东昆仑造山带海德乌拉铀矿床沥青铀矿年代学特征及成因

Age and Genesis of Pitchblende of the Haidewula Uranium Deposit, East Kunlun Orogen and Its Geological Significance

海德乌拉铀矿床位于东昆仑造山带东段,是西北地区最近发现的与火山岩有关的独立铀矿床,对其研究有助于揭示青藏高原热液铀成矿机制.利用扫描电镜、电子探针和激光原位分析等对海德乌拉铀矿床沥青铀矿开展了化学成分分析和同位素定年等工作.结果显示海德乌拉铀矿床沥青铀矿具有较高的Ca和REE含量,较低的LREE/HREE比值.沥青铀矿电子探针U-Th-Pb化学年龄为226~350 Ma,峰值为289 Ma;U-Pb同位素年龄为234.6±1.2 Ma(MSWD=0.99,n=17).两组年龄的差异可能与海德乌拉铀矿床沥青铀矿中存在普通铅而导致电子探针U-Th-Pb化学定年失准有关.研究认为海德乌拉铀矿床沥青铀矿形成于岩浆期后富Ca的中温热液,矿床的形成可能与古特提斯构造域布青山-阿尼玛卿洋北向俯冲-碰撞后的伸展环境有关.

The Haidewula uranium deposit, which is located in the eastern part of the East Kunlun orogenic belt, is the newly discovered independenturanium mineralization deposit related to volcanic rocks in northwest China. Therefore, the study on this deposit is beneficial to reveal the formation mechanism of hydrothermal uranium mineralization in the Qinghai-Tibet Plateau.In this paper,scanning electron microscope, electron probe analysis, and Laser Ablation Inductively Coupled Plasma Mass Spectrometry in-situ analysis were carried out to explore the metallogenic age and genesis of the pitchblende at the Haidewula deposit. Analysis results show that the pitchblende shows high Ca and ∑REE contents and low LREE/HREE ratios.It has a U-Th-Pb chemical age of 226 to 350 Ma with a peak of 289 Ma, and a U-Pb isotopic age of 234.6±1.2 Ma(MSWD=0.99,n=17). The difference between the ages obtained by the two methods may be related to the inaccurate U-Th-Pb chemical age caused by a certain amount of common lead in the pitchblende of the Haidewula uranium deposit.We suggest that the pitchblende in the Haidewula uranium deposit were formed in post-magmatic Ca-rich medium-temperature hydrothermal fluids. And the formation of the Haidewula uranium deposit is related to the extensional environment after northward subduction-collision of the Buqingshan-Animaqing Ocean in the Paleo-Tethys tectonic domain.