变质地体内金矿脉和银铅锌矿脉的成因与联系：以熊耳山地区蒿坪沟Au-Ag-Pb-Zn矿床为例

Gold veins and silver-lead-zinc veins hosted in high-grade metamorphic terranes are among the important sources of gold and silver in the world. However, the two types rarely occur in the same district; and whether they formed in the same process and are genetically related remains not well understood. The Haopinggou Au-Ag-Pb-Zn polymetallic deposit in the Xiongershan district, southern North China Craton, is unique in that both gold and silver-lead-zinc veins are well developed, providing an ideal opportunity to conduct a comparative study on the formation and genesis of these veins. In this proposal, a systematic mineralogical, geochemical and geochronological study will be carried out to better understand the composition, nature, and evolution of the gold and silver-lead-zinc veins of the Haopinggou deposit. Based on field investigation, ore petrography and fluid inclusion microthermometry will be conducted to constrain the compositions and properties of the ore fluids responsible for the gold and silver-lead-zinc veins. The association and distribution of trace elements in sulfide minerals from the two types of veins will be investigated by using laser ablation ICP-MS analysis. Lastly, Re-Os and Rb-Sr isotopic dating of sulfides are used to provide constraints on the formation ages of the gold and silver-lead-zinc veins. These new data combined with the regional geological data and previous geochemical and geochronological constrains will be used to discuss the genesis of the gold and silver-lead-zinc veins and their possible genetic relationships, aiming to build a geologically reasonable metallogenic models for the Haopinggou Au-Ag-Pb-Zn deposit. The proposed study not only shed significant insights into the formation mechanisms of the gold and silver-lead-zinc veins hosted in metamorphic terranes and a possible genetic link between the two, but also provide useful guide to mineral exploration for gold and silver-lead-zinc deposits in the southern North China craton.

位于华北克拉通南缘熊耳山地区的蒿坪沟Au-Ag-Pb-Zn矿床是世界上少有的同时发育金矿脉和银铅锌矿脉的多金属矿床，为开展变质地体内金矿脉和银铅锌矿脉成矿机制的对比研究及探讨二者之间可能存在的成因联系提供了极佳的条件。本项目拟对蒿坪沟矿床的金矿脉和银铅锌矿脉开展详细的野外地质调查和系统的矿相学和流体包裹体研究，对主要矿石矿物黄铁矿和闪锌矿的化学组成进行微区原位分析和Re-Os及Rb-Sr等时线定年，以揭示金矿脉和银铅锌矿脉的成矿流体组成和性质，查明两种矿脉硫化物中微量元素的组成和分布，准确限定金矿脉和银铅锌矿脉的形成时代。结合区域地质资料和前人研究成果深入讨论金矿脉和银铅锌矿脉的形成机制及二者之间可能存在的联系，建立正确合理的成矿模式。预期研究成果不仅有助于深刻理解变质地体内脉状金矿床和银铅锌矿床的成矿机制及相互关系，而且对华北克拉通南缘脉状金矿床和银铅锌矿床的找矿预测工作具有指导意义。

世界上古老变质地体内常发育金矿脉和银铅锌矿脉，但这两种矿脉之间的关系研究仍比较薄弱。蒿坪沟矿床位于华北克拉通南缘晚太古代-早元古代太华群变质岩内，由大量NNE向发育的金矿脉和银铅锌矿脉所构成，是研究变质地体内脉状金矿化和银铅锌矿化成因和关系的理想对象。本项目以蒿坪沟矿床金矿脉和银铅锌矿脉为研究对象，基于黄铁矿微观结构和微量元素分析探讨金和银的赋存状态和富集机理，通过黄铁矿和方铅矿原位铅同位素分析揭示金矿脉和银铅锌矿脉的物质来源，结合已有数据探讨金矿脉和银铅锌矿脉的成因和联系。野外地质观察显示，金矿脉通常被银铅锌矿脉所充填或切割，指示金矿脉成矿时间较早。金矿脉和银铅锌矿脉均有三个世代的黄铁矿被识别出（Py1-Py3，Py4-Py6），其中金矿脉内黄铁矿富集元素Au, As, Co, Ni和Bi，而银铅锌矿脉内相对富集元素Ag, Pb, Zn, Sn和Sb。金矿脉内Py2和Py3含有大量的不可见晶格金，并且Au的含量与As关系密切。自然金等金矿物主要出现在Py3及同期矿物内，推测是由先期赋存在黄铁矿内的晶格金受塑性构造变形影响再次活化并富集而来。这一认识得到金矿脉内黄铁矿颗粒EBSD分析结果的证实。银铅锌矿脉内不可见Ag主要同Sb一起富集在方铅矿的晶格内。银铅锌矿脉内同时发育有种类多样的含银矿物，这些银矿物可能由黝铜矿和方铅矿的Ag-Cu交换反应或随着温度下降直接从方铅矿中出溶出来。金矿脉和银铅锌矿脉内硫化物的原位铅同位素组成存在较大差异，指示二者有不同的成矿物质来源。其中银铅锌矿脉内硫化物铅同位素组成与矿床附近的花岗斑岩体内钾长石铅同位素组成较为一致，暗示二者可能有成因关系。综合以上研究及前人年代学数据，认为蒿坪沟矿床金矿脉和银铅锌矿脉形成于两期相互独立的成矿事件，其中银铅锌矿脉与早白垩世岩浆活动有关，而金矿脉可能形成于三叠纪区域碰撞造山过程中。在此基础上建立了蒿坪沟矿床成矿模式，该模式对华北克拉通南缘脉状金矿床和银铅锌矿床的找矿预测工作具有一定指导意义。