Ore metal transport in hydrous silicate melts and silicate-rich aqueous fluids

花岗岩和其他长英质侵入岩可能蕴藏着对高科技产业至关重要的稀有元素矿藏。含水硅酸盐熔体和饱和硅酸盐热液在与侵入岩有关的矿床形成中起着关键作用，是岩石圈质量传递的重要因素。这些液体的热力学和传输性质反映了它们的原子或分子级结构；因此，了解液体结构对于理解物理和化学过程是必不可少的，例如矿石金属的动员、传输和沉积。这项拟议的研究将直接研究高温高压下含水硅酸盐熔体、超临界富硅酸盐水溶液和饱和硅酸盐水溶液的结构，以确定这些参数的变化如何影响稀有元素Ta、Nb和稀土元素(REE)在演化岩浆系统中的溶解。为了实现这些目标，这项研究将利用分析方法方面的最新进展，能够在地壳和上地幔存在的各种压力和温度条件下，在巴西特型热液金刚石顶压室中对富含挥发性硅酸盐液体进行现场讯问。计划进行一系列实验，使用高能(~100keV)X射线散射、X射线吸收光谱和拉曼光谱来研究高温高压下样品中Ta、Nb和Rees的拓扑结构(即描述网络的原子之间的互连)和局域结构环境。我和我的学生还将使用高分辨率三维纹理和化学测绘、激光烧蚀电感耦合等离子体质谱仪和拉曼光谱来调查主要稀有元素矿床中熔体和流体包裹体(困在矿物中的微小流体样本)的来源和组成。包裹体数据将被用来表征成矿过程中涉及的流体的组成，并帮助约束一些将进行实验研究的模拟成分。拟议的实验和包裹体研究将填补我们在理解含水硅酸盐熔体和富硅酸盐水溶液的分子尺度性质以及这些液体在岩石圈中迁移和运输稀有元素的能力方面的巨大空白。这一结果对于检验模拟硅酸盐-水体系结构和动力学的理论方法，以及开发适用于广泛条件的微量元素分配的定量预测模型是必要的。更好地了解硅酸盐液体结构及其对稀土元素分布的影响，对于模拟岩浆系统的分馏趋势，以及开发更准确的稀有元素成矿过程的成因模型，以便制定新的勘探战略，是至关重要的。对Ta、Nb和Rees在岩浆系统和地壳深部流体中的行为的了解，对于解释被广泛用于破译地球化学过程和构造环境的微量元素模式也很重要。

Granites and other felsic intrusive rocks may host rare-element ore deposits that are critical to high technology industries. Hydrous silicate melts and silicate-saturated hydrothermal fluids play a key role in the formation of intrusion-related ore deposits and are important agents of mass transfer in the lithosphere. The thermodynamic and transport properties of these liquids reflect their atomic or molecular scale structure; hence, knowledge of liquid structure is essential to understand physical and chemical processes such as ore metal mobilization, transport and deposition. The proposed research will directly investigate the structure of hydrous silicate melts, supercritical silicate-rich aqueous liquids, and silicate-saturated aqueous solutions at high temperatures and pressures in order to determine how changes in these parameters may affect the solution of the rare-elements, tantalum (Ta), niobium (Nb), and rare earth elements (REE) in evolving magmatic systems. To achieve these objectives, the study will utilize recent advances in analytical methods that enable in situ interrogation of volatile-rich silicate liquids in a Bassett-type hydrothermal diamond anvil cell over a range of pressure and temperature conditions that exist in the crust and upper mantle. A series of experiments are planned that will use high energy (~100 keV) x-ray scattering, x-ray absorption spectroscopy, and Raman spectroscopy to examine the topology (i.e., interconnections between atoms that describe the network) and the local structural environment surrounding Ta, Nb and REEs in samples at high temperatures and pressures. My students and I will also investigate the origin and composition of melt and fluid inclusions (tiny samples of fluid trapped in minerals) from major rare-element deposits using high-resolution three-dimensional textural and chemical mapping, laser-ablation inductively coupled plasma mass spectrometry, and Raman spectroscopy. The inclusion data will be used to characterize the composition of fluids involved in ore-forming processes and to help constrain some analog compositions that will be investigated experimentally.The proposed experimental and inclusion studies will fill the large gap in our understanding of the molecular-scale properties of hydrous silicate melts and silicate-rich aqueous fluids and the capacity of these liquids to mobilize and transport rare-elements in the lithosphere. The results are needed for testing theoretical methods that simulate the structure and dynamics of silicate-water systems, and for the development of quantitative predictive models of trace element partitioning that can be applied over a wide range of conditions. An improved understanding of silicate liquid structure and its effect on rare-element distribution is essential for modelling fractionation trends in magmatic systems and for developing more accurate genetic models of rare-element ore-forming processes upon which new exploration strategies can be based. Knowledge of the behavior of Ta, Nb and REEs in magmatic systems and in deep crustal fluids is also important for interpreting trace element patterns that are widely used to decipher geochemical processes and tectonic settings.