Native copper formation associated with serpentinization in the Cheshmeh-Bid ophiolite massif (Southern Iran)
Native copper formation associated with serpentinization in the Cheshmeh-Bid ophiolite massif (Southern Iran)
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DOI：
10.1016/j.lithos.2020.105953
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发表时间：
2021-02
期刊：
影响因子：
3.5
通讯作者：
A. Eslami;B. Malvoisin;G. Grieco;L. Aradi;C. Marchesi;A. Cavallo;A. Montanini;G. Borghini;R. Mathur;K. Ikehata;D. Davis;Chun-hui Li;C. Szabó
中科院分区：
文献类型：
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作者：
A. Eslami;B. Malvoisin;G. Grieco;L. Aradi;C. Marchesi;A. Cavallo;A. Montanini;G. Borghini;R. Mathur;K. Ikehata;D. Davis;Chun-hui Li;C. Szabó
在Khajeh-Jamali蛇绿岩带（伊朗南部）的Cheshmeh-Bid地区，地幔橄榄岩被大量的辉石岩脉侵入。这些岩墙中有几个是值得注意的自然铜的出现与交代反应带的发展。岩墙逐步反应，从他们的边缘向中心，与角闪石+叶蛇纹石边缘，其次是厘米厚的单斜辉石+叶蛇纹石组合，最后，由天然含铜带单斜辉石+辉长岩+叶蛇纹石。自然铜沿着解理和部分愈合的裂隙出现在单斜辉石中，并以块状颗粒与叶蛇纹石共生。铜同位素特征和热力学计算表明，反应带形成的主要驱动力是钙交代作用。自然铜在反应区中以辉铜矿为代价形成。这种反应只能发生在还原条件下，与流体包裹体成分分析显示H2和CH 4一致。这些流体可能来自地幔岩石的水化作用。因此，所观察到的反应带和自然铜矿化解释为大洋岩石圈热液蚀变过程中钙交代的结果。这与钛铁矿的U/Pb测年结果一致，表明形成于阿尔比期，当时岩墙暴露在海底的超俯冲环境中。铜同位素显示成矿物质可能为幔源。
In the Cheshmeh-Bid district of the Khajeh-Jamali ophiolitic massifs (Southern Iran), mantle peridotites are intruded by abundant pyroxenite dykes. A few of these dykes are remarkable for the occurrence of native copper associated with the development of a metasomatic reaction zone. The dykes are progressively reacted, from their margins towards the center, with an amphibole + antigorite selvage, followed by a centimeter-thick clinopyroxene + antigorite assemblage and, finally, by the native copper-bearing zone consisting of clinopyroxene + chlorite + antigorite. Native Cu occurs along cleavages and partially healed fractures in clinopyroxene, and as massive grains intergrown with antigorite. Copper isotope signatures and thermodynamic calculations show that the main driver for reaction zone formation is Ca-metasomatism. Native copper forms at the expense of chalcocite in the reaction zone. Such a reaction can only occur in reducing conditions, in agreement with the analysis of fluid inclusions composition displaying H2and CH4. Such fluids presumably originated from the hydration of mantle rocks. The observed reaction zone and native copper mineralization are thus interpreted as the result of Ca-metasomatism during hydrothermal alteration of the oceanic lithosphere. This is consistent with U/Pb dating of titanite, suggesting formation during the Albian when the dykes were exposed on the seafloor in a supra-subduction setting. The source for copper mineralization, as revealed by Cu isotopes, is probably mantle-like.