Towards Resolving Dipping Contacts Undercover in the Capricorn Orogen Using AEM

Abstract

The Capricorn Orogen is located in central Western Australia and includes several Proterozoic sedimentary basins. The Yerrida and Earaheedy basins are located in the south-east of the orogen and were formed, and deformed, over multiple orogenic events. The complexity and thickness of these basins and presence of conductive regolith has hindered minerals exploration within the region. A recently acquired TEMPEST AEM survey across the Capricorn provides an extensive dataset to aid in the mapping of the basin lithologies and assessment of the potential for mineralisation within these basins. Before detailed interpretations can be made from 1D inversions of these data, an understanding of the reliability of TEMPEST AEM inversions is desirable.

1D time-domain inversion algorithms are useful for interpreting TEMPEST AEM data. However, it is important to understand the limitations of using such codes in geologically complex regions such as the Capricorn Orogen. The response from three simple scenarios involving a dipping conductive contact within a resistive basement, and a dipping conductive contact under a varying conductive regolith have been inverted using a 1D layered earth algorithm. Results show that conductive units in a resistive host dipping steeper than 25° are poorly resolved. When moderately conductive to resistive cover is present, the dip and thickness of dipping features can be defined, however, this is dependent on the depth of the conductive unit. Knowledge of the limitations of 1D AEM modelling provides some confidence for making geological interpretations from 1D inversions, as falsely resolved dipping features can be eliminated from the interpretation process.