Himalayan coals: their nature, composition, formation and rank

Abstract

The results of maceral, microlithotype and reflectance analyses, so far carried out on the Palaeozoic (Permian) and Tertiary coals of Himalaya, have been presented along with the details of geological and chemical (proximate) studies. The Permian coals, enclosed in the sediments dispersed as thrust slices in the eastern Himalaya, are characterized by their high rank and the dominance of the maceral vitrinite. In general, these coals are classified as semianthracite, except for the Bhutan coals which are of low rank and high volatile bituminous in nature. Almost all the macerals contain fairly high amount of mineral matter. Finely disseminated argillaceous matter is the most common mineral suite present in the coals followed by carbonates and iron sulphide (pyrite). In most of the cases, the mineral matter is present as infillings in numerous sets of fissures which traverses the coals. These infillings seem to have been developed during the tectonic activity and represent secondary minerals impregnated in various macerals. Often the presence of high amount of mineral matter has greatly reduced the quality of coal. Besides, the marine animal fossil-bearing mineral concretions (coal balls) have indicated that these coals were formed in a series of lagoons under the influence of marine conditions.

The Upper Tertiary coals, associated with the Tipam sediments in the eastern Himalaya, occur as small lenses, very thin impersistent seams and pockets which are characterized by the dominance of maceral vitrinite. It is generally represented by the structured variety (telinite). In general, the cellular structures indicate that these coals have been formed by the burial of wood logs in the fluvial sediments. An important feature of telinite is the presence of folded tissues which attain prominence in the coals occurring closer to the main boundary faults. The coals in this area exhibit lignite-bituminous stage in rank and are comparable to the Mesozoic coals in peninsular India. This stage in rank has been possible mainly due to the tectonic disturbances.

The Lower Tertiary coals of Jammu area are the only economically workable deposits in the Himalayas. These are associated with the beds containing marine animal remains. This indicates that coal formation took place under near-shore environment. These coals are comparable to the Permian coals of the eastern Himalayas. They are also rich in maceral vitrinite and semianthracitic in rank. Such a high rank of these Tertiary coals may be attributed to the effect of tectonic movements in the Himalayan areas.