辽宁鞍本地区BIF型磁铁矿富矿成矿流体来源与铁质富集机制

辽宁鞍本地区是世界上规模最大、最具代表性的BIF型磁铁矿富矿成矿区，发育“弓长岭式”和“齐大山式”两类规模和蚀变类型不同的磁铁矿富矿，它们都是流体改造BIF导致铁质富集的产物，但成矿流体来源和铁质富集机制存在争议。本申请以这两类磁铁矿富矿为研究对象：采用光薄片下原位高精度测年方法，厘定与磁铁矿共生的独居石和磷钇矿形成年龄，约束成矿时代，查明成矿流体的产生与区域地质事件的联系；在矿物结构分析基础上，应用原位分析技术测定磁铁矿富矿石和BIF中石英氧同位素组成并进行对比，结合矿化蚀变地球化学研究，揭示成矿流体来源和性质；利用成矿流体中元素活动性的差异，通过相同剖面上BIF和磁铁矿富矿石的化学成分对比，查明铁质超常富集形成大规模磁铁矿富矿的机制。综合对比两类磁铁矿富矿在成矿条件上的差异，探讨形成大规模磁铁矿富矿的关键控矿要素，丰富BIF型富铁矿成矿理论，为BIF型磁铁矿富矿深部找矿提供科学依据。

The Anshan-Benxi area in Liaoning Province is the largest and most representative cluster of BIF-hosted high-grade magnetite ore deposits in the world, and hosts two types of deposits with different sizes and alteration features, namely the Gongchangling and the Qidashan type. Both of the two types have been interpreted as replacement products of BIF protore by epigenetic hydrothermal fluid, but the source of ore-forming fluid and mechanism of iron enrichment remain contentious. In-situ ion microprobe U-Pb geochronology on monazite and xenotime intimately intergrown with magnetite will be performed to determine the age of the Qidashan-type high-grade magnetite mineralization, and then to link the generation of ore-forming fluid with specific regional tectonic event. On the basis of mineral texture examination, in-situ analysis technology will be carried out to determine and compare the oxygen isotope values of quartz from the high-grade magnetite ore and BIF, and then to constrain the source and nature of the ore-forming fluid in combination with alteration geochemistry. According to the differences of element activity in the ore-forming fluid, a detailed geochemical comparison between the BIF and high-grade magnetite ore in the same profile will be carried out, in an order to reveal whether desilicification or iron activation-reprecipitation acted as the leading mechanism for the high-grade magnetite mineralization. A comprehensive comparison of the ore-forming conditions between the Gongchangling- and Qidashan-type high-grade magnetite mineralization will be conducted to discuss the metallogenic factors for the formation of large-scale high-grade magnetite ores. This application will not only provide important constraints to the metallogenesis of BIF-hosted high-grade ore deposits worldwide, but also provide important support to deep prospecting of BIF-hosted high-grade magnetite ores.