CAREER: Partitioning of Rare Earth Elements (REE) Between Minerals and Aqueous Fluids in Ore Deposits

稀土元素(REE)具有相似但略有不同的离子半径和原子质量，这使得研究化学元素的基本行为及其在自然体系中的矿物结构中的结合成为可能。它们的磁性使其成为风力涡轮机、混合动力汽车电池和节能照明用荧光粉的永久磁铁的重要组成部分。矿物的稀土元素组成也被用于地学，以追踪地壳中的地质过程。矿床通常在深部通过水溶液中金属的活化和热液矿脉中的矿化而形成。流体和矿物的性质将影响不同稀土元素的分馏方式。目前，关于如何系统地量化流体-岩石相互作用和成矿过程中矿物的微量元素特征，我们有很多需要发现的问题。这份职业计划通过实验室实验、数值模拟和捕获天然矿物中的流体包裹体，探索了稀土元素如何在矿床中的水溶液和矿物之间进行分馏。热流体项目将通过为本科生准备流体和矿物暑期班、开放获取手册和专门的动手热力学教程网页来启动。该项目的一个主要目的是提供一个教育平台，并展示热力学在地球科学中更广泛的意义。方解石、萤石和磷灰石是与稀土和其他矿床共生的常见脉石矿物。这些矿物记录了可用于确定与成矿过程有关的温度、流体化学和潜在的流体路径的地球化学特征。这项研究涉及一系列在100至350摄氏度的水热实验，以确定稀土在水中流体-方解石、-磷灰石和-萤石之间的分配作为温度和流体组成(即盐度、pH和配体活性)的函数。这些实验数据将被用来开发一个新的热力学模型，用于预测和量化这些热液矿物中的稀土元素特征。为了验证这一模型，将研究北美过碱性、碳酸盐和氧化铁-磷灰石矿床中的一组矿物微量元素组成和流体包裹体。拟议研究的目标是提供一个框架，用于模拟矿藏中与流体-岩石反应有关的痕量金属的分配，并提高我们模拟和解释成矿过程的能力。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The rare earth elements (REE) have similar but slightly different ionic radii and atomic masses, which permits studying the fundamental behavior of chemical elements and their incorporation in mineral structures in natural systems. Their magnetic properties make them important components in permanent magnets used in wind turbines, batteries of hybrid cars, and phosphors in energy efficient light. The REE composition of minerals is also used in geosciences to trace geological processes in the Earth's crust. Ore deposits commonly form at depth through the mobilization of metals in aqueous fluids and the mineralization in hydrothermal veins. The properties of both, the fluid and the minerals, will affect how the different REE are fractionated. Currently, we have much to discover about how to quantify systematically the trace element signatures of minerals with regards to fluid-rock interaction and ore-forming processes. This CAREER proposal explores how REE fractionate between aqueous fluids and minerals in ore deposits using laboratory experiments, numerical modeling and fluid inclusions trapped in natural minerals. The THERMO fluids project will be initiated with the preparation of a Fluids & Minerals summer school for undergraduate students, an open access booklet, and a dedicated hands-on thermodynamics tutorial webpage. A major aim of this project will be to provide an education platform and demonstrate the broader significance of thermodynamics in geosciences. Calcite, fluorite and apatite are common gangue minerals associated to REE and other mineral deposits. These minerals record geochemical signatures that may be used to determine temperature, fluid chemistry and potentially fluid pathways associated to ore-forming processes. This research involves a comprehensive series of hydrothermal experiments at 100 to 350 degrees C for determining the partitioning of REE between aqueous fluid-calcite, -apatite and -fluorite as a function of temperature and fluid composition (i.e., salinity, pH and ligand activity). The experimental data will be used to develop a new thermodynamic model for predicting and quantifying REE signatures in these hydrothermal minerals. To test the model, a set of mineral trace element compositions and fluid inclusions will be studied in peralkaline, carbonatite, and iron oxide-apatite hosted ore deposits in North America. The objective of the proposed research is to provide a framework for simulating the partitioning of trace metals associated to fluid-rock reactions in ore deposits and advance our capabilities of modeling and interpreting ore-forming processes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.