Copper export and mobility in acid mine drainage are difficult to understand with conventional approaches. Within this context, Cu isotopes could be a powerful tool and here we have examined the relative abundance of dissolved (<0.22 μm) Cu isotopes (δ⁶⁵Cu) in the Meca River which is an outlet of the Tharsis mine, one of the largest abandoned mines of the Iberian Pyrite Belt, Spain. We followed the chemical and isotopic composition of the upstream and downstream points of the catchment during a 24-h diel cycle. Additional δ⁶⁵Cu values were obtained from the tributary stream, suspended matter (>0.22 μm) and bed sediments samples. Our goals were to 1) assess Cu sources variability at the upstream point under contrasted hydrological conditions and 2) investigate the conservative vs. non conservative Cu behavior along a stream. Average δ⁶⁵Cu values varied from −0.47 to −0.08‰ (n = 9) upstream and from −0.63 to −0.31‰ downstream (n = 7) demonstrating that Cu isotopes are heterogeneous over the diel cycle and along the Meca River. During dry conditions, at the upstream point of the Meca River the Cu isotopic composition was heavier which is in agreement with the preferential release of heavy isotopes during the oxidative dissolution of primary sulfides. The more negative values obtained during high water flow are explained by the contribution of soil and waste deposit weathering. Finally, a comparison of upstream vs. downstream Cu isotope composition is consistent with a conservative behavior of Cu, and isotope mass balance calculations estimate that 87% of dissolved Cu detected downstream originate from the Tharsis mine outlet. These interpretations were supported by thermodynamic modelling and sediment characterization data (X-ray diffraction, Raman Spectroscopy). Overall, based on contrasted hydrological conditions (dry vs flooded), and taking the advantage of isotope insensitivity to dilution, the present work demonstrates the efficiency of using the Cu isotopes approach for tracing sources and processes in the AMD regions.

常规方法难以理解酸性矿山排水中的铜出口和流动性。在这方面，铜的同位素可以是一个功能强大的工具，在这里我们已经研究溶解（<0.22微米）的相对丰度的Cu同位素（δ ⁶⁵ Cu）中的梅卡河这是塔尔西斯矿的出口，其中一个最大的西班牙伊比利亚黄铁矿带的废弃地雷。我们在24小时diel周期内跟踪流域上游和下游点的化学和同位素组成。附加δ ^65个从支流得到的Cu值，悬浮物（> 0.22微米）和床沉积物样品。我们的目标是1）在相反的水文条件下评估上游点的铜源变异性，并2）研究沿流的保守和非保守铜行为。平均δ ⁶⁵Cu值从上游的-0.47至-0.08‰（n = 9）变化，从下游的-0.63至-0.31‰（n = 7）变化，表明Cu同位素在diel循环中和沿Meca河是异质的。在干燥条件下，在麦加河的上游，铜同位素组成较重，这与伯硫化物的氧化溶解过程中优先释放重同位素有关。在高水流量下获得的更多负值可以通过土壤和废物沉积物的风化作用来解释。最后，上游和下游铜同位素组成的比较与保守的铜行为是一致的，并且同位素质量平衡计算估计，下游检测到的溶解铜中有87％来自塔里西斯矿山出口。这些解释得到热力学模型和沉积物表征数据（X射线衍射，拉曼光谱）的支持。总体而言，基于对比的水文条件（干与淹），并利用同位素对稀释不敏感的优势，本研究证明了使用铜同位素方法追踪AMD区域的来源和过程的效率。