Copper isotopic fractionation (in δCu) and leachate characterization were studied in the context of heap leaching at the Tschudi copper mine in northern Namibia. The leached solution is of Mg-SO type with high Al and Fe concentrations. The source of Mg and Al in the leachate can be from the alteration of micas such as Mg-bearing muscovite confirmed by X-ray diffraction and scanning electron microscopy; however, the source of Mg cannot be determined with certainty. The principal secondary minerals identified in the leached ore are gypsum and jarosite. The value of pH in leachate is ∼1.21 and the concentration of dissolved Cu, occurring mostly as CuSO and Cu, is about 2 g/L. In comparison with unleached ore (avg. δCu −1.47 ‰), leached ore exhibits lighter isotopic values (avg. δCu −6.01 ‰) with apparent isotopic fractionation ΔCu of about −4.54 ‰. In contrast, there is isotopic enrichment of leachate in heavier Cu isotope (leachate δCu 0.34 ‰) with apparent isotopic fractionation ΔCu value of +1.81 ‰. These results are in good agreement with Cu isotopic fractionation and depletion in heavier Cu isotope reported for dissolution experiments in laboratory and groundwater linked to the porphyry copper ore deposits around the world. The leaching of heaps can be considered an analogy of upper part of gossans, but here the supergene enrichment zone is missing due to extremely low pH and oxidizing conditions.

中文翻译：

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使用铜同位素和浸出液化学鉴定纳米比亚北部 Tschudi 矿的铜矿石堆浸过程


在纳米比亚北部 Tschudi 铜矿的堆浸过程中研究了铜同位素分馏（以 δCu 表示）和浸出液表征。浸出液为 Mg-SO 型，Al 和 Fe 浓度较高。经X射线衍射和扫描电镜证实，渗滤液中镁、铝的来源可能是含镁白云母等云母的蚀变；然而，镁的来源无法确定。浸出矿石中发现的主要次生矿物是石膏和黄钾铁矾。渗滤液的pH值约为1.21，溶解的Cu浓度约为2 g/L，主要以CuSO4和Cu的形式存在。与未浸出矿石（平均δCu -1.47 ‰）相比，浸出矿石的同位素值较轻（平均δCu -6.01 ‰），表观同位素分馏ΔCu约为-4.54 ‰。相比之下，渗滤液中较重的Cu同位素存在同位素富集（渗滤液δCu 0.34‰），表观同位素分馏ΔCu值为+1.81‰。这些结果与在与世界各地斑岩铜矿床相关的实验室和地下水溶解实验中报告的铜同位素分馏和重铜同位素的消耗非常一致。堆的浸出可以被认为是铁帽上部的类比，但这里由于极低的 pH 值和氧化条件而缺少表生富集区。