MEASUREMENT OF PGEs , Re , Mo , W AND Au IN METEORITIC Fe - Ni METAL

Introduction: The concentrations of Ni, Ga, Ge, and Ir are typically used to assign an iron meteorite to one of the chemical groups [cf., 1-3]. The improvements in analytical techniques, mainly INAA, and the systematic study of a large number of iron meteorites resulted in the development of an extensive database on their chemical compositions [4] which has been used in deciphering the origins of iron meteorites. Other sources of high-quality data for trace elements are isotopic studies of iron meteorites [5-7]. The quality of the analytical data varies depending upon the time and technique used to acquire the data. Recently [8] we have initiated a study aiming to model the trace element behavior during the early stages of planetary evolution together with the isotopic evolution of both long-lived (e.g., Re-Pt-Os) and extinct (e.g., Pd-Ag, and Hf-W) isotope systems. For the purpose of this study we needed high quality elemental and iso-they are either of low quality or even missing for many samples of interest. To create a consistent database for our project, we started analyzing a series of iron meteorites for PGEs, Mo, Re, W, and other trace elements using our LA-ICP-MS system. Several research groups [9-11] have already used the LA-ICP-MS techniques to measure concentrations of trace elements in iron meteorites, but essentially no data other than on the kamacite/plessite distribution coefficients have been reported so far. Samples and Methods: The 266-nm laser ablation system (NewWave-Merchantek UP266) interfaced to the VG-PQ2+ ICP-MS in addition to the JEOL Super-Probe 733 were used to measure chemical compositions of kamacite and plessite in the (IA) irons and in the Divnoe primitive achondrite. Before making the LA-ICP-MS measurements, all octahedrites were lightly etched with 0.5% Nital to reveal kamacite bands and plessite fields. Pure metals and Fe,Ni alloys served as the EMPA standards; the LA-ICP-MS standards were the iron meteorites Filomena (IIA) and Hoba (IVB). The chemical compositions of Filomena and Hoba are