Morphology, Maceral Association and Distribution of Pyrite in the Tertiary Coals of Northeast India: a Proposal for the Classification of High Sulphur Coals

This paper is an attempt to focus on the Micro-Morphological characterization of pyrite and its quantitative distribution in the Tertiary coal deposits of Northeast India with the help of improved incident light microscopic techniques. The coal deposits of this region occur in the states of Meghalaya, Assam, Arunachal Pradesh and Nagaland, and are known to have originated in two distinct Tectono-Sedimentary settings. The coal bearing sequences of Meghalaya are Eocene in age and have evolved over platform areas under stable shelf conditions. On the other hand, the coal deposits of Assam, Arunachal Pradesh and Nagaland are Oligocene in age and have originated in the foreland basins Pillar coal samples from all the coal seams (Measuring a metre or more in thickness), either exposed as outcrops or in mine workings, have been subjected to this study.

The results of petrographic examination reveal that the coals of platform areas in Meghalaya are comparatively rich in pyrite. The mode of occurrence of pyrite identified are disseminated, cavity filling, framboidal, fissure and cleat fillings, Discrete-Grains and massive replacement (Dendritic form). In the coals of platform areas, the dominant form of pyrite is massive replacement whereas framboidal pyrite is the most common form in the coals of foreland basins. The study indicates that the concentration of Framboidal(>5 to 50 μm size), massive replacement (>lo to >15O μm size) and disserninated forms (