The Olympic Cu-Au province is an early Mesoproterozoic (~1570-1600 Ma) metallogenic belt along the eastern margin of the Gawler Craton, containing the Olympic Dam and Prominent Hill iron oxide Cu-Au (IOCG) deposits. Almost entirely concealed by cover, the province extends over 500 km from the Moonta-Wallaroo district through the Olympic Dam district to the Mt Woods Inlier. Based on the criteria below, and open-file company data, we propose extensions of the province to the Peake and Denison Inlier, Coober Pedy Ridge, and Mabel Creek Ridge.
Guides for high-level style IOCG
Hiltaba Suite felsic and mafic intrusive complexes - pancake-like intrusions emplaced at high crustal levels, which we view as symptoms of elevated heat flow around 1590 Ma that also drove hydrothermal fluid flow; mafic/ultramafic intrusive magmatism and mantle-like Sm-Nd- and S-isotopic signatures are less obvious at the sub-economic prospects than at Olympic Dam.
- Regional host sequence composition - Palaeoproterozoic metasedimentary rocks of diverse composition are favourable as fluid source(s), buffers and traps; rock types include oxidised meta-arkosic units, feldspathic argillites/siltstones, carbonates and BIF.
- Gawler Range Volcanics - Their presence in a district is a plus for preservation of high-level IOCG mineralisation; volcanic/maar/diatreme centres have been best documented at Olympic Dam and are not recognised at the sub-economic prospects.
- Major fault networks - A major set striking NW to WNW, and dipping NE in Olympic Dam district, partly controlled hydrothermal fluid flow at ~1570-1600 Ma; a conjugate NE-striking set may be in part younger. Some of these faults probably developed during during the Kimban (~1700-1730 Ma) and/or Neil (~1850 Ma) compressive orogenies.
- Regional to district scale alteration - Extensive alteration zones of magnetite, K-feldspar, actinolite, pyrite, apatite, carbonate, quartz, and minor chalcopyrite, producing magnetic-gravity anomalies; a first-order guide to the possible presence of high-level IOCG mineralisation. Regional high-temperature brines were sourced from, and/or reacted with, metasedimentary rocks but direct magmatic-hydrothermal or leached igneous contributions cannot be ruled out.
- Local (deposit) scale alteration & mineralisation - Zones of abundant hematite, sericite, chlorite and carbonate are spatially and temporally associated with Cu-Fe sulfides, pyrite, fluorite, barite, and REE minerals. These oxidised alteration zones may be either above or lateral to magnetite alteration, with highest grade Cu-Au mineralisation predicted within hematitic alteration, near (10's to 100's of metres) the transition to magnetite alteration.
Guides for deeper-level style IOCG (e.g., parts of Moonta-Wallaroo district & Mt Woods Inlier):
- Regional host sequence composition, regional structure and intrusive associations are likely to be similar to those of high-level style IOCG, but the following regional characteristics will differ.
- Volcanics coeval with mineralisation (e.g., Gawler Range Volcanics) will not be preserved if IOCG deposits have been exhumed.
- Host structures - Shear zones and other brittle-ductile (rather than brittle) structures will be the dominant host structures, although tectonic-hydraulic breccias may be present if strain rates and/or fluid pressures were high (e.g., Ernest Henry style breccias).
- Regional alteration - Dominated by albite-actinolite ± clinopyroxene ± magnetite rather than K-feldspar rich; additionally, magnetite-biotite alteration with minor to significant chalcopyrite-pyrite-REE mineralisation is common in deeper-level style IOCG systems, particularly in zones proximal to sulphide mineralisation.
- Local (deposit) alteration - Magnetite-biotite-K-feldspar-bearing proximal alteration assemblages in felsic host rocks; intermediate to mafic host rocks will contain less feldspar and more Fe-Mg silicate alteration (e.g., amphiboles, chlorite) and carbonate.
