Adapting the use of AEM for Greenfields VMS Exploration under Cover

Download Article as PDF

In partnership with Aarhus Geophysics and Sandfire Resources, we presented the results of our work exploring for greenfields base-metals at AEM 2018 in Denmark.

Exploring under conductive cover in the Bryah and Yerrida Basins of central Western Australia poses serious limitations to the use of AEM for direct targeting of conductive bedrock anomalies potentially associated with VMS deposits. We present an alternative approach, where robust geological modelling based on AEM plays a major role in the exploration strategy.

The AEM is not only directed at targeting of bedrock conductors, but importantly, at supporting the development of a robust basin-wide geological model to identify priority areas for follow up surface geophysics and geochemistry. A patchwork of AEM surveys has been acquired by various explorers and contractors between 2009 and 2018. Systems and system specifications vary greatly. Accurate geological interpretation cannot be derived from either raw data or fast/approximate conductivity products provided by contractors. All datasets require reconciliation with a common workflow and robust modelling strategy, which also takes prior geological information into account. Historic AEM data have been reprocessed and reinverted. The central block has just been flown and is currently subject to the same workflow.

The end result will be a seamless basin-wide 3D conductivity model (extending over 6500 km2) which will inform the geological interpretation and subsequent follow-up exploration efforts. The new 3D models already allow clear identification and modelling of pyritic black shale horizons, enabling the anomalous geochemistry and strongly conductive nature of these units to be discounted in the targeting process.