Carbonates at the supergiant Olypmic Dam Cu-U-Au-Ag deposit, South Australia part 2: Sm-Nd, Lu-Hf and Sr-Pb isotope constraints on the chronology of carbonate deposition

Mineralization at the supergiant Cu-U-Au-Ag Olympic Dam deposit (South Australia), ‘uranium endmember’ of iron-oxide copper–gold (IOCG) spectrum ore deposits, is hosted in a breccia complex developed entirely within granite 1.59 Ga Hiltaba Suite (Gawler Craton). Earlier studies suggested brecciation and mineralization occurred magmatically-driven hydrothermal system Ga, with critical role for mafic–ultramafic intrusions. In contrast, recent radiometric dating indicates prolonged, multi-stage history from to 0.5–0.4 Ga. Ca-Fe-Mg-Mn-carbonate gangue minerals are associated virtually every stage mineralization. companion study (Apukhtina et al., 2020), this mineralogically, texturally compositionally diverse carbonate mineral suite was assigned seven associations defined on basis host lithology texture. Here we report Sm-Nd, Pb-Pb Lu-Hf isotope ages these carbonates, which used examine chronology deposition. Initial Sr-Nd isotopic compositions place constraints fluid sources. Sm-Nd systematics calcite veins ~1.59 IOCG indicate 1.59–1.55 deposition ages. Likewise, locally abundant laminated siderites have age interval. A world-first attempt apply an yields that 70–100 Ma younger than corresponding ages, presumably reflecting exchange systems rocks. carbonates other (hosted highly altered inferred basalt picrite; settings granite-dominated breccia; megaclasts green red bedded sandstone/mudstone sequences; ~0.82 doleritic dykes) more range 0.5 The structurally youngest (unbrecciated fluorite-barite veins; matrix polymict conglomerate above complex) yield ~0.50 Inferred broadly consistent dates (e.g., hematite, uraninite, apatite, fluorite). They suggest initiated reworked possibly increased size response large-scale tectonic, magmatic, sedimentary events. 87Sr/86Sr higher variable (0.710–0.752, average ~0.721) could be explained by formation magmatic-hydrothermal fluids during single event model favored several earlier studies. By over long period, as presented here, would allow ingrowth 87Sr granitic rocks develop heterogeneous initial recorded carbonates. Carbonate-bearing appear sourced Nd (and most likely also Sr) locally, breccia, contributions mafic emerging evidence protracted, implies single-stage models need revisited all sulfide require careful dating. We speculate polymetallic nature unusually large metal reserves related its history.