四川大梁子富锗铅锌矿床的控矿构造样式及成矿机制研究

大梁子富锗铅锌矿床位于扬子板块西南缘,是四川-云南-贵州(川滇黔)铅锌矿集区大型矿床之一,其矿石储量4.5 Mt,Pb+Zn平均品位10%~12%,矿体主要以筒状、脉状赋存于严格受断裂构造控制的富有机质破碎带“黑色破碎带”中,赋矿围岩为震旦系灯影组的白云岩。矿区断裂十分发育,主要发育NWW向断裂、NW向断裂和NE向断裂。通过详细分析各组断裂的几何学和运动学特征,厘清了成矿前、成矿期和成矿后断裂活动特征及构造动力学特征。成矿前,该矿区受近N-S向挤压应力作用,形成NWW向逆断层;成矿期,受古特提斯洋的俯冲消减和碰撞造山作用,研究区构造应力场转变为NW-SE向挤压应力,形成矿区的NWW向张扭性断层、NW向扭张性断层和NE向逆断层;成矿后,区域构造应力场转变为近EW向,形成NWW向、NW向和NE向的破矿断裂。NWW向断裂是矿区的主控断裂,是流体运移的通道;NW向断裂是NWW向断层的主要配套断裂,是流体混合和矿体就位的空间,NWW向断裂和NW向断裂组成的负花状构造是大梁子富锗铅锌矿床最具特色的控矿构造样式。来自深部的富金属离子的流体与来自寒武系富有机质地层的还原型流体在NWW向断裂和NW向断裂控制的张裂空间的混合,是该床的主要成矿机制。矿区南部和西部类似的构造样式区是下一步找矿的方向。

Structural control and metallogenic mechanism of the Daliangzi Ge-rich Pb-Zn deposit in Sichuan Province,China

The Daliangzi large Ge-rich Pb-Zn deposit is located in the Sichuan-Yunnan-Guizhou (Chuan-Dian-Qian) Pb-Zn metallogenic belt on the western margin of the Yangtze block. It contains 4.5 million tons of ores, 10%-12% of which are Pb-Zn ores. The pipe- and vein-like Pb-Zn ore bodies are hosted in well developed fault-controlled black breccia zones that cut through the ore-hosting dolostone of the Sinian Dengying Formation. The NWW-, NW- and NE-trending faults are well developed in the mining area, and their activity and tectonic dynamics are clearly defined through detailed analysis of the geometric and kinematic features of these faults. The NWW-striking thrust faults were formed by N-S compressive stress prior to mineralization. During the ore-forming process, due to the subduction of the Paleo-Tethys Ocean and the late Indosinian orogeny, the regional tectonic stress field was transformed into NW-SE compressive stress, and then the NWW-trending tensional and torsional faults, NW-trending tensional faults and NE-trending reverse faults were formed in the sutdy area. After mineralization, the regional tectonic stress field changed to near E-W direction, causing the formation of the NWW-, NW- and NE-trending faults that cut through and/or dislocated the ore bodies. The NWW-trending faults are the major ore-controlling faults, possibly acting as the migration pathway for the ore-bearing fluid. The NW-trending faults are the secondary main faults in the mining area, where hydrothermal fluid mixing and orebody emplacement took place. The distinct ore-controlling structure in the Daliangzi Ge-rich Pb-Zn deposit is the negative flower structure consists of the NWW- and NW-trending faults. The main metallogenic mechanism of this deposit is the mixing of two fluids-the mineral-rich deep fluid and the reduced fluid from the Cambrian organic-rich strata-under tensional stress from the NWW- and NW-trending faults. Areas with similar tectonic patterns, such as the southern and western mining area, are the next prospecting target.