Stable isotope evidence for the origin of the Mesoproterozoic Starra Au-Cu deposit, Cloncurry district, northwest Queensland

New stable isotope data are consistent with a metasomatic origin for the controversial Mesoproterozoic ironstone-hosted Au-Cu deposit at Starra in the Cloncurry district of northwest Queensland. This supports ex-tural and mineralogical evidence that the ore-bearing ironstones formed after the peak of metamorphism and were strongly controlled by brittle-ductile deformation. Three dominant paragenetic stages are recognized. These are: (1) early, widespread Na-Ca metasomatism (quartz-albite-scapolite-actinolite), (2) localized K-Fe metasomatism (biotite-magnetite-hematite-quartz-pyrite), and (3) mineralization (quartz-anhydrite-barite-hematite-ca•cite-g••d-•yrite-cha•c••yrite-b•rnite-cha•c•cite-ch••rite-musc•vite). Cros utting anhydrite veins associated with carbonate + hematite are rare in the upper parts of the system but more common at depths greater than 700 m. Stage 3 minerals demonstrate that the ore fluid was highly oxidized. A restricted range of Fe oxide •1sO implies isotopically similar fluids were responsible for the magnetite ironstones and later hematite alteration associated with gold and sulfides (between-0.2 to +3.3%0 except for one magnetite at 5.4%0). Sulfur isotope compositions suggest that pyrite (-0.2 to +3.9%0), chalcopyrite (-5.8 to-0.7 and-14.6%o), bornRe (-4.7%o), chalcocite (-0.1%o), and anhydrite (1.1-2.4%o) all formed from the same sulfur source. Anhydrite •a4S falls within the sulfide range, suggesting that the sulfate inherited its •a4