Mechanisms of concentration of the platinmn-group and other chalcophile elements iu several plati-num-group element deposits in layered intrusions are evaluated in light of recently published ata on element partitioning between immiscible sulfide and silicate melts. The similarity of the partition coefficieut r'•sulfide mel•t/silicate melt-P,r..1. c r • ß •... •.. • 1 • c ß--c •.t • ot lr to mat m ru 1noneares mat me ooserveo •ractlonatlon m tnese elements in nature resulted from a process other than or in addition to sulfide liquid immiscibility. In experiments designed to test he possibilib • that his fractionation was due to the presence of Os-Ir ailoy, sulfide and silicate melts xvere quilibrated with Ir metal at 1,450øC, 8 kbars total pressure, and under sulfur and oxygen fugacity conditions appropriate for nature. The Ir content of the sulfide liquid was found to be-•3.7 wt percent and that of the coexisting silicate nlelt inferred to be- • 1,000 ppb. These concentrations arefar in excess of the Ir contents of natural sulfides or rocks and indicate that Os-Ir alloys are not stable in the presence of sulfide or silicate melts in nature. Using our preferred values of D '" •.... •""' •..... •t for the chalcophile e ments and their estimated concentra-tions in the mantle, limits are determined for the possible ranges of concentrations and relative abundances of these elements in immiscible sulfide liquid formed in magma derived by partial melting of the mantle. The ratios of highly chalcophile to moderately chalcophile elements and of metal to sulfur of several deposits,
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Peach et al. (1996) studied this question.