粤北下庄-诸广铀矿集区糜棱岩特征及其构造意义

Mylonite, as a geological information carrier of structured fault zone or polymetallic metallogenic belt, has been widely investigated by structural geologists and ore deposit geologists. As a matter of fact, not only several mylonite zones but also ore-bearing mylonite in the siliceous fault zones were found in the Xiazhuang-Zhuguang uranium ore field; and the formation age of mylonite is close to that of mineralization of the uranium ore deposits. The mylonite zones might, hence, have been one of the vital ore-controlling and ore-forming structures in the study area. However, there is no consensus about the origin of the mylonite, and this has influenced the understanding about the role of the mylonite zones in the mechanism of uranium metallization.In order to deepen the study on the mylonite zones and establish the metallogenic model of uranium deposits under the background of ductile shearing in this area, it is the target of the proposed project to conduct a systematic research on the mechanical properties, kinematic characteristics and geological environment of formation of the mylonite zones based on the investigation of their spatial distribution. This will be achieved through a series of identification and measurements on the lithology, microstructure and fabrics of the mylonites. According to the chronological data from Ar-Ar dating, we will then explore the formation era of these mylonites and its association with the uranium mineralization age. Furthermore, the inherent relationship between the activation and transfer of the rock components and the stress and strain of the geological environment will be revealed after a tectonogeochemical analysis. In this way, it will be possible to elucidate the mechanism of uranium mineralization in the ductile shearing environment, and to improve our understanding on the diagenesis of the mylonites, which can provide guidance for uranium ore prospection.

糜棱岩作为蕴含构造断裂带或金属成矿带丰富地质信息的载体，已越来越受到构造地质学家和矿床学家的广泛重视。粤北下庄-诸广铀矿集区已发现有数条糜棱岩带，在硅质断裂带中也有不少含矿糜棱岩，且糜棱岩的形成时代与某些铀矿床成矿年龄相近，糜棱岩带可能是该铀矿集区一种重要的控矿与成矿构造。然而该区糜棱岩的成因尚存在分歧，一定程度制约了对该区糜棱岩带及其对铀成矿作用机理的认识。为深化本区糜棱岩带的研究，建立韧性剪切背景下的铀矿床成矿模式，本项目拟在查明糜棱岩带展布的基础上，通过糜棱岩岩性、显微构造及岩石组构等要素的鉴定和测量，系统研究糜棱岩带的力学性质和运动学特点及其形成的地质环境；根据糜棱岩年代学资料探讨糜棱岩形成时代与铀成矿年龄的耦合关系，结合构造地球化学的研究，探索岩石组分活化、转移与应力、应变的内在联系，揭示韧性剪切环境下的铀成矿机制，对提升该区糜棱岩成因认识和指导找矿实践都具有重要意义。

糜棱岩作为蕴含构造断裂带或金属成矿带丰富地质信息的载体，已越来越受到构造地质学家和矿床学家的广泛重视。粤北下庄—诸广铀矿集区已发现有数条糜棱岩带，在硅质断裂带中也有不少含矿糜棱岩。野外宏观构造观察与室内显微构造学显示，研究区糜棱岩具有旋转碎斑，δ型旋转斑、石香肠、核幔构造、石英亚晶粒化、石英的动态重结晶、波状消光、机械双晶、云母扭折带等构造。不对称压力影、旋转碎斑系、云母鱼、S-C组构等显微构造指示糜棱岩所受剪切方向主要为左行剪切，其应变类型属于压扁形应变，变形温度以中低温（250°-350℃）韧性变形为主，中高温（350°-450℃）韧性变形次之。白云母40Ar/39Ar年代学结果显示，南雄糜棱岩带形成于早燕山期，而塘洞糜棱岩带形成时间稍早，为晚印支期。在构造作用过程中发生的糜棱岩化和碱交代作用叠加促使元素发生迁移，控制了铀元素的空间分布。