A track record of Au-Ag nanomelt generation during fluid-mineral interactions.

Recent studies have reported the significant role of Au-bearing nanoparticles in the formation of hydrothermal gold deposits. Despite the ever-increasing understanding of the genesis and stability of Au-bearing nanoparticles, it is still unknown how they behave when exposed to hydrothermal fluids. Here, we study the nanostructural evolution of Au-Ag nanoparticles hosted within Co-rich diarsenides and sulfarsenides of a natural hydrothermal deposit. We use high-resolution transmission electron microscopy to provide a singular glimpse of the complete melting sequence of Au-Ag nanoparticles exposed to the hydrothermal fluid during coupled dissolution-precipitation reactions of their host minerals. The interaction of Au-Ag nanoparticles with hydrothermal fluids at temperatures (400-500 ºC) common to most hydrothermal gold deposits may promote melting and generation of Au-Ag nanomelts. This process has important implications in noble metal remobilization and accumulation during the formation of these deposits.