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Native copper formation associated with serpentinization in the Cheshmeh-Bid ophiolite massif (Southern Iran)
Lithos ( IF 3.5 ) Pub Date : 2020-12-27 , DOI: 10.1016/j.lithos.2020.105953
Alireza Eslami , Benjamin Malvoisin , Giovanni Grieco , László Előd Aradi , Claudio Marchesi , Alessandro Cavallo , Alessandra Montanini , Giulio Borghini , Ryan Mathur , Kei Ikehata , Donald W. Davis , Chun-Hui Li , Csaba Szabó

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 H2 and 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.



中文翻译:

Cheshmeh-Bid蛇绿岩地块(伊朗南部)中与蛇纹石化有关的天然铜形成

在Khajeh-Jamali卵石质断层块的Cheshmeh-Bid地区(伊朗南部),地幔橄榄岩被大量的辉石岩脉侵入。这些堤坝中的一些堤坝对于与交代反应区发展有关的天然铜的发生是显着的。堤坝从边缘到中心逐渐与闪石+蛇纹石缠结,然后是厚度为1厘米的斜柏石+蛇纹石组合,最后是由斜柏石+亚氯酸盐+蛇纹石组成的天然含铜区。天然铜出现在斜向辉石的劈裂和部分愈合的裂缝中,并且块状晶粒与退蛇毒共生。铜同位素特征和热力学计算表明,反应区形成的主要驱动因素是钙的致突变性。在反应区以天然辉铜矿为代价形成天然铜。此类反应只能在还原条件下发生,这与分析显示H的流体夹杂物成分一致2和CH 4。这些流体可能源自地幔岩石的水化作用。因此,观察到的反应区和天然铜矿化作用被解释为海洋岩石圈热液改变过程中Ca-换相作用的结果。这与钛铁矿的U / Pb测年相吻合,表明在高俯冲环境中将堤暴露在海底时在Albian形成。如铜同位素所示,铜矿化的来源可能像地幔一样。

更新日期:2021-01-01
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