Collaborative Research: Experimental Determination of Iron (Fe) Isotope Fractionations in Sulfide Minerals

智力优势。 铁（Fe）同位素地球化学领域发展迅速，目前文献包括来自世界上20多个研究小组的75篇论文中的数千种同位素分析。这项工作的大部分集中在自然系统，只有少数实验确定的动力学和平衡分馏因子和相关的交换动力学数据可用于地质相关的系统。地球上Fe同位素组成的最大变化记录在硫化物中，其中几乎5 permil范围内的56 Fe/54 Fe比值被发现在沉积黄铁矿和3 permil范围内的高温热液硫化物，但Fe同位素分馏机制在水和矿物Fe-S系统知之甚少。本文提出了一个综合性的实验方案，以确定在~250 ℃温度范围内含水Fe-S物种和硫化物矿物之间的Fe同位素分馏。该实验计划将探讨同位素分馏在三个系统，涵盖了一些最常见的水和矿物物种。动力学和平衡铁同位素分馏将进行研究，包括不同的硫化物形成途径和相关的同位素交换动力学，可能发挥重要作用，在确定硫化物矿物的铁同位素组成的问题的探索。除了温度，我们将探讨pH值和微量金属替代对铁同位素分馏和交换动力学的影响。 硫化物的铁同位素地球化学已被用于研究从生命起源和演化到热液矿床中金属来源的问题。这些数据的解释将加强本研究产生的同位素分馏机制的可用性。此外，将采用新的实验方法，将普遍适用于矿物合成的其他实验研究。该研究小组融合了来自三个机构的同位素和实验地球化学方面的基本专业知识。该项目将支持和教育来自三个机构的几名研究生和一名博士后。其中包括一个博士。一名来自加纳的女学生和一名来自乌拉圭的女博士后科学家。此外，该研究将涉及一个早期的职业助理教授。

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.