Acid Mine Drainage Impoundments in the Nkangala District South Africa

Hypothesis: Temporally stable mine-site impoundments (pit lakes, tailings, return, and seepage ponds) accumulate acid mine drainage (AMD) with higher rare-earth element (REE) concentrations than natural waters which are contaminated by AMD. These can be systematically mapped, screened, and quantified to prioritise recovery and remediation. What the data are: A spatial inventory of AMD impoundments across the Nkangala District, South Africa. The core product is a polygon layer of 2,886 AMD-containing waterbodies, with a detailed attribute table including geometry, morphometrics, monthly Sentinel-2 reflectance statistics (2024), and screening variables for AMD/REE potential. Key fields: Geometry; area (area_m2, area_km2); coordinates; reflectance statistics (mean, min, max, stdDev, selected indices); estimated depth and volume (m³, L) from DEM-based shoreline proxy; water type label (pit lake, tailings, seepage, return pond); monthly reflectance band stats (Jan–Dec 2024) for B1–B12 and B8A. How it was built: Mining boundaries were refined in QGIS by reconciling multiple datasets. In Google Earth Engine, Sentinel-2 L2A imagery (cloud/shadow masked) was processed; the AWEI index was selected after testing and applied with a threshold > −0.35. Features ≥ 4 pixels (~400 m²) and present in ≥ 50 % of 2024 monthly composites were retained. Polygons were vectorised, some were visually classified, and linked to morphometric data derived from Copernicus GLO30 DEM shoreline buffers. Temporal medians informed conservative depth proxies; volume = area × depth. Monthly reflectance values were computed per polygon across B1–B12 and B8A (± 7 days). 2023 field sampling inside vs outside mining boundaries confirmed higher sulfate, lower pH, and measurable REEs within mine sites compared to bodies sampled within a 10km radius of a mine. What the data show: AWEI combined with temporal persistence filters delineated 2,886 AMD impoundments across the study area. DEM benchmarking reproduced approximately 78–80 % of known capacities, supporting the reliability of the volumetric estimates. Indicative ∑REE concentrations derived from reflectance-based comparisons suggest an average of 419 mg/L in these AMD waters, with lows of 89 mg/L. How to interpret: Best used as a screening layer to: map AMD extent, target high-priority ponds for sampling, treatment, or REE recovery, and support techno-economic scoping. Volumes are lower-bound estimates (based on 30 m DEM); concentrations are indicative, not assay results. Users should pair this layer with site visits, water chemistry, and high-resolution elevation data. Format: GeoJSON (EPSG:4326) Software: QGIS, Google Earth Engine. Limitations: DEM resolution, empirical thresholds, sparse paired reflectance–chemistry samples, and no flow or residence-time data. Volumes are conservative; REE values are screening outputs.假设：时间上稳定的矿山场蓄水体（露天矿坑湖、尾矿池、回用水塘及渗滤塘）会蓄积酸性矿山排水（Acid Mine Drainage，AMD），其中稀土元素（Rare-earth Element，REE）浓度高于受AMD污染的天然水体。此类蓄水体可通过系统化制图、筛查与量化，优先开展修复与资源回收工作。 数据集内容：南非恩坎加拉区（Nkangala District）范围内AMD蓄水体的空间清查数据集。核心成果为包含2886个含AMD水体的多边形图层，配套详细属性表，涵盖几何信息、形态测量参数、2024年哨兵二号（Sentinel-2）月度反射率统计数据，以及用于评估AMD/REE潜力的筛查变量。 核心字段：几何信息；面积（area_m2、area_km2）；坐标；反射率统计数据（均值、最小值、最大值、标准差、选定指数）；基于数字高程模型（Digital Elevation Model，DEM）岸线代理值估算的水深与体积（单位：立方米、升）；水体类型标签（露天矿坑湖、尾矿池、渗滤塘、回用水塘）；2024年1-12月B1至B12及B8A波段的月度反射率统计值。 数据集构建流程：通过整合多源数据集，在QGIS中优化了矿区边界。在Google Earth Engine中处理哨兵二号L2A影像（已完成云/云阴影掩膜）；经测试后选用自动水体提取指数（Automated Water Extraction Index，AWEI），并以>−0.35作为阈值进行提取。保留满足以下条件的要素：像素数≥4（约400平方米），且在2024年月度合成影像中出现占比≥50%。将提取结果矢量化，对部分要素进行目视分类，并关联源自哥白尼GLO30 DEM岸线缓冲区的形态测量数据。以时间中位数作为保守水深代理值，体积计算公式为：体积=面积×水深。针对每个多边形，计算2024年1-12月B1至B12及B8A波段（±7天时间窗）的月度反射率值。2023年的野外采样对比验证显示：矿区内部采样点的硫酸盐浓度更高、pH值更低，且可检测到REE，而对照采样点位于矿区10公里半径范围内。 数据集展示内容：结合AWEI指数与时间持续性过滤条件，在研究区内共勾勒出2886个AMD蓄水体。通过DEM基准验证，估算体积约为已知库容的78%~80%，证实了体积估算结果的可靠性。基于反射率对比得到的总REE（∑REE）指示浓度显示，此类AMD水体的平均浓度为419mg/L，最低浓度为89mg/L。 数据集解读指南：该数据集最佳应用场景为筛查图层，可用于：绘制AMD分布范围、锁定高优先级水塘开展采样、治理或REE回收工作，以及支撑技术经济范围规划。体积估算为下限值（基于30米分辨率DEM）；浓度为指示性数值，而非实验室化验结果。使用者应将该图层与野外实地考察、水体化学分析及高分辨率高程数据结合使用。 格式：GeoJSON（EPSG:4326） 所用软件：QGIS、Google Earth Engine。 局限性说明：存在DEM分辨率限制、经验阈值依赖、反射率-化学配对采样稀疏，且无水流或停留时间数据。体积估算为保守值；REE浓度值仅为筛查输出结果。