A geological assessment of airborne electromagnetics for mineral exploration through deeply weathered profiles in the southeast Yilgarn Cratonic margin,Western Australia

Mineral exploration in regolith-dominated environments is challenging, requiring the development of new technical tools and approaches. When airborne electromagnetics (AEM) is combined with information on stratigraphy, mineralogy, geochemistry, drilling and landscape observations in a geological context, it becomes a powerful approach to describe the architecture of the regolith cover. This has significant implications for mineral exploration in any regolith-dominated terrain (RDT). This research presents two case studies of AEM data, integrated in a geological context for mineral exploration in the Yilgarn craton margin/Albany–Fraser Orogen (AFO).In one of the study sites presented (study site 1: Neale tenement), the availability of AEM data allowed for lateral and vertical extrapolation of the information contained in datasets at specific locations, thereby creating a 2D architectural model for the regolith cover. In addition, it was determined: (1) the total thickness of the regolith cover and its variability (between 2 m and ~ 65 m); (2) that low conductivity transported overburden and silcrete units, with a total thickness between ~ 5 and 45 m, is widely distributed, capping the upper saprolite; and (3) that the silcrete unit varies laterally from being completely cemented to permeable, and that these permeable areas (“windows”) coincide vertically with mineralogical/textural/moisture/salt content changes in the underlying saprolite, resulting in increased conductivity. This has been interpreted as resulting from more intense vertical weathering, and consequently a higher vertical geochemical dispersion of the basement signature towards surface. AEM has been used to assist in identifying and describing the lateral continuity of these “windows” in areas with no direct field observations. Surface geochemical sampling above these permeable areas may deliver more reliable geochemical basement signatures.In the second study site (Silver Lake tenement) the AEM data was strongly influenced by the high conductivity of the hypersaline groundwater. This had a significant effect on the AEM response, resulting in reduced depth penetration and reduced resolution of subtle conductivity contrasts between cover units. Despite this, the AEM data set, combined with geological observations in the area, was able to map the presence and extent of a buried palaeochannel network, the most significant architectural sedimentary feature in the cover. This interpretation allowed for a more efficient drilling campaign to be designed to sample the fresh basement rock suites in the area, by avoiding drilling into palaeochannels.Integrated and constrained by the geological context, the application of AEM conductivity models by geologists is envisioned as one of the most promising tools within the exploration geologist toolbox to understand the architecture of the cover.