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含有对高科技工业至关重要的稀有元素矿床。含水硅酸盐熔体和硅酸盐饱和的热液流体在与侵入岩有关的矿床的形成中起着关键作用，是岩石圈中物质迁移的重要媒介。这些液体的热力学和输运性质反映了它们的原子或分子尺度结构;因此，液体结构的知识对于理解物理和化学过程，如矿石金属动员，运输和沉积是必不可少的。拟议的研究将直接调查含水硅酸盐熔体的结构，超临界富含硅酸盐的含水液体，以及硅酸盐饱和的水溶液在高温和高压下，以确定这些参数的变化如何可能会影响溶液中的稀有元素，钽（Ta），铌（Nb）和稀土元素（REE）在不断发展的岩浆系统。为了实现这些目标，该研究将利用分析方法的最新进展，在地壳和上地幔存在的压力和温度条件范围内，在Basset型热液金刚石对顶砧单元中对富含挥发性的硅酸盐液体进行现场询问。计划进行一系列实验，这些实验将使用高能（~100 keV）X射线散射、X射线吸收光谱和拉曼光谱来检查拓扑结构（即，描述网络的原子之间的互连）和高温高压下样品中Ta、Nb和RE周围的局部结构环境。我和我的学生还将使用高分辨率三维纹理和化学制图、激光烧蚀电感耦合等离子体质谱和拉曼光谱研究主要稀有元素矿床中熔体和流体包裹体（矿物中捕获的流体的微小样品）的起源和组成。包裹体数据将被用来表征成矿过程中流体的组成，并有助于限制一些将要进行实验研究的类似成分。拟议的实验和包裹体研究将填补我们对含水硅酸盐熔体和富含硅酸盐的含水流体的分子尺度性质以及这些液体动员和运输稀有金属的能力的理解中的巨大空白。岩石圈中的元素测试的结果是必要的理论方法，模拟硅酸盐-水系统的结构和动力学，并为微量元素分区的定量预测模型的发展，可以应用在广泛的条件。更好地了解硅酸盐液体结构及其对稀有元素分布的影响，对于模拟岩浆系统中的分馏趋势和开发更准确的稀有元素成矿过程成因模型至关重要，新的勘探战略可以基于此。Ta，Nb和稀土元素在岩浆系统和地壳深部流体中的行为的知识也是重要的解释微量元素模式，广泛用于破译地球化学过程和构造环境。

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.