Intellectual Merit. The field of Iron (Fe) isotope geochemistry has grown rapidly and the literature now contains several thousand isotopic analyses in over 75 papers from two-dozen research groups in the world. Most of this work has focused on natural systems, and only a handful of experimentally determined kinetic and equilibrium fractionation factors and associated exchange kinetic data are available for geologically relevant systems. The largest variations in Fe isotope compositions on Earth are recorded in sulfides, where almost a 5 permil range in 56Fe/54Fe ratios is found in sedimentary pyrite and a 3 permil range in high-temperature hydrothermal sulfides, and yet Fe isotope fractionation mechanisms in aqueous and mineral Fe-S systems poorly known. A comprehensive experimental program is planned for determining the Fe isotope fractionations among aqueous Fe-S species and sulfide minerals over the temperature range up to ~250 C. The experimental program will explore isotopic fractionations in three systems covering some of the most common aqueous and mineral species. Both kinetic and equilibrium Fe isotope fractionations will be investigated, including exploration of different sulfide formation pathways and their associated isotopic exchange kinetics, issues that may play a major role in determining the Fe isotope compositions of sulfide minerals. In addition to temperature, we will explore the effects of pH and trace metal substitution on Fe isotope fractionation and exchange kinetics.
Broader Impacts. Iron isotope geochemistry of sulfides has been used to investigate problems ranging from the origin and evolution of life to the sources of metals in hydrothermal ore deposits. Interpretations of these data will be enhanced by availability of isotopic fractionation mechanisms generated by this study. In addition, new experimental approaches will be employed that will be generally applicable to other experimental studies of mineral synthesis. The research team blends essential expertise in isotope and experimental geochemistry from three institutions. The project will support and educate several graduate students and a post-doc from the three institutions. These include a Ph.D. student from Ghana and a female post-doctoral scientist from Uruguay. In addition, the research will involve an early-career Assistant Professor.
