黔西南雄武地区大际山铀多金属矿床控矿构造解析与找矿预测

Analysis of Ore-controlling Structures and Prospecting Prediction of Dajishan Uranium Polymetallic Deposit in Xiongwu Area,Southwest Guizhou

大际山铀多金属矿床地处黔西南碳酸盐岩台地相区,赋矿围岩以碳酸盐岩和碎屑岩为主。详细的野外观测和构造解析表明,该矿床主要有NE-NEE向张扭性断裂、NNE向压扭性断裂和层间破碎带/层间滑脱构造三种控矿构造类型,形成“断控型”和“层控型”两种铀多金属矿体。矿区内构造分级控矿特征显著,区域性NE-NEE向张扭性断裂带控制了成矿区带的整体展布,张扭性断裂带凹凸转换拉张部位决定了矿床的产出位置,与NE-NEE向张扭性断裂贯通的层间破碎带、层间滑脱部位和NNE向压扭性断裂控制了矿体的形态和规模。依据矿区内不同构造行迹的相互穿插关系,厘定出早北东向、晚北东向和北北西向三期构造带。其中,早北东向构造带导致层间破碎带的形成,为成矿流体的侧向贯入提供了先决条件;晚北东向构造带控制了NE-NEE向张扭性断裂的形成和展布,为成矿流体的垂向运移和矿床的就位提供了主要场所和空间;北北西向构造带在促使NNE向压扭性断裂形成的同时,驱动了成矿流体从势能高的地方向势能低的地方运移。由此构建了NE-NEE向张扭性断裂构造与层间破碎带/层间滑脱构造联合控矿模式,并将浅表构造解析与CSAMT地球物理探测相结合,预测了大际山矿区深部及外围黄泥堡‒下银厂地区仍具有良好的找矿前景,为下一步铀多金属找矿勘查提供了新的思路和方向。

The Dajishan U-polymetallic deposit is located inside a carbonate platform,Southwest Guizhou,and the orebodies are hosted in the Jialingjiang Formation carbonate and clastic rocks.Field observation and structural analysis revealed that the ore-controlling structures in the deposit consist of the NE-NEE-striking transtensional fault,the NNE-striking compressional fault,and the interformational fractured zone,which control the emplacement of the“fault-controlled”and“stratabound”U-polymetallic ore bodies.The Dajishan U-polymetallic deposit is obviously controlled by the hierarchical structures,such as the region NE-NEE-striking transtensional fault controlled the distribution of the U-polymetallic mineralization belts,the localization of the U-polymetallic deposit is controlled by the extensional duplex of the NE-NEE-striking transtensional fault and the NNE-striking compressional fault,the interformational fractured zone and the interformational detachment structures which connected with the NE-NEE-striking transtensional fault yielded the space for the ore body emplacement.According to the crosscutting relationship of the different structural styles,three metallogenic tectonic systems can be recognized in the Dajishan area,the early NE-trend structural belt in the early Yanshanian,the late NE-trend structural belt in the late Yanshanian,and the NNW-trend structural belt in the Himalayanian,respectively.The early NE-trend structural belt controlled the formation of the interformational fractured zone which provides a prerequisite for the lateral migration of ore-bearing fluid.The late NE-trend structural belt controlled the formation and distribution of the NE-NEE transtensional fault,and provided space for the vertical migration of ore-bearing fluid and the emplacement of the Dajishan U-polymetallic deposit.The NNW-trend structural belt not only triggered the formation of the NNE-striking compressional fault,but also drove the migration of ore-bearing fluid.Based on reconstruction the history of the metallogenic tectonic evolution,it can be inferred that the deposit was formed under the conjunct control of the NE-NEE-striking transtensional fault and the interformational fractured zone.Moreover,combining shallow structure analysis and deep CSAMT geophysical exploration,a promising exploration prospecting is predicted at the deep and peripheral parts of the Dajishan U-polymetallic deposit.This model may be applicable to analogous settings elsewhere in the Southwest Guizhou and provide a new approach for U-polymetallic prospecting and exploration.