EAGER: Development of Tellurium Stable Isotopes as Paleoredox Indicator

碲(Te)是一种有毒元素，用于光伏太阳能电池板，集中在一些矿山废物中，是某些类型金矿床的关键成分。它的化学性质因条件而异：在缺氧、还原的条件下，它往往以固体形式固定，但当暴露在大气中时，它可以溶解在水中。在现代环境中，检测Te从氧化的、可移动的形式转变为还原的、固定的形式的时间和地点的测量可以帮助我们预测其移动性和毒性。这样的测量还应该提高对含Te矿床的了解。在拼凑地球上生命的历史时，对古老岩石的测量揭示了Te氧化的存在或不存在，可以为地球大气和海洋中生物临界氧浓度随时间的变化提供证据。该项目将开发一种追踪Te氧化和还原的新方法，使用对Te稳定同位素比率(128Te/125Te)微小变化的新测量。这种新的地球化学工具在针对现代环境、矿床和地球历史的一系列应用中应该是有用的。一名博士生将接受高级地球化学培训，应用于古代岩石和现代环境。该项目计划从STEM代表性不足的群体中招收一名本科生；该学生将被介绍到环境地球化学领域。K-12年级的学生将学习收集和分析河水，以确定当地火山灰蓄水池的渗漏是否会影响河流水质。这个探索性项目的目标是确定(1)同位素变化是否发生在现代风化环境中，以及(2)Te稳定同位素是否可以作为前寒武纪氧化作用的古氧化还原代理。新的分析方法使用氢化物发生MC-ICPMS和双尖峰(120Te和124Te)来获得高精度的128Te/125Te比值的测量，同时需要非常少量的Te(10 Ng)。对现代土壤、风化页岩和尾矿的测量将揭示在活跃的风化环境中氧化还原循环过程中128Te/125Te移动的幅度。对古代铁石、页岩和古土壤的测量将提供古代环境中Te同位素位移或缺失的记录。Te同位素应该提供一个新的古氧化还原替代物，其氧化还原阈值介于U和Cr同位素替代物之间，因此，可能为新元古代O2水平提供新的见解。这样的工具可以提供关于氧化条件的上升和多细胞生命的增殖的有价值的信息。

Tellurium (Te) is a toxic element that is used in photovoltaic solar panels, is concentrated in some mine wastes, and is a key constituent of some types of gold ore deposits. Its chemical properties vary with conditions: In oxygen-poor, "reducing" conditions it tends to be immobilized in solid forms, but when exposed to atmospheric oxygen it can dissolve in water. In the modern environment, measurements that detect when and where Te transitions from its oxidized, mobile form to its reduced, immobile form can help us predict its mobility and toxicity. Such measurements should also improve understanding of Te-bearing ore deposits. In piecing together the history of life on earth, measurements of ancient rocks that reveal the presence or absence of Te oxidation can provide evidence for changes in biologically critical oxygen concentrations in the earth's atmosphere and oceans over time. This project will develop a new way to trace Te oxidation and reduction, using novel measurements of small variations in Te stable isotope ratios (128Te/125Te). This new geochemical tool should be useful in a range of applications aimed at modern environments, ore deposits, and earth history. A doctoral student will be trained in advanced geochemistry applied to both ancient rocks and the modern environment. The project plans to recruit an undergraduate student from an underrepresented group in STEM; the student will be introduced to the field of environmental geochemistry. K-12 students will learn to collect and analyze river waters to determine if seeps from a local coal ash impoundment affect river water quality.The objectives of this exploratory project are to establish if (1) isotopic shifts occur in modern weathering environments and (2) if Te stable isotopes can serve as a paleoredox proxy of Precambrian oxygenation. The new analytical method uses hydride generation MC-ICPMS and a double spike (120Te and 124Te) to obtain highly precise measurements of 128Te/125Te ratios while requiring very small amounts of Te (10 ng). Measurements of modern soils, weathered shales and mine tailings will reveal the magnitude of 128Te/125Te shifts imparted during redox cycling in active weathering environments. Measurements of ancient ironstones, shales, and paleosols will provide a record of Te isotopic shifts, or lack thereof, in ancient environments. Te isotopes should provide a new paleoredox proxy with an intermediate redox threshold between those of the U isotope and Cr isotope proxies, and thus, may provide new insights into O2 levels during the Neoproterozoic. Such a tool could provide valuable information about the rise of oxidizing conditions and the proliferation of multicellular life.