钾玄岩系列:藏东玉龙铜矿带含矿斑岩Sr、Nd、Pb同位素组成

SHOSHONITIC SERIES:Sr,Nd,AND Pb ISOTOPIC COMPOSITIONS OF ORE BEARING PORPHYRY FOR YULONGCOPPER ORE BELT IN THE EASTERN XIZANG(TIBET)

西藏东部玉龙铜矿带，包括玉龙、扎拉尕、莽总、多霞松多和马拉松多含矿斑岩，马牧普钾质碱性斑岩和总郭碱性火山岩等Ｓｒ、Ｎｄ、Ｐｂ同位素组成比较一致，其数据点均分布在地幔演化区，接近ＥＭＩ地幔端元，暗示其物质来源于交代地幔源区。

Some multi metallic deposits containing Cu,Mo,Pb,Zn,Au,Ag and Pt of the porphyry types such as middle types of Zalagar and Mangzong,large types of Doxarsumdo and Malasumdo and super large type of Yulong from the Yulong Copper Ore Belt(YCOB) are located in the middle part of Ailaosha Jingshajiang Cenozoic shoshonitic series magmatic rock belt in Eastern Tibet.Studies of the isotopic samples were conducted in the ore bearing porphyry and coexisting alkaline plutonic rocks and volcanic rocks.Sr,Nd and Pb isotopic compositions of orebearing porphyry and coexisting rocks have been analyzed in the isotopic geochemistry laboratory of Guangzhou Institute of Geochemistry,Chinese Academy of Sciences.Mass spectrum analysis for Sr,Nd and Pb isotopes was done by VG354. 87S/86Sr and 143Nd/144Nd ratios were standardized by 86Sr/88Sr=0119 4 and 145Nd/144Nd=0.348 417.Lead isotope ratios were determined using NBS981 as standard to calibrate mass discrimination,and the precision is about 0.02%.Analytical results show that the ore bearing porphyry and coexisting alkaline potassic plutonic rocks and volcanic rocks have very similar Sr,Nd and Pb isotopic compositions with variance range of 0,512 427-0.512 552 for 143Nd/144Nd,0.705 1-0.706 8 for 87Sr/86Sr,18.75-18.88 for 206Pb/204Pb,15.62-15.66 for 207Pb/204Pb and 38.90-38.99 for 208Pb/204Pb,which indicates that their material was originated from the same source region of mantle. Being partial overlap with Kerguelen in south Indian Ocean,most of the plots in Sr Nd,Pb Sr and Pb Nd correlation diagrams are concentrated and close to the East Africa Rift and appoximately close to the EMII end member of the mantle,which implies obvious difference from MORB and a metamorphic mantle derived source.Quantitatively modelling results suggest that mantle derived component (98.7%-99.2%) is much preponderant than crust derived one (0.8%-1.3%),which is compatible with the theories that crust derived contamination will be rare for the volcanic rocks and alkaline plutonic rocks.