Sulfide Melt Silicate Melt Distribution Coefficients for Nickel and Iron and Implications for the Distribution of Other Chalcophile Elements

Distribution coefficients for Fe and Ni between sulfide and silicate melts have been determined as functions of f(O2) and f(S2). Experiments were carried out in a piston-cylinder apparatus at 1450-degrees-C and 8 kbars. In a system at sulfide saturation the f(S2), f(O2) and a(FeO) are interdependent; therefore, it was possible to vary f(O2)/f(S2) systematically by changing the bulk Fe content of the starting materials. This was accomplished in two ways, first by varying the sulfide to silicate mass ratio, and second by synthesizing silicate starting materials of differing FeO contents. The f(O2)/f(S2) was further constrained by the choice of graphite capsule material combined with pre-oxidation of the starting silicate. This produced melts which were saturated or nearly saturated in C-O-S vapor. The f(O2) and f(S2) were computed from the independent relationships of f(O2)/f(S2) with vapor and silicate melt compositions.