Geology and organic petrology of some selected Permian and Jurassic coals of Western Australia
Keywords:Macerals, Minerals, Depositional environment, Permian, Jurassic, Western Australia
The commercial coal resources of Western Australia occur in sediments ranging in age from Permian to Jurassic. The coal from each period has distinctive geographical, biological and geological characteristics which effects its utilization in industry and power generation. Currently the Permian intracratonic Collect Basin is the only producing coalfield in Western Australia. The annual production from this coalfield is approximately 6million tonnes, which is mostly used for power generation. Another Permian coal deposit in the Vasse Shelf, located in the southern part of the Perth Basin has potential for export to Asian markets. The Early Jurassic coal of the Hill River area in the northern Perth Basin has been fully explored and is ready for mining as a source for power generation. All three coal deposits represent a measured in situ resource in excess of 1500 million tonnes for Western Australia.
Similar to the Gondwana coals of Australia, the coals are finely banded and the dominant lithotypes are dull banded with minor bright and bright banded types. The maceral composition of the coal is variable, however, the macerals of vitrinite and inertinite groups dominate, and the exinite and mineral matter contents are low, particularly in the Permian coals. On the basis of petrology of coal and the inter-seam sediments the depositional environment for the Permian coal was braided fluvial and fluvio-lacustrine, with marked fluctuations in the water table. The low water table accounts for fusain and inertodetrinite in the coal. The depositional environment for the Jurassic coal was of a low delta with some marine influence, supported by the presence of framboidal pyrite and acritarchs in the coal measures.