The partitioning of chalcophile and siderophile elements (CSEs) between sulfide liquid and carbonated melt

Abstract

Carbonated melts play a significant role in mobilizing lithophile and volatile elements in the Earth's mantle and mantle metasomatism. However, there has been limited investigation into their potential for mobilizing chalcophile and siderophile elements (CSEs). In this study, we experimentally determine the sulfide liquid- -carbonated melt partition coefficients of CSEs ( D Sul / C melt CSE) for a range of elements, including Co, Ni, Cu, Zn, Se, Mo, Ag, Cd, In, Sn, Re, and Pb, at 1300-1600 degrees C, 1.0-3.0 GPa, and oxygen fugacity (fO2) close to the graphiteCO2 fluid buffer. Furthermore, the D Sul / C melt values for lithophile elements Cr, Mn, Rb, Sr, Y, Zr, Nb, Cs, Ba, Hf, and Ta ( D Sul / C melt LithoE ) are also determined. The obtained D Sul / C melt values are 34-1230 for Co, 380-75200 for Ni,CSE 200-14900 for Cu and Ag, 0.5-28 for Zn and Mo, 42-98 for Se, 24-640 for Cd, 5-52 for In and Sn, 650-15200 for Re, and 22-2470 for Pb. The obtained D Sul / C melt LithoE values are below 1-10. The variations of D Sul / C melt and D Sul / C melt CSE LithoE are primarily influenced by the FeOtot content in the carbonated melts. A partitioning model was developed to parameterize D Sul / C melt and D Sul / C melt LithoE as a multi-function of pressure, temperature, composition of the carbonCSE ated melt (mainly the FeOtot content), and composition of the sulfide liquid. Our parameterization can explain the observed large variations of D Sul / C melt and D Sul / C melt CSE LithoE for most of the trace elements studied. Using our D Sul / C melt parameterization, we model the CSE and U-Th contents of low-degree partial melts of carbonated CSE mantle peridotite and slab eclogite with sulfur concentrations ranging from 50 to 500 mu g/g. The modeling results can generally explain the trace element patterns observed in natural kimberlites and carbonatites; however, the peridotite- or slab-derived carbonated melts have a low capability in mobilizing CSEs, which can extract less than 3 % of Cu, Ni, Co, Re, and Os, 3-30 % of Mo, Pb, and Se, but up to 30-50 % U and Th from the source lithology. Consequently, the influence of carbonatite metasomatism on the Cu, Ni, Co, Re, and Os systematics of the Earth's mantle is minimal, although local enrichments of CSEs may occur when sulfides precipitate from carbonated melts. Because of the elevated concentrations of U and Th and the corresponding U/Pb and Th/Pb ratios in the carbonated melts, the mantle lithology that has undergone metasomatism by these melts can become a geochemical reservoir with high 208 Pb/ 206 Pb ratios. However, the effect of carbonatite metasomatism on Re-Os isotopic systems of the mantle is minimal due to the low Re concentrations in the carbonated melts. Accordingly, the radiogenic Pb-Os isotopic signatures of HIMU ocean island basalts cannot be explained solely by carbonatite metasomatism in the mantle