oa Depth to Basement calculation in Southern Thomson, QLD.

The southern extension of the Thomson Orogen near the New South Wales border in southern Queensland is an underexplored greenfields area with mineral potential. The uncertainty surrounding cover thicknesses in the area leads to increased exploration risk. Calculation of a depth to basement surface lowers risk for greenfields explorers and is a valuable contribution to regional geological understanding.

Available drillholes show basement depths vary from about 100 m to over 3 km in the study area but data is too sparse to create a reliable surface. A combination of different automatic depth to basement techniques, including Euler deconvolution and Naudy, were used to create a depth to basement surface. These techniques were preferred due to a regionally extensive high frequency, low amplitude magnetic signature attributed to shallow sources in one of the cover sequences in the study region.

A combination of Geosoft’s Located Euler and standard Euler Deconvolution were used to calculate depth to basement solutions. Naudy depths were also compared to the Euler solutions, particularly in areas where the drill holes indicated the basement was relatively shallow (where smoothing associated with gridding can cause overestimation of source depths) or dyke-like features were present.

Seismic data available in the north of the study area was interpreted and used as a secondary quality control check (along with the drill hole data) on the basement surface. The final depth to basement surface defines an area of shallow basement in the south-west of the study area.