华南鹿井铀矿田NE向QF_(2)断裂特征及其与铀成矿关系探讨

The Geological Features of QF2 Fault and its Relationship with Uranium Mineralization in Lujing Uranium Ore-field,South China

鹿井铀矿田处于桃山-诸广铀成矿带的南西部,已探明鹿井、黄峰岭、高昔等10个铀矿床,是我国主要的花岗岩型铀矿田之一。区内NE向QF2断裂是鹿井铀矿田主断裂之一,黄蜂岭、下洞子、高昔矿床分布于其两侧,是重要的导矿、控矿断裂。本文通过分析该断裂地表特征,解剖钻孔揭露的断裂分带,查明该断裂地质特征及其与铀成矿之间的关系,为下一步找矿提供新思路。研究表明:(1)该断裂存在五期活动,第一期为早白垩世早期在张性应力环境下形成块状石英;第二期为深部地幔物质沿着断裂上涌形成煌斑岩脉;第三期为早白垩世中晚期强烈挤压环境促使岩石发生挤压破碎,形成硅化角砾岩、断层泥等;第四期为晚白垩世在拉张环境下深部流体上升形成赤铁矿化花岗碎裂岩、碎裂花岗岩;第五期为新近纪及后期张性环境下形成松散构造角砾岩。(2)区内存在至少两期铀成矿阶段,早期铀成矿形成于QF2断裂第一期往第二期的伸展拉张过程;晚期铀成矿形成于第四期拉张活动过程。(3)第三期的构造产物对晚期铀成矿热液运移起屏蔽作用,对下一步找矿具有较好指示意义,断裂下盘200 m范围是重要找矿部位,第五期构造活动错动矿体,值得进一步关注。

The Lujing ore field is located in the southwest of the Taoshan-Zhuguang uranium metallogenic belt.Besides the Lujing deposit,tens of other uranium deposits also occur in this ore field,such as the Huangfengling and Gaoxi.The Lujing ore field is one of the most important granite type uranium ore field in China.The NE-trending QF2 fault is one of the mineralizing control faults in the Lujing uranium ore field.The Huangfengling,Xiadongzi and Gaoxi deposits occur along this fault.In this paper,the geological characteristics of the QF2 fault and its relationship with uranium mineralization are studied by analyzing the surface characteristics of the fault and alternation zoning revealed by drilling holes.The results show that the QF2 fault have five stages of pulsating activities.The first stage of the activities was the formation of the massive quartz via tensional stress during the early Early Cretaceous.In the second stage,the lamprophyre dikes were formed by the upwelling of deep mantle materials along the fault.In the third stage,the strong compression led to the formation of the silicified breccia and the fault gouge.In the fourth stage,ascending of the deep fluid formed the hematite granite cataclastic rock and the cataclastic granite during the late Cretaceous.In the fifth stage,the loose breccia was formed in the extensional tectonic environment during Neogene or Quaternary.There are two or more stages of uranium mineralization.The early stage uranium mineralization was formed during the transition of the extensional tectonic environment from the first stage to the second stage.The late stage uranium mineralization was formed under the extensional tectonic environment of the fourth stage.The silicified breccia and fault gouge,which formed in the third stage,screened the late stage uranium mineralization.The footwall of the fault with a thickness of about 200 m is an important prospecting area,nonetheless,special attention should be paid to the dislocation effects of the fifth stage faulting.