青海南部东莫扎抓矿区挤压断层带结构及其对铅锌成矿的控制

Internal structure of fault zone and its control on mineralization: A case study of Dongmozhazhua Pb_Zn deposit, southern Qinghai Province

大量逆断层控矿的实例表明挤压断层带具有较大含矿潜力,但挤压环境下矿质运移沉淀的过程尚不清楚。文章从断层带结构解剖入手,以东莫扎抓铅锌矿床为例,研究挤压断层带对成矿的控制。控矿断层可分为碎裂化带、浑圆角砾带和扁长角砾带3部分,其中碎裂化带内灰岩角砾中含有细脉状矿化,浑圆角砾带无矿化,扁长角砾带的角砾内部发育不规则脉状矿化,角砾间有浸染状、角砾状、团块状矿化。矿脉形态及与围岩接触关系表明成矿受断裂控制,矿质充填与灰岩破裂基本同时发生。分析认为,断层带经历了两个阶段的生长过程,成矿流体在第二次挤压的早期阶段贯入,挤压过程中的碎裂化和压溶作用为矿质运移和沉淀提供了重要保障。

Numerous deposits are controlled by compression faults, but the ore-bearing fluid flow and precipitation process in compression setting is not clear. In this paper, the internal structure of the fault zone was studied for the case of compression fault zones affecting lead-zinc mineralization in the Dongmozhazhua deposit, which is sit- uated in central Tibet, approximately 100 km southwest of Yushu. Outcrop mapping shows that fault zones are composed of different fault-related breccias. They include predominantly matrix supported by angular and round- ed clasts in fault core （fault core I ） and clast supported by angular clasts in damage zone. The transition type is developed between the above breccias and consists of lenticular breccias with little fault gouge （fault core II ）. Matrix in fault core I consists usually of calcite veins and calcareous gouge. Mineralization at Dongmozhazhua occurs as veinlets in breccias and disseminations between breccias. The ore vein contains calcite and primary sul- fides （sphalerite, galena, pyrite, etc. ） , and their texture suggests that they are controlled by the fault zone. Some veins are asymptotic with and linked into the vein core, creating large rhombic fragments of limestone. These observations suggest that limestone fragments were generated in the vein formation process. A two-stage evolution model of fault zone was built, and ore-bearing hydrothermal fluid was concentrated at the incipient stage during second compression stress. Cataclastic action and pressure solution were important {or flow and pre- cipitation of ore-bearing fluid in compression setting.