Annual General Meeting & "Estimating Cover Thickness in the Southern Thomson Orogen – A Comparison of Applied Geophysics Estimates with Borehole Results"

Date & time

5.30–7pm 17 April 2018


Jaeger Seminar Room, RSES (building 61), ANU


Mr. James Goodwin (Geoscience Australia)

Event series


 Patrick Carr

The geology of the southern Thomson Orogen in northern New South Wales and southern Queensland is rarely exposed with tens to hundreds of metres of overlying regolith and sedimentary rocks largely consisting of Eromanga Basin sediments) obscuring the basement geology. These cover sequences are a significant impediment to mineral discovery and highlight the need for new precompetitive data to be collected to increase our understanding of the basement geology and its mineral potential in a poorly understood region of Australia’s geology.

One of the ways in which new data was collected was through stratigraphic drilling. Before drilling was undertaken, however, estimates of the cover thickness were sought to reduce the risk associated with intersecting the basement geology. Estimates of cover thickness were derived by applying the geophysical techniques of refraction seismic, Audio-MagnetoTellurics (AMT) and Targeted Magnetic Inversion Modelling (TMIM). These techniques highlight that the basement-cover interface of the Southern Thomson Orogen can be recognised by its seismic velocity, electrical conductivity and magnetic susceptibility contrasts, respectively.

However, the cover thickness estimates shown here are, in some cases, not coincident and it is important to take into account each technique’s unique limitations and uncertainties when assessing their results. This was undertaken at three sites where the geophysical estimates could be compared to boreholes that intersected the basement geology. This provided an insight into the nature and character of the cover and the effectiveness of each of the geophysical techniques in determining cover thickness.

James graduated from Monash University with a Bachelor of Science (Honours) before joining Geoscience Australia as a Geophysicist. His work involves the collection, modelling and interpretation of various geophysical datasets to provide new information that supports exploration in Greenfields terranes. This includes the integration of geology and geophysics, through 3D modelling, to provide interpretations of basement geology obscured by cover. James is actively involved in the Australian Society of Exploration Geophysicists and has recently commenced his second term as the ACT Branch President.

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