Redox control of the partitioning of platinum and palladium into magmatic sulfide liquids

The partitioning behavior of platinum group elements in magmas is critical for their use as tracers of planetary accretion and in understanding magmatic sulfide deposits. Here we use laboratory experiments to determine sulfide liquid-silicate melt partition coefficients for platinum and palladium at 1.5 GPa, 1400 degrees C, and oxygen fugacity 1.5-2 log units above the fayalite-magnetite-quartz buffer. We find that the partitioning coefficients of these elements are 2.3 x 105 to 1.1 x 106 and are independent of the platinum and palladium concentration in the system. Combined with previous data obtained at oxygen fugacity below the fayalite-magnetite-quartz buffer, this indicates redox-controlled partitioning behavior whereby at oxidizing conditions platinum- and palladium-enrichments are achieved through their dissolution in sulfide liquids, while at reducing conditions the entrapment of platinum- and palladium-rich clusters in sulfide liquids is more critical. This redox-controlled partitioning behavior should be considered when studying crust-mantle differentiation and the formation of magmatic sulfide deposits. High-pressure and high-temperature experiments suggest a redox-controlled partitioning behavior of platinum group elements between sulfide liquid and basaltic melt, which could help constrain the formation mechanisms of magmatic sulfide deposits