Shale gas is becoming a very important energy resource throughout the world. 10 borehole samples of varying depths from 755-1480m belonging to Barren Measures (upper Permian), Raniganj (upper Permian) and Panchet (lower Triassic) formations of Raniganj coal basin have been selected. Various analyses have been carried out viz. technological, elemental composition, X-ray diffraction, Fourier transform infrared (FTIR), rock eval pyrolysis, organic petrography and sorption analyses. Different types of organo-petrographic entities viz. sandy clay, clayey sand, organosandyclay, humic clay and organic clay were identified. Shaly-microlithotypes were also differentiated. The macerals (organic matter in shales) exhibit normal maturity course. Sorption studies were used for estimating Langmuir volume of shale samples which depicts good correlation with total organic carbon (TOC), organic clay and organo-silty-clay separately. Langmuir volume was also observed to indicate good correlation with shaly-microlithotype which point towards positive role of organic matter and clay association in gas adsorption. Vt60 (volume of vitrinite grains with reflectance greater than 0.60%) indicates that Barren Measures and Raniganj Formation has good hydrocarbon generation potential.

The Palaeo to Mesoproterozoic Dalma volcano-sedimentary basin (DVSB) is a typical greenstone belt sequence within the North Singhbhum Mobile Belt (NSMB) of Singhbhum Crustal Province (SCP), eastern India. The volcano-sedimentary belt is situated in the central portion of NSMB and separates the Chaibasa and Dhalbhum formation lying at its south from the Chandil Formation at its north. The metasedimentary unit comprises carbonaceous phyllite, carbonaceous cherty quartzite, quartz mica schist and quartzite. In the present work, the Au-rich carbonaceous metasedimentary rocks were studied to understand the source rocks characteristic, paleoweathering history and possible tectonic set-up. Geochemical classification diagrams based on the major oxide data indicates that these units belong to arkose to wacke field and the protolith underwent moderate to high degree of chemical weathering. Based on critical elemental ratios, it is inferred that the sediments were subjected to moderate degree of physical weathering, associated with sediment sorting and recycling. A fractionated REE pattern coupled with prominent negative Eu anomaly and elevated Th/Sc ratios indicate a felsic provenance for these metasedimentary units. The data further suggests that the sediments were deposited in a passive margin tectonic setting, during a prolonged period of upliftment and erosion of the Archean Singhbhum granite complex.

In the present work, gold‐bearing carbonaceous phyllites in the Dalma volcano‐sedimentary belt (DVSB), occupying the central region of the North Singhbhum Mobile Belt in eastern India were studied to understand the nature and mode of occurrence of gold mineralization. We propose that the protolith of the carbonaceous phyllites, that is, organic‐rich black shale, was the major source of Au in the phyllite‐hosted gold mineralization reported from the DVSB. LA‐ICP‐MS analysis of pyrite in this study reveals elevated Au contents in the early‐formed sedimentary pyrite (syngenetic and diagenetic pyrite). Trace element systematics confirms the presence of invisible Au with in the sedimentary pyrite as solid solution (invisible gold). Petrographical evidences suggest a close spatial relationship of Au‐enriched pyrite and carbonaceous material. Stable carbon isotope values confirm the organic nature of the carbonaceous matter. Further, the high organic carbon content of these samples falls well within the favourable range of an auriferous carbonaceous host rock. These evidences suggest that the organic carbon played a key role in fixation of gold in the carbonaceous shales. Subsequent diagenesis resulted in the release of Au from the organic matter and its incorporation onto the coeval sedimentary pyrite. Field observations and reports by previous workers indicate that these rocks were subjected to a late‐stage metamorphic/hydrothermal event. Paragenesis of pyrite coupled with its trace element systematics reveals that this late‐stage event resulted in the formation of younger euhedral pyrite and pyrrhotite and released invisible gold from the pre‐existing sedimentary pyrite followed by its precipitation in the quartz reefs. Based on these studies, we propose a two‐stage model of gold mineralization, wherein gold was initially incorporated in black shale‐hosted sedimentary pyrite and later released and precipitated in quartz veins.

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.