Generation of porphyry copper deposits by gas-brine reaction in volcanic arcs
Generation of porphyry copper deposits by gas-brine reaction in volcanic arcs
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DOI：
10.1038/ngeo2351
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发表时间：
2015-03-01
影响因子：
18.3
通讯作者：
Gilmer, A.
中科院分区：
文献类型：
--
作者：
Blundy, J.;Mavrogenes, J.;Gilmer, A.
斑岩铜矿，即与岩浆室上升的热液有关的铜矿，提供了世界上75%的铜。它们通常与俯冲带上方地壳中的岩浆侵入有关，表明岩浆作用在驱动矿化方面发挥了主要作用。然而，目前尚不清楚单一的富铜岩浆流体是否会在热液蚀变岩带内同时引发铜的浓缩和硫化物矿石矿物的沉淀。在这里，我们利用现代俯冲带火山作用的观察，提出了斑岩铜矿形成的另一种过程。我们认为，铜的富集最初涉及含金属的岩浆高盐度液体或卤水，这些液体从聚集在浅地壳中的大型岩浆侵入体中渗出，时间长达数万年至数十万年。在接下来的步骤中，硫化物矿石的沉淀是由积累的卤水与富硫气体的相互作用触发的，这些气体是从下面的镁铁质岩浆短暂爆发中释放出来的。我们使用高温高压实验室实验来模拟这种气体-卤水相互作用。这些实验在700-800摄氏度的岩浆温度下产生了铜铁硫化物矿物和氯化氢气体，其结构和化学特征与斑岩铜矿中的相似。因此，我们认为斑岩铜矿的形成经历了卤水富集和气体诱导沉淀两个阶段的过程。
Porphyry copper deposits, that is, copper ore associated with hydrothermal fluids rising from a magma chamber, supply 75% of the world's copper. They are typically associated with intrusions of magma in the crust above subduction zones, indicating a primary role for magmatism in driving mineralization. However, it is not clear that a single, copper-rich magmatic fluid could trigger both copper enrichment and the subsequent precipitation of sulphide ore minerals within a zone of hydrothermally altered rock. Here we draw on observations of modern subduction zone volcanism to propose an alternative process for porphyry copper formation. We suggest that copper enrichment initially involves metalliferous, magmatic hyper-saline liquids, or brines, that exsolve from large, magmatic intrusions assembled in the shallow crust over tens to hundreds of thousands of years. In a subsequent step, sulphide ore precipitation is triggered by the interaction of the accumulated brines with sulphurrich gases, liberated in short-lived bursts from the underlying mafic magmas. We use high-temperature and high-pressure laboratory experiments to simulate such gas-brine interactions. The experiments yield copper-iron sulphide minerals and hydrogen chloride gas at magmatic temperatures of 700-800 degrees C, with textural and chemical characteristics that resemble those in porphyry copper deposits. We therefore conclude that porphyry copper ore forms in a two-stage process of brine enrichment followed by gas-induced precipitation.