新疆冰草沟地区构造角砾岩与铀成矿关系探讨

Discussion on the Relationship Between Structural Breccia and Uranium Mineralization in Bingcaogou Area,Xinjiang

新疆冰草沟地区经历了二叠纪早期裂谷拉张到晚期萎缩的过程,形成了大量层状中基性火山岩,并沿层间构造破碎带发育大量铀矿化。文章通过对冰草沟地区构造角砾岩岩相学、地球化学等特征的研究,结合其与铀矿体的空间关系,分析岩浆及成矿流体源区特征,探讨构造角砾岩与铀成矿关系。研究结果表明,冰草沟地区构造角砾岩为玄武安山岩破碎后被晚期长英质熔体充填胶结,胶结物具有深部长英质向浅部方解石变化特征,向浅部突变的界面是定位铀矿体的重要构造标志。构造角砾岩和玄武安山岩稀土、微量元素特征显示均具有富集地幔和不同程度地壳混染的一致性特征,晚期长英质熔体具有较高的氧逸度,更加有利于磷、铀的活化和迁移。矿石中Nb/Ta、Cl/F值显示成矿流体基本无地幔岩浆参与,为长英质熔体中出溶的富钠碱性热液,是顺层构造及后期地壳部分重熔热事件活动的产物。

Bingcaogou area in Xinjiang experienced a process from Early Permian rift extension to Late Permian shrinkage,formed a large number of layered intermediate basic volcanic rocks,and developed a large amount of uranium mineralization along the interlayer structural fracture zone.Through the study of petrography and geochemistry of structural breccia in Bingcaogou area,the characteristics of magma and ore-forming fluid source areas were analyzed and the relationship between the breccia and uranium mineralization was discussed with their spatial relationship.The research results showed that the structural breccia in Bingcaogou area was basaltic andesite,which was fractured and then filled and cemented by late felsic melt.The cement is of the characteristics of deep felsic to shallow calcite.The interface that sharply changes towards the shallow is an important structural indicator for locating uranium ore bodies.The REE characteristics of the structural breccia and basaltic andesite showed that they have the same characteristics of enriched mantle and different degrees of crustal contamination.Felsic melts had high oxygen fugacity,which was more conducive to the activation and migration of phosphorus and uranium.The Nb/Ta and Cl/F ratios in the ore indicated that the ore-forming fluid was originally derived from mantle magma involvement.Sodium rich alkaline hydrothermal solution dissolved in felsic melt.It was a product of bedding structures and later crustal partial remelting thermal events.