Geophysical characterisation of the Trident gold deposit, Western Australia

Abstract

The Trident gold deposit is contained in the Plutonic Well Greenstone Belt, about 900 km northeast of Perth, Western Australia. The deposit is hosted in a highly sheared ultramfic unit overthrusted by granite. This project examined the physical properties of the important rock units to determine whether they contrast sufficiently to allow mapping of mineralisation, geology and structure. It investigated the possible occurrence at Trident of the most important mineralised lithological unit in the district, the `mine mafic'. The project also investigated the nature of the thrusted contact between granites and greenstones, one of the most important structures in the district. Drill core samples representing the major lithologies at Trident underwent a range of petrophysical testing. Gravity profiles were collected over the deposit and these were analysed along with high resolution airborne magnetic and radiometric data. The magnetic and radiometric data were assessed qualitatively with comparisons to maps of geology, regolith and known mineralisation. Gravity and magnetic data were computer modelled using drilling information and petrophysical data. The host ultramafic unit was readily mapped and modelled to depth using magnetic data. Mineralisation itself was expressed as a relative low within the magnetic ultramafic unit. The down dip extension of the mineralised ultramafic presents a good drill target. The gravity profiles are not long enough to allow accurate interpretation, but modeling shows that it is unlikely that the mine mafic is present at Trident. Radiometric data mapped broad geology and regolith trends but did not show an anomaly related to mineralisation. The results from IP and resistivity tests on core samples indicated that these techniques were not well suited for targeting this style of mineralisation.