Syn-metamorphic sulfidation of the Gamsberg zinc deposit, South Africa

Abstract The Mesoproterozoic Aggeneys-Gamsberg ore district, South Africa, is one of the world´s largest sulfidic base metal concentrations and well-known as a prime example Broken Hill-type deposits, traditionally interpreted metamorphosed SEDEX deposits. Within this Gamsberg deposit stands out for its huge size strongly Zn-dominated ( >14 Mt contained Zn). New electron microprobe analyses element abundance maps sulfides silicates point to fluid-driven sulfidation during retrograde metamorphism. Differences in chemistry sulfide inclusions within zoned garnet grains reflect different degrees interaction with high metal/sulfur-ratio sulfur-rich metamorphic fluid. Independent evidence metamorphism comes from graphic-textured aggregates that previously have been quenched melts, replacement pyrrhotite by pyrite along micro-fractures, phyllic alteration zones. Limited availability fluid under conditions caused locally segregation Fe-rich sphalerite into Zn-rich pyrite, thus considerable heterogeneity chemistry. invoked fluids would able sulfidize metal-rich zones whole camouflage potential pre-metamorphic oxidation. These findings support recently established hypothesis pre-Klondikean weathering-induced oxidation event challenge traditional explanation deposits merely Instead, we suggest massive experienced complex history, starting initial SEDEX-type mineralization, followed near-surface spatial separation, then oxidized medium- high-grade