Assessing future exploration potential of the central and southern Cobar District using integrated 3D geological modelling and geophysical inversion of magnetic data

The late Silurian to early Devonian Cobar Supergroup hosts a variety of poly-metallic mineral systems and is one of the most prospective regions in Australia for gold and base metal exploration. Early research on its geology and geophysical characteristics produced numerous insights into the mineral system. However, the region has not yet benefited from many modern approaches, including integrated geological and geophysical modelling, and prospective areas undercover remain underexplored. The aim of this paper is to test the current understanding of geology and mineralisation processes, particularly structural control, in the central Cobar District, and propose a new approach based on these new technologies to identify prospective areas within the underexplored southern Cobar District. 3D geophysical inversion of magnetic data was undertaken in key areas of the central and southern Cobar Basin to identify the location and geometry of potential magnetised mineral deposits. The inversion results were then incorporated into 3D fault models to identify connections between the regional architecture and localisation of the mineral deposits. Magnetic inversion was performed using VOXI Magnetic Vector Inversion (MVI) software, which solves the 3D inverse problem mathematically using magnetisation vectors. VOXI MVI results are also compared with traditional voxel inversions and VPmg inversions, both of which assume that all magnetisation is induced. The unconstrained magnetic inversion produced magnetised bodies coincident with some major deposits in the area. Furthermore, it identified new areas of interest within the underexplored areas of the Cobar District. Inversion results suggest that major N- to NNW-trending faults might control the location of the known mineral occurrences and potentially prospective rocks at the regional scale. The latter are frequently localised on or next to NE- and NW-trending strike-slip faults that crosscut the major structures at the camp scale. This suggests that in the south Cobar District, dilation zones might have focused ore-fluid flux and subsequent mineral deposition, which is a main mechanism already invoked for mineralisation in the central Cobar District. VOXI MVI results suggest that remanent magnetisation is significant in some of these deposits, highlighting that remanent magnetisation should be incorporated into models to maximise the likelihood of successful geophysical targeting of Cobar-type systems.