Transient non-soluble noble metal transport in hydrothermal ore systems

Abstract

Abstract The transport of noble metals (Au, Ag) by metal-rich melts in hydrothermal ore systems is now acknowledged as a complementary mechanism to complexing ligands in solution. However, it is unclear where/when both mechanisms coexist and whether metal-rich melts can be physically transported by hydrothermal fluids. Here we show evidence for a suspension-like transport of nano-to-micron-sized metal-rich sulfide-sulfosalt melts within epithermal fluids at <400 °C, forming irregular and bleb-like polymineral inclusions of Ag-Au-Cu-Pb(-Fe-Zn)-As-Sb-S-Se upon cooling. These polymineral inclusions, 5 nm to 40 µm in size, are cogenetic with fluid inclusions in quartz. Numerical modeling based on particle fluidization and settling theory shows hydrothermal fluids can mechanically transport metal-rich sulfide-sulfosalt nano-micromelts at fluid flow rates <10–1 m/s. The chemical similarity between nano- and micron-scale polymineral inclusions suggests the coalescence of nanomelt precursors during transient transport from their source(s) to deposition sites, playing a key role in noble metal mineralization.