Nanoparticle suspensions from carbon-rich fluid make high-grade gold deposits

Economic gold deposits require 100- to 10,000-fold enrichment of Au relative to crustal background. In orogenic systems, Au transport occurs via deeply sourced hydrothermal fluids, but the low solubility of Au in aqueous solutions implies additional processes are needed to form high-grade veins. Although Au nanoparticles (NPs) have been reported in some high-grade veins, the nucleation and deposition processes remain unclear. Here we show that formation of metal nanoparticles (Au, AuAg, Cu, Ag2O) is an essential contributor to efficient, focused Au deposition. We document systematic, previously unrecognized metal nanoparticles preserved in amorphous silica and/or carbonic phases in five high-grade deposits. The metal–silica–carbonic associations constrain multiple reactive processes in Au, Cu and Ag metallogenesis and the formation of high-grade gold mineralisation.

Laura Petrella, Nicolas Thébaud, Denis Fougerouse, Brian Tattitch, Laure Martin, Stephen Turner, Alexandra Suvorova, Sarah Gain