地学前缘 ›› 2020, Vol. 27 ›› Issue (2): 20-44.DOI: 10.13745/j.esf.sf.2020.3.8

• 矿床研究方法与综述 • 上一篇    下一篇

再论中国大陆斑岩Cu-Mo-Au矿床成矿作用

侯增谦,杨志明,王瑞,郑远川   

  1. 1. 中国地质科学院 地质研究所, 北京 100037
    2. 中国地质大学(北京), 北京 100083
  • 收稿日期:2019-12-18 修回日期:2020-03-11 出版日期:2020-03-25 发布日期:2020-03-25
  • 作者简介:侯增谦(1961—),男,博士,中国科学院院士,矿物学、岩石学、矿床学专业,主要从事矿床学研究。E-mail:houzengqian@126.com
  • 基金资助:

    国家重点研发计划项目(2016YFC0600310);国家杰出青年科学基金项目;国家自然科学基金重点项目和国际合作项目

Further discussion on porphyry Cu-Mo-Au deposit formation in Chinese mainland.

HOU Zengqian,YANG Zhiming,WANG Rui,ZHENG Yuanchuan   

  1. 1.Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
    2.China University of Geosciences (Beijing), Beijing 100083, China
  • Received:2019-12-18 Revised:2020-03-11 Online:2020-03-25 Published:2020-03-25

摘要:

本文在综述斑岩铜矿(PCDs)最新研究进展基础上,结合最新资料,重点阐释了中国大陆非弧环境PCDs的地球动力学背景、成矿岩浆起源、岩浆流体系统演化、成矿金属(Cu,Au,Mo)和H2O来源及富集过程。中国大型PCDs除少量产于岩浆弧外,主要产于碰撞造山环境的构造转换和地壳伸展阶段、陆内造山环境的岩石圈伸展和崩塌阶段以及活化克拉通的边缘及内部。这些非弧环境成矿斑岩多呈彼此孤立的近等间距分布的岩株或岩瘤产出,以高钾为特征,显示埃达克岩地球化学亲和性。成矿岩浆主要起源于加厚的镁铁质新生下地壳或拆沉的古老下地壳,少数起源于遭受早期俯冲板片流体/熔体交代改造过的富集地幔。大陆碰撞和陆内俯冲引起的地壳大规模增厚和紧随其后的板片撕裂、断离、岩石圈拆沉和软流圈上涌,是形成这些成矿岩浆的主要动力机制。与岩浆弧环境斑岩类似,非弧环境斑岩也相对富水(>4%H2O)和高f(O2)值(ΔFMQ≥+2),但H2O不是来自俯冲板片,而是主要来自新生下地壳的角闪石分解或/和幔源富水超钾质岩浆水注入;金属Cu(Au)主要来自新生的镁铁质下地壳中含Cu硫化物的熔融分解,或者来自拆沉下地壳熔体与金属再富集的地幔岩反应,而金属Mo则主要来自具有高Mo丰度的大陆地壳。不论在岩浆弧还是非弧环境,成矿岩浆通常相对富集成矿金属(Cu,Au,Mo),但PCDs的形成并不要求成矿岩浆在初始阶段就异常富集金属组分,但要求金属硫化物相在岩浆流体出溶前没有从岩浆中饱和分离。浅成侵位的斑岩体(1~6 km)虽然可以出溶成矿流体,但大型PCDs通常要求成矿流体出溶自深部(侵位深度≥6 km)、有镁铁质岩浆持续补给的稳定大体积岩浆房。斑岩体可以分凝出不混溶的低盐度的气相和高盐度的液相,岩浆房则直接出溶出高温低盐度的富金属超临界流体。高盐度液相和低密度的超临界气相流体均可以迁移金属,伴随大规模热液蚀变,形成PCDs。

关键词: 斑岩铜矿, 成矿岩浆来源, 下地壳熔融, 水和金属来源, 富集机制, 成矿环境

Abstract:

By reviewing the latest research progress of porphyry copper deposits (PCDs) and combining with the new data, this paper focuses on discussing the geodynamic background of nonarc PCDs in Chinese mainland, the origin of oreforming magma, the evolution of magmatichydrothermal system, the sources of oreforming metals (Cu, Au, Mo) and H2O, and their enrichment process. Except for a few PCDs formed in island arcs in China, most PCDs were formed during the stages of tectonic transformation and crustal extension in a collisional orogenic setting, and the stages of lithosphere extension and collapse, in the edge and interior of a reactivated craton. These nonarc porphyries are mostly isolated or nearly evenspaced stocks or bosses, and are characterized by high K contents and adakitic compositions. The oreforming magmas are mainly originated from the newly formed thickened mafic crust or delaminated ancient lower crust, and a few originated from subduction fluid/melt metasomatized lithospheric mantle. Intercontinental collision and subduction led to largescale crustal thickening, and the triggers for crustal melting include slab tearing, slab breakoff, lithosphere delamination, and asthenospheric mantle upwelling. Similar to the island arc porphyries, the nonarc porphyries are also rich in water (> 4 wt% H2O) and f(O2) (ΔFMQ ≥+2). We think H2O does not come from the subducting slab, but mainly from the decomposition of amphibole in the newly formed lower crust or injection of H2Orich ultrapotassic melt. Cu (Au) mainly comes from the decomposition of Cubearing sulfides in the newly formed lower mafic crust, or from the metalrich lithospheric mantle reacted with delaminated lower crust. In contrast, Mo mainly comes from the continental crust in high Mo abundance. Regardless of island arc or nonarc settings, oreforming magmas are generally enriched with metals (Cu, Au, Mo). Formation of PCDs does not require the incipient magma abnormally rich in metals, but requires sulfides not being saturated and separated from magma before exsolution of magmatic fluid. Although shallowly emplaced porphyry (16 km) can dissolve oreforming fluids, largescale PCDs usually require oreforming fluids to dissolve from the deep part (emplacement depth ≥6 km) and have continuous mafic melt input. Shallowly emplaced porphyry can separate and condense immiscible lowsalinity vapor phase and highsalinity liquid phase, while the deepseated magma chamber directly dissolves hightemperature and lowsalinity metalrich supercritical fluid. Both highsalinity liquid phase and lowdensity supercritical vaporphase fluid can transport metals and form PCDs with largescale hydrothermal alteration.

Key words: porphyry copper deposit, origin of oreforming magma, melting of lower crust, water and metal source, enrichment mechanism, metallogenic setting

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