Oxygen, Sulfur and Carbon Isotopic Study of Pore Fluid Evolution in the Creede Formation

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This project involves an integrated petrographic and stable isotopic study of samples selected from core obtained during drilling in the Creede Formation of southwestern Colorado for the purpose of documenting progressive changes in the oxygen, sulfur and carbon isotopic compositions of secondary minerals which precipitated from pore fluids during the course of diagenesis and hydrothermal activity in the Creede hydrothermal system. The textural relationships and mineral compositions of pore-filling, fracture-filling, and wall rock alteration minerals will be examined in order to establish the relative timing of secondary mineral precipitation. Laser-based in situ extraction techniques will be employed whenever possible to measure oxygen and sulfur isotopes in fine-grained minerals and test for isotopic variation within minerals. Oxygen (and to a lesser extent sulfur and carbon) isotopic partitioning between appropriate minerals will be measured and combined with experimentally and theoretically derived fractionation factors in order to constrain temperatures of precipitation. The measured isotopic compositions of oxygen, sulfur, and carbon in secondary mineral minerals will be combined with temperature constraints and mineral-fluid fractionation factors to calculate the stable isotopic compositions of the solutions from which the minerals precipitated. The sequence of stable isotopoic variation reconstructed from data for the secondary minerals will be used to assess the relative importance of closed-system processes (e.g. local fluid-rock reaction) and open-system processes (e.g. groundwater or hydrothermal fluid influx) in controlling the isotopic compositions of oxygen, sulfur, and carbon in the pore fluids.