Carbonate Replacement as the Principal Ore Formation Process in the Proterozoic McArthur River (HYC) Sediment-Hosted Zn-Pb Deposit, Australia

Abstract The McArthur River (HYC) Zn-Pb-Ag deposit in the Carpentaria Zn belt, northern Australia, is one of world’s largest and most studied sediment-hosted base metal deposits, owing to its lack deformation preservation sedimentary ore textures. However, formation process (syngenetic vs. epigenetic) still a subject controversy. In this paper we focus on key characteristics HYC that remain unexplained: carbonate (dolomite) association with Zn, role thallium (Tl) manganese (Mn) distribution orebody. Our findings demonstrate sequence events during formation: Tl hosted almost exclusively within euhedral pyritic overgrowths around early diagenetic pyrite; sphalerite mineralization occurred after Tl-bearing pyrite overgrowths, acid dissolution (replacement) laminated nodular dolomite across subbasin; outer rims are enriched Mn preserved at reaction front contact sphalerite. New thermodynamic fluid chemistry modeling demonstrates paragenesis can be explained by acidic, oxidized fluids entering pyrite-dolomite host lithology, allowing reduction pH buffering dissolution, resulting stepwise deposition an evolving fluid. We argue represents strong evidence for epigenetic HYC. Furthermore, primary control not synsedimentary faulting rather, chemical potential reduced, sulfidic lithologies appears critical importance precipitation