西秦岭南段金龙山—丘岭矿田金矿床成因的矿物微区地球化学研究

The West Qinling orogeny in central China hosts numerous sediment-hosted disseminated gold deposits and one of the largest gold-producing areas in the country. However, the age of mineralizations, ore genesis, and the source of ore-forming fluids of these deposits have been highly debated. The proposed project will focus on textural and geochemical microanalysis of ore and hydrothermal accessory minerals from the Guloushan-Qiuling-Yaojian-Jinlongshan disseminated gold deposits. Pyrite from different wall-rocks and ore will be analyzed by SIMS for in-situ sulfur isotopic compositions. Also, pyrite will be analyzed by LA-ICP-MS for trace elements. These microanalytic data, in combination with textural analysis of ore and alteration minerals, will provide significant insights into the sources of metals and ore-forming fluid, the evolution of hydrothermal system. Hydrothermal monazite associated with pyrite and arsenopyrite will be dated using U-Pb method. Hydrothermal calcite will be dated by Sm-Nd method. The new isotopic data will provide precise constraints on the age of mineralization. Therefore, results of the proposed project will significantly promote the understanding of ore genesis of sediment-hosted disseminated gold deposits in West Qinling belt.

西秦岭是我国大型的赋存在沉积岩中微细浸染型金矿省之一，但对区内大多数矿床的成矿时代、成矿物质和成矿流体来源以及矿床成因的认识目前还存在很大争议。本项目拟在前期工作基础上，选取西秦岭南段金龙山—丘岭矿田四个微细浸染型金矿床为研究对象，基于详细的野外地质调查和矿相学观察，开展黄铁矿等硫化物的微区原位微量元素和硫同位素分析，结合已有分析数据，系统地揭示成矿物质和成矿流体的来源及演化过程。进一步对独居石等伴生热液副矿物进行原位U-Pb定年和热液方解石Sm-Nd等时线定年，精确限定金龙山—丘岭矿田金矿床的形成时代，查明矿床成因并建立合理的成矿模式。

对金龙山-丘岭微细浸染型金矿床进行了详细研究，在西秦岭地区赋存在沉积岩中的微细浸染型金矿成矿物质和成矿流体来源、成矿时代和成因机制等重要科学问题上取得重要进展，并开发了适合微区原位分析的硫化物Fe-S同位素标样，建立了多种微区原位分析方法。（1）利用电子探针、LA-ICP-MS和SIMS等原位分析手段对载金矿物-含砷黄铁矿和毒砂的主微量元素和硫同位素进行了系统分析，获得了一大批高精度数据，查明了金龙山-丘岭金矿载金矿物的结构和金的赋存状态，证明金主要以固溶体金的形式存在于载金矿物中。（2）获得了丘岭金矿的年龄数据，结合区域其他矿床的年龄限定了成矿时代为晚三叠世。（3）建立了石榴石微区原位U-Pb定年方法。（4）建立了飞秒激光诱导击穿光谱主量元素分析方法。（5）研发了适合SIMS和LA-MC-ICPMS的Fe-S同位素微区原位分析的硫化物标样。（6）初步揭示了金龙山-丘岭金矿床的成矿机制，建立了成矿模型。