玛曲格尔珂金矿田旋涡状构造及其控矿作用

Whirl structure and constraint on the mineralization in Ge'erke gold orefield,Maqu,northern Qinghai-Tibet Plateau

玛曲格尔珂金矿田位于青藏高原北东部,主要包括大水、格尔托和贡北三个金矿床,成矿作用受印支-燕山期构造活动的控制。本项研究识别出区内存在的旋涡状构造,它与金矿田的成矿作用关系密切,二者的规模与分布范围吻合,直径达4500m左右。中心部大理岩化白云岩和深部可能存在的隐伏岩体,构成旋涡状构造的砥柱。旋涡状构造包括6个放射状弧形旋回层,其中南部4个旋回层的的旋扭面(弧形断裂)凸向W-NW,属于张性结构面;北部2个旋回层的旋扭面凸向NE,为压性断裂,从而可认为旋涡状构造是由2个性质不同的旋扭构造所构成。在ETM遥感影像图和地形图上,旋涡状构造清晰可见,地势较高,桔黄色旋回层正地形与深蓝色负地形带相间,砥柱区高峰4000m,相对高差500m。旋回层内的石英闪长岩脉产状与旋扭面一致。贡北、大水和格尔珂金矿床分别位于旋涡状构造编号为1,4和6的NW向旋回层、NE向旋回层和SE向旋回层,这3个旋回层宽度较大,平面上构成了旋涡构造的主体。旋涡状构造的张性结构面成为容矿构造,所以,具张性旋扭特征的南部旋回层,其旋扭面是主要的容矿构造;而具压性特点的北部旋回层,容矿构造与旋扭面相交。依据旋涡状构造的控矿特性,预测区内其它旋回层的扩容区或张性结构面具有较好的找矿远景。

Ge'erke gold orefield,Maqu County,is located in northern Qinghai-Tibet Plateau and includes Dashui district,Ge'ertuo district and Gongbei district with structural control on the mineralization in Indosinian-Yanshanian epoch. This work identified a whirl structure,about 4500m in diameter,that was closely related to the mineralization in the orefield,and both of them have coincident scale and distribution. The nuclear column of the whirl structure is consisted of marbleized dolomite and concealed rock body. There are 6 radial arc cyclothems in the whirl structure,of which the vertical surfaces (arc fracture) of 4 cyclothems at south are convex to W-NW and belong to tensional structural planes,and the vertical surfaces of 2 cyclothems at north are convex to NE and belong to compressional planes. They are two rotation-shear structures with different features that compose the whirl structure. The whirl structure is clearly visible in the ETM remote sensing image and terrain maps,orange positive-landform cyclothem surfaces alternate with dark blue negative-landform zone; apex of the vertical column area is about 4000m,relative elevation difference is 500m. A lot of quartz diorite veins occurred in the vertical surfaces. Gongbei district,Dashui district and Ge'ertuo district are respectively located at No. 1,4 and 6 cyclothems,i.e. at NW,NE and SE trend cyclothems that have larger scales. It is the tensional structure planes of the cyclothems that became ore-host structures. Therefore,the rotation-shear planes are main host structures in southern tensional cyclothems and the ore-host structures intersect with rotation-shear planes in northern compressional cyclothems. According to the ore-controlling characteristics of the whirl structure,we suggest to pay more attentions to the tensional structure planes of all cyclothems to find new ore deposits in this region.