GEOLOGY, PETROLOGY AND UTILIZATION POTENTIAL OF SOME TERTIARY COALS OF THE NORTHEASTERN REGION OF INDIA

The coal-bearing Tertiary sediments of the northeastern region of Indi a range in age from Palaeocene to Oligocene. The coal deposits of Megh alaya and the Mikir and North Cachar hills of Assam contain generally thin seams of Eocene age and were formed under stable shelf condition in peripheral platform areas. The coal deposits of Oligocene age occur in a narrow, linear belt of overthrusts referred to as the 'belt of S chuppen', that extends from Nagaland through Assam to Arunachal Prades h; they were deposited in near-shore, deltaic, wet forest swamps to ma rshy environments, close to a geosynclinal trough. The coal seams atta in considerable thickness in the Makum and Namchik-Namphuk coalfields. Comparisons of coal type and rank variations in the Eocene and Oligoc ene coals indicate that the coals are broadly similar. The coals are v itrinite-rich (>70 vol%, mineral-matter-free hereafter referred as mmf ), with moderate amounts of liptinite (>8 vol%, mmf) and inertinite (> 5 vol%, mmf). The coals are high in volatile matter (38-57 %, dry, min eral-matter-free basis, hereafter referred as dmf), sulphur(1-10 %) an d hydrogen contents (4-9% dmf). The carbon content of the coals ranges from 68% to 85% (dmf). The coals have caking properties in restricted zones. The vitrinite reflectance of the Oligocene coals (%R(r) = 0.53 -0.74) is slightly higher than that of the Eocene coals (%R, = 0.37-0. 67). As per ASTM Standard, the Eocene coals are classified as sub-bitu minous C to high volatile bituminous C, and the Oligocene coals as sub -bituminous A to high volatile bituminous B. Microscopic examination o f the coals shows a number of features which indicate that the northea stern coals may have generated hydrocarbons. Most of the Eocene and Ol igocene coals are suitable for combustion and conversion (e.g., liquef action) processes. The coals with caking properties are being used at rates up to 5-10% in blends for metallurgical coke provided their sulp hur content is below 3% and their ash content below 10%.