15th June 2017

With most exposed geological terrain in New South Wales considered ‘mature’ in terms of mineral exploration, there is an increasing drive to broaden the search space for new mineral discoveries.

This means there is a need to explore beneath more recently deposited sedimentary basins and thick unconsolidated sedimentary layers. Methodologies for sampling top-of-basement under cover, including cheaper drilling, are currently under development and there is great potential for significant discoveries in covered terrains across the state.

The new product is a depth to basement (DTB) model that covers all NSW. The model aims to constrain the thickness of post-Carboniferous cover that overlies the crystalline basement, as well as define the geometry of the overlying basins, as can be seen with the top of basement surface presented in Figure 1.

This first pass version of the statewide model is constrained by interpreted lithology from approximately 150,000 water bores, combined with pre-existing seismic picks, basement contours and magnetic source depth models all validated by collating and interpreting lithological logs from approximately 25,000 mineral, petroleum and coal drill holes (Figure 2). Surface basement and basin exposure is constrained using the line work from the Seamless geology and the Surface Geology of New South Wales 1:1 500 000 map line work.

The statewide model delivers three lithological volumes (unconsolidated cover, consolidated cover and basement), three surfaces (topographic surface, base of unconsolidated cover and top of basement), 2D contour maps of total cover thickness and thickness of unconsolidated cover, and a confidence volume model.

The thickness of cover overlying prospective belts will affect the economic viability of exploration programs targeting various styles on mineralisation, both in terms of the potential resource size relative to mining methods (costs of exploiting any resource) and exploration methods. Having a constraint on the regional-scale thickness of cover is a fundamental first step in assessing any region for its basement exploration potential.