ISSN 1009-6248CN 61-1149/P 双月刊

主管单位：中国地质调查局

主办单位：中国地质调查局西安地质调查中心
中国地质学会

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    西秦岭金山金矿床成矿机制：来自毒砂和绿泥石地球化学特征的证据

    Metallogenic Mechanism of Jinshan Gold Deposit in West Qinling Orogenic Belt: Evidence from Geochemical Characteristics of Arsenopyrite and Chlorite

      摘要
    • 摘要:
      目的 毒砂（Apy）和绿泥石（Chl）是热液型金矿床中常见的金属硫化物及蚀变矿物，已被广泛应用于金矿成矿物理化学条件的反演之中。甘肃金山金矿位于西秦岭成矿带夏河–西和–凤县–黄柏塬成矿亚带，成矿条件优越，以发育多阶段的Apy及Chl为特征。
      方法 笔者以金山金矿床矿石样品中各类Apy及Chl为研究对象，在金山金矿3个成矿阶段的划分基础上，利用电子探针测定各阶段Apy（Apy-II~III）及Chl（Chl-I~III）的主量元素组成，并据此划分Chl-I~III的化学类型，计算Chl-I~III及Apy-II~III的形成温度、氧逸度（lgfO2）、硫逸度（lgfS2）及PH值，进而分析对比各阶段Apy及Chl形成环境及物化条件，探讨金山金矿床的金成矿机制。
      结果和结论 结果表明，成岩–浅变质期Chl-I具有低温、低lgfO2和低lgfS2的特征，热液成矿期Chl-II及Apy-II温度、lgfO2、lgfS2及PH值相较I阶段显著升高，表明II阶段存在大量CO2等酸性组分流失，推测热液成矿期存在强烈的流体混合及沸腾作用发生。随后在热液成矿期II~III阶段，沸腾作用致使温度、压力及流体中的S含量明显降低，促进Au以自然金形式大规模沉淀，并在低硫逸度及中性PH值的条件下以Au-As类质同象于毒砂中形成大量的不可见金。

       

      Abstract:
      Objective‌ Arsenopyrite (Apy) and chlorite (Chl) are abundant sulfide or altered minerals in hydrothermal gold deposits, which been widely used in the inversion of the physical chemical conditions of gold mineralization. The Jinshan gold deposit in Gansu Province is located in the Xiahe-Xihe-Fengxian-Huangbaiyuan metallogenic sub-belt in the eastern section of the West Qinling metallogenic belt, with superior mineralization conditions, characterized by the development of multiple generations of arsenopyrite and chlorite.
      Methods In this study we take the various types of arsenopyrite and chlorite in ore samples from the Jinshan gold deposit as the research object. Based on the division of the three mineralization stages in Jinshan Gold deposit, using electron probes to determine the major elemental composition of Apy (Apy II~III) and Chl (Chl I~III) at each stage, dividing the chemical types of Chl I~III, calculating the formation temperature, oxygen fugacity (lgfO2), sulfur fugacity (lgfS2), and pH value of Chl I~III and Apy II~III. Furthermore, analyzing the formation environment and physicochemical conditions of Apy and Chl at each stage, and exploring the gold mineralization mechanism of the Jinshan gold deposit.
      Results and Conclusion The results indicate that the diagenetic shallow metamorphic stage of Chl-I exhibits characteristics of low temperature, low lgfO2, and low lgfS2. During the hydrothermal mineralization stage, the temperature, lgfO2, lgfS2, and pH values of Chl-II and Apy II significantly increased compared to stage I, indicating the loss of a large amounts of acidic components such as CO2 in Stage II, it is speculated that there was strong fluid mixing and boiling during the hydrothermal mineralization stage. Subsequently, during the hydrothermal mineralization stages II-III, boiling causes a significant decrease in temperature, pressure, and S content in the fluid, promoting large-scale precipitation of Au in the form of natural gold, thereby promoting the large-scale precipitation of Au in the form of natural gold. Meanwhile, under low sulfur fugacity and neutral pH value conditions, a large amount of invisible gold was formed in arsenopyrite as Au-As like substances.

       

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