Geochemistry and U-Pb Dating of Heavy Mineral Zircons and Their Significance in Lamproites and Associated Rocks from Ningxiang,Hunan Province

Heavy mineral zircons were separated from diamondiferous lamproites and their associated rocks in Ningxiang and nearby area,Hunan province,and their main and trace element compositions,interior structure and the U-Pb isotopic ages were obtained with EPMA,cathodoluminescence microscope and LA-ICPMS measurement.The zircons in lamproites from different locations generally have similar geochemical characteristics.The U-Pb dating of zircons suggests that the lamproites were probably formed during multi-stages.A young age of(101.6±5.1)Ma was obtained on four zircon samples from No.1 and No.3 pipe lamproites.The zircon collected from the Cretaceous red strata in Shangwutong area has a concordant 207Pb/ 206Pb age of(2 008±29)Ma.These results cannot specifically determine the source rocks of diamond in the study area.