白云鄂博矿床白云石型矿石中独居石单颗粒U-Th-Pb-Sm-Nd定年  

Single-grain U-Th-Pb-Sm-Nd dating of monazite from dolomite type ore of the Bayan Obo deposit.

作　　者：刘玉龙[1] 陈江峰[1] 李惠民[2] 钱卉[1] 肖国望[3] 张台荣[3] 

机构地区：[1]中国科学技术大学地球物质循环实验室 [2]天津地质矿产研究所,天津300170 [3]包头钢铁公司白云鄂博铁矿,包头014000

出　　处：《岩石学报》2005年第3期881-888,共8页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划(973)项目(C199943201)中国科学院合肥地区联合分析测试中心基金资助项目

摘　　要：使用交换树脂TRU Spec同时分离REE、U、Th、Pb及其他的元素,然后用阴离子交换树脂纯化Pb并用萃淋树脂分离纯化Sm和Nd,Sm、Nd、U和Pb的定量测定借助同位素稀释法,Th的定量测定则用ICP-MS分析,Nd和Pb同位素组成分析用质谱法(TIMS),从而实现独居石U-Th-Pb-Sm-Nd联合定年。用这种方法可以在同一样品上,同时得到U-Th-Pb和Sm-Nd同位素年龄记录。白云鄂博矿床白云石型稀土矿石中12个单颗粒独居石的U-Th-Pb-Sm-Nd同位素联合定年给出Sm-Nd等时线年龄为1008±320 Ma,其中8个独居石的Th-Pb等时线年龄为1231±200 Ma,此二年龄在误差范围内相似。在同一组独居石样品上得到一致的Th-Pb与Sm-Nd的中元古年龄,表明白云鄂博在中元古代的稀土成矿作用是可能的。本文独居石的Th-Pb 和Sm-Nd年龄与以前报道的独居石加里东期Th-Pb年龄差别很大,此问题尚需进一步研究。To date monazite by combined U-Th-Pb-Sm-Nd dating technique, we used TRU Spec ion exchange resin to separate REE, U, Th, Pb and other elements, and further used anion exchange resin to purify Pb, HDEHP resin to separate and purify Sm and Nd. Sm, Nd, U and Pb concentrations were determined by the isotope dilution, while Th by ICP-MS. Isotopic ratios of Nd and Pb were measured on thermal ionization mass-spectrometer （TIMS）. U-Th-Pb and Sm-Nd ages are obtained on the same sample using this method. The combined U-Th-Pb-Sm-Nd dating for 12 single grains of monazite from a dolomite type REE ore, Bayan Obo deposit,gives a Sm-Nd isochron age of 1008 ± 320 Ma and a Th-Pb isochron age of 1231 ± 200 Ma（8 grains）. These two ages are similar when uncertainties are considered. These ages obtained from the same monazite samples indicate that REE mineralization might occur in the Meso-Proterozoic. The Th-Pb and Sm-Nd ages presented in this study differ significantly from the Caledonian Th-Pb ages of monazites reported formly. This difference in dating results merits further investigation.

关 键 词：白云鄂博 独居石 TRU SPEC U—Th—Pb—Sm—Nd联合定年 

分 类 号：P597.3[天文地球—地球化学]