投稿时间：2023-02-09
修订日期：2023-09-23
网络发布日期：2023-12-29
中文摘要:铁元素是岩浆-热液成矿系统中参与成矿的重要金属元素之一，岩浆-热液矿床中富铁矿物（黄铁矿、磁铁矿、黄铜矿、磁黄铁矿、斑铜矿、毒砂、菱铁矿）的δ56Fe值变化较大（-2.07‰~+1.58‰），指示铁同位素在岩浆演化、流体出溶和热液演化过程中均存在明显的分馏，因此，在约束岩浆-热液成矿系统中成矿金属的迁移-富集-沉淀过程和示踪成矿物质来源方面具有巨大的应用潜力。通过整理和分析前人研究资料，文章总结了岩浆-热液成矿系统岩浆演化、流体出溶和热液演化过程中铁同位素地球化学行为的研究现状。岩浆演化过程中铁同位素会发生显著分馏，如部分熔融过程中，熔体相比残余固相富集重铁同位素；矿物分离结晶会引起残余熔体铁同位素组成的变化，主要受含Fe2+或Fe3+矿物结晶的影响，如磁铁矿分离结晶会导致残余熔体铁同位素组成变轻，总体反映岩浆氧化还原状态对铁同位素分馏的主要控制作用，因此，含矿岩体铁同位素组成及其变化可用于确定岩浆的氧化还原状态。流体出溶是含矿岩浆演化成为岩浆热液矿床的关键过程，出溶流体相对于母岩富集轻铁同位素，但实验研究表明出溶流体铁同位素组成可能受其中铁的迁移形式、与流体平衡的含Fe2+或Fe3+矿物的比例、相分离和流体混合等多种因素影响。热液演化过程中，含铁热液矿物沉淀会引起流体铁同位素组成的变化，磁铁矿沉淀会导致流体富集轻铁同位素，而含铁硫化物（如磁黄铁矿）沉淀则会使得流体逐渐富集重铁同位素，显示热液流体氧化还原状态对铁同位素分馏的控制作用。由于黄铜矿被认为可以有效记录流体的铁同位素组成，其铁同位素值被用于区分热液流体氧化还原状态。铁元素作为岩浆-热液成矿系统中直接参与成矿的元素，为直接示踪成矿物质来源提供了可能性，然而，岩浆演化、流体出溶和热液演化过程中铁同位素的明显分馏，导致利用铁同位素示踪成矿物质来源的特殊性。进一步明确流体出溶、热液演化等地质过程中的分馏规律，是利用铁同位素示踪成矿物质来源的关键。
Abstract:Iron element is one of the important metal elements involved in mineralization in the magmatic-hydrothermal metallogenic system. The δ56Fe values of iron-rich minerals (pyrite, magnetite, chalcopyrite, pyrrhotite, bornite, arsenopyrite, siderite) in magmatic-hydrothermal deposits vary considerably(-2.07‰~+1.58‰), indicating that the iron isotope has obvious fractionation during the magmatic evolution, fluid exsolution and hydrothermal evolution, therefore, it has great application potential in constraining the migration-enrichment-precipitation process of ore-forming metals and tracing the source of ore-forming materials in the magmatic-hydrothermal metallogenic system. Based on sorting out and analyzing the data of previous studies, this paper summarizes the research status of iron isotope geochemical behavior in magmatic evolution, fluid exsolution and hydrothermal evolution of magmatic-hydrothermal metallogenic system. The iron isotope will undergo significant fractionation in the process of magmatic evolution, and the melt phase is enriched in heavy iron isotope than the residual solid phase during partial melting; the iron isotope composition of the residual melt is changed due to the separation and crystallization of minerals, which are mainly affected by the crystallization of minerals containing Fe2+ or Fe3+, for example, separation and crystallization of magnetite will lead to enrichment of light iron isotope composition in the residual melt, which generally reflects the main control of the redox state of magma on the fractionation of iron isotopes. Therefore, the composition and variation of iron isotope in ore-bearing rocks can be used to determine the redox state of magma. Fluid exsolution is a key process in the evolution of ore-bearing magma into magmatic hydrothermal deposits, the exsolution fluid is rich in light iron isotope relative to the host rock, however, the experimental studies show that the iron isotope composition of the exsolution fluid may be affected by many factors, such as the migration form of iron, the proportion of Fe2+ or Fe3+ containing minerals in equilibrium with the fluid, the phase separation and the fluid mixing. During the hydrothermal evolution, the precipitation of iron bearing hydrothermal minerals will cause changes in the iron isotope composition of the fluid, the magnetite precipitation will cause the fluid to enrich the light iron isotope, and the precipitation of iron-bearing sulfides (such as pyrrhotite) makes the fluid gradually enrich the heavy iron isotopes, which shows that the redox state of hydrothermal fluid controls the fractionation of iron isotopes. Since chalcopyrite is considered to be able to effectively record the iron isotope composition of the fluid, its iron isotope value is used to distinguish the redox state of hydrothermal fluid. As an element directly involved in mineralization in the magmatic hydrothermal metallogenic system, iron provides a possibility for direct tracing of the source of ore-forming materials, however, the obvious fractionation of iron isotopes in magmatic evolution, fluid dissolution and hydrothermal evolution leads to the particularity of tracing the source of ore-forming materials with iron isotopes. It is the key to trace the source of ore-forming materials by iron isotopes to further clarify the fractionation rules in the geological processes such as fluid dissolution and hydrothermal evolution.
keywords:Fe isotope magmatic-hydrothermal metallogenic system geochemical behavior application research status
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基金项目:本文得到国家自然科学基金项目（编号：42273062、42130102）和西北大学地质学系科研基金项目的联合资助
引用文本：
王续文,李宇轩,安芳.2023.岩浆-热液成矿系统中铁同位素地球化学研究现状[J].矿床地质,42(6):1214~1228WANG XuWen,LI YuXuan,AN Fang.2023.Status and progress on geochemical behavior of iron isotope in magmatic-hydrothermal system[J].Mineral Deposits42(6):1214~1228
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