鹿井地区铀矿床断裂控矿作用与矿体保存状况研究

The Lujing area is one of the main uranium producing areas in south China. After several decades of exploration practice and detailed study, a number of results about uranium deposits were reported including mineralization epoch, geologic characteristic, lithogeochemistry, etc. However, the ore-controlling regularity of fault and the preservation of uranium deposit in study area were less documented in previous studies, especially the issues about the deformation stages of fault and the uplift-exhumation process of mountain, which have close relationship with ore prospecting during Mesozoic-Cenozoic in Lujing area. In order to identify the characteristic of ore-controlling fault and preserve situation of uranium deposit, remote sensing images interpretation, field observation and microscopic structure analysis will be used to research the laws and stages of fault movement and the location of uranium ore body on different levels. In the combination with the relevant thermochronological dating, the temporal of fault activities and the history of mountain uplift-exhumation will be limited. Then, the stages of fault deformation and the characteristics of ore-bearing fault will be ascertained, and the uplift-exhumation process of the mountain will be quantitative reconstructed. We will clarify the fault structure has a great control on ore body of uranium and the uplift-exhumation has reconstructive effect to the uranium deposit. This study will provide basis for potential mineralization assessment and ore prospecting in Lujing area.

鹿井地区是华南主要产铀地区之一，经过几十年的勘探研究，在铀矿的成矿时代、赋矿岩性及岩石地球化学特征等方面有诸多报道。但对铀矿区的断裂控矿规律和成矿后矿体的保存问题前人鲜有涉及，特别是矿区中新生代以来的断裂活动期次和山体的隆升剥露过程等与找矿密切相关的问题。为了查明铀矿的断裂控矿规律和保存状况，本项目拟采用遥感解译、野外实地观测和显微构造分析，从不同层次研究断裂运动规律和活动期次以及铀矿体的空间定位，并通过相关年代学技术约束断裂主要活动时间和山体隆升剥露历史。最终确定鹿井地区中新生代断裂变形期次和含矿期断裂特征，定量恢复山体的隆升剥露过程，进而阐明断裂构造对铀矿的控制作用和隆升剥露对铀矿的改造作用，为鹿井地区铀矿成矿潜力评价和找矿预测提供依据。

理清鹿井地区构造控矿特征、区域构造热演化和矿体保存状况对区域找矿预测具有重要意义。通过野外地质调查和显微构造变形分析，认为NE向断裂是鹿井地区主要控矿和含矿断裂，属浅层次构造变形，具有多期构造-热液活动特征：经历了早期（晚侏罗世—早白垩世）的压性、中期（早白垩世—古近纪）的张-张扭性和晚期（新近纪）的右行压扭性变形过程。铀矿（化）体主要发育在NE向断裂破碎带中，结合铀成矿时代，主成矿期断裂力学性质表现为张性、张扭性，后期NE向断裂右行压扭变形派生出近EW向、NW向和NS(NNE)向的剪裂隙。根据构造组合特征及其控矿规律，认为NE向断裂破碎带中，沿走向存在不连续的脉状、透镜状富铀矿体，而在其他方位的断裂带中可能存在部分铀矿体。通过系统采样及(U-Th)/He和裂变径迹测试，2个寒武系砂岩样品锆石(U-Th)/He（ZHe）年龄为133-106Ma，1个白垩系砂岩和7个中生代花岗岩锆石ZHe年龄分别为154-83Ma和167-36Ma，ZHe年龄揭示了丰州盆地沉积物来源于周边沉积岩和火成岩。磷灰石裂变径迹（AFT）测试显示了相对一致的年龄（61-54Ma）和单峰式封闭径迹特征，未矿化样品磷灰石(U-Th)/He（AHe）年龄为67-19Ma。热史模拟表明鹿井地区经历了早白垩世相对快速隆升剥蚀、早白垩世晚期至晚白垩世埋深加热以及到现今的隆升至地表过程。热史模拟为古丰州盆地具有更大的覆盖面积提供佐证，晚白垩世晚期至现今鹿井地区的剥蚀量约为1.2-4.8km。结合铀矿成矿年龄和温压条件，认为鹿井地区形成于晚白垩世及之前的矿体可能遭受一定程度的剥蚀。