小秦岭NNE向金矿脉构造变形特征与成矿关系

小秦岭金矿田位于华北克拉通南缘的华熊地块北缘,发育有产出于不同走向剪切带内的金矿脉。但是,目前研究和认识对矿脉和剪切带、以及不同方向矿脉之间的构造关系并不清晰。选择小秦岭中部善车峪一带的典型NNE向矿脉开展构造变形与矿化特征研究。结果表明:NNE向金矿脉以右阶排列的石英脉透镜体为特征,主体产状为120°∠70°; 矿脉产出于与之近平行的左行逆冲剪切带内,并改造了早期近EW向剪切带,其所处构造应力场环境为近EW向水平伸展; 矿体的主要矿石矿物为方铅矿、黄铁矿、闪锌矿等多金属硫化物,这些金属矿物多呈条带状或条纹状沿剪切面理或小角度斜交的张剪性面理贯入,显示与左行逆冲变形同期形成的特征。构造变形序列和矿化特征对比分析显示,小秦岭地区NNE向矿脉叠加改造了近EW向矿脉,其构造应力场环境分别与早白垩世和晚三叠世区域应力场特征一致。前人对于岩浆作用、成矿流体和成矿时代等方面的研究结果认为,小秦岭地区经历了印支期和燕山期两期构造与成矿作用的叠加,从而推测NNE向金矿脉应形成于燕山期陆内构造变形阶段,而近EW向矿脉可能形成于印支期华北板块和扬子板块碰撞拼贴阶段。

Structural Deformation and Mineralization of NNE-striking Gold-bearing Veins in Xiaoqinling Area,Central China

The Xiaoqinling gold orefield is located on the northern margin of Huaxiong block in the southern margin of North China Craton. There are some gold-bearing veins occurring in the shear deformation belts with different strikes. The structural relationships between the gold-bearing veins and shear deformation belts, as well as the veins with different strikes, are still poorly understood. Structural deformation and mineralization characteristics of the NNE-striking vein, which is located at Shancheyu area in the central of Xiaoqinling area, were analyzed. The results show that the NNE-striking veins, which mainly trend to 120° with dip of 70°, are characterized by lenticular quartz veins with a right-stepping echelon arrangement. The vein occurs in a nearly parallel sinistral thrust shear belt and superimposes on an earlier nearly EW shear belt, where the stress field is nearly EW horizontal extension. The main ore minerals contain the galena, pyrite, sphalerite and other polymetallic sulfide, which are banded and striped intruded along the shear or transtensional foliation with small angle to the shear foliation, and are also concurrent with the sinistral thrust deformation. Comparative analysis of deformation sequence and mineralization characteristics reveals that the NNE-striking veins superimpose on the nearly EW-striking veins in Xiaoqinling area, and the tectonic stress field corresponds to the Early Cretaceous and Late Triassic, respectively. Previous studies on magmatism, ore-bearing fluid and mineralization age indicate that the superimposition of tectonic and metallogenic processes are developed in Indosinian and Yanshanian in Xiaoqinling area, it is indicated that the NNE-striking veins should have been formed in Yanshanian intracontinental deformation stage, while the nearly EW-striking veins might have been formed in Indosinian continental collision between North China and Yangtze plates.