Scandium transport in hydrothermal systems: New insight from experimental, theoretical and field-based studies

热液流体中矿石金属输运的定量数据对于了解地壳流体流动和经济矿床的形成至关重要。金属在高P-T条件下的溶解度和络合作用的实验和理论第一性原理研究对于建立热液成矿系统的定量过程模型至关重要。实验研究为普通碱和贵金属的水热行为提供了定量数据，但许多具有重要经济意义的稀有金属尚未得到充分的研究。钪是一种稀有金属，在新兴的绿色气候中和技术中变得越来越重要，但人们对成矿系统中驱动钪热液动员、运输和富集的过程知之甚少。钪在化学上与Al相似，但也与REE和Y相似，这使它成为岩浆和热液系统中元素分馏的有希望的代表。关键的未解决的问题是氯化物和氟化物作为配体对Sc络合的相对重要性，Sc与REE和Y之间的溶解度和形态差异，以及岩浆和热液过程在矿化体系中导致Sc富集的相对作用。该项目将通过将高温溶解度实验和Sc络合的第一性原理模拟与岩浆-热液系统中Sc浓度的流体包裹体研究和热液中Sc运输的地球化学模拟相结合的综合方法来解决Sc的热液运输问题。该项目分为四个工作包，它们将共同对Sc的热液地球化学产生根本性的新认识。工作包A将通过在100-300℃温度下的批量溶解度实验来研究Sc在氯水和氟溶液中的溶解度。工作包B将利用第一性原理模拟研究Sc在水热氯化物和氟化物溶液中的络合作用。实验和第一性原理结果将用于建立一个一致的热液流体中Sc溶解度和形态形成的热力学模型。工作包C将提供有关运送钪的岩浆热液流体化学组成的流体包裹体限制，包括天然流体中的钪浓度。工作包D将通过地球化学-热力学建模解决关键系统参数（温度、压力、盐度、氟浓度、pH）对岩浆-热液系统中Sc运输的影响，并将研究Sc、REE和Y之间溶解度和形态行为的差异。

Quantitative data for the transport of ore metals in hydrothermal fluids are essential for understanding fluid flow and formation of economic mineral deposits in the Earthʼs crust. Experimental and theoretical first-principles studies of the solubility and complexation of metals at elevated P-T conditions are critical for developing quantitative process models for hydrothermal ore-forming systems. Experimental research has provided quantitative data for the hydrothermal behavior of common base and precious metals, but many economically important rare-metals have not been adequately studied. Scandium is a rare-metal that is becoming increasingly important for emerging green climate-neutral technologies, but the processes that drive hydrothermal mobilization, transport and enrichment of Sc in ore-forming systems are poorly understood. Scandium shares chemical similarities with Al but also with the REE and Y, which makes it a promising proxy for elemental fractionation in magmatic and hydrothermal systems. Key unresolved questions are the relative importance of chloride and fluoride as ligands for Sc complexation, the differences in solubility and speciation between Sc and the REE and Y, and the relative role of magmatic and hydrothermal processes that lead up to Sc enrichment in mineralized systems. The proposed project will address the hydrothermal transport of Sc through an integrated approach that links high-temperature solubility experiments and first-principles simulation of Sc complexation with fluid inclusion studies of the Sc concentration in magmatic-hydrothermal systems and geochemical modeling of hydrothermal Sc transport. The project is organized as four work packages, which will jointly result in fundamentally new understanding of the hydrothermal geochemistry of Sc. Work package A will study the solubility of Sc in aqueous chloride and fluoride solutions through batch solubility experiments at temperatures of 100-300 ºC. Work package B will investigate the Sc complexation in hydrothermal chloride and fluoride solutions using first-principles simulation. The experimental and first-principles results will be used to develop a consistent thermodynamic model for Sc solubility and speciation in hydrothermal fluids. Work package C will provide fluid inclusion constraints on the chemical composition of Sc transporting magmatic-hydrothermal fluids, including Sc concentrations in natural fluids. Work package D will address the impact of key system parameters (temperature, pressure, salinity, fluorine concentration, pH) on transport of Sc in magmatic-hydrothermal systems through geochemical-thermodynamic modeling, and will also look at the differences in solubility and speciation behavior between Sc, the REE and Y.