Fluid transport of sulfur and metals between sulfide melt and basaltic melt

Experiments were performed at 1.0 GPa and temperatures between 1225 and 1450 degreesC to demonstrate the transport of sulfur and metals Cu, Ni and Pt into a basaltic melt via a sulfurous fluid phase. Experiments were performed inside graphite-lined Pt capsules by converting a mixture of FeS2 + NiS2 + CuS into sulfide melt + a sulfurous fluid, which was kept separate from a basaltic melt inside the same Pt capsule by a gas-permeable graphite membrane. The sulfurous fluid is rapidly transported, and the basaltic melt achieves S concentrations similar to saturation values (within 2 sigma) in times less than 1 hour, even though the two melts are not in physical contact. The sulfurous fluid is shown to transport significant quantities of Cu, Ni and Pt in 1 hour. Gold is transported out of the melt. A process similar to the one experimentally modeled could occur in nature as magmatic systems heat country rocks to temperatures at which pyrite converts to pyrrhotite + a sulfurous fluid, potentially containing significant quantities of ore metals. The volume change of this reaction could crack the country rocks and allow the fluid to enter the magma chamber. These fluids could then saturate the melt, causing the formation of immiscible sulfide droplets enriched in base and precious metals, eventually forming either the progenitor of an ore deposit or the ore deposit itself.