Copper transport by high temperature, sulfur-rich magmatic vapor: Evidence from silicate melt and vapor inclusions in a basaltic andesite from the Villarrica volcano (Chile)

Silicate melt inclusions have been analyzed in co-crystallized plagioclase, olivine and clinopyroxene in a typical arc-related basaltic-andesite from the Villarrica volcano (Chile). The melt inclusions show identical compositions with respect to most major and trace elements in all host minerals. However plagioclase hosted melt inclusions are variably enriched in Cu (up to ~ 4800 ppm) and Ag (up to ~ 950 ppb). We interpret the elevated Cu and Ag concentrations to be the result of heterogeneous entrapment of silicate melt with a sulfur-rich, chlorine-poor high-temperature magmatic vapor phase in which Cu and Ag were strongly compatible. This assumption is supported by the presence of individual Cu-rich vapor inclusions in some plagioclase crystals. Such a magmatic vapor phase may play a significant role in the transport of S, Cu and Ag within or between magmatic reservoirs and, consequently, in the formation of porphyry-type ore deposits.