Petrology and palynology of select coal samples from the Permian Waterberg Coalfield, South Africa

Abstract

The petrology and palynology of coals from the Permian-aged Waterberg Coalfield, situated in the Limpopo Province of South Africa, are considered. The Waterberg Coalfield contains a significant portion of the country's coal reserves, but is still comparatively underexplored. Detailed maceral analyses, combined maceral-microlithotype analyses, mean random and maximum vitrinite reflectance analyses, etching, and palynology studies were undertaken on coals from four productive horizons. There is a general upward trend in vitrinite content through the sequence (15–59 vol% mineral matter free), dominated by collotelinite, along with a slight decrease in coal rank. The lower Vryheid Formation coal has a comparatively low mineral matter and high inertinite content, dominated by inertodetrinite. The upper Grootegeluk Formation samples contain above 35 vol% mineral matter, and liptinite contents ranging from 14 to 21 vol%. The use of blue-light fluorescence in conjunction with incident light (single-scan method) revealed that liptinite is intimately associated with inertodetrinite and mineral matter, specifically clays and occasionally pyrite. It is evident that the liptinite maceral content has previously been under-reported in the Waterberg coals. The palynofloras correlate with the well-studied Witbank Coalfield. The petrography, along with the palynology, essentially confirm the palaeoenvironment of the Karoo Basin as progressing from a cooler, more oxidising environment, to a wetter, seasonal environment.