Determining cover variability in the Capricorn Orogen with airborne EM

Abstract

This paper focuses on elucidating cover variability throughout the Capricorn Orogen in Western Australia. We use, as a baseline, data from a widely spaced airborne electromagnetic (AEM) fixed-wing survey acquired for the Geological Survey of Western Australia in 2014. The Capricorn 2013 AEM survey is the largest AEM survey by area flown in Australia to date, covering over 146 300 km2. The Capricorn Orogen is a highly mineral prospective under explored orogeny located between the Pilbara and the Yilgarn Craton. Whilst the western part of the Orogen is particularly well exposed, and as a result the surface geology, geological history tectonic setting is well understood, the north west and eastern regions are characterised by a variably thick and complex regolith. The region is relatively under-explored, although host to significant mineralisation, including mesothermal orogenic gold, copper?gold volcanogenic massive sulphides, and channel iron ore deposits. In a region of variable cover, geophysical (aeromagnetic, electromagnetic and gravity) and geochemical techniques are critical aids to the mapping of lithostratigraphic units that are covered by regolith materials, but also in providing an understanding of the regional geological factors that control the mineralisation. Here we discuss some initial results from the smooth model layered earth inversion of 30,119 line km of AEM data. We consider sections from geologically contrasting parts of the Orogen. The results show the complexity and variability of conductive cover in the region and suggest some areas in the orogen could be beneath 200m of transported and in-situ regolith cover. The regional regolith framework that is being developed from the AEM data will provide a basis for better understanding and interpreting regolith geochemistry that has been acquired across a region, particularly where outcrop is limited.