西藏尼雄矽卡岩铁矿成矿流体演化与成矿作用机制

The Nixiong rich iron ore belt, located in the northern of Gangdese margin volcanic - magmatic arc, is an important part of Gangdise iron copper metallogenic belt. The Nixiong iron deposit, as the representative one of the skarn iron deposit, has a relatively low research degree. The ore bodies are mainly occurred in the contact zone, which are laid between the intrusive rock and the Dibucuo Formation of Permian; some are also located in the interlayer fracture zone of Dibucuo Formation. There are also a lot of skarn and retrograde alteration minerals in the contact zone of intrusive rock and country rock. The project intends Nixiong iron deposit as the research object, explore the relationship between ore-forming fluids evolution and skarn iron mineralization, which is also the inadequate of previous research. In order to achieve the research aim, mineralogy of skarn and retrograde alteration minerals as well as the fluid inclusions in which will be study detailed. Emerging techniques such as fluid inclusions SRXRF analysis and iron isotope and also conventional geochemical analysis will be used to accurately determine the origin and evolution of ore-forming fluids, and the source and evolution of mineralization metal elements. In this way, the relationship between evolution of ore-forming fluids and the capture, transport, precipitation, constraints of metal elements can be comprehended well. Above all, mineralization mechanism of Nixiong skarn iron deposit maybe explore clearly.

尼雄富铁矿带位于西藏冈底斯陆缘火山-岩浆弧北侧，隶属冈底斯铁铜多金属成矿带。尼雄铁矿是冈底斯碰撞前增生造山阶段矽卡岩铁成矿作用的典型代表。矿体主要产于侵入岩与二叠系敌不错组的接触带及敌不错组层间破碎带中，接触带发育大量的矽卡岩和退化蚀变矿物。项目针对前人在成矿流体演化与成矿作用关系方面的研究不足，拟通过对矽卡岩及退化蚀变矿物的成因矿物学及其中流体包裹体的研究，利用流体包裹体同步辐射X射线荧光技术和Fe同位素分析技术，结合传统地球化学分析方法，准确判断成矿流体来源、演化特征和成矿物质来源及其在流体中演化规律，分析流体演化对金属捕获、运移、沉淀富集的制约，探讨尼雄矽卡岩富铁床成矿作用机制。

项目通过对尼雄铁矿矽卡岩及退化蚀变矿物的成因矿物学及其中流体包裹体的研究和雄村铜金矿床成矿流体研究，分析流体演化对金属捕获、运移、沉淀富集的制约。提出尼雄铁矿是与花岗质岩浆有关的高温高盐度岩浆热液交代夕卡岩型铁矿床，成矿流体和矿质都是源自花岗质岩浆热液系统，认为矽卡岩成矿是温度、氧逸度、pH动态变化的过程。雄村矿床成矿流体是直接从岩浆熔体中出溶的具高温度、高氧化性的、高盐度的富含 Cu、Au、Mo、Fe等元素的岩浆流体，成矿元素在流体出溶和分离各相中的不均匀分配是成矿元素最终富集成矿的关键因素。通过对比白垩纪中北部拉萨地块和南部羌塘地块成矿事件的差异，提出控制中北部拉萨地块113±3Ma岩浆活动和Fe（-Cu）成矿事件受控于向南俯冲的班公湖-怒江洋壳在113Ma发生板片断离。