板块俯冲与斑岩铜金成矿  

Plate subduction and porphyry Cu-Au mineralization

作　　者：张丽鹏 李贺[1,2,3] 王鲲 ZHANG LiPeng;LI He;WANG Kun(Center of Deep Sea Research,Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China;Laboratory for Marine Mineral Resources,Qingdao National Laboratory for Marine Science and Technology,Qingdao 266237,China;Center for Ocean Mega-Science,Chinese Academy of Sciences,Qingdao 266071,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院海洋研究所,深海研究中心,青岛266071 [2]青岛海洋科学与技术试点国家实验室,海洋矿产资源评价与探测技术功能实验室,青岛266237 [3]中国科学院海洋大科学研究中心,青岛266071 [4]中国科学院大学,北京100049

出　　处：《岩石学报》2020年第1期113-124,共12页Acta Petrologica Sinica

基　　金：国家重点研发计划(2016YFC0600408);国家自然科学基金项目(41803032、41473029)联合资助

摘　　要：绝大多数斑岩铜金矿床分布在汇聚板块边缘。研究表明高氧逸度和洋壳部分熔融是控制斑岩铜金矿床形成的两个关键因素。作为亲硫元素,铜金的性质主要受还原态的硫(S^2-)控制,而硫的价态和性质则强烈受氧逸度的影响。矿床学家很早就发现氧逸度ΔFMQ+2是斑岩铜金矿床成矿的魔幻数字。研究发现其原因是硫的性质在此氧逸度附近发生巨变,在低氧逸度时,硫主要以硫化物的形式存在,但是当氧逸度在ΔFMQ+1.5以上时,硫主要以硫酸根的形式存在。硫酸盐在岩浆中的溶解度通常是硫化物的10倍左右,因此在部分熔融过程中,高氧逸度可以大幅度提高硫在岩浆中的溶解度,有利于源区硫化物被破坏,以硫酸根的形式被熔出,从而大幅度提高初始岩浆中的铜(金)含量;与此同时,硫化物在岩浆演化过程中可以保持不饱和状态,有利于作为中度不相容元素的铜(金)通过岩浆演化进一步富集。在磁铁矿结晶等过程中,岩浆体系的氧逸度降低,硫酸根被还原,还原态的硫(S^2-)将岩浆中的铜金萃取,富集到流体相,从而形成斑岩铜金矿床。这种高氧逸度岩浆通常出现在汇聚板块边缘。由于洋壳铜、金、硫含量远高于陆壳和地幔,而且俯冲带氧逸度高出地幔和下地壳约2个数量级,因此俯冲洋壳部分熔融形成岩浆的初始铜、金、硫含量远高于陆内岩浆,有利于成矿。年轻洋脊的俯冲因其高热量是显生宙以来最容易发生俯冲洋壳部分熔融的地质过程,且同时具有高氧逸度,因此洋脊俯冲是形成大型、超大型斑岩铜金矿床的最佳途径。统计结果显示,全球主要超大型斑岩铜金矿床均与洋脊俯冲有关。Most porphyry Cu-Au deposits are distributed in convergence margins.Previous studies show that high oxygen fugacity and partial melting of subducted oceanic crust are two key factors for porphyry Cu-Au mineralization.Copper and Au as chalcophile elements are mainly controlled by reduced sulfur(S^2-),while the valence and properties of sulfur are controlled by magma oxygen fugacity.ΔFMQ+2 as the magic magma oxygen fugacity number for porphyry Cu-Au mineralization had long been discovered.Studies found that the main reason is that the sulfur species change dramatically near this oxygen fugacity.Sulfur mainly exists in the form of sulfide at a low oxygen fugacity,but when the oxygen fugacity is aboveΔFMQ+1.5,the sulfur mainly exists in the form of sulfate.The solubility of sulfate in magma is usually about 10 times that of sulfide.Therefore,high oxygen fugacity can greatly improve the solubility of sulfur in magma during partial melting,which is beneficial to the sulfide in the magma source being destructed and being melted in the form of sulfide,resulting in significantly improving the Cu(Au)contents in initial magma.At the same time,sulfides can remain unsaturated during magma evolution,which is favor of the further enrichment of Cu(Au)as moderately incompatible elements.When magnetite starts to crystallize as the magma evolution,the oxygen fugacity of magmatic system decreases,sulfate is reduced to sulfide,and reduced sulfur(S^2-)extracts and concentrates Cu and Au from the magma into the fluid phase,forming porphyry Cu-Au deposits.The high oxygen fugacities commonly occur in the convergent plate margins.Given that the Cu,Au,S contents in oceanic crust are far higher than in continental crust and mantle,then the oxygen fugacity of subduction zone is about two orders of magnitude higher than that of the mantle and lower continental crust.Thus the magmas derived from partial melting of subducted oceanic crusts have far higher Cu,Au,S contents than that sourced from intraplate,which is beneficial to mineralization

关 键 词：板块俯冲 斑岩铜金矿床 氧逸度 埃达克岩 洋脊俯冲 

分 类 号：P542[天文地球—构造地质学] P618.41[天文地球—地质学]