Microfabric Characteristics of Cherts of Bafangshan-Erlihe Pb-Zn Ore Field in the Western Qinling Orogen
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摘要:
硅质岩是造山带内广泛发育的一类岩石, 该岩石的组成以SiO2为主, 具有较高的稳定性.对于经历过造山作用、成矿作用和重结晶作用等影响的硅质岩, 其宏观组构和微观组构特征可以很好地反映它所遭受到的改造.秦岭造山带西段八方山-二里河Pb-Zn矿的宏观及微观组构特征分析表明: 该区硅质岩具有明显的热水沉积特征.由于受到压扭性和张性两种性质的应力作用, 矿区在宏观上形成了东西向压扭性断裂和北北东、北北西两组张性断裂, 微观上形成了微裂隙、微褶皱和压扁拉长的石英颗粒.矿区岩石发生了明显的变质作用, 除应力作用造成的动力变质作用外, 还发生了其他类型的变质作用和重结晶作用.硅质岩中微量碳酸岩矿物的存在以及应力作用对矿床的形成具有非常重要的意义, 特别是其可以为金属硫化物热液提供运移的通道和沉淀成矿的空间.
Abstract:With high stability, chert is widely distributed in the orogens, whose major composition is SiO2.Affected by the orogeny, metallogenesis and recrystallization, the metamorphic processes can be well revealed by the megatectonics and microfabric characteristics.The study of the megatectonics and microfabric characteristics of the cherts of Bafangshan-Erlihe Pb-Zn ore field in the western Qinling orogen reveals that there are obvious hydrothermal sedimentary characteristics in the cherts.Because of the stresses, two types of which are extensional and compresso-shear, there are megatectonics of compresso-shear faults with EW direction and gapping faults with NNE and NNW directions.What's more, there are microfabric characteristics of microcracks and microcorrugations and stretched-out grains of quartzs.In the rocks of this ore deposit field, the dynamic metamorphism, metamorphic recrystallization and other kinds of metamorphisms are clearly revealed.The trace carbonate minerals and the stress are both important to the metallogenesis of this ore deposit, which provide the pathway and space for the metallic sulphide fluids to travel and deposit.
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Key words:
- western Qinling /
- Pb-Zn ore /
- fabric analysis /
- metallogenesis /
- hydrothermal sedimentation
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图 1 八方山-二里河Pb-Zn矿矿床地质图(底图据田民民等, 2004修改)
F1. 商州-丹凤断裂; F2. 礼县-山阳断裂; F3. 临潭-镇安断裂; F4. 略阳-玛曲断裂; Fa. 压扭性断层; Fb. 张性横断层; Fc. 张性纵断层; D3x3. 砂质千枚岩; D3x2. 绿泥石千枚岩; D3x1. 铁白云石-炭质千枚岩; D2g2. 灰岩; δμ. 闪长玢岩
Fig. 1. Geological map of the Bafangshan-Erlihe Pb-Zn deposit
图 2 显微镜微下硅质岩的微裂隙(a)和微褶皱(b)
Fig. 2. Micrographs of the fissure (a) and cataclase crystal (b) in cherts_x10
图 4 含矿岩石的显微图片及拉曼定向分析结果(A→J)
Fig. 4. Micrographs and Raman shift for mine-bearing rocks
图 7 硅质岩的SEM图像
M_C.碳酸盐; M_Q.石英; M_S.硫化物; M_S(Pyr).黄铁矿
Fig. 7. SEM of metallic and carbonate minerals in cherts
图 8 硅质岩中碳酸盐矿物颗粒附近的金属硫化物分布形式
a.环状分布; b, 零星状和裂隙充填分布; c.裂隙充填分布; P.能谱测试点位
Fig. 8. Distribution of the metallic sulphide near the carbonate minerals in cherts
表 1 曲线上不同点位特征拉曼峰强度比值
Table 1. Ratio values of the characteristic peak intensity
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