桂北地苏铜镍矿镁铁质—超镁铁质岩体侵位时代、地球化学特征及其成矿成岩分析  

Zircon U-Pb geochronology, geochemical characteristics and metallogenesisof the Disu Cu-Ni-bearing mafic-ultramafic intrusion in northern Guangxi

作　　者：孙建勋 王宗起[1] 马收先[1] 庞绪勇 宫江华[1] 覃小锋[3] 傅振洋 SUN Jianxun;WANG Zongqi;MA Shouxian;PANG Xuyong;GONG Jianghua;QIN Xiaofeng(MLR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources, CAGS,Beijing,100037;China University of Geoscietices,Beijing,100083;Callege of Eurth Science,Guilin University of Technology,Guilin,Guangxi,511004)

机构地区：[1]中国地质科学院矿产资源研究所自然资源部成矿作用与资源评价重点实验室,北京100037 [2]中国地质大学(北京),北京100083 [3]桂林理工大学地球科学学院,广西桂林541004

出　　处：《地质学报》2019年第5期1081-1095,共15页Acta Geologica Sinica

基　　金：中国地质调查局项目(编号DD20160124)资助成果

摘　　要：桂北宝坛地区作为为数不多的新元古代岩浆Ni-Cu硫化物矿田,对区内成矿岩体开展岩浆演化过程和构造背景方面研究具有重要意义。本文以地苏赋矿镁铁质—超镁铁质岩体为研究对象,进行岩相学特征、锆石U-Pb年龄、地球化学等方面的综合分析。分析结果显示,岩体自西向东发育三个脉动韵律:辉石岩、辉橄岩-橄辉岩-辉石岩-辉长岩、闪长岩,铜镍硫化物矿化形成于前两个韵律底部;闪长岩锆石U-Pb年龄857±8Ma限定其成矿时代为新元古代早期;岩体Mg~#值为71.91～80.07,m/f比值为2.56～4.02,MgO与Al_2O_3、CaO负相关。稀土元素配分曲线显示轻稀土富集、重稀土平坦的配分模式。大离子亲石元素Rb、Th、U相对富集,高场强元素Nb、Ta、Ti明显亏损,与陆缘弧亚碱性玄武岩相似;δ^(34)S值在2.3‰～3.8‰之间,与MORB地幔结果不同(-1.57‰～+0.60‰)。岩石组合和地球化学特征表明岩浆源区为受过地壳混染和流体交代改造的部分熔融岩石圈地幔,具有岛弧岩浆的地球化学特征,表明桂北宝坛铜镍硫化物矿床形成于俯冲环境。岩浆侵位过程中地壳物质混染、岩浆结晶分异作用是促使桂北宝坛地区镁铁质—超镁铁质岩浆发生硫饱和及硫化物熔离的主要因素。As one of several known magmatic sulfide deposits that formed in the Neoproterozoic in China, the magmatic evolution and tectonic setting of the ore-forming plutons in the Baotan area of northern Guangxi are highly debated. The study carried out an integrated analysis of petrography, zircon U-Pb dating, geochemistry for the Disu ultramafic-mafic complex. The results show that the complex developed three magmatic pulsations: pyroxenite, pyroxene peridotite-olivine pyroxenite-pyroxenite-grabbo and diorite, and the sulfide ore occurs at the bottom of the former two pulsations. Zircon U-Pb age 857±8 Ma of diorite constrains the ore-forming time to the Early Neoproterozoic;Mg# of the complex is 71.91~80.07, with an m/f ratio of 2.56~4.02, and content of MgO is negatively correlated to Al2O3 and CaO. The rare earth elements(REE) patterns show enriched light rare earth elements(LREE) and flat heavy rare earth elements(LREE). The complex is characterized by enrichment in large ion lithophile elements(LILE, such as Rb, Th, U) and pronounced depletion in high field strength elements(HFSE, such as Nb, Ta, Ti), which are similar to that of subalkaline continental arc basalt. And δ34S values of sulfide range from 2.3‰ to 3.8‰, obviously different from the value(-1.57‰ to +0.60‰) of MORB. Rock assemblages and geochemical characteristics indicate that primitive magma of the Disu mafic-ultramafic complex sourced from partially melted lithosphere mantle which has been modified by crustal contamination and fluid metasomatism. Thus, the Cu-Ni deposits in the Baotan area formed in a subduction setting. Crustal contamination and fractional crystallization during the magmatic emplacement were the main factors to promote sulphur saturation and sulfide segregation of mafic-ultramafic magma in the Baotan area of northern Guangxi.

关 键 词：桂北 铜镍硫化物 四堡群 U-PB年龄 构造环境 

分 类 号：P618.2[天文地球—矿床学] P597.3[天文地球—地质学] P587