GEO-CM: Trace metals in sphalerite from polymetallic, porphyry-lode mineral deposits of southwest Montana

闪锌矿是锌的主要矿物，它通常含有高浓度的其他金属杂质，其中许多被美国地质调查局指定为“关键矿物”。关键矿产包括对国家经济和安全至关重要的金属，但目前必须从其他国家进口。蒙大拿州比尤特的矿山富含铜、银、铅、锌和锰。Philipsburg矿区位于Butte西北60公里处，面积较小，但具有许多相同的地质特征。对Butte和Philipsburg闪锌矿样品的初步分析表明，它们都富含关键金属镓、铟、锗和钨，以及铜和银。最近的研究表明，在手持式紫外灯下，这些金属杂质最丰富的闪锌矿发出明亮的红色荧光。这种现象可以为不同浓度的微量金属闪锌矿提供一种低成本、简单的分选方法。这项研究的第一个目标是分析来自Butte和Philipsburg的样品，以绘制出每个矿区（几平方英里，深达1英里）范围内闪锌矿中金属杂质的分布。第二个目标是在实验室中制造出含有与自然标本中发现的相同微量金属的闪锌矿颗粒。然后，研究人员将比较人造和天然样品的荧光行为。该项目将在蒙大拿理工大学（MTU）培养经济地质学领域的本科生和研究生。MTU是EPSCoR州的主要本科院校（PUI）。该项目的结果可能为闪锌矿和其他矿石矿物研究矿床提供新的途径。本研究对发光闪锌矿在材料科学与工程中的应用也有一定的应用价值。蒙大拿州的Butte是科迪勒式带状斑岩矿床的典型例子，也是美国历史上最重要的铜、锌、银和锰产地之一。这项研究将利用蟒蛇研究实验室（ARL）的收集，这是一套从蒙大拿州Butte和其他矿山收集的超过50,000个手部样本，存档于蒙大拿州理工学院校园。利用ARL收集的数据，以及来自活跃的大陆斑岩铜钼矿的新样本，研究人员将从整个Butte地区的已知地点，到地表以下5000英尺的深度，组装一套包含闪锌矿和其他硫化物矿物的200个抛光矿石样本。利用光学显微镜、光致发光光谱（PLS）、拉曼光谱（Raman）、激光烧蚀ICP-MS、电子探针微量分析（EPMA）和高光谱阴极发光（HP-CL）对闪锌矿样品进行分析，揭示从微米尺度到千米尺度的微量元素分布的时空格局。机器学习工具将用于识别闪锌矿数据库中元素之间的相关性，这将有助于阐明微量元素进入ZnS结构的潜在机制。例如，研究人员假设上面提到的深红色荧光与闪锌矿晶格中Cu(+1), Ga（+3）和W（+6）对Zn（+2）的耦合取代有关。他们将利用水热法合成已知微量元素组成的闪锌矿，并比较合成样品和天然样品的HP-CL、拉曼和PLS特征。最后，他们将与一个同步加速器实验室建立合作关系，该实验室能够使用XANES验证其金属掺杂ZnS和天然闪锌矿样品中钨和其他微量元素的氧化状态。该项目将支持蒙大拿州理工大学（前身为蒙大拿州矿业学院）在经济地质学方面的前沿研究和研究生培训，该学院是EPSCoR州的一所主要本科院校。该项目的研究结果可能为闪锌矿和其他矿石矿物研究矿床提供新的途径，并可能在材料科学和工程中应用发光ZnS。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Sphalerite is the primary ore mineral of zinc, and it oftens contains elevated concentrations of other metals as impurities, many of which are designated as “critical minerals” by the U.S. Geological Survey. Critical minerals include metals that are important to the country’s economy and security, but must currently be imported from other countries. Mines in Butte, Montana are rich in copper, silver, lead, zinc and manganese. The Philipsburg mining district is located 60 km northwest of Butte is smaller but shares many geologic features. Preliminary analyses of sphalerite samples from Butte and Philipsburg show that they are both highly enriched in the critical metals gallium, indium, germanium, and tungsten, as well as copper and silver. Recent research has shown that sphalerite that is richest in these metal impurities fluoresces bright red under a hand-held UV lamp. This phenomenon could provide a low-cost and simple way to sort sphalerite ores with different concentrations of trace metals. The first goal of this study is to analyze samples from Butte and Philipsburg to map out the distribution of metal impurities in sphalerite at the scale of each mining district (several square miles by up to 1 mile deep). The second objective is to make sphalerite grains in the laboratory that contain the same trace metals that are found in the natural specimens. The researchers will then compare the fluorescence behavior of the man-made and natural specimens. This project will train undergraduate and graduate students in the field of economic geology at Montana Technological University (MTU). MTU is a primarily undergraduate institution (PUI) in an EPSCoR state. Results from this project may reveal new ways that sphalerite and other ore minerals can be used to study mineral deposits. This research may also have applications to the use of luminescent sphalerite in materials science and engineering. Butte, Montana is the type example of a zoned, Cordilleran-style, porphyry-lode deposit, as well as being one of the nation’s top historic producers of Cu, Zn, Ag, and Mn. This study will take advantage of the Anaconda Research Lab (ARL) Collection, a set of over 50,000 hand samples collected from Butte and other mines in Montana that is archived at Montana Tech campus. Using the ARL Collection, as well as new samples from the active Continental porphyry Cu-Mo mine, the researchers will assemble a suite of 200 polished ore specimens containing sphalerite and other sulfide minerals from known locations across the entire Butte district, to depths of up to 5000 ft. below the surface. The sphalerite samples will be analyzed by optical microscopy, photoluminescence spectroscopy (PLS), Raman spectroscopy, laser ablation ICP-MS, electron probe microanalysis (EPMA) and hyperspectral cathodoluminescence (HP-CL) to reveal spatial and temporal patterns in trace element distribution, from the micron scale to the km scale. Machine learning tools will be used to identify correlations between elements in the sphalerite database that will help illuminate the underlying mechanisms by which trace elements enter the ZnS structure. For example, the researchers hypothesize that the deep red fluorescence mentioned above is linked to coupled substitution of Cu(+1), Ga(+3), and W(+6) for Zn(+2) in the sphalerite lattice. They will synthesize sphalerite of known trace element compositions using hydrothermal methods and compare the HP-CL, Raman, and PLS signatures of the synthetic and natural specimens. Finally, they will establish collaboration with a synchrotron laboratory capable of using XANES to verify the oxidation state of tungsten and other trace elements in their metal-doped ZnS and natural sphalerite samples. This project will support cutting-edge research and graduate-student training in economic geology at Montana Technological University, formerly the Montana School of Mines, a primarily undergraduate institution (PUI) in an EPSCoR state. Results from this project may reveal new ways that sphalerite and other ore minerals can be used to study mineral deposits, and may have applications to the use of luminescent ZnS in materials science and engineering.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.