Use of geochemical attributes to evaluate the authogenetic characteristics of Eocene coals from Jaintia Hills, Meghalaya, India

Abstract

In Meghalaya, coal is present in the Lakadong sandstone formation (25 to 250 meters thick) of the Eocene epoch. The three major clusters of coalfields in Meghalaya are the Garo Hills, Khasi Hills, and Jaintia Hills. Based on petrographic studies, tectonics, and sulphur content, done by many scientists, it has been suggested that the coal-bearing strata of Jaintia Hills were formed from swamp forest on the platform areas and repeatedly subjected to marine transgression and regression. The present investigation is based upon geochemical attributes extracted from the inorganic component of coal to supplement the previous findings and also to develop a detailed understanding of the paleo deposition condition of these coals. Coal samples from two coal seams at nine locations of the Sampar coalfield of Jaintia Hills were collected and studied. The samples are subjected to X-Ray Fluorescence Spectroscopy, X-Ray Diffraction Analyses, Fourier Transform Infrared Spectroscopy, and ash analysis to study geochemical and mineralogical composition and ash yield. Mineralogical and geochemical data generated during the study were used to predict the autogenetic character of these coals. The study reveals that coals of Jaintia Hills deposited in coastal swamps and lagoons on stable platform areas with a minuscule grade of tectonic activity, which is influenced by the seawater incursion. These coals were deposited in reducing to significantly reducing conditions and warm and humid to semi-arid climatic conditions. No signature of geothermally active fluid has been found.