Palaeo-weathering Characteristics and Nature of Source Lithology of a Carbonaceous Metasedimentary Unit in the Dalma Volcano-sedimentary Belt, North Singhbhum Mobile Belt, Eastern India

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.