内蒙古大井矿床碳氧同位素组成及其成因意义(英文)  

Carbon and Oxygen Isotopic Composition and Its Genetic Significance in the Dajing Deposit,Inner Mongolia,China

作　　者：王长明[1] 

机构地区：[1]中国地质大学(北京)地质过程与矿产资源国家重点实验室/岩石圈构造、深部过程及探测技术教育部重点实验室,100083

出　　处：《吉林大学学报（地球科学版）》2010年第4期810-820,共11页Journal of Jilin University：Earth Science Edition

基　　金：国家“973”计划项目(2009CB421008);教育部长江学者和创新团队项目(IRT0755);“111”计划项目(B07011);中国博士后基金项目(20090460400)

摘　　要：利用碳氧同位素组成可以很好地判别其形成的沉积环境。以内蒙古大井矿床为例,对该矿床16个菱铁矿样品进行碳、氧同位素分析,δ13CPDB变化范围为-1.8‰～-6.6‰,δ18OVPDB变化范围为-23.1‰～-17.3‰。根据矿物δ13C与δ18O值投影到δ13C-δ18O图解中,样品数据在图中的投点落入热水沉积区,说明其形成过程中具有热水沉积作用的发生。古温度可以通过T=16.998-4.52(δ1c8O-δ1w8O)+0.03(δ1c8O-δ1w8O)2计算,其形成时的温度平均值为117℃,比海底和湖底的温度要高得多,主要原因在于热水流体参与成矿。碳酸盐的成矿环境可以通过公式Z=2.048(δ13C+50)+0.498(δ18O+50)计算:Z值大于120,表示成矿环境为海水;如果Z值小于120,表示成矿环境为淡水或湖水。内蒙古大井矿床菱铁矿的Z值为100～114,结合区域地质背景,大井矿床形成的古环境为深水湖泊环境。通过对碳氧同位素的分析,结合成矿地质背景、矿床地质特征以及微量元素组成,认为在大井矿床成矿的早期阶段曾经发生过热液沉积作用,本次研究不仅有利于全面理解和认识大井矿床成矿过程的全貌,而且有益于对古湖相环境热液事件的探索。Carbon and oxygen isotopic values provide criteria for the evaluation of depositional environment. Sixteen siderite samples from the Dajing ore deposit, Inner Mongolia, China, were analyzed in order to determine depositional environments. Siderites at the Dajing ore deposit are characterized by δ13CPDB from -1.8 ‰ to -6.6 ‰ and δ18OVPDB from -23.1 ‰ to -17.3 ‰, and their values lie in the hydrothermal sedimentary area on a δ13C versus δ18O diagram, showing hydrothermal sedimentary genesis of siderite. The palaeotemperature is estimated, based on the following equation： T=16.998-4.52（δ18cO-δ18wO） ＋ 0.03（δ18cO-δ18wO）2. A higher palaeotemperature, averaging 117°C, suggests that the mineralizing fluids are from hydrothermal sedimentary fluids and deep lacustrine water. Depositional settings of limestone can be inferred from equation： Z=2.048（δ13C＋50）＋0.498（δ18O＋50）. Samples with Z value above 120 would be classified as marine, while those with Z below 120 as fresh-water ones. The synthetic Z parameter （between 100 and 114） in the Dajing ore deposit, also suggests lacustrine environments. Together with tectonic setting, deposit geology, and rare-earth element composition, the hydrothermal systems are recognized in a lacustrine setting in the early mineralization, which is important not only for a better understanding and interpretation of the genesis of the Dajing deposit but also for exploration of hydrothermal events in the lacustrine environment.

关 键 词：碳氧同位素 热水沉积作用 湖相环境 大井矿床 

分 类 号：P618[天文地球—矿床学]