Partitioning of Ru, Rh, Pd, Re, Ir, and Au between Cr-bearing spinel, olivine, pyroxene and silicate melts

Abstract

A series of high temperature experiments was undertaken to study partitioning of several highly siderophile elements (HSE; Ru, Rh, Pd, Re, Os, Ir, Pt and Au) between Cr-rich spinel, olivine, pyroxene and silicate melt. Runs were carried out on a Hawaiian ankaramite, a synthetic eucrite basalt, and a DiAn eutectic melt, at one bar, 19 kbar, and 20 kbar, respectively, in the temperature range of 1200 to 1300°C, at oxygen fugacities between the nickel-nickel oxide (NNO) and hematite-magnetite (HM) oxygen buffers. High oxygen fugacities were used to suppress the formation of HSE-rich “nuggets” in the silicate melts. The resulting oxide and silicate crystals (<100 μm) were analyzed using both SIMS and LA-ICP-MS, with a spatial resolution of 15 to 50 μm. Rhenium, Au and Pd were all found to be incompatible in Cr-rich spinel ( D Re sp/melt = 0.0012–0.21, D Au sp/melt = 0.076, D Pd sp/melt = 0.14), whereas Rh, Ru and Ir were all found to be highly compatible ( D Rh sp/melt = 41–530, D Ru sp/melt = 76–1143, D Ir sp/melt = 5–22000). Rhenium, Pd, Au and Ru were all found to be incompatible in olivine ( D Re oliv/melt = 0.017–0.073, D Pd oliv/melt = 0.12, D Au oliv/melt = 0.12, D Ru oliv/melt = 0.23), Re is incompatible in orthopyroxene and clinopyroxene ( D Re opx/melt = 0.013, D Re cpx/melt = 0.18–0.21), and Pt is compatible in clinopyroxene ( D Pt cpx/melt = 1.5). The results are compared to and combined with previous work on HSE partitioning among spinel-structured oxides, and applied to some natural magmatic suites to demonstrate consistency.