Experimental determination of the partitioning of Zn, Pb, and Cu between brine and dolomite at temperatures and pressures of sediment-hosted base metal ore deposit formation

沉积物基底金属矿床形成温度和压力下卤水和白云石之间 Zn、Pb 和 Cu 分配的实验测定

• 批准号: 2114403
• 负责人: Martin Appold
• 金额: $ 32.1万
• 依托单位: University of Missouri-Columbia
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-01-01 至 2024-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2114403&HistoricalAwards=false
• 关键词: Experimental; determination; partitioning; Zn; Pb

Many of the world’s most important ore deposits of the metals, lead (Pb), zinc (Zn), and copper (Cu), including those in the U.S., were deposited from hot groundwater (i.e. hydrothermal fluids) in porous sedimentary rocks. Some typical characteristics of these fluids are now well known from previous research, such as their temperature and the concentrations of the most abundant dissolved elements. However, the concentrations of many less abundant elements in the fluids like Pb, Zn, and Cu are not well known for most deposits. Knowledge of these metal concentrations is important because it helps to answer fundamental questions about the origin of the deposits, such as whether anomalously metal-rich fluids were needed to form the deposits, how much time was needed to form the deposits, and what chemical reactions caused the metals to dissolve into and eventually precipitate from the fluids. Further, sound knowledge of how ore deposits form is essential for successful mineral exploration and assessing the U.S. domestic resource base. Because most Pb, Zn, and Cu deposits formed in the distant geologic past, the fluids that are present at the ore deposits now are no longer the same fluids that formed the deposits. However, some of the minerals that these ancient fluids precipitated provide a record of some of the properties of the ancient fluids, including their metal concentrations. For example, the mineral, dolomite, which is a common constituent of many Pb, Zn, and Cu deposits, tends to incorporate trace amounts of these metals into its crystal structure. In general, the higher the concentrations of these metals in the fluid, the higher the concentrations of these metals in the dolomite. If this proportionality factor, called a partition coefficient, can be quantified for each metal, then the concentration of each metal in the ancient fluid can be calculated based on its measured present concentration in the dolomite. The purpose of the proposed research is to determine the partition coefficients for Pb, Zn, and Cu for water and dolomite over a range of typical ore-forming temperatures. The proposed research would be carried out over three years, with the first year focused on Zn, the second year focused on Pb, and the third year focused on Cu. Experiments for each metal would be conducted at 125°, 150°, and 200° C for durations of 10, 20, and 40 days at metal concentrations of 50, 100, and 1000 ppm, a pressure of 10 MPa, and a pH of 5.5. The experimental fluid would have a major element composition typical of ore-forming sedimentary hydrothermal fluids. The precipitation of dolomite in the experiments would be confirmed by X-ray diffraction (XRD). The composition of the dolomite crystals would be determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The elemental composition of the experimental fluid at the end of each experiment would be measured using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The expected results of the study are a suite of temperature-dependent partition coefficients that could be used to determine the Zn, Pb, and Cu concentrations of hydrothermal fluids based on the concentrations of these metals in dolomite that the fluid precipitated.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.

世界上许多最重要的金属矿床，铅（Pb），锌（Zn）和铜（Cu），包括美国的矿床，是由多孔沉积岩中的热水（即热液）沉积而成。 这些流体的一些典型特征现在从以前的研究中已经众所周知，例如它们的温度和最丰富的溶解元素的浓度。 然而，许多不太丰富的元素，如铅，锌，铜的流体中的浓度是不为人所知的大多数矿床。 这些金属浓度的知识很重要，因为它有助于回答有关沉积物起源的基本问题，例如是否需要富含金属的流体来形成沉积物，需要多少时间来形成沉积物，以及什么化学反应导致金属溶解并最终从流体中沉淀出来。 此外，对矿床如何形成的充分了解对于成功的矿产勘探和评估美国国内资源基础至关重要。 由于大多数铅、锌和铜矿床都是在遥远的地质历史中形成的，所以现在矿床中存在的流体不再是形成矿床的流体。 然而，这些古代流体沉淀的一些矿物提供了古代流体的一些性质的记录，包括其金属浓度。 例如，白云石是许多铅、锌和铜矿床的常见成分，它的晶体结构中往往含有微量的这些金属。 通常，流体中这些金属的浓度越高，白云石中这些金属的浓度越高。 如果这种比例因子，称为分配系数，可以量化每种金属，那么古代流体中每种金属的浓度可以根据其在白云石中的测量浓度计算出来。 建议的研究的目的是确定在一个典型的成矿温度范围内的水和白云石的Pb，Zn和Cu的分配系数。 拟议的研究将在三年内进行，第一年侧重于锌，第二年侧重于铅，第三年侧重于铜。 每种金属的实验将在125 ° C、150 ° C和200 ° C下进行，持续时间为10天、20天和40天，金属浓度为50 ppm、100 ppm和1000 ppm，压力为10 MPa，pH值为5.5。 实验流体具有典型的成矿沉积热液的主要元素组成。 通过X射线衍射（XRD）证实了实验中白云石的析出。 白云石晶体的组成将通过激光烧蚀-电感耦合等离子体质谱法（LA-ICP-MS）测定。 使用电感耦合等离子体原子发射光谱法（ICP-AES）测量每个实验结束时实验流体的元素组成。 该研究的预期结果是一套随温度变化的分配系数，可用于确定锌，铅，铜浓度的热液流体的基础上，这些金属的浓度在白云石的流体precipitated.This奖项反映了NSF的法定使命，并已被认为是值得的支持，通过评估使用基金会的智力价值和更广泛的影响审查标准。