Surface and borehole geophysical analysis of structures within the Callide Basin, eastern Central Queensland

Traditional geophysical techniques, such as electrical, magnetic, seismic and gamma spectroscopic methods, have been deployed across the Callide Basin, Eastern Central Queensland, intent on delineating basin -wide structures. Further, innovative surface and borehole geophysical techniques have been applied for coal mine -scale exploration and production with the intention of reducing global geological ambiguity and optimising exploration resources at Callide Coalfields.

A very low frequency electromagnetic surface impedance mapping method, the SIROLOG downhole technique, acoustic scanning, electromagnetic tomography and

full wave -form sonic borehole logging have been trialed for geological hazard and mine design applications at Callide Coalfields as the precursor to their wider

application and acceptance in the Australian coal industry.

In this thesis, the theoretical basis for these techniques is provided. However, more importantly, the case studies presented demonstrate the role that these geophysical

techniques have played in identifying geological structures critical to mining.

Reverse faults that daylight in highwalls and intrusions constitute geological hazards that affect safety, costs and scheduling in mining operations. Identification of the limit

of oxidation of coal seams (coal subcrop) is critical in mine design. During the course of this thesis, the application of geophysical techniques resulted in:

a) a major structure (the "Trap Gully Monocline") being redefined from its original

interpretation as a normal fault to a monocline that is stress -relieved by minor scale thrust faulting;

b) two previously unidentified intrusions (the Kilburnie "Homestead" plug and The Hut "Crater" plug) that impinge on mining have been discovered;

c) the delineation of two coal subcrop lines has resulted in the discovery of an additional 1.5 million tonnes of coal reserve at Boundary Hill mine and the successful redesign of mining strips at The Hut Central Valley and Eastern

Hillside brownfield sites; and

d) the first ever attempt to petrophysically characterise the lithotypes within the Callide Basin.