EXPERIMENTAL PARTITIONING STUDIES NEAR THE FE-FES EUTECTIC, WITH AN EMPHASIS ON ELEMENTS IMPORTANT TO IRON METEORITE CHRONOLOGIES (PB, AG, PD, AND TL)

Partition coefficients (D) for metal/sulfide liquid, troilite/sulfide liquid, and schreibersite/sulfide liquid have been experimentally determined for Ag, Au, Mo, Ni, Pb, Pd, and Tl. With these partition coefficients, it should be possible to better understand the Pd-107-Ag-107 and Tl-205-Pb-205 systems of iron meteorites. In general, our schreibersite/metal and troilite/metal partition coefficients for ''compatible'' elements are quite similar to those inferred from natural assemblages. In contrast, these same partition coefficients for ''incompatible'' elements often do not even qualitatively agree with analyses of iron meteorites. We suggest that analyses of incompatible elements in iron meteorites may sometimes be dominated by minor/trace phases. Identification of such phases may allow refinement of the initial isotopic composition of Pb in the early solar system. If our trace impurity model is correct, it may also be possible to reconcile iron meteorite cooling rates inferred from silver isotopic systematics with those deduced from metallography.