Thermally altered coals from bore core EBM-1, East Bokaro coal field, Damodar Valley, India: A petrographic inference

Abstract

Petrographic analysis of the coals from bore core EBM-1 of East Bokaro Coalfield revealed characteristic changes as a result of thermal alteration by an intrusive body. The enhancement of ‘rank’ (increase in the VRr% values) is observed in the heat affected coal in the lower part of the bore core. The vitrinite in the coal at a depth of 984.95 m showed devolatilization vacuoles and initiation of mosaic structure due to heat alteration, dessication cracks and micropores. Meta-liptinite having reflectance value higher (1.67%) than that of the host vitrinite (1.09% - 1.36%) was also recorded. Bi-reflectance values of the un-altered coals were normal in the range of 0.06% - 0.09% where as the altered coal at a depth of 984.95 m showed an abnormal increase in the values (0.23%). Presence of secondary injected mineral matter and char particles further indicate the effect of thermal alteration. Palynological investigation of both altered and un-altered coal reveals that the palynomorphs recovered from the altered coal are dark and opaque due to the charring effect while the palynomorphs from un-altered coals exhibit a clear internal structure and can be easily identified.