Partitioning of chalcophile and siderophile elements during partial melting of serpentinized peridotite in subduction settings

Enrichment of subduction derived magmas in chalcophile and siderophile elements plays a key role in the formation of economically important ore deposits. Melting of mantle wedge peridotite induced by fluxing slab-derived fluids is the first step in the chemical transfer from the slab to melts (Spandler and Pirard, 2013). Changes in redox conditions, sulfur content, amount of fluid, and P-T conditions affect the elements partitioning between melts and residual phases (Dale et al., 2009; Li and Audetat, 2012; Perchuk et al., 2018; Rielli et al., 2018). However, to date there is a few systematic data on mineral-melt partitioning for economically important elements during partial melting of peridotite in mantle wedge conditions.

We determined experimentally mineral-melt partition coefficients for a range of chalcophile and siderophile elements (V, Co, Cu, Zn, As, Se, Mo, Ru, Rh, Pd, Ag, Cd, Sb, Re, Os, Ir, Pt, Au, Tl, Bi) at different P-T conditions. Slightly serpentinized peridotite (3 wt.% H₂O; Debret et al., 2013) was used as a starting material for all experiments. A set of experiments with 1 wt.% of FeS added to the peridotite was also performed in order to study the effect of S on element partitioning. Starting materials were doped with 100-200 ppm of targeted elements. The experiments were performed at pressures of 1-2 GPa and at temperatures between 1100 and 1300°C in end-loaded 0.5” piston-cylinder apparatus in the newly established high-pressure laboratory at the University of Liege (Belgium). In order to avoid Fe-loss, chemical reduction and volatile loss of experimental charges, double Au₈₀Pd₂₀ capsules pre-saturated with Fe were used. Major and trace element composition in synthesized experimental products were measured by electron microprobe and LA-ICP-MS respectively.

In this study, we report a wide range of partition coefficients determined between coexisting silicate, oxide, sulfide minerals and melt as a function of P-T and S content. The results provide further insights into mobility of economically important elements during genesis of ore-forming magmas in subduction settings.

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