Gravity surveys

Two new major gravity surveys were undertaken in May and June, 2009. Nearly 4000 new gravity stations in the Broken Hill district now provide coverage at a 2 km × 2 km grid. This extends the existing high-precision gravity coverage over the world-renowned Broken Hill deposit into surrounding areas facilitating mineral exploration. A further 2500 new gravity stations in the Jerilderie–Oaklands Basin area providing coverage at 2 km × 2 km and 4 km x 4 km grids, will support energy and mineral exploration in this area.

Teleseismic survey

Teleseismic surveys are being conducted over the Murray Basin in the southwest of NSW in collaboration the Australian National University. Seismic equipment from ANSIR (Australian National Seismic Imaging Resource) is used to map variations in seismic travel times from distant earthquakes. Tomographic inversion produces a 3-dimensional model of variations in seismic wave speed in the upper mantle below southeastern Australia.

The results of the completed teleseismic surveys are summarised in Quarterly Notes 129. Presently, the resulting images reveal that the upper mantle consists of several distinct domains of fast and slow P-wave velocity (Vp) that provide unprecedented insight into compositional and temperature variations related to lithosphere of different origin, and more recent processes such as Cenozoic volcanism. A main result is that the transition from Precambrian to Palaeozoic lithosphere appears to occur much further east than previously reported. This boundary is distinguished by a clear contrast between higher velocities in the west and lower velocities in the east. Consequently, the Stawell Zone, traditionally seen as part of the Lachlan Orogen, is now interpreted at upper mantle depths, to have closer affinities with the Delamerian Orogen.

The project will be extended to provide teleseismic coverage of most of NSW between 2009–2011.