Characteristics and formation mechanism of the veins in Mengxi porphyry Cu-Mo deposit, eastern Junggar, Xinjiang, China.
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摘要: 蒙西斑岩铜钼矿床位于东准噶尔伊吾县琼河坝花岗岩北侧,以发育细脉、网脉状矿化为特征。脉体类型多样,包括石英脉、石英硫化物脉和硫化物脉等。根据脉体力学成因机制,其又可划分为水压破裂充填脉和构造破裂充填脉。构造破裂充填脉体按破裂形成的位错特征有正断与逆断两种。地表石英脉产状陡立,明显受断裂控制。脉体体积分数统计结果显示流体富集区呈向北缓倾的带状分布于深100~400m范围内,并与矿化富集带有较好的对应关系。脉体富集带内,脉体以共轭形式存在,一组为倾角较小的逆断破裂充填脉,另一组为倾角较大的正断破裂充填脉,他们可能为缓倾逆冲剪切带的次级破裂与充填脉,即富矿带内脉体是沿矿区低角度逆冲断裂次级破裂面充填的。矿区地表及深部(400m以下)脉体以陡立为主,矿化较弱。矿区流体的运移具先沿水压直立破裂往上运移,进入剪切带后沿剪切带次级破裂侧向和向上运移,并在剪切带中富集成矿。低温矿物组合脉体穿切高温矿物组合脉体的特征说明脉体形成过程矿区处于隆升构造环境,这对斑岩铜矿成矿有利。Abstract: The Mengxi porphyry Cu-Mo deposit located north of the Qiongheba granite in the Yiwu County, eastern Junggar, was characterized by the abundance of various ore-bearing veins and veinlets, such as quartz vein, quartz-sulfide vein and sulfide vein. On the basis of formation mechanics, veins can be classified into two types: Hydrofracture-filled vein and tectonic fracture-filled vein. According to dislocation along tectonic fractures, sliding fracture and thrusting fracture were recognized. The exposed veins were mainly quartz veins with big dip angles, and their distribution were controlled by faults. Statistic result of volume fraction of veins in three drill holes of the line 14 show that the ore-bearing fluid were concentrated along a low north-dipping zone in a depth between 100m and 400m, which was corresponded to the location of ore-bodies. In this fluid concentrated zone, veins and their corresponding fractures were conjugate, thrusting fracture with small dip angle plus sliding fracture with big dip angle. These conjugate fractures were interpreted as second-order fractures of a thrusting shear zone. This indicated that the ore-bearing fluids were filled along these second-order fractures. Veins in shallow (400m in depth) had big dip angles and were characterized by low Cu-content. It was suggested that ore-forming fluids in the Mengxi porphyry Cu-Mo deposit possibly migrated upwards through hydrofracture in deep, and flowed laterally and upwards along the second-order fractures within the shear zone where sulfide precipitated to form orebody. Evidence that some veins containing minerals formed at relative higher temperature were cut by those formed at relative lower temperature suggested that it was possibly in uplifting setting when these veins were formed.
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