Constraints on the structural setting, relative timing, and geochemistry of the Fimiston, Hidden Secret, and Oroya gold-telluride lode types, Kalgoorlie gold camp, Western Australia

Late-stage metamorphic (ca. 2.64 Ga) and punctuated magmatic-hydrothermal mineralization models (2.67-2.64 Ga) are proposed for gold mineralization in the Kalgoorlie gold camp (similar to 2300 t Au; Archean Yilgarn craton, Western Australia). We present structural, whole-rock geochemical, pyrite trace element, and multiple sulfur isotope data to evaluate these models. Both the Fimiston and Hidden Secret lodes were emplaced in ca. 2675 Ma D-2b transtensional settings as releasing bends developed along the Golden Mile and Towns faults, respectively, and are related to the ingress of a H2O-CO2-Au-Te-As-S-K-Rb-Ba fluid concomitant with the intrusion of andesitic dikes. In the Hidden Secret orebody, this magmatic-hydrothermal fluid evolved from an early, As-enriched, greenstone-buffered fluid during the formation of disseminated pyrite mineralization (delta S-34(pyrite) = 3.42 to 3.85 parts per thousand; Delta S-33(pyrite) = 0.25 to 0.43 parts per thousand) to an Ag-Cu-Pb-Sb-Te-Tl-V-Zn-enriched fluid during the development of banded quartz-carbonate-sericite-pyrite veins (delta S-34(pyrite) = - 10.74 to - 0.17 parts per thousand; Delta S-33(pyrite) = 0.06 to 0.19 parts per thousand). Oroya gold-telluride lode mineralization formed during later, ca. 2660 Ma D-2c transpression from a V-S-Au-Ag-Hg-Te-enriched magmatic-hydrothermal fluid represented by delta S-34(pyrite) = - 11.56 parts per thousand to - 4.96 and Delta S-33(pyrite) = 0.08 to 0.17 parts per thousand. The Fimiston/Hidden Secret and Oroya mineralization events record oxidized magmatic-hydrothermal fluids represented by delta S-34(pyrite) <= 0 parts per thousand and Delta S-33(pyrite) similar to 0.0 to 0.2 parts per thousand. These oxidized magmatic-hydrothermal fluids interacted with surrounding wall rock, which lowered fluid fO(2) and buffered delta S-34(pyrite)/Delta S-33(pyrite) values to delta S-34(pyrite) = similar to 1 to 5 parts per thousand/Delta S-33(pyrite) = similar to 0.2 to 0.7 parts per thousand in greenstone rock environments and to delta S-34(pyrite) = similar to 1 to 5 parts per thousand/Delta S-33(pyrite) = similar to <= 0.3 parts per thousand and >= 0.7 parts per thousand in black shale environments. Anomalous Delta S-33 values in ore-stage sulfides formed locally due to the incorporation of sulfur during fluid-wall rock interaction. The early, magmatic-hydrothermal Fimiston/Hidden Secret and Oroya gold-telluride lodes differ texturally, geochemically, and mineralogically from the D-3 Mt. Charlotte stockwork veins, which formed subsequent to ca. 2650 Ma and better adhere to a late-stage metamorphic devolatilization model.

Automated summary

Late-stage metamorphic and punctuated magmatic-hydrothermal mineralization models are proposed for gold mineralization in the Kalgoorlie gold camp. Structural, geochemical, and sulfur isotope data were used to evaluate these models, showing the interaction of oxidized magmatic-hydrothermal fluids with surrounding wall rock during different mineralization events.