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

热液中金属迁移的定量数据对于了解ʼS地壳中流体的流动和经济矿床的形成是必不可少的。实验和理论第一性原理研究金属在P-T升高条件下的溶解度和络合作用，是建立热液成矿系统定量过程模型的关键。实验研究已经为普通贱金属和贵金属的水热行为提供了定量的数据，但许多具有重要经济意义的稀有金属还没有得到充分的研究。Sc是一种稀有金属，对于新兴的绿色气候中性技术正变得越来越重要，但推动成矿系统中Sc的热液动员、运输和浓缩的过程却知之甚少。Sc与Al有化学上的相似之处，但也与REE和Y有相似之处，这使它成为岩浆和热液系统中元素分馏的有希望的替代物。尚未解决的关键问题是氯化物和氟化物作为Sc络合配体的相对重要性，Sc与REE和Y在溶解度和形态上的差异，以及岩浆和热液作用在矿化系统中导致Sc富集的相对作用。拟议的项目将通过一种综合方法解决Sc的热液迁移问题，该方法将高温溶解度实验和Sc络合作用的第一性原理模拟与流体包裹体研究联系起来，研究岩浆-热液系统中Sc的浓度，并对热液Sc迁移进行地球化学模拟。该项目被组织为四个工作包，这将共同从根本上对SC的热液地球化学有新的理解。工作包A将通过在100-300℃下的批量溶解度实验研究Sc在氯化物和氟化物水溶液中的溶解度。工作包B将使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。实验和第一性原理的结果将被用来建立一个关于Sc在热液流体中的溶解度和形态的一致热力学模型。工作包C将提供对输送岩浆-热液流体的Sc化学成分的流体包裹体约束，包括天然流体中的Sc浓度。工作包D将通过地球化学-热力学模型研究关键系统参数(温度、压力、盐度、氟浓度、pH)对Sc在岩浆-热液系统中迁移的影响，并将研究Sc、REE和Y在溶解度和形态行为方面的差异。

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.