Architecture, evolution and fertility of the Delamerian Orogen: Insights from zircon

Magmatic arcs represent a critical source of modern civilisation’s mineral wealth, with their importance only enhanced by the ongoing global transition to a low-carbon society. The ~830-495 Ma Delamerian Orogen, formed at Australia’s eastern cratonic margin, represents rocks ascribed to rift/passive-margin, convergent margin arc, orogenic, and post-orogenic settings. However, poor exposure has limited exploration activity across much of the orogen, despite demonstrated potential for numerous mineral systems. To address this issue, an orogen-wide zircon Hf-O isotope and trace element survey was performed on 55 magmatic samples to constrain the crustal architecture, evolution, and fertility of the Delamerian Orogen, and in turn map parameters that can be used as a guide to mineral potential. These new data define two broad magmatic episodes at: (1) ~585-480 Ma, related to rift/passive margin, convergent arc, orogenic, and post-orogenic activity (Delamerian Cycle); and (2) magmatism associated with the ~490-320 Ma Lachlan Orogen, with peaks at ~420 Ma (onshore, Tabberabberan Cycle) and ~370 Ma (western Tasmania). Isotopic and geochemical mapping of these events show that the ~585-480 Ma Delamerian Cycle has significant orogen-wide variation in magmatic Hf-O isotopes and oxidation-state, suggesting a spatial variation in the occurrence and type of potential mineral systems. The ~420 Ma magmatic event involved predominantly mantle-like Hf-O and oxidised magmatism, whilst the ~370 Ma magmatism shows opposing features. In general, The potential to host Cu-Au porphyry and VMS mineralisation (e.g., Stavely, Koonenberry) is present, but restricted, whereas signatures favourable for Sn-W granite-hosted systems (e.g., Tasmania), are more common. These new data constrain time-space variations in magma composition that provide a valuable geological framework for mineral system fertility assessments across the Delamerian Orogen. Furthermore, these data and associated maps can used to assess time-space mineral potential and facilitate more effective exploration targeting in this covered region. Citation: Mole, D., Bodorkos, S., Gilmore, P.J., Fraser, G., Jagodzinski, E.A., Cheng, Y., Clark, A.D., Doublier, M., Waltenberg, K., Stern, R.A., Evans, N.J., 2023. Architecture, evolution and fertility of the Delamerian Orogen: Insights from zircon. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, https://dx.doi.org/10.26186/148981