Geology and Genesis of Major Copper Deposits and Districts of the World
Geology and Genesis of Major Copper Deposits and Districts of the World
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DOI：
10.5382/sp.17
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
J. W. Hedenquist;Michael Harris;F. Camus
中科院分区：
文献类型：
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作者：
J. W. Hedenquist;Michael Harris;F. Camus
在过去的世纪中，人们已经认识到，铜矿床与许多其他金属矿床一样，不均匀地集中在地球的上地壳中，导致在数亿年的时间间隔内，在几个离散的成矿时期产生的区域有限的铜省。例如，环太平洋岩浆弧的各个部分的总含铜量相差两个数量级。每个成矿时代都有自己的存款类型，其中斑岩铜（和相关的矽卡岩），其次是沉积物托管的层状铜，然后是氧化铁铜金（IOCG），是全球最突出的。尽管如此，铜矿区的起源仍然有些神秘，也是一个持续争论的话题。各种矿床规模的几何和地质特征和因素强烈影响斑岩铜、沉积物容矿层状铜和/或IOCG矿床的规模和/或品位。例如，主要斑岩铜矿床/地区的发展得益于存在成簇蚀变-矿化中心、镁铁质或块状碳酸盐寄主岩、大量岩浆热液角砾岩、有利于铜沉积的低硫化状态核心区（如辉长岩±蓝辉长岩）、深生和表生硫化物富集以及矿化矽卡岩形成，加上缺乏后期的严重稀释，低级斑岩侵入体和角砾岩。此外，所有存款类型的铜的禀赋无疑受益于所涉及的成矿过程的优化。构造环境对铜成矿也起着基础性作用。收缩构造岩浆带是由板块俯冲或弧-陆碰撞（不太常见）造成的，其特征是地壳增厚和高速率的隆升和折返，似乎是大多数大型、高品位深成斑岩铜矿的所在地。这种成熟的弧壳在斑岩铜矿形成过程中也经历了基性岩浆的输入。主要的沉积物承载的层状铜矿省形成于随后经历构造反转的扩张或内陆伸展沉积盆地中。IOCG矿床的产生与伸展/transtension和长英质侵入体，后者显然是由深层次的镁铁质岩浆在克拉通或俯冲设置。这些不同构造环境的根本不同的折返速率特征很好地解释了铜存款类型的长期分布，特别是相对于沉积物托管层状和IOCG矿床的大多数斑岩的年轻。尽管这些矿床规模的地质、区域构造和侵蚀速率标准对于有效的铜存款形成和保存具有重要意义，但它们似乎不足以解释主要铜矿省的定位，如安第斯山脉中部、北美西南部和中非铜矿带，在这些铜矿带中，不同的存款类型在几个离散的时代产生。出于同样的原因，在其他一些明显相似的地质环境中，铜矿化的缺乏也仍然无法解释。这里提出，主要的铜省发生在岩石圈的限制部分倾向于上地壳铜浓度在整个地球历史的长时间间隔。这种倾向最有可能是在氧化和铜的引入过程中获得的俯冲衍生流体，含有金属和挥发物提取的水合玄武岩和沉积物在下行板。因此，超地壳岩石圈地幔和最低地壳交代，以及获得含铜硫化物的累积在岩浆分异过程中，使他们肥沃的挖掘在随后的俯冲或，不常见的，板内伸展相关的岩浆事件，产生斑岩铜和IOCG区或带。一些增生造山带下方肥沃的岩石圈在早期的碰撞事件中（通常是在前寒武纪时期）被合并。相对氧化的地壳剖面--与那些由还原的沉积物质主导的剖面相反--也是所有主要铜矿有效形成所必需的。大型沉积盆地下或毗邻氧化和潜在的铜异常地壳，并填充最初由未成熟的红层地层含有岩浆弧衍生的碎屑提供了大规模的，沉积物托管层状铜矿化的最佳场所。穿层断裂带作为一个巨大的垂向系统，通常在确定各种类型的主要铜矿、铜矿区和铜矿带的位置方面起着关键作用。这些建议解决了长期争论的金属继承的概念，在俯冲交代地幔岩石圈和最低地壳在全球铜成矿作用中发挥的基本作用。
It has been recognized for the past century that copper deposits, in common with those of many other metals, are heterogeneously concentrated in Earth’s upper crust, resulting in areally restricted copper provinces that were generated during several discrete metallogenic epochs over time intervals of up to several hundred million years. Various segments of circum-Pacific magmatic arcs, for example, have total contained copper contents that differ by two orders of magnitude. Each metallogenic epoch introduced its own deposit type(s), of which porphyry copper (and related skarn), followed by sediment-hosted stratiform copper and then iron oxide copper-gold (IOCG), are globally preeminent. Nonetheless, genesis of the copper provinces remains somewhat enigmatic and a topic of ongoing debate. A variety of deposit-scale geometric and geologic features and factors strongly influence the size and/or grade of porphyry copper, sediment-hosted stratiform copper, and/or IOCG deposits. For example, development of major porphyry copper deposits/districts is favored by the presence of clustered alteration-mineralization centers, mafic or massive carbonate host rocks, voluminous magmatic-hydrothermal breccias, low sulfidation-state core zones conducive to copper deposition as bornite ± digenite, hypogene and supergene sulfide enrichment, and mineralized skarn formation, coupled with lack of serious dilution by late, low-grade porphyry intrusions and breccias. Furthermore, the copper endowment of all deposit types undoubtedly benefits from optimization of the ore-forming processes involved. Tectonic setting also plays a fundamental role in copper metallogeny. Contractional tectonomagmatic belts, created by flat-slab subduction or, less commonly, arc-continent collision and characterized by crustal thickening and high rates of uplift and exhumation, appear to host most large, high-grade hypogene porphyry copper deposits. Such mature arc crust also undergoes mafic magma input during porphyry copper formation. The premier sediment-hosted stratiform copper provinces were formed in cratonic or hinterland extensional sedimentary basins that subsequently underwent tectonic inversion. The IOCG deposits were generated in association with extension/transtension and felsic intrusions, the latter apparently triggered by deep-seated mafic magmas in either intracratonic or subduction settings. The radically different exhumation rates characteristic of these various tectonic settings account well for the secular distribution of copper deposit types, in particular the youthfulness of most porphyry relative to sediment-hosted stratiform and IOCG deposits. Notwithstanding the importance of these deposit-scale geologic, regional tectonic, and erosion-rate criteria for effective copper deposit formation and preservation, they seem inadequate to explain the localization of premier copper provinces, such as the central Andes, southwestern North America, and Central African Copperbelt, in which different deposit types were generated during several discrete epochs. By the same token, the paucity of copper mineralization in some apparently similar geologic settings elsewhere also remains unexplained. It is proposed here that major copper provinces occur where restricted segments of the lithosphere were predisposed to upper-crustal copper concentration throughout long intervals of Earth history. This predisposition was most likely gained during oxidation and copper introduction by subduction-derived fluids, containing metals and volatiles extracted from hydrated basalts and sediments in downgoing slabs. As a result, superjacent lithospheric mantle and lowermost crust were metasomatized as well as gaining cupriferous sulfide-bearing cumulates during magmatic differentiation—processes that rendered them fertile for tapping during subsequent subduction-or, uncommonly, intraplate extension-related magmatic events to generate porphyry copper and IOCG districts or belts. The fertile lithosphere beneath some accretionary orogens became incorporated during earlier collisional events, commonly during Precambrian times. Relatively oxidized crustal profiles—as opposed to those dominated by reduced, sedimentary material—are also required for effective formation of all major copper deposits. Large sedimentary basins underlain by or adjoining oxidized and potentially copper-anomalous crust and filled initially by immature redbed strata containing magmatic arc-derived detritus provide optimal sites for large-scale, sediment-hosted stratiform copper mineralization. Translithospheric fault zones, acting as giant plumbing systems, commonly played a key role in localizing all types of major copper deposits, districts, and belts. These proposals address the long-debated concept of metal inheritance in terms of the fundamental role played by subduction-metasomatized mantle lithosphere and lowermost crust in global copper metallogeny.