Genesis and Controls of Graphite Mineralisation in Daspalla Belt - A Greenfield Prospect in Nayagarh District, Odisha, Eastern India

ABSTRACT The Proterozoic Eastern Ghats Mobile Belt (EGMB) in the eastern Indian shield is not only characterised by its structural and metamorphic complexity but is also known for its rich deposits of graphite and manganese. In Odisha, graphite is reported in six geographical belts in the northern part of the EGMB. A new greenfield prospect, the Daspalla Graphite Belt (DGB) in the Nayagarh District of Odisha, is reported in the present investigation. An attempt has been made to study the genesis, control and mode of occurrence of graphite in the DGB. Laser Raman Spectroscopy (LRS) was conducted to characterise and decipher the molecular structure of graphite, and carbon isotope studies were conducted to determine δ13C values and total organic carbon content. In EGMB, graphite is present in high-grade granulite facies metasediments, including its migmatised variants. Graphite occurrence is primarily governed within selective lithology, while its mineralisation is controlled by regional structural fabrics. In DGB, graphite, along with the host rock, forms a pair of westerly plunging antiform and synform structures. The northern limb of the antiform is truncated by the WNW-ESE-trending Mahanadi Shear Zone (MSZ), whereas the southern limb of the synform is truncated against the NNW-SSE-trending Rushikulya Shear Zone, resulting in an S-shape to the belt. Axial trace of the antiform and consecutive synform trends is almost E-W. LRS study indicates the presence of a single major ~1580 cm−1 (G) band. Some minor bands at ~1350– 1360 cm−1 and ~2720 cm−1 are also observed. In the carbon isotope study, the δ13C of samples ranges from −23.4‰ to −27.6‰ with total organic carbon content from 2.3 to 11.5%. The δ13C value less than −20‰ suggests that the graphite of DGB was formed by conversion of organic or carbonaceous matter during granulite facies metamorphism of the sediments.