Genesis of the Sulfide Hosted Refractory Gold Occurrences within the Carbonaceous Metasedimentary Units of the Dalma Volcano-sedimentary Basin, North Singbhum Mobile Belt, Eastern India

Abstract Paleo-Mesoproterozoic (1.0-2.4 Ga) north Singhbhum mobile belt (NSMB) is one of the prominent polymetallic mineral belt within the Singhbhum crustal province of eastern India lying between Chotanagpur gneissic complex (CGC) in the north and the Archaean Singhbhum craton (>2.4 Ga) in the south. The study area is located along the northern fringe of Dalma volcano-sedimentary basin. Lithological variations, structure, metamorphism and tectonic setting indicate good prospect for regional gold exploration within this area. Extensive work by Geological Survey of India (GSI) within this basin reveals gold occurrences with its concentrations ranging from 0.1 to 4 ppm within the carbonaceous cherty quartzite. Gold mineralization within the area has been reported to be associated with quartz ± quartz carbonate vein either as disseminated gold or as refractory gold within the sulfides. A detailed study on the occurrence of refractory gold associated with carbonaceous cherty quartzite has not been carried out by any of the previous workers. The present work report the occurrence of refractory gold associated with sulfides within the carbonaceous host rocks. Detailed petrographic studies of the carbonaceous host rock reveal the presence of sulfides such as pyrrhotite, pyrite, chalcopyrite, arsenopyrite. EPMA studies of the host rocks indicate the presence of invisible gold within the sulfides varying in concentration from 100 to 1000 ppm. Total organic carbon (TOC), high resolution X-ray diffraction (HR-XRD) and Fourier transform infrared spectrometry (FTIR) analysis show the presence of organic carbon within the samples. Presence of organic carbon facilitates reducing environment required for gold mineralization within carbonaceous host rock in the study area.