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系统中矿物结构中的结合成为可能。它们的磁性使它们成为风力涡轮机、混合动力汽车电池和节能灯荧光粉中使用的永磁体的重要组成部分。矿物的稀土元素组成也被用于地球科学，以追踪地壳的地质过程。矿床通常是通过水流体中金属的动员和热液脉体中的矿化作用在深部形成的。流体和矿物的性质将影响不同稀土元素的分选。目前，如何在流体-岩石相互作用和成矿过程中系统地量化矿物的微量元素特征还有待探索。本CAREER提案通过实验室实验、数值模拟和天然矿物中的流体包裹体，探讨了稀土元素如何在矿床的含水流体和矿物之间分馏。THERMO流体项目的启动将包括为本科生准备流体与矿物暑期学校、一本开放获取的小册子和一个专门的动手热力学教程网页。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、萤石和磷灰石是常见的脉石矿物，伴生于稀土等矿床。这些矿物记录的地球化学特征可用于确定温度、流体化学以及与成矿过程相关的潜在流体路径。本研究在100 ~ 350℃范围内进行了一系列的水热实验，以确定方解石、磷灰石和萤石水溶液中稀土元素的分配随温度和流体组成（即盐度、pH值和配体活性）的变化。实验数据将用于建立一个新的热力学模型来预测和量化这些热液矿物的稀土特征。为了测试该模型，将在北美的过碱性、碳酸盐岩和氧化铁磷灰石矿床中研究一组矿物微量元素组成和流体包裹体。拟议研究的目的是为模拟与矿床流体-岩石反应相关的痕量金属的分配提供一个框架，并提高我们建模和解释成矿过程的能力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.