Stabilities of laurite RuS2 and monosulfide liquid solution at magmatic temperature

We have reversed the equilibria Ru+S2=RuS2 and 2FeO+S2=2FeS+O2 under controlled temperature, oxygen fugacity (fO2), and sulfur fugacity (fS2) at 1 atm, to test if the platinum-group mineral laurite (RuS2) has a stability field at magmatic temperature outside that of magmatic monosulfide liquid. The fS2 in equilibrium with Ru and RuS2 is given by log fS2=6.9–12190/T (1173 to 1673 K), whereas the fS2 at sulfide saturation of a basaltic melt may be approximated from log fS2=6.7–12800/T−2 log XFeO+Δlog fO2 (1473 to 1673 K). Our experiments support the notion that the sulfide mineral laurite can crystallize directly out of a sulfur-bearing, sulfide-undersaturated silicate melt, as implied by laurite–chromite intergrowth textures in natural chromite ore.