Interpreting airborne electromagnetic data unburdened from induced polarisation effects: an unconventional mineral discovery case study from the eastern Yilgarn region of Western Australia

Induced Polarisation (IP) effects commonly distort time-domain Airborne ElectroMagnetic (AEM) data, resulting in atypically fast decaying transients and non-monotonic decay curves. These effects are not always easily recognisable visually, and can subdue, negate, or even overturn the localised expression of potential bedrock conductive sources worthy of exploration focus. The inclusion of such affected data in inversion routines can result in misleading models featuring unusually high resistivity values, erroneously shallower resistive zones, and higher conductivity artefacts near the bottom of the models. Simultaneously solving for chargeability and resistivity during inverse modelling can drastically improve the resistivity models produced, honouring both the measured AEM data and the geology more closely. These enhanced resistivity models can then be used to simulate what the AEM data would have looked like in absence of IP effects and form the basis for finer interpretation of the profile AEM data. The resulting 'IP-free' AEM data can also be used as input dataset for other forward and inverse modelling routines otherwise not yet accounting for the contribution of the IP phenomenon. This innovative workflow has been successfully applied to a historical heliborne EM dataset acquired in the eastern Yilgarn region of Western Australia. Although significant parts of the survey were initially deemed non-prospective due to the lack of discrete conductors, several distinct weakly conductive features originally masked by IP effects could be recovered and accurately delineated. Drill testing of one of these IP-corrected AEM anomalies intersected disseminated nickel sulphide mineralisation returning 8m @ 0.64% Ni within a broader interval of 17m @ 0.40% Ni from 102m at a depth predicted by traditional thin-plate modelling. The mineralised occurrence has no surface expression or discernible response in the raw AEM data.