Analytical variation in Australian coals related to coal type and rank

Abstract

Analyses of Australian coals, ranging in age from Permian to Miocene, are reviewed principally by using the van Krevelen diagram (atomic O/C vs. H/C), but also by plotting calorific value vs. volatile matter. Groups of coals of particular ages or from particular areas or seams within coalfields plot in well-defined parts of the diagrams. Each group, however, covers only part of the rank range from lignite to semi-anthracite. Accordingly, the New Zealand (NZ) Coal Band, based on medium to high H/C Late Cretaceous and Cenozoic coals, is used as a reference maturation path. The extremes of H/C in low-rank Australian coals are shown by the particularly high H/C Jurassic Queensland coals and the low H/C Triassic Queensland (Callide) coals. The majority of coals plot between these extremes. These include Cenozoic Victorian lignites (brown coals) which, except for high H/C pale and light lithotypes, are similar to New Zealand lignites. Vitrains from Australian Permian coals plot across the width of the NZ Coal Band, and the range of Permian coals extends into much lower H/C parts of the van Krevelen diagram. The spectrum of all coals is continuous throughout the extensive range of H/C. Comparison with data on maceral group compositions shows close relations between H/C ratios and the proportion of vitrinite, provided allowance is made for the counteracting effects of high H/C liptinite and low H/C inertinite. In most coals, vitrinite is the dominant maceral group, and the range of H/C ratios of vitrain samples from Permian coals shows that vitrinite composition also must be significant in influencing the elemental composition of the heterogenous coal.