oa Geophysics in greenfields regions to determine cover thickness: pre-competitive drilling in the Stavely region of Victoria

Fifteen pre-competitive stratigraphic holes have been drilled to test geological and mineral system models in the ‘greenfields’ Stavely region of western Victoria. Prior to drilling, seismic reflection and refraction, gravity, and airborne magnetic data were used to estimate the thickness of cover at the selected drill sites. This analysis also tested the reliability of the geophysical techniques in a range of geological conditions.

Comparisons with preliminary drilling data indicate that seismic refraction data successfully predicted cover thickness at six out of seven sites. Estimates of depth to magnetic source at the top of basement, derived from airborne magnetic data successfully predicted cover thickness at eight of ten sites. Seismic reflection was the least reliable technique with one out of four successful predictions. However, despite their success rate, neither the refraction nor the magnetic data gave reliable cover thickness estimates where cover materials were highly magnetic or had high seismic velocities.