Mass transfer between sulfide and silicate liquids is often discussed by reference to a mass ratio between hypothetical liquid reservoirs at equilibrium, defined as R. In an open system not at equilibrium the mass of silicate melt from which a growing sulfide droplet appears to have scavenged chalcophile elements will depend on diffusivities Di and DFeS of the element and of the FeS component in the silicate melt, respectively, on the degree of supersaturation of the melt with FeS CFeSo, on the radius a of the droplet and on the velocity v with which the droplet is advected through the melt, so that R = 1/CoFeS(Di + 1/2 √aDiv/DFeS + 1/2 √aDFeSv). Chalcophile elements are expected to show inter-element variations in D spanning several orders of magnitude in some melts, leading to large inter-element variations in effective R in a given sulfide body. These variations in effective R will lead to spatial separations between zones of maximum enrichment of chalcophile elements produced during fractional segregation of sulfide in layered intrusions. Whereas it has proven impossible to model the generation of spatially offset stratiform horizons in the Australian Munni Munni layered intrusion using equilibrium partition coefficients, the present kinetic model reproduces the observed patterns with great fidelity.

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Journal of Petrology
Department of Earth Sciences

Mungall, J.E. (2002). Kinetic controls on the partitioning of trace elements between silicate and sulfide liquids. Journal of Petrology, 43(5), 749–768.