西天山塔尔塔格铁矿床岩浆演化过程中铁富集机制研究

The genesis for iron deposits in the Western Tianshan is poorly constrained and remains controversial. The key issue is the mechanism of iron enrichment in magma system. The recently discovered Taertage iron deposit in this region, is hosted in the diorite porphyry, which has a high magnetite content. Iron ores display porphyritic textures with phenocrysts of plagioclase and magnetite in groundmass, and lack hydrothermal alteration assemblages. Ore textures in Taertage are markedly different from that of other iron deposits in the Western Tianshan, thus provide a significant insight for understanding the genesis of the volcanogenic iron deposit in this region. This project focus on the mechanism of iron enrichment during magma evolution in the Taertage iron deposit. Based on the detailed investigations of mineralization characteristics, petrography, whole-rock major and trace element, and Sr-Nd isotope of diorite porphyry and ores are used to trace their parent magma source and evolution. Trace element compositions of magnetite, apatite and titanite by EMPA and in-situ LA-ICP-MS analysis, in combination with oxygen isotope compositions of magnetite and plagioclase, are applied to determine the source of iron and its enrichment mechanism as well as the temperature of magnetite deposition. Apatite SIMS U-Pb dating are employed to constrain the formation ages of iron ores. The genesis of Taertage is proposed on the multiple investigations, and is then compared to the genesis of other iron deposits in the Western Tianshan, to ascertain whether they were produced by a single metallogenic system. This project can provide significant scientific contributions to the complement of iron deposit types, the thorough understanding of metallogenic processes, and the development of genetic theory of the volcanogenic iron deposits in the Western Tianshan.

西天山地区火山岩型铁矿成因机制一直存在争议，其核心科学问题是岩浆系统中铁的富集机制。该区新发现的塔尔塔格铁矿产于闪长玢岩中，表现出全岩矿化，矿石为斑状结构，主要由斜长石斑晶和磁铁矿基质组成，不发育热液蚀变，明显不同于西天山其他火山岩型铁矿，为成矿机制的研究提供了新的切入点。本申请拟以塔尔塔格铁矿岩浆演化过程中铁富集机制为研究主题，在查明成矿地质特征的基础上，通过岩相学、主微量元素及Sr-Nd同位素研究，分析成矿母岩浆源区与演化过程；重点开展磁铁矿、磷灰石、榍石的EMPA与LA-ICP-MS综合分析，查明微量元素特征，结合磁铁矿、斜长石的氧同位素组成，分析铁质来源、富集机制与成矿温度；利用磷灰石SIMS U-Pb测年，厘定成矿时代；综合探讨成矿机制，并与西天山其他铁矿进行对比，明确它们是否属于同一成矿系统。本研究对于丰富西天山火山岩型铁矿类型，深入认识成矿过程，完善成矿理论有重要的科学意义。

西天山地区火山岩型铁矿成因机制一直存在争议，其核心科学问题是岩浆系统中铁的富集机制。塔尔塔格铁矿产于粗面安山玢岩与辉长闪长岩中，代表了研究区内一个特殊的火山岩型铁矿类型。本项目以塔尔塔格铁矿为研究对象，开展矿物学、岩石学、地球化学与年代学研究，查明成矿岩体岩石属性与源区性质，厘定成岩成矿时代，探讨成矿机理。.项目研究揭示塔尔塔格磁铁矿具有高Ti、V、Al含量，δ18O为1.9-4.2 ‰，δ56Fe介于-0.10‰至-0.31‰，发育出溶钛铁氧化物结构，指示磁铁矿由高温富铁熔体结晶形成；查明成矿母岩浆为富铁碱性岩浆，起源于受俯冲带熔体交代的地幔楔熔融；碱性长石的分离结晶造成了铁的富集；成矿构造背景为南天山洋俯冲晚期阶段的区域伸展环境，动力学过程受板片后撤与断裂的控制。通过矿石中锆石的SHRIMP U-Pb测年，厘定成矿时代为314.7 Ma，与阿吾拉勒成矿带内其他火山岩型磁铁矿形成时代一致，认为区内火山岩型铁矿床形成于同一富铁岩浆-热液成矿系统。这些认识揭示了塔尔塔格铁矿成矿母岩浆源区的性质与演化以及铁质富集成矿过程，丰富了区内的火山岩型铁矿类型，进一步完善了区内火山岩型铁矿的成矿模型。项目发表学术论文2篇，其中国外SCI论文1篇，国内核心期刊论文1篇。