| 东昆仑夏日哈木铜镍矿区榴辉岩地球化学特征及成矿响应 |
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| 引用本文： | 潘彤,张勇.东昆仑夏日哈木铜镍矿区榴辉岩地球化学特征及成矿响应[J].大地构造与成矿学,2020(3):447-464. |
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| 作者姓名： | 潘彤 张勇 |
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| 作者单位： | 青海省地质矿产勘查开发局;青海省第三地质勘查院 |
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| 基金项目： | 中国地质调查局地质调查项目“青海省矿产资源调查成果综合集成与服务产品开发”(DD20160346);青海省重大科技专项“柴达木盆地南北缘成矿系统与勘查开发示范”(2016-SF-A3)联合资助。 |
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| 摘 要： | 夏日哈木超大型铜镍矿床是近年在东昆仑发现的首例岩浆熔离型矿床。矿区内分布有大量的榴辉岩,本文对主矿体旁侧的榴辉岩进行了岩石地球化学、锆石U-Pb年代学和Hf同位素,以及矿物电子探针分析研究。研究结果显示,榴辉岩SiO2含量为47.56%~57.8%,m/f比值为0.72~1.39,Mg#值在47~60之间;稀土元素标准化配分曲线总体呈现轻稀土元素弱富集,具有弱的Eu负异常,相对富集大离子亲石元素K、Rb、Ba等,以及活泼不相容元素Th,亏损高场强元素Nb、Ta、Zr、Hf,Sr、P、Ti呈现“V”型谷等特征,显示原岩为分异程度较高的铁质辉长岩,形成于大陆边缘裂谷环境。经电子探针分析,石榴子石成分主要为Alm(56~63)Spess(0.22~2.84)Cross(26~37)Pyrope(2.36~6.46)。年代学研究获得榴辉岩峰值变质年龄为415.0±5.5 Ma(MSWD=0.04,n=5),并识别出原岩结晶年龄可能为777~773 Ma。Hf同位素测定显示^176Hf/^177Hf比值介于0.281118~0.282950,εHf(t)值的变化范围较大,介于?41.9~14.2之间,显示榴辉岩主要形成于幔源区,并有大量的先存地壳组分的加入改造、再循环。陆陆碰撞过程中,榴辉岩原岩为成矿提供了一定的物质来源;陆壳折返过程中,榴辉岩退化变质产生了富水、富硫的熔/流体,并被注入到含矿岩浆房中,导致含矿岩浆房硫饱和与氧逸度降低,促使硫化物持续熔离,最终形成了夏日哈木超大型铜镍矿床。
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| 关 键 词： | 榴辉岩 岩石地球化学 成矿响应 夏日哈木铜镍矿 东昆仑 |
Geochemical Characteristics and Metallogenic Response of the Eclogite from Xiarihamu Magmatic Ni-Cu Sulfide Deposit in Eastern Kunlun Orogenic Belt |
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| PAN Tong,ZHANG Yong.Geochemical Characteristics and Metallogenic Response of the Eclogite from Xiarihamu Magmatic Ni-Cu Sulfide Deposit in Eastern Kunlun Orogenic Belt[J].Geotectonica et Metallogenia,2020(3):447-464. |
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| Authors: | PAN Tong ZHANG Yong |
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| Institution: | (Bureau of Geology and Mineral Exploration and Development of Qinghai Province,Xining 810001,Qinghai,China;The Third Geological and Exploration Institute of Qinghai Province,Xining 810029,Qinghai,China) |
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| Abstract: | The super-large Xiarihamu Cu-Ni deposit was the first magmatic liquation deposit found in the eastern Kunlun orogenic belt in recent years.As there are lots of eclogites in the mining area,this contribution presents detailed whole rock geochemistry,zircon U-Pb geochronology and Hf isotopic compositions,as well as electron microprobe analysis for the eclogite close to the main ore body.The eclogite samples have SiO2 of 47.56%–57.8%,m/f ratio of 0.72–1.39,Mg^# value of 47–60.Chondrite-normalized REE patterns show LREE enrichment and slightly negative Eu anomalies.The samples with V-type pattern of Sr,P,Ti elements are enriched in large ion lithophile elements like K,Rb,Ba,active incompatible elements like Th,and depleted in high field strength elements such as Nb,Ta,Zr,Hf,indicating that the protolith is highly fractionated ferruginous gabbro formed on a continental margin rift.Electron microprobe analyses demonstrated that the garnets are mainly composed of Alm(56–63),Spess(0.22–2.84),Cross(26–37),Pyrope(2.36–6.46).Zircon crystals in the eclogite samples are long prism,granular,with few oscillatory zoning as shown on CL images.Analyses of the zircon grains yielded Th/U ratios of 0–1.1,metamorphic age of 415.0±5.5 Ma(MSWD=0.04,n=5)for the eclogite,and crystallization age of 777–773 Ma for the protolith.The zircon grains from the eclogite have ^176Hf/^177Hf ratios of 0.281118–0.282950,high initialεHf(t)values of?41.9 to+14.2,indicating the eclogite was derived from a mantle source with a lot of crustal component added.During the continental-continental collision,the eclogite provides some metallogenic material.The eclogite underwent retrograde metamorphism and produced aquiferous and sulfur-rich melt,then be injected in ore magma chamber triggered sulfur saturation and lowered the oxygen fugacity,prompted the continuous melt away of sulfides during the exhumation of the continental crust,which finally contributed to the super large Cu-Ni sulfide deposit. |
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| Keywords: | eclogite geochemical metallogenic response Xiarihamu Ni-Cu deposit eastern Kunlun |
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