Nanoscale Mineralogy and Geochemistry of Arsenian Pyrite in Ore Deposits

富砷（砷）黄铁矿是砷（As）最常见的来源，它在风化过程中释放污染水和土壤，还含有大量的其他微量元素，包括Ag、Au、Bi、Cd、Co、Cu、Hg、Ni、Pb、Sb、Se、Te、Tl和Zn。这些元素中有许多是环境问题，而金和银具有重要的经济意义。如果我们要了解将元素释放到环境中并将其困在矿床中的过程，就需要更好地了解控制这些微量元素取代为砷黄铁矿的因素。即将开展的项目将通过观察各种地质环境中材料的纳米级矿物学和地球化学来澄清这些因素。该小组先前的工作表明，卡林型金矿中砷黄铁矿中金的固溶体极限是由一个连接金和砷浓度的线性方程定义的。在新项目中，该团队将测试其他类型矿床（浅成热液、中温热液、矽卡岩、斑岩铜）中的砷黄铁矿是否也含有金，并具有类似的As-Au固溶体关系。他们还将测试其他微量元素是否在砷黄铁矿中表现出类似的溶解度极限，以及当这些元素的浓度超过溶解度极限时，它们是否占据纳米结构域。最后，他们将测试砷黄铁矿中的成分带是否由晶体层的生长和吸附的微量元素的扩散形成，是否可以在样品之间建立真正的生长带，以及它们是否可以用于追踪单个矿床的流体路径。纳米尺度的观测将通过高分辨率透射电子显微镜（HRTEM）和高角度环形暗场扫描透射电子显微镜（HAADF-STEM）进行，这是一种近原子尺度的z对比成像技术。砷黄铁矿的微米级分析将采用次级离子质谱（SIMS）方法对S、Fe、Co、Ni、Cu、Se、Ag、Cd、Sb、Te、Au和Hg的浓度进行分析，并通过同步加速器x射线荧光（SXRF）对元素的氧化态进行分析。该研究将培训学生表征具有经济和环境重要性的微量元素的矿物的方法，并将提供急需的通过SIMS和激光烧蚀，电感耦合质谱（LA-ICP-MS）方法进行痕量元素分析的实验室间比较。它还将澄清砷、汞、锑、碲和其他有毒元素分散到土壤和地下水中的过程，并确定使从热液矿石中回收金、银和其他重要经济金属复杂化的地质因素，这些金属是我们工业社会这些金属的主要来源。最后，它将提供关于形成纳米粒子的自然过程的信息，这将有助于开发生产合成纳米粒子的方法。

Arsenic-rich (arsenian) pyrite is the most common source of arsenic (As) that is released during weathering to contaminate water and soils, and it also contains significant amounts of other trace elements including Ag, Au, Bi, Cd, Co, Cu, Hg, Ni, Pb, Sb, Se, Te, Tl, and Zn. Many of these elements are of environmental concern and Au and Ag are economically important. Better understanding of the factors that control the substitution of these trace elements into arsenian pyrite is needed if we are to understand the processes that release elements into the environment and trap them in ore deposits. The project to be undertaken will clarify these factors by observation of the nanoscale mineralogy and geochemistry of material from a wide range of geologic environments. Previous work by the group has shown that the limit of solid solution for Au in arsenian pyrite from Carlin-type Au deposits is defined by a linear equation linking the concentrations of gold and arsenic. In the new project, the team will test whether arsenian pyrite in other types of ore deposits (epithermal, mesothermal, skarn, porphyry copper) also hosts Au and has similar As-Au solid-solution relations. They will also test whether other trace elements show similar solubility limits in arsenian pyrite and whether these elements occupy nanodomains when their concentrations exceed the solubility limit. Finally, they will test if compositional zones in arsenian pyrites are formed both by growth of crystal layers and by diffusion of adsorbed trace elements, whether true growth zones can be correlated from sample to sample, and whether they can be used to trace fluid pathways through individual deposits. Nanoscale observations will be carried out by high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning TEM (HAADF-STEM), which is a Z-contrast imaging technique at the near-atomic scale. Micrometer-scale analyses of arsenian pyrite will be made by secondary ion mass spectrometric (SIMS)methods for concentrations of S, Fe, Co, Ni, Cu, Se, Ag, Cd, Sb, Te, Au,and Hg, and by synchrotron X-ray fluorescence (SXRF) for oxidation states of the elements. The research will train students in methods to characterize minerals containing trace amounts of elements of economic and environmental importance and it will provide much-needed interlaboratory comparisonsof trace element analyses by SIMS and laser-ablation, inductively-coupled mass spectrometry (LA-ICP-MS) methods. It will also clarify processes by which As, Hg, Sb, Te and other toxic elements are dispersed into soils and groundwater and identify geological factors that complicate the recovery of Au, Ag and other economically important metals from hydrothermal ores, which are the main source of these metals to our industrial society. Finally, it will provide information on natural processes that form nanoparticles, which will aid in development of methods to produce synthetic nanoparticles.