Stabilities of laurite RuS2 and monosulfide liquid solution at magmatic temperature

We have reversed the equilibria Ru + S-2 = RuS2 and 2FeO + S-2 = 2FeS + O-2 under controlled temperature, oxygen fugacity (f(O2)), and sulfur fugacity (f(S2)) at 1 arm, to test if the platinum-group mineral laurite (Ru-S2) has a stability field at magmatic temperature outside that of magmatic monosulfide liquid. The f(S2) in equilibrium with Ru and Ru-S2 is given by log f(S2)=6.912190/T (1173 to 1673 K), whereas the f(S2) at sulfide saturation of a basaltic melt may be approximated from log f(S2)=6.712800/T-2 log X-FeO+Deltalog foe (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. (C) 2004 Elsevier B.V. All rights reserved.