Geochemical differentiation of terrestrial mantle in view of platinum group elements

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The platinum group elements are considered to reflect a feature of cumulate phase during magmatic differentiation. However, the geochemical behavior of the elements is not known well. The aim of the research is to clarify the geochemical behavior of the elements using an isotope dilution technique. A negative thermal ionization technique using a small and economical quadrupole mass spectrometer is presented. Intense ion beam of negatively charged oxides of Re, Os, Ir and Ru were observed. The principal molecular species produced in this technique are ReO_4^-, OsO_3^-, IrO_2^- and RuO_3^-. The production of these ion species in the distinct mass ranges allows the isotopic analyzes without any chemical separation of these elements each other. For 5ng Os, all Os isotopic ratios were determined with the precision of better than <plus-minus>0.5% except ^<184>Os/^<192>Os because of very low isotopic abundance of ^<184>Os. For 30ng Re, 10ng Ir and 30ng Ru, isotopic measurements were also made with the precision of better than <plus-minus>0.5%. The precision Os the isotopic ratio measurements for Re, Os, Ir and Ru is sufficient for the isotope dilution technique to determine the concentration of these elements in geological samples/ In addition, a iridosmine from Hokkaido was analyzed for Os and Ir by direct loading technique, and ^<187>Os/^<186>Os ratio of 1.0220<plus-minus>0.0089 was obtained.