新疆萨尔托海石英菱镁岩相关的金矿床成矿流体特征及其对矿床成因的限定

Listwaenite is the mesothermal metasomatic product of ultramafic rocks in ophiolitic mélanges and associated with gold mineralization. As a new type of deposit discovered in ophiolites, the source of ore-forming fluid, metallogenic mechanism, and ore genesis of listwaenite-related gold deposits still need further study. This kind of gold deposit has been found in the Sartohay ophiolitic mélange of Xinjiang and is characterized by two kinds of orebodies, composing of gold-bearing mylonitized listwaenite and gold-bearing quartz vein. This project mainly focus on comparative study on ore-forming fluid of these two kinds of orebodies of listwaenite-related gold deposit in Sartohay, combining with study on C-H-O stable isotope of quartz and carbonates, in-situ S isotope of pyrite, and 40Ar-39Ar dating of mariposite and muscovite, to determine the sources and evolution of ore-forming fluid, and discuss the metallogenic mechanism and ore genesis. The correlation between gold mineralization and listwaenite, as well as shear zones will be further discussed. This project will contribute to deeply understand the listwaenite-related gold mineralization in Sartohay of Xinjiang. It will also improve the metallogenic theory and support prospection and exploration of this type gold deposit.

石英菱镁岩是蛇绿岩中超基性岩发生中温热液交代的产物，与金矿化关系密切。石英菱镁岩相关的金矿床是近年来在蛇绿岩中发现的重要矿床类型，其成矿流体来源、金成矿机制和矿床成因问题尚待深入研究。新疆萨尔托海蛇绿混杂岩带中广泛发育石英菱镁岩相关的金矿床，矿体为含金糜棱岩化石英菱镁岩和含金石英脉。本项目拟对萨尔托海石英菱镁岩相关金矿床中两种矿体的成矿流体特征进行对比研究，结合石英和碳酸盐矿物C-H-O稳定同位素、黄铁矿原位硫同位素以及铬/白云母40Ar-39Ar年代学分析，查明两种矿体的成矿流体来源及演化，探讨金的迁移形式及控制金沉淀的关键因素，进而限定矿床成因。通过成矿流体与形成石英菱镁岩的剪切带流体特征对比，进一步探讨金矿化与石英菱镁岩及剪切带之间的关联。本研究将有助于全面理解新疆萨尔托海石英菱镁岩相关的金成矿作用过程，也将为完善此类金矿床的成矿理论及找矿勘探提供科学依据。

石英菱镁岩相关的金矿床是近年来在蛇绿岩中发现的重要矿床类型，深入解析此类金矿床的成矿作用过程，对完善矿床成矿理论及指导找矿具有重要意义。本项目以新疆萨尔托海与石英菱镁岩相关的金矿床为研究对象，通过系统的岩石学、矿物学、同位素地球化学及年代学研究工作，对成矿条件和成矿时代做出限定，进而推测矿床成因及其与石英菱镁岩及剪切带的关系。主要成果包括：（1）查明含金糜棱岩化石英菱镁岩成矿（I阶段成矿）时的体系为较封闭的还原体系，而含金石英脉成矿（II阶段成矿）时体系相对氧化；（2）确定两阶段成矿的成矿流体来源均为变质水，成矿流体中的硫来源于地幔。成矿物质可能来自超基性岩围岩；（3）推测成矿流体中Au以Au(HS)2-络合物的形式迁移, 流体沸腾导致CO2逃逸，pH升高，Au溶解度降低是金沉淀的主要因素；（4）获得石英菱镁岩的成岩时代为~300Ma，并在280-277Ma发生剪切变形，金成矿时代不早于277Ma；（5）初步建立了成矿模式：剪切带演化过程中，石英菱镁岩通过韧性变形作用将超基性原岩中的成矿元素富集到变质热液中形成含矿流体，在韧脆性变形转换-脆性变形阶段，由于体系物理化学条件改变，Au沉淀成矿。该研究成果丰富了与石英菱镁岩相关金矿床的成矿理论，并在一定程度上指导了新疆萨尔托海地区此类金矿床的找矿勘探工作，具有一定的学术价值和实际应用价值。