Features and characterization of graphite in Almora Crystallines and their implication for the graphite formation in Lesser Himalaya, India

Abstract

Layers, bands, lenses and pockets of graphite are confined to mica schists, garnet-mica schist, micaceous quartzites and black carbonaceous phyllites of the Almora Group, forming graphite prospect in Indian Lesser Himalaya. The field and microscopic features of graphite reveal that the graphite in Almora Group was crystallized from metamorphism of the organic material before Himalayan thrusting. Upto 100 μm size nodular and <5 μm size circular features points to the involvement of biogenic carbonaceous material in graphitization as also substantiated by δ 13C values and probably by the presence of V and P associated with this graphite. Impurities consisting Si, Al, Mg, O, Fe, Ti, V, Ca and K, are common with graphite. These are derived from associated minerals such as muscovite, quartz, biotite, garnet etc. Raman shifts obtained from this graphite suggest that it is an ordered graphite, with its fine dust scattered in the host rocks. The calculated degree of graphitization varies from 64 to 89, with no systematic spatial variation in the estimated temperatures (cf. 485–568 °C) of graphite formation. Within this range the temperatures for the intensely folded graphite are higher, probably promoted by the Himalayan tectonics. Although high end thermal records reported from the Almora Group are not evident in graphite, however these temperatures obtained from graphite match with host rock thermometry implying that the graphite was formed during regional metamorphism.