AN EXPERIMENTAL-STUDY OF SILVER AND PALLADIUM PARTITIONING BETWEEN SOLID AND LIQUID-METAL, WITH APPLICATIONS TO IRON-METEORITES

Solid metal/liquid metal partition coefficients for Ag and Pd were det ermined experimentally as a function of the S concentration of the met allic liquid. Silver is incompatible in solid metal and strongly sensi tive to the S content of the metallic liquid; partition coefficients f or Ag decrease more than an order of magnitude with increasing S conte nt of the metallic liquid and can be expressed as: k(Ag) = exp[0.772 l n [1 - 2 (1.09)X-S] - 1.917] where k(Ag) is the molar solid metal/liqu id metal partition coefficient and X-S is the molar S content of the m etallic liquid. The partition coefficient of Pd is less variable but c hanges from modestly incompatible to modestly compatible in solid meta l with increasing S content of the metallic liquid: k(Pd) = exp[-0.506 ln [1 - 2 (1.09) X-S] - 0.723] With these new partition coefficients for Pd and a fractional crystallization model, Pd abundance trends rec orded in iron meteorite groups are modeled successfully. Measured Ag d istribution between troilite-rich nodules and adjacent metal in iron m eteorites also agree well with experimental solid metal/liquid metal e quilibrium values. However, observed Pd metal/nodule distributions do not agree with experimentally determined partition coefficients, which suggests a more complex history than simple solid metal/liquid metal equilibrium.