Are Vapor-Like Fluids Viable Ore Fluids for Cu-Au-Mo Porphyry Ore Formation?

Abstract Ore formation in porphyry Cu-Au-(Mo) systems involves the exsolution of metal-bearing fluids from magmas and transport metals magmatic-hydrothermal plumes that are subject to pressure fluctuations. Deposition ore minerals occurs as a result cooling decompression hydrothermal partly overlapping shells. In this study, we address role vapor-like through numerical simulations metal using Gibbs energy minimization software, GEM-Selektor. The thermodynamic properties hydrated gaseous metallic species necessary for modeling solubility moderate density (100–300 kg/m3) were derived results experiments investigated aqueous HCl- H2S-bearing vapors. Metal precipitation simulated numerically function temperature, pressure, fluid composition (S, Cl, redox). concentrations ratios compared those observed intermediate-density inclusions deposits, well gas condensates active volcanoes. thermodynamically predicted Cu, Au, Ag, Mo decreases during isothermal decompression. At elevated is similar content measured deposits (at ~200–1,800 bar). ambient approaches volcanoes ~1 bar), which several orders magnitude lower than high-pressure environment. During isochoric cooling, decreases, whereas Au reaches maximum between 35 ppb 2.6 ppm depending on composition. Similar observations made compilation inclusion data showing contents decrease with decreasing temperature. Increasing Cl concentration promotes chloride species. Molybdenum highest under oxidizing conditions low S content, gold at intermediate redox content. strongly affects ratios. Thus, there Cu/Au ratio increases 0.1 1 wt %, opposite case Mo/Ag ratio; >1 also decreases. summary, calculations based involving predict may efficiently precipitate sufficient form deposits. Finally, pressure-temperature evolution paths have strong effect potentially exert an important control their zoning.