Experimental Measurement of PGE and Semi-metal Partitioning during Sulfide Melt Crystallization at Controlled fO2-fS2 Conditions

摘要

In order to better understand the behaviour of platinum-group elements (PGE) and semi-metals (SM;As,Se,Sb,Te and Bi) during the solidification of sulfide magmas,we have conducted a series of partitioning experiments between monosulfide solid solution (MSS) and sulfide melt,as well as MSS and intermediate solid solution (ISS),at fO2-fS2 close to natural conditions.We found that Re,Os,Ir,Ru and Rh are compatible in MSS,relative to sulfide melt,whereas Au,Ag,Pd,as well as the SM,are incompatible.MSS/ISS partitioning experiments reveal that Ru,Os,Ir,Rh and Re are partitioned into MSS by factors >50,whereas Pd,Pt,Ag,Au and the semi-metals partition weakly (Se,Te) to strongly (Ag,Au) into ISS.Calculated ISS/melt partition coefficients of Se and Te are close to unity while the other elements partition preferentially into the melt phase.Uniformly low MSS- and ISS-melt partition coefficients for the SM,Pt,Pd,Ag and Au will lead to enrichment of these elements in the residual sulfide liquid,possibly leading to saturation in SM-bearing accessory minerals or immiscible melts.