铁同位素体系及其在矿床学中的应用

Fe isotope systematics and its implications in ore deposit geology

本文报道了世界范围内不同含铁矿物的Fe同位素组成,进一步了解了铁同位素在不同含铁矿物中的基本分布特征;系统总结了铁同位素在不同储库和不同类型矿床中的分布特征,构筑了铁同位素体系的基本框架;结合最新的研究成果,较全面地总结了铁同位素在矿床学领域的应用,得出了铁同位素可以用来示踪流体出溶、流体演化、表生蚀变作用和成矿物质来源的基本认识。在流体出溶过程中,相对于岩体,出溶的流体富集铁的轻同位素;成矿流体体系的演化过程中,矿物的结晶沉淀会导致铁同位素发生分馏,随着Fe(Ⅲ)矿物的结晶沉淀,流体逐渐富集铁的轻同位素,随着Fe(Ⅱ)矿物的结晶沉淀,流体逐渐富集铁的重同位素,随着矿物的结晶沉淀,流体的Fe同位素组成随时间发生演化;在成矿后的表生蚀变作用过程,高温蚀变作用形成的产物相对于原矿物富集铁重同位素,低温蚀变作用形成的产物基本保留了原矿物的铁同位素组成;Fe同位素在示踪成矿物质来源具有应用潜力,流体出溶、流体演化等重要成矿作用过程中Fe同位素组成的变化规律是利用Fe同位素示踪Fe来源的关键所在。

On the basis of Fe isotope compositions of different Fe-bearing minerals worldwide reported in this paper, together with literature data, Fe isotope distributions of different minerals and reservoirs, as well as different types of deposits, were summarized in some detail, which provide a reference framework of Fe isotope system. Applications of Fe isotope system in the study of ore deposits were reviewed. Fe isotope fractionation occurs during fluid exsolution and that fluid is enriched in light isotopes relative to stock. In a hydrothermal fluid system, iron isotopes fractionate during fluid evolution due to precipitation of Fe-bearing minerals. Precipitation of Fe （Ⅲ） minerals leaves the remaining fluid enriched in light isotopes, while precipitation of Fe （Ⅱ） minerals makes the Fe isotopic composition of the fluid progressively heavier. Precipitation of Fe-bearing minerals results in the Fe isotope composition of residual fluids evolving with time. Fe isotopes potentially serve to identify precursors in ore alteration products. The high-T altereation minerals are enriched in heavy isotopes relative to precursors, while the low-T alteration minerals inherit the composition of precursors throughout. The regularity of Fe isotope fractionation during fluid exsolution and evolution processes lays an important foundation in using Fe isotopes as a tracer for metallogenic material source.