江西省铅山县篁碧铅锌矿区同位素年代学和稳定同位素组成

摘要

江西省铅山县篁碧铅锌矿区位于华南扬子板块与华夏板块结合的北武夷地区,该地区是钦杭结合带的重要组成部分,以发育一系列的中生代火山岩盆地为主要特征.篁碧铅锌矿之西侧冷水坑地区,东侧的梨子坑、仙霞岭都已有了同位素年代学研究成果.本次研究选取了篁碧矿石中闪锌矿进行同位素年代学测试；Rb-Sr法和Sm-Nd法两种同位素年龄测试,得到其等时线年龄分别为135.4±4.4Ma( SMWD =0.52)和139±15Ma (SMWD =0.118).结果表明该矿床系形成于早白垩世,另一方面也显示了闪锌矿可以作为测年的理想矿物.V5号矿脉的铅锌矿石和方解石脉的C、S、O同位素分析结果:铅锌矿的34SV-CDT为2.5％ ～5.1‰,方解石脉的13 CV-PDB为-2.6％ ～ -4.7％,18 OV-PDB为-23.9‰～ -27.7％,18 OV-SMOW为2.3‰～6.2％.以上数据显示矿石中S主要为岩浆热液来源,方解石脉中C、O显示其来源比较复杂,指示源于基性岩或地幔源,并有大气降水.综上说明该矿床为早白垩世的岩浆热液矿床.上述研究丰富了北武夷地区的成矿年代学研究成果.结合前人资料,认为中生代成矿时代由西往东渐新.岩浆源方解石脉的发现暗示北武夷隐伏基底断裂可能深达地幔,为钦杭结合带南界的厘定提供了新的依据.%The northern Wuyi region, located in the conjoining area of the Yangtze plate and Cathaysian plate, is an important part of the Qinzhou-Hangzhou juncture zone and is characterized by series of Mesozoic volcanic basins. Systematic geochronological researches on its adjacent areas such as Lengshuikeng, Lizikeng and Xianxialing have been conducted, while in this area less research has been done. In this investigation, sphalerite was selected for isotopic chronological analyses. The Rb-Sr dating and Sm-Nd dating yields isochron ages of 135.4±4.4Ma (SMWD=0.52) and 139±15Ma (SMWD=0. 118), respectively. In addition, the C, O, S isotope compositions on lead-zinc ores and the associated calcite veins have been analyzed and MSV.COT of the lead and zinc minerals arern2. 5%~5. l%,13Cv-PDB of the calcite veins are - 2. 6%~4. 7%,18Ov-PDB are - 23. 9%~-27. 7% and 18OV.SMOW are 2. 3% ~rn6. 2%. These data suggest that S in the ores was derived from magmatic source, C and 0 in the calcite veins were originated not only from basic rocks or mantle source, but also from meteoric water. It is suggested that these deposits are magmatic deposits formed in the Early Cretaceous and that sphalerite can be used as an ideal mineral for dating. Our results provide new geochronological data for the volcanic belt in northern Wuyi, and reveal that metallogenetic age in Mesozoic became younger from west to east in general. The magmatic source of calcite veins leads to assumption that basement faults in northern Wuyi might extend deep to mantle, providing new evidences for constraining the south boundary of the Qinzhou-Hangzhou juncture.