江西银坑铅锌银矿田基底褶皱构造特征与南北向矿化带研究

Research on the characteristics of basement fold structure and SN-trending mineralization zone in the Yinkeng lead-zinc-silver orefield in Jiangxi

为了探究银坑铅锌银多金属矿田的构造特征和找矿潜力,选取区内基底复式褶皱作为研究区,开展野外调查和室内分析。揭示基底褶皱几何学和应力场特征并探讨对成矿的控制作用,重点研究褶皱作用晚期纵张断裂中的SN向交代充填石英矿脉的成矿特征。通过实测褶皱轴迹与两翼产状,分析其几何形态特征为:枢纽走向由北至南为NE→NNE→SN→NNW,翼间角范围为33°~52°,褶皱类型为紧闭陡立尖棱状褶皱。通过褶皱分析法与节理统计法,求得基底褶皱自加里东期至燕山期主应力方向变化为EW→NWW→NNW→NEE。基底地层早期受EW向挤压而形成SN向构造带与大量的SN向褶劈理带。应力场转换期间地层受到的应力由挤压向拉张转换,促进褶劈理带内形成SN向纵张裂隙,为后期NE向矿化提供空间。通过实测与观察,基底褶皱首次发现近SN向矿化石英矿脉充填于褶皱作用晚期的切层纵张和次级横张裂隙。含矿性分析显示,脉中铅、锌平均含量为0.133%和0.190%,金、银的平均含量0.127 g/t和15.33 g/t,具有较高的矿化特征。在桥子坑矿区地表和牛形坝矿区60、104和140中段新发现12条SN向矿脉,表明该区有巨大的成矿潜力。

In order to explore the structural characteristics and prospecting potential of the Yinkeng lead-zinc-silver polymetallic orefield,the authors selected the basement folds in this area as the research area to conduct field investigation and indoor analysis and reveal the basement fold geometry and stress field characteristics.The focus was on the mineralization characteristics of SN-trending metasomatic filling quartz veins,which are developed in the longitudinal tension faults formed in the late stage of folding.Through the actual measurement of the fold axis trace and the attitudes of the two wings,the geometric characteristics were summarized as follows:the direction of the hub is NE→NNE→SN→NNW from north to south,the angle between wings ranges from 33°to 52°,and the fold type is the closed,steep and sharp prismatic fold.Through the fold analysis method and the joint statistical method,the principal stress directions of the basement folds from the Caledonian to the Yanshanian were EW→NWW→NNW→NEE.The basement strata were squeezed in the EW direction in the early stage to form an SN-trending structural belt and a large number of SN-trending fold cleavage belts.During the transition of the stress field,the stress on the formation changed from compression to tension,which promoted the formation of SN-trending longitudinal fractures in the fold cleavage zone,and provided space for later NS-trending mineralization.Through actual measurement and observation,it is the first time to discover mineralized quartz veins in nearly SN direction in the basement fold.This quartz vein filled the longitudinal and secondary transverse tension fractures in the section at the late stage of folding.Mineralization analysis shows that the quartz vein has high mineralization characteristics.The average values of lead and zinc in mineralized quartz veins are 0.133%and 0.190%,and the average values of gold and silver are 0.127 g/t and 15.33 g/t.Twelve new SN-trending veins were discovered on the surface of the Qiaozikeng mining area and the 60,104,and 140 level of the Niuxingba mining area,indicating that this area has huge metallogenic potential.