GOLD: Geophysical setting of BIF-hosted gold deposits at Tuckabianna, Western Australia

Abstract

Tuckabianna Gold Mine is located about 25 km east of Cue, on the Mount Magnet-Meekatharra Shear Zone. The mine sequence consists largely of basalt, dolerite to gabbro, mafic schists, banded iron-formation (BIF), and intrusive quartz-feldspar porphyry dykes and sills. Gold mineralisation is hosted by the NE-striking, E-dipping BlFs with shears localising the ore zones. Laterite derived from the weathering of these BlFs may contain a significant gold resource. Downhole logging has shown that the BlFs typically have lower relative gamma activity and higher densities, resistivities and susceptibilities compared with the mafic units and porphyry. Petrophysical measurements of magnetic susceptibility, anisotropy of magnetic susceptibility and natural remanent magnetisation have characterised two BIF types, although no relationship between gold mineralisation and the BIF types has been conclusively demonstrated. Tuckabianna's regional geophysical dataset consists of Bureau of Mineral Resources (BMR) aeromagnetic and gravity data and high-resolution aeromagnetic and radiometric data. Of these, the most useful have been the high-resolution aeromagnetic data, because they clearly define the BlFs and structures which can localise gold mineralisation. Such lithological and structural detail cannot be recognised in either the BMR regional magnetic and gravity datasets or the high-resolution radiometric dataset. The Geoscan remote-sensing system has been flown over Tuckabianna. However, the laterite cover (1-21 m thick) has blanketed much of the geology and only some rock types and major lineaments can be identified from the data. Ground geophysical surveys have been dominated by the magnetic method, which has been extremely useful in delineating the BlFs and structural features, as has the gravity method. Electrical surveys, including magnetometric resistivity, induced polarisation (frequency and time-domain) and electromagnetic methods have also been used. These electrical techniques have not been completely successful in the direct detection of mineralised zones. However, the resistive nature of the BIF is such that these methods may be successfully used to locate the BIF and porphyry, in addition to delineating some structures.