Naturally-sourced groundwater quality issues are common, but there is rarely a geochemical and mineralogical dataset of aquifer properties for comparison. This study utilizes geochemical and mineralogical data to characterize naturally-occurring minerals that are potential groundwater contaminants in the Cambrian Eau Claire – Mount Simon aquitard-aquifer system of west-central Wisconsin, U.S.A. A high-resolution portable x-ray fluorescence elemental analysis was used for initial characterization of geochemistry and chemostratigraphy of well cutting and drill core samples. Then, a subset of sample materials was analyzed mineralogically and geochemically using XRD and ICP-MS, respectively. Elevated concentrations of arsenic, phosphorous, strontium, and various metals within the aquitard-aquifer sandstone were identified, mostly associated with sulfide minerals and iron (hydr)oxides and suggestive of Mississippi Valley-type mineralization. Similar elemental contaminants in surface and groundwater in the study area indicate that the observed trace element-bearing minerals are a natural source of groundwater contamination, most likely through release into groundwater during fluctuating redox and pH conditions near the water table. Co-occurrence of iron (hydr)oxide-coated sulfide minerals near the water table, and observations of sulfide oxidation post-drilling, suggests sulfides in these units are actively oxidizing. Well construction recommendations based on these results should mitigate current or future pumping of trace element-contaminated groundwater and in the vast majority of cases eliminate naturally-occurring contaminants as a potential source. This study provides an extensive baseline dataset of aquifer mineralogy and trace element composition (and an efficient approach for data collection) that is necessary for interpreting and attributing possible future groundwater quality issues.

天然来源的地下水质量问题很常见，但很少有含水层特性的地球化学和矿物学数据集进行比较。本研究利用地球化学和矿物学数据来表征美国威斯康星州中西部寒武纪欧克莱尔-西蒙山隔水层-含水层系统中作为潜在地下水污染物的天然矿物 使用高分辨率便携式 X 射线荧光元素分析用于井切割和钻探岩心样品的地球化学和化学地层学的初步表征。然后，分别使用 XRD 和 ICP-MS 对一部分样品材料进行矿物学和地球化学分析。确定了含水层-含水层砂岩中砷、磷、锶和各种金属的浓度升高，主要与硫化物矿物和铁（氢）氧化物有关，暗示密西西比河谷型矿化。研究区域地表水和地下水中的类似元素污染物表明，观察到的微量元素矿物质是地下水污染的天然来源，很可能是通过在地下水位附近波动的氧化还原和 pH 条件下释放到地下水中。在地下水位附近同时出现铁（氢）氧化物涂层的硫化物矿物，以及钻井后硫化物氧化的观察结果表明，这些单元中的硫化物正在积极氧化。基于这些结果的井建设建议应减少当前或未来抽取受微量元素污染的地下水，并在绝大多数情况下消除作为潜在来源的自然产生的污染物。