Chemical characteristics of liptinite macerals in humic and sapropelic coals

Abstract

According to previous studies alginite does not occur in humic coals. However, in coals from the Saar District, F.R. Germany, alginite was identified by fluorescencemicroscopy. In addition, high amounts of an undeterminable liptinite maceral were found and tentatively explained as an alteration product of alginite. Therefore, organic geochemical methods were used to characterize and identify this unknown liptinite maceral. Organic geochemical parameters such as CPI, pristane/phytane ratio and methylphenanthrene index, show not only a dependence from coal rank but also yield additional information about the type of organic matter input and the depositional environment of the coals. A series of coals of different origins around 0.8% vitrinite reflectance were investigated, to determine how far the geochemical parameters reflect change in facies. The samples included cannel, boghead and resinite-rich coals, as well as isolated durain bands. With increasing amounts of alginite in the coal, the CPI, pristane/phytane- and C 4-naphthalene/phenanthrene ratios of the extracts decrease. As illustrated by two representatives samples, some resinite- and sporinite-rich coals show a primarily naphthalene derived aromatic composition, whereas some alginite-rich coals of the same rank show phenanthrene and its derivatives to be dominant. With respect to technological properties most coals from the Saar District correspond with a higher rank than indicated by reflectance measurements. Those coals in general show lower values of the aforementioned ratios in comparison with Ruhr coals of similar vitrinite reflectance values.