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粤北曲仁盆地北缘铅锌硫化物矿床黄铁矿成因矿物学特征研究

Mineralogical characteristics of pyrite genesis in Pb−Zn sulfide deposits on northern margin of Quren Basin, northern Guangdong

  • 摘要: 曲仁盆地北缘赋存了2类硫化物矿床,一类是以西岗寨、罗村、羊角山为代表的黄铁矿矿床;另一类是以凡口和杨柳塘为代表的黄铁铅锌矿床,它们之间的成因联系与差别一直引人关注。通过光学显微镜、扫描电镜、X射线衍射、单矿物化学成分、电子探针和硫同位素等手段对曲仁盆地北缘的罗村、杨柳塘和凡口3个代表性矿床不同世代的黄铁矿进行成因矿物学特征研究。结果表明:代表性矿床中热液黄铁矿可分为3个世代,其中黄铁矿矿床中的第一世代黄铁矿(Py1)、第二世代黄铁矿(Py2)环状结构不发育,富S亏Fe,低As、Co,硫源单一;而黄铁铅锌矿床中的第一世代黄铁矿(Py1)成因标型特征与黄铁矿矿床第一世代黄铁矿(Py1)相似,第二世代黄铁矿(Py2)环状结构发育,富Fe亏S,高As、Co,硫源具多源特征,第三世代黄铁矿(Py3)晶粒细小,富S亏Fe,高As、Co,硫源具有多源特征;这些特征表明,黄铁矿矿床的成矿过程比较单一,而黄铁铅锌矿床成矿过程比较复杂,为多期次成矿过程的叠加、改造而成。由此可见,曲仁盆地北缘铅锌硫化物矿床为具有多成矿物质来源、多成矿物理化学条件和多控矿因素组合的典型多因复成铅锌硫化物成矿系统。多世代矿物成因标型特征的研究,可以作为一种厘定多因复成矿床类型及查明其成因机制的有效工具。

     

    Abstract: Two types of sulfide deposits occur on the northern margin of the Quren Basin: one type is pyrite deposits represented by Xigangzhai, Luocun, and Yangjiaoshan; the other is pyrite-Pb−Zn deposits represented by Fankou and Yangliutang. The genetic relationship and differences between these two types have long attracted attention. In this study, the genetic mineralogical characteristics of different generations of pyrite from 3 representative deposits (Luocun, Yangliutang, and Fankou) on the northern margin of the Quren Basin were investigated by means of optical microscopy, scanning electron microscopy, X-ray diffraction, monomineralic chemical composition analysis, electron microprobe analysis (EPMA), and sulfur isotope analysis. The results show that hydrothermal pyrite in the representative deposits can be divided into 3 generations. In the pyrite deposits, the first-generation pyrite (Py1) and second-generation pyrite (Py2) are characterized by nondevelopment of annular structures, S enrichment, Fe depletion, low As and Co content, and a single sulfur source. As for the pyrite-Pb−Zn deposits, the Py1 exhibits genetic typomorphic characteristics similar to those of Py1 in the pyrite deposits. The Py2 is characterized by developed annular structures, Fe enrichment, S depletion, high As and Co content, and multiple sulfur sources. The third-generation pyrite (Py3) is characterized by fine grains, S enrichment, Fe depletion, high As and Co content, and multiple sulfur sources. These characteristics indicate that the mineralization process of the pyrite deposits is relatively simple, whereas that of the pyrite-Pb−Zn deposits is complex, resulting from superposition and transformation by multiphase and multistage mineralization. It is thus concluded that the Pb−Zn sulfide deposits on the northern margin of the Quren Basin constitute a typical polygenetic composite Pb−Zn sulfide metallogenic system with multiple sources of ore-forming materials, multiple physicochemical conditions of mineralization, and multiple ore-controlling factors. The study of genetic typomorphic characteristics of multi-generation minerals can serve as an effective tool for determining the types of polygenetic composite deposits and elucidating their genetic mechanisms.

     

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