopur, Onssa, auriferous quartz veins with stringers and rich disseminations of sulphides occur in the latcntes derived by tropical weathering of metabasaltic rocks. Minute to coarse irregular gold grains were hand picked from the panned heavies obtained by washing the excavated wall rock materials of the quartz veins which are composed of powdery latente ± kaolinite ± quartz. The gold grains display pitted, fractured, striated, wavy surface and occasional smooth contour pattern. The gold content of the quartz veins and latentic wall rocks vanes widely from < 1 ppm to 9 ppm SEM-EDS and microprobe analytical results of four gold grains reveal contrasting chemical characters. One gold gram exhibits nmward increase in fineness value indicating that silver has been preferentially leached out by supergene fluid. This grain possibly represents the residually concentrated hypogene gold. The other gold grains do not show chemical gradients within the domain of individual gram and formed by precipitation from supergene fluids.