Tertiary Volcanic Fields of Eastern Australia: Regional Characteristics and Implications for Coal Quality and Mining

ACARP project C22023 focused on the influence of Cenozoic basalts on coals of the Bowen Basin and nearby basins in eastern Australia. The project included a compilation of drillhole data, which illustrate regional-scale variations in the thickness of basalts. These thicknesses tend to be greatest near volcanic centres on the western margin of the Bowen Basin, and the overall volume of basalt decreases southward. An isopach map generated from drillhole data illustrates that, in many places, Cenozoic basalts fill channels that were incised into a late Mesozoic or early Cenozoic landscape. Examples of basalt-filled channels are well-exposed at the Meandu Mine in the Tarong Basin, where they are sourced from the nearby Bunya Mountains. Geochemical data from both basalt and coal at the Meandu Mine demonstrate that coal in close proximity to basalt frequently has trace element concentrations that are elevated compared to coal at significant distance from basalt. The transfer of trace elements from basalt to coal is likely via hydrothermal circulation, which may also form clays that have important geotechnical consequences. On a regional-scale, our study found only subtle geochemical differences between so-called "lava fields" and "central volcanoes," suggesting that the geochemical influences of Cenozoic basalts on sediments of the Bowen Basin are relatively uniform, despite potential differences in the generation of these basalts.

This report is divided into five subsequent sections. Section 2 provides an introduction to some of the issues that arise from interactions between coal and intrusive or extrusive rocks. This section also includes reference to some previous case studies. Section 3 focuses on variations in basalt thickness in the Bowen Basin and surrounding regions. Section 4 investigates geochemical differences between so-called "lava fields" and "central volcanoes" in eastern Australia. Section 5 is a case study of the physical and chemical characteristics of basalt in the Meandu Mine of Queensland. Finally, a list of references is provided in Section 6.