Strontium and stable C and O isotopic composition of carbonates in the Ernest Henry deposit, Queensland, Australia: implications for genesis and exploration

The Ernest Henry IOCG (iron-oxide copper gold) deposit is hosted within Paleoproterozoic meta-sedimentary and meta-igneous rocks of the eastern succession of the Mt Isa inlier. The mineralization is mostly breccia-hosted, with K-feldspar altered clasts cemented by biotite-carbonate-magnetite-sulfides. The breccias grade out to crackle breccias and then veins, with the breccia/crackle breccia contact typically demarcating economic mineralization. The origin of brecciation and mineralization remains controversial, but numerous elemental enrichments suggest multiple fluids with a mixed origin including magmatic and/or saline metamorphic fluids. Foremost among the proposed mechanism for IOCG formation at Ernest Henry is that CO2 release directly from enriched mantle, or indirectly from mafic magmas, played an important role in breccia formation and in scavenging ore components from local wallrocks, particularly mafic rocks. This hypothesis is mainly based on the regional interpretation of stable C and O isotopes from carbonates within the eastern succession of the Mt Isa inlier, including limited samples from Ernest Henry.