福建紫金山低硫化型银多金属矿成矿机制研究

Due to the totally different origin and evolution of hydrothermal fluids and their tectonic setting, the co-occurrence of high sulfidation (HS) and low sulfidation (LS) type epithermal systems are rarely found. However, three types of deposits formed an approximate typical porphyry-epithermal metallogenic system that consist of the unusual co-occurrence of the Zijinshan HS type epithermal Au–Cu deposit, the Yueyang LS type Ag-polymetallic deposit, and the Luoboling porphyry Cu–Mo deposit in the Zijinshan ore district. Those deposits may have some genetic relationships due to their close connections in time and space. Thus, studying the co-occurrence mechanism of these porphyry-epithermal systems can help us to better understand the evolution of the porphyry-epithermal deposits, and revealing its geodynamic background. Based on my previous research on the Zijinshan HS Au–Cu deposit and the Luoboling porphyry Cu–Mo deposit, the Yueyang LS type deposit is chosen as the research subject in this project, and a systematic study on petrogenesis and metallogenic mechanism is planned to be conducted. The petrogenesis of the ore-bearing rocks, the metal source, the physicochemical conditions and the evolution of the ore-forming process of the Yueyang LS system will be studied by measuring the temperatures of fluids inclusions, the major and trace elements compositions and Sr–Nd–Hf isotope compositions of ore-bearing rocks, and the trace elements and sulfur isotope compositions of minerals, and then the metallogenic mechanism can be discussed. By compared with the Zijinshan HS and the Luoboling porphyry systems, the possible link between HS, LS and porphyry systems will be analyzed, and the model of this unique and complex porphyry-epithermal system can be built. This will not only provide new evidence for the metallogenic theory of epithermal deposits and the geodynamic mechanism, but also is beneficial to further ore prospecting significantly.

高硫化型与低硫化型浅成低温热液矿床产于不同的地质环境，具不同的成矿流体来源及演化进程，这导致两者往往不具共伴生关系。福建紫金山矿集区汇集了齐全的斑岩型、高硫化型与低硫化型浅成低温热液成矿系统，且具有密切的时空关系，暗示其相互之间可能存在成因联系。而查明其共生的成因机制将对研究斑岩—浅成低温热液体系的演化机理及其地球动力学背景具有重要意义。为此，本项目拟在前期对区内高硫化型和斑岩型矿床详细研究的基础上，选取研究薄弱的悦洋低硫化型矿床，开展系统的成岩成矿作用机制研究，着重利用流体包裹体，主微量元素，Sr–Nd–Hf同位素，矿物原位微量元素及原位S同位素分析等手段，查明成矿岩浆的成因、成矿物质来源与成岩成矿的物理化学条件，揭示低硫化型浅成低温热液系统矿质迁移富集机理；并与高硫化型及斑岩型矿床对比，探讨三者间可能的成因联系，建立斑岩—浅成低温热液体系的成矿模型，指示地球动力学背景并服务于找矿勘探。

高硫化型与低硫化型浅成低温热液矿床产于不同的地质环境，具不同的成矿物质来源，这导致两者往往不具共伴生关系。福建紫金山矿集区汇集了齐全的斑岩型、高硫化型以及低硫化型浅成低温热液成矿系统，且具有密切的时空关系，暗示其相互之间可能存在成因联系。因而，查明其共生的成因机制，对研究斑岩—浅成低温热液体系的演化机理及其地球动力学背景具有重要意义。项目以申请人前期对区内高硫化型和斑岩型矿床的详细研究为基础，选取研究薄弱的悦洋低硫化型矿床，系统开展成岩成矿作用机制研究：利用流体包裹体，主微量元素，Sr–Nd–Hf同位素，矿物原位微量元素及Cu-Fe同位素分析等手段，查明含矿岩浆主要为壳幔混合来源且以壳源物质为主，成矿物质主要来源于含矿岩浆。岩浆分异与流体演化成矿作用过程是控制成矿元素富集的关键。流体成矿过程中发生的沸腾作用和流体混合作用是控制Ag-Au-Cu元素沉淀的关键，流体演化过程存在由高温到低温的转变。通过与紫金山高硫化型及罗卜岭斑岩型矿床对比，确认矿集区内斑岩—浅成低温热液体系分属三个不同的成矿体系，并指示本区仍有巨大的找矿潜力。