幔源挥发性组分参与302铀矿床成矿作用的氦同位素证据  

Mantle-derived volatile components involved in uranium mineralization:Evidence from He isotopes of the No.302 uranium deposit

作　　者：张国全[1,2] 胡瑞忠[1] 蒋国豪[1] 刘 朱维光[1] 田建吉[1] 双燕 范效仁 

机构地区：[1]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵州贵阳550002 [2]浙江省有色金属地质勘查局,浙江绍兴312000 [3]重庆地质矿产研究院,重庆400042

出　　处：《地球化学》2010年第4期386-395,共10页Geochimica

基　　金：中国科学院知识创新工程重要方向项目(KZCX3-SW-125,KZCX2-102-3);国家自然科学基金重点项目(40634020)

摘　　要：对取自302铀矿床井下与沥青铀矿矿石共生的9件紫黑色萤石、肉红色方解石样品进行了流体包裹体的He同位素测定,3He/4He测定值为0.03～0.57 Ra(绝大部分在0.11～0.25 Ra之间),位于地幔与地壳的氦同位素值范围之间,显示成矿流体中的氦同位素具有壳、幔两个端元混合的特点,表明有大量幔源挥发性组分参与铀成矿作用。该矿床碳同位素值与流体包裹体证据均表明,地幔挥发性组分确实大规模参与了铀成矿作用。研究显示,几乎华南所有的热液铀矿床都形成于白垩纪—古近纪,且这些矿床的碳同位素组成均显示成矿流体中的矿化剂CO2来自地幔,暗示它们成矿时具有相似的成矿动力学背景:可能均与华南中-新生代岩石圈伸展作用所控制的幔源挥发性组分具有密切的关系。Helium isotopic compositions from fluid inclusions of 9 pieces of atropurpureus fluorite and pale red calcite intergrowth with pitchblende ores, collected from the underground of the No. 302 uranium deposit, have been determined. The results show that 3He/4He ratios range from 0. 03 Ra to 0. 57 Ra, with most of ratios varying from 0. 11 Ra to 0.25 Ra. These values are significantly lower than that of the Earth＇s mantle, and higher than that of the crust, indicating that He in the ore-forming fluids is a mixture of mantle- and crust-derived components, and that there were many mantle-derived volatile components involved in uranium mineralization. Recent studies revealed that most of hydrothermal uranium deposits in South China occurred during the Cretaceous to the Paleogene. Previous carbon isotope and fluid inclusion studies suggested that the CO2 as mineralization agent in the ore-forming fluid was derived from the mantle. Therefore, it suggests that most U deposits in South China formed under similar metallogenic geodynamic settings, and possibly has a genetic link with mantle-derived volatile matters, which were controlled by the Mesozoic to the Cenozoic lithosphere extension. Therefore, uranium mineralization and lithosphere extension were closely connected by mantle-derived volatile components.

关 键 词：氦同位素 成矿流体 302铀矿床 热液铀矿床 华南 

分 类 号：P597[天文地球—地球化学] P619.14[天文地球—地质学]