Halogen Geochemistry and Cl Isotopes of the Stillwater and Bushveld Complexes

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9705507 Boudreau The Bushveld complex in South Africa is among the few intrusions that contain extensive stratigraphic sections in which halogen-bearing minerals are unusually rich in chlorine. This study has three major objectives: 1) Because halogen geochemistry of the platiniferous Merensky Reef of the Bushveld complex and associated marginal sills are still poorly known, we propose to sample these rocks more completely to investigate the compositions of halogen-bearing minerals using electron microprobe. The associated sills are of particular interest as their compositions may preserve evidence of the original halogen concentrations of Bushveld magma(s). 2) We propose to analyze and compare stable Cl isotopic characteristics with existing data for Sr, O and H isotopic trends for the Bushveld complex, their country rocks and associated contemporaneous sills and dikes. Along with petrographic and field evidence, this data should allow us to constrain models suggesting that high Cl is due to a mantle fluxing event, contamination or metamorphic fluid infiltration from the country rocks. 3) We will investigate possible correlations between PGE (Platinum Group Elements) and halogens. Evolution of Cl-rich fluids from intercumulus liquids could be a potentially useful transport mechanism for the platinum-group elements (PGE). We will determine to what extent of background PGE (to be analyzed by ICP-MS) , S , base metals and Cl are correlated. These data will be combined with petrographic and geochemical studies, augmented with quantitative modeling of degassing, PGE transport and mineral-liquid-fluid equilibria, to test models of PGE transport and concentration.