Petrographic and geochemical characterization of coals from Tiru valley, Nagaland, NE India

Abstract

In Tiru valley region of Mon district coals occur in Barail Formation and are of Oligocene age. This study is the first investigation on the petrographic and geochemical characterization of these coals. These thinly bedded seams (<2 m) need systematic exploration for proper evaluation of the resource.The coals are bright to moderately bright in appearance and at places look moderately dull. The study reveals that Tiru valley coals are sub-bituminous to bituminous-D in rank. The chemical study reveals that these coals are perhydrous in nature with moderately high volatile matter content. The sulphur content was probably increased with pyrite inclusion as the most abundant mineral. Vitrinite is the most dominant maceral group constituting nearly 98% of all the macerals while liptinite and inertinite occur in very low concentration. Facies-critical models used to decipher the paleodepositional environment suggest that these coals evolved under wet moor with moderately high flooding in the paleomire which allowed the sulphate reducing bacteria to thrive.