Nanoscale Mineralogy and Geochemistry of Arsenian Pyrite in Ore Deposits

矿床中砷黄铁矿的纳米矿物学和地球化学

• 批准号: 0537626
• 负责人: Stephen Kesler
• 金额: --
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-12-01 至 2010-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0537626&HistoricalAwards=false
• 关键词: Nanoscale; Mineralogy; Geochemistry; Arsenian; Pyrite

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.

富砷黄铁矿是风化过程中释放出来的砷（As）污染水和土壤的最常见来源，它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。这些元素中的许多是环境关注的，并且Au和Ag是经济上重要的。如果我们要了解释放元素到环境中并将其捕获在矿床中的过程，就需要更好地了解控制这些微量元素替代成砷黄铁矿的因素。即将开展的项目将通过观察来自各种地质环境的材料的纳米级矿物学和地球化学来澄清这些因素。该小组以前的工作表明，卡林型Au矿床中含砷黄铁矿中Au的固溶极限由金和砷浓度的线性方程确定。在新项目中，该团队将测试其他类型矿床（浅成热液矿床、中温矿床、夕卡岩矿床、斑岩铜矿）中的砷黄铁矿是否也含有Au，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，它们是否占据纳米畴。最后，他们将测试砷黄铁矿中的成分区是否是通过晶体层的生长和吸附的微量元素的扩散形成的，真正的生长区是否可以在样本之间进行关联，以及它们是否可以用于追踪通过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TEM（HAADF-STEM）进行，这是一种近原子尺度的Z对比成像技术。将通过二次离子质谱法对砷黄铁矿的S、Fe、Co、Ni、Cu、Se、Ag、Cd、Sb、Te、Au和Hg的浓度进行微米级分析，并通过同步加速器X射线荧光法对元素的氧化态进行分析。该研究将培养学生的方法来表征矿物含有微量元素的经济和环境的重要性，它将提供急需的实验室间比较微量元素分析的西姆斯和激光烧蚀，电感耦合质谱（LA-ICP-MS）方法。它还将阐明砷、汞、锑、碲和其他有毒元素扩散到土壤和地下水中的过程，并查明使从热液矿石中回收Au、Ag和其他经济上重要的金属复杂化的地质因素，热液矿石是这些金属在我们工业社会的主要来源。最后，它将提供有关形成纳米颗粒的自然过程的信息，这将有助于开发生产合成纳米颗粒的方法。