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

热液中矿石金属迁移的定量数据对于了解地壳中流体流动和经济矿床的形成至关重要。在升高的 P-T 条件下金属的溶解度和络合的实验和理论第一性原理研究对于开发热液成矿系统的定量过程模型至关重要。实验研究为普通贱金属和贵金属的热液行为提供了定量数据，但许多具有经济重要性的稀有金属尚未得到充分研究。钪是一种稀有金属，对于新兴的绿色气候中性技术变得越来越重要，但人们对成矿系统中驱动热液动员、运输和富集钪的过程知之甚少。钪与铝、稀土元素和钇的化学成分相似，这使其成为岩浆和热液系统中元素分馏的有前途的代表。未解决的关键问题是氯化物和氟化物作为钪络合配体的相对重要性、钪与稀土元素和钇之间溶解度和形态的差异，以及导致矿化系统中钪富集的岩浆和热液过程的相对作用。该项目将通过一种综合方法来解决钪的热液输运问题，该方法将高温溶解度实验和钪络合的第一原理模拟与岩浆-热液系统中钪浓度的流体包裹体研究以及热液钪输运的地球化学模型联系起来。该项目由四个工作包组成，这将共同带来对 Sc 热液地球化学的全新认识。工作包 A 将通过 100-300 ℃ 温度下的批量溶解度实验研究钪在氯化物和氟化物水溶液中的溶解度。工作包 B 将使用第一原理模拟研究热液氯化物和氟化物溶液中的 Sc 络合。实验和第一原理结果将用于开发热液中钪溶解度和形态形成的一致热力学模型。工作包 C 将提供对输送岩浆热液的钪化学成分的流体包裹体约束，包括天然流体中的钪浓度。工作包D将通过地球化学-热力学模型解决关键系统参数（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，还将研究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.