An Overview of Meghalaya Tertiary Coals of the North-Eastern Region of India

ABSTRACT This paper embodies the review of the research on Meghalaya coals. The coal deposits of Meghalaya are located within the Lakadong Sandstone Formation, which dates back to the Eocene epoch, and are primarily confined to platformal settings. These coal-bearing successions experienced multiple phases of marine transgressions and regressions during the Eocene epoch. The coalfields are spread across three hilly districts of Meghalaya: Garo, Khasi, and Jaintia Hills. The coals of Meghalaya are low in moisture (<4%), moderate ash yield (up to 28%), high volatile matter (40-60%), and fixed carbon content (>40%). They are rich in carbon content, averaging 75%, with significant hydrogen (more than 4%) and oxygen (<12% average). However, it has low nitrogen content (<1%). The coals are rich in sulphur content, reaching upto 12%, with most sulphur in organic forms, followed by pyritic forms. Petrographic analysis reveals that these coals are predominantly composed of vitrinite, accounting for ~ 70% of the maceral content, with low concentrations of inertinite and moderate liptinite content. Mineral matter is also present in an appreciable amount, reaching up to 21%. The vitrinite reflectance values, ranging from 0.40 to 0.68%, classify these coals as sub-bituminous C to high volatile bituminous type C. The occurrence of single, double, and multicelled teleutospores suggests that these coals have evolved from typical Tertiary flora. Based on maceral composition, the coals of the Garo Hills are interpreted to have originated predominantly in reed-dominated to open-water swamp environments under telmatic to limno-telmatic conditions. In contrast, the coals of the Khasi Hills were primarily formed in forest swamp settings, also influenced by telmatic to limno-telmatic depositional conditions. Additionally, the abundance of resinous material indicates a substantial contribution from coniferous vegetation within the swampy depositional environments. Geochemical analysis suggests that the Meghalaya coals are primarily gas-prone, with limited oil-prone potential, and contain type III kerogen, characterised by a mixed type II/III composition. These coals have a bright prospect due to their low moisture content, low ash, high volatile matter, and high carbon and hydrogen content.