Iron isotope fractionation during skarn-type metallogeny: A case study of Xinqiao Cu–S–Fe–Au deposit in the Middle–Lower Yangtze valley
Iron isotope fractionation during skarn-type metallogeny: A case study of Xinqiao Cu–S–Fe–Au deposit in the Middle–Lower Yangtze valley
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DOI：
10.1016/j.oregeorev.2010.12.004
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发表时间：
2011-12
影响因子：
3.3
通讯作者：
Yue Wang;Xiangkun Zhu;J. Mao;Zhihong Li;Yanbo Cheng
中科院分区：
文献类型：
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作者：
Yue Wang;Xiangkun Zhu;J. Mao;Zhihong Li;Yanbo Cheng
对新桥铜硫铁金矽卡岩型存款矿床的矿物分离物和全岩样品进行了铁同位素组成研究。δ 57 Fe值总体变化范围为-1.22 ‰ ~+0.73‰，具有一定的规律性。内矽卡岩和最早形成的铁矿物相磁铁矿的δ 57 Fe值分别约为1.2 ‰和1.5 ‰。与石英-二长石英岩相比，低0.3‰，表明其出溶流体富含轻Fe同位素。δ 57 Fe值的时空变化反映了流体演化过程中铁同位素的分馏作用。含铁矿物的沉淀导致残余流体的铁同位素组成随时间而变化。沉淀的Fe（III）矿物结合重铁同位素优先离开剩余的流体富集轻同位素，而沉淀的Fe（II）矿物优先采取轻铁同位素，并使流体的Fe同位素组成逐渐加重。新桥存款中铁同位素在流体出溶和演化过程中的变化规律表明，该矿床铁的主要来源是岩浆。研究结果表明，铁同位素组成在揭示成矿过程和制约矿床金属来源方面具有很大的潜力。
Fe isotope compositions of mineral separates and bulk samples from Xinqiao Cu–S–Fe–Au skarn type deposit were investigated. An overall variation in δ57Fe values from −1.22‰ to +0.73‰ has been observed, which shows some regularity. The δ57Fe values of endoskarn and the earliest formed Fe-mineral phase magnetite are ca.1.2‰ and ca. 0.3‰ lower, respectively, relative to the quartz–monzodiorite stock, indicating that fluid exsolved from the stock is enriched in light Fe isotopes. Moreover, spatial and temporal variations in δ57Fe values are observed, which suggest iron isotope fractionation during fluid evolution. Precipitation of Fe-bearing minerals results in the Fe isotope composition of residual fluids evolving with time. Precipitation of Fe (III) minerals incorporating heavy iron isotopes preferentially leaves the remaining fluid enriched in light isotopes, while precipitation of Fe (II) minerals preferentially taking-up light iron isotopes, and makes the Fe isotopic composition of the fluid progressively heavier. The regularity of Fe isotope variations occurred during fluid exsolution and evolution indicates that the dominant Fe source of Xinqiao deposit is magmatic. Overall, this study demonstrates that Fe isotope composition has great potential in unraveling ore-forming processes, as well as constraining the metal sources of ore deposits.