Small thick walled vesicles in submarine volcanic rocks and vapor cavities of melt inclusions in phenocrysts typically contain CO2-H2O magmatic fluids. Some also contain coatings of Fe, Cu, Zn, Ni, Cl, S and As. Ag and Au have been detected by ToF-SIMS. These coatings must have precipitated from the trapped magmatic fluids. Mixing of such fluids with deeply circulating heated seawater can provide an enriched source of metals to form large volcanogenic massive sulfide deposits. Examples will be presented from the modern seafloor and ancient ores.