Australia's cover

Last updated:22 August 2018

The Australian continent is estimated to be 80% covered by Cenozoic and younger rocks. Where basement rocks crop out, many are deeply weathered. One of the first-order challenges for industry is being able to reliably predict at the deposit-, district-, province- and continent-scale: 1) the depth to prospective basement, and 2) the character of the overlying cover.

Methods will be developed to improve the cover depth and character predictions at the district-scale through new data acquisition and experimentation. A range of methods will be used and predictions made prior to validation by drilling. The southern Thomson Orogen and the Stavely region of western Victoria will be the first areas to be drill tested, with other terranes to be tackled in subsequent years.

Methods will be developed to improve province-scale cover depth and character predictions. One method being considered for baseline cover mapping is a very-broad spaced (nominal 110 km) Airborne Electromagnetic (AEM) survey for the entire continent. A National AEM survey is analogous to the AWAGS reference survey for magnetic and radiometric data. Before this method is 'rolled out' nationally, a test area will be acquired across the southern Thomson Orogen. The results will be integrated with the other multi-disciplinary regional-scale cover studies in the same region.

Ground conditions and cover character change dramatically across the continent, making it difficult to easily produce a consistent map of cover thickness across Australia. By integrating the knowledge acquired at the regional-to province-scales across many areas of the continent, Geoscience Australia plans to generate a seamless national map by integrating the smaller scale cover maps with larger scale data. Where possible, the map will be constrained by drilling. This cover thickness map will provide explorers with a first-order screening tool for the whole continent.

To improve exploration success in greenfield areas, Geoscience Australia will also develop techniques to map the geochemistry of thin cover (<5 m depth) by applying multi-covariate modelling and advanced sample designs (Latin hypercube) to existing datasets. The techniques will be tested initially in the southern Thomson Orogen, and later used to produce new national maps of near-surface cover, focusing on key regolith geochemical components such as carbonate, silica, iron, potassium, uranium and thorium. These maps will link to a new National Regolith Map, which will integrate all existing regolith maps from across the States and Territories. Together these surface materials maps will assist explorers in understanding landscape evolution at the district- to province-scale and in designing and interpreting geochemical sampling programmes.

Mapping depth and character of cover in the Northern Territory using Airborne Electromagnetics (AEM).