Geophysical response of the Hercules base metals deposit: a case study from western Tasmania

Abstract

The Hercules volcanic-hosted massive sulphide Zn-Pb-Cu-Ag-Au mineralisation in western Tasmania presents a difficult geophysical target even though it is hosted within highly resistive volcanics. The deposit is made up of a number of small, steeply dipping, ore lenses. Limited petrophysical data indicates the ore to be poorly conductive, non-magnetic, of moderate density and moderately chargeable. Regional aeromagnetic, airborne electromagnetic and gravity surveys do not appear to identify the mineralisation. Responses from electromagnetic surveys are attributed to the overlying black shale sequence. Mineralisation has been detected from induced polarisation surveys, however, the black shale sequence is often found to be chargeable. The Hercules deposit lies within the same alteration system as the Rosebery volcanic-hosted base-metals deposit, located approximately 7 km to the north. Mineralisation at Rosebery is contained within larger pods, is more conductive and easier to detect when the overlying black shales are thin or absent.