Characterisation of lignite lithotypes from the "Kovin" deposit (Serbia) - Implications from petrographic, biomarker and isotopic analysis

Abstract

Four lignite lithotypes (matrix coal, xylite-rich coal, mixture of matrix and mineral-rich coal and mixture of matrix and xylite-rich coal), originating from the Kovin deposit, were investigated in detail. The paper was aimed to determine the main maceral, biomarker and isotopic (delta C-13) characteristics of investigated lithotypes. Based on these results the sources and depositional environment of organic matter in 4 lithotypes were established. These samples were also used as substrates for investigation of the influence of diagenetic alteration on delta C-13 signatures of biomarkers, as well as for assessment of the most convenient utilization for each lithotype. The investigated lithotypes differ in accordance with the composition of huminite macerals. Xylite-rich coal notably distinguishes from other lithotypes beacuse of the highest content of conifer resins vs. epicuticular waxes. The mixture of matrix and mineral-rich coal is characterised by the greatest contribution of algae and fungi and the most intense methanotrophic activity at the time of deposition. In all coal lithotypes diagenetic aromatisation influenced isotopic composition of individual biomarkers. Xylite-rich coal has the poorest grindability properties. However, this coal lithotype is the most suitable for fluidized bed gasification, whereas the mixture of matrix and mineral-rich coal has the lowest applicability for this process. The calorific value decreases in order: xylite-rich coal > matrix coal > mixture of matrix and xylite-rich coal > mixture of matrix and mineral-rich coal. The increase of organic carbon content and calorific value is controlled by the increase of contribution of wood vegetation vs. herbaceous peat-forming plants, as well as by stability of water table during peatification.