Petrology and Depositional Environment of Early Jurassic Coal, Western Australia

摘要

The Early Jurassic sub-bituminous coal of the Hill River area located in the Dandargan Trough of the northern Perth Basin Western Australia has been fully explored since 1981. A total coal resource of approximately 450 million tonnes has been delineated for open cut mining in the near future. The vitrinitc reflectance ranges from 0.47% to 0.50% which places the coal in sub-bituminous rank as per Australian standards. The coal has a high ash and moisture content and it is considered suitable fuel on or near site power station. Similar to the Permian coals of Western Australia, the coal is finely laminated with a subdued lustre and the dominant lithotypes are dull banded, dull and banded with minor bright and bright banded. The dominant maceral groups of the coal are vitrinite and inertinite followed by mineral matter and the exinite group of macerals. The mineral matter associated with the macerals consists of clay, pyrite and quartz. The sulphur content in the coal from the borehole CPCH1 ranges between 0.92% to 2.36%. On the basis of petrographic analyses, type of pyrite and trace elements distribution in the coal samples of the bore hole CPCH1 of the Mintaja block, the depositional environment postulated for the coal is an upper to lower delta type with a regressive phase of a marine transgression. This model for the depositional environment is also supported by the association of acritarchs and palynomorphs in the coal measures of the Hill River area.