How to make porphyry copper deposits
How to make porphyry copper deposits
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DOI：
10.1016/j.epsl.2019.115868
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发表时间：
2020-01-01
影响因子：
5.3
通讯作者：
Tang, Ming
中科院分区：
文献类型：
--
作者：
Lee, Cin-Ty A.;Tang, Ming
世界上大部分的经济铜矿资源都赋存于斑岩铜矿（PCD）中，这些浅层次的岩浆侵入体大多与厚（> 45 km）的岩浆弧（如成熟的岛弧和大陆弧）有关。然而，一个众所周知的，但尚未解决的矛盾，是弧岩浆穿越厚地壳，特别是在大陆弧，一般是贫铜，而在岛弧，PCD是不太常见的，岩浆成为富集铜。在这里，我们表明，PCD的形成需要一个复杂的序列的地壳内岩浆过程，从下地壳到上地壳。当地壳变厚（> 45公里），足以使石榴石结晶时，就会形成PCD。石榴子石分馏作用使岩浆中的Fe贫化，这促使硫化物分离并将大部分岩浆中的Cu移到下地壳中，仅在残余岩浆中留下少量的Cu以形成PCD。然而，由于石榴石中的三价铁被耗尽，岩浆中剩余的Fe逐渐被氧化，最终将硫化物氧化为硫酸盐，从而将硫化物结合的Cu从岩浆中释放到溶液中。这种岩浆的自氧化作用，使深源石榴石分馏成为可能，增加了内生岩浆流体的能力，以自我铜从大量的，否则铜贫岩浆，然后运输和浓缩铜的岩浆体的顶部。对安第斯山脉中部PCD的研究表明，在岩浆活动结束之前，大陆弧达到其最大厚度（> 60公里）时，就会形成矿石。(C)2019爱思唯尔B.V.保留所有权利。
Much of the world's economic copper resources are hosted in porphyry copper deposits (PCDs), shallow level magmatic intrusions associated mostly with thick (> 45 km) magmatic arcs, such as mature island arcs and continental arcs. However, a well-known, but unresolved paradox, is that arc magmas traversing thick crust, particularly in continental arcs, are generally depleted in Cu whereas in island arcs, where PCDs are less common, magmas become enriched in Cu. Here, we show that the formation of PCDs requires a complex sequence of intra-crustal magmatic processes, from the lower crust to the upper crust. PCDs form when the crust becomes thick (> 45 km) enough to crystallize garnet. Garnet fractionation depletes Fe from the magma, which drives sulfide segregation and removal of most of the magma's Cu into the lower crust, leaving only small amounts of Cu in the residual magma to make PCDs. However, because garnet is depleted in ferric iron, the remaining Fe in the magma becomes progressively oxidized, which eventually oxidizes sulfide to sulfate, thereby releasing sulfide bound Cu from the magma into solution. This auto-oxidation of the magma, made possible by deep-seated garnet fractionation, increases the ability of endogenic magmatic fluids to self-scavenge Cu from large volumes of otherwise Cu-poor magmas and then transport and concentrate Cu to the tops of magmatic bodies. Examination of the occurrence of PCDs in the central Andes shows that ore formation occurs when continental arcs reach their maximum thickness (> 60 km), just before the termination of magmatism. (C) 2019 Elsevier B.V. All rights reserved.