Assessing future exploration potential of the Cobar District using integrated 3D geological modelling and geophysical inversion.

The late Silurian to early Devonian Cobar Supergroup hosts a variety of polymetallic mineral systems, forming the most mineralised sedimentary sequence within the Palaeozoic Lachlan Orogen. However, several areas undercover are still unmapped, posing a serious impediment to the discovery of new resources. 3D geological modelling has become a fundamental tool for understanding the architecture and unravelling the mineral potential of buried terranes. 3D modelling and geophysical inversion was undertaken in key areas of the central and southern Cobar Basin in order to identify connections between the broad scale architecture and the localisation of mineral deposits and provide an updated framework for future exploration. Datasets used in the construction of 3D geological and structural models include surface geological mapping, geological cross-sections, well data, digital elevation models, airborne electromagnetic surveys, gravity and magnetic data. Geophysical inversion was performed using the VOXI magnetic vector inversion (MVI), which solves the 3D inverse problem using unconstrained magnetisation vectors (attempting to account for induced magnetisation, remanence, anisotropy and self- demagnetisation mathematically). The unconstrained VOXI MVI not only highlighted source bodies reflecting the CSA, Peak Gold and Nymagee deposits, but also identified prospective rocks within the Cobar mineral system that are underexplored. Regional scale magnetics shows that the Cobar-type deposits are controlled by major N-S-trending faults at the regional scale, whereas 3D EM inversions suggest that mineralisation is localised by NE- and NW-trending lateral faults at the camp scale. VOXI MVI results also suggest that remanent magnetization accounts for a component of the magnetic signature of these deposits and ignoring remanent magnetization could prove a costly mistake in targeting Cobar type systems. The outputs of this research provide new insights for undercover extension of known mineralisation within the Cobar Basin and will assist in future exploration.