Resolving the syn-genetic mineralization age of a metamorphosed Archean VHMS deposit using multiple geochronological approaches

Accurately determining the timing of mineralization is essential for exploring syn-genetic stratiform mineral systems, such as volcanic-hosted massive sulfide (VHMS) deposits. This study integrates multiple geochronological techniques to constrain both the age of syn-genetic mineralization and subsequent overprinting magmatic, metamorphic and deformation events at the King VHMS deposit, Western Australia. The timing of syn-genetic mineralization is collectively constrained by consistent ages from U–Pb zircon geochronology of host felsic volcanic rocks (2725 ± 10 Ma), a Re–Os pyrite isochron (2730 ± 26 Ma), and Pb–Pb galena model ages (ca. 2714–2718 Ma). Pyrrhotite, formed via metamorphic desulfidation of pyrite, records a younger Re–Os age of 2652 ± 32 Ma, overlapping with the timing of prograde metamorphism dated by in situ Lu–Hf garnet analysis at 2680 ± 28 Ma. A Re–Os age from massive sulfide ore (2664 ± 23 Ma), reflecting a mixture of pyrite and pyrrhotite, produces a geologically meaningless average due to metamorphic re-equilibration, highlighting limitations of bulk Re–Os dating in high-grade metamorphosed systems. Quartz monzonite intrusions that crosscut the deposit and are associated with the regional M2 metamorphism yielded weighted mean U–Pb zircon ages of ca. 2676–2665 Ma, and are associated with minor molybdenite mineralization (Re–Os ages ca. 2650–2655 Ma). Collectively, these results confirm that the King Zn deposit represents the first phase of VHMS mineralization during the formation of the Kalgoorlie-Kurnalpi Rift (KKR), and significantly predates other VHMS deposits of the Eastern Goldfields. This study also demonstrates that the Re–Os isotopic signature of syn-genetic pyrite can be retained through amphibolite-facies metamorphism, providing a new opportunity to directly date VHMS deposits affected by high-grade metamorphism in Archean cratons globally. In contrast, Re–Os ages of pyrrhotite record prograde metamorphism, offering a potential tool for constraining metal remobilization events.