Chemical and isotopic compositions in acid residues from three meteorites

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Chemical compositions of acid residues obtained from three types of meteorites, 1) Canyon Diablo (IA), 2) Allende (CV3) and 3) Nuevo Mercurio (H5) were determined. Refractory elements were generally enriched in these acid residues. The results match the features that acid residues contain primary condensates from the cooling solar gas as well as extra-solar grains. In the cases of Allende and Canyon Diablo, the contents of a series of refractory siderophile elements such as W, Re, Os, Ir, Mo, Ru and Pt were determined by INAA and AAS. Particularly, in acid residue of Allende, enrichment factors of these elements relative to CI are generally higher (7-20 times/CI), whereas in the cases of W and Mo, they are slightly depleted compared with those of Canyon Diablo. Since both elements would be the first metals to be oxidized under high oxygen fugacity, acid residue of Allende should contain fractions that were produced under oxidizing conditions. In these samples, the isotopic compositions of Ru have been measured by thermal ionization mass spectrometry. So far, in the measurements of acid residue of Allende, all Ru isotope ratios were found to be indistinguishable from terrestrial values within the experimental errors, though errors were large because of small Ru ion beam intensities.
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