Mobility of Au and related elements during the hydrothermal alteration of the oceanic crust: implications for the sources of metals in VMS deposits
Mobility of Au and related elements during the hydrothermal alteration of the oceanic crust: implications for the sources of metals in VMS deposits
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DOI：
10.1007/s00126-015-0598-8
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发表时间：
2016-02
影响因子：
4.8
通讯作者：
C. Patten;I. Pitcairn;D. Teagle;M. Harris
中科院分区：
文献类型：
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作者：
C. Patten;I. Pitcairn;D. Teagle;M. Harris
火山块状硫化物 (VMS) 矿床通常富含铜、锌和铅，也可能不同程度地富含金、砷、锑、硒和碲。这些元素在洋壳热液蚀变过程中的行为尚不清楚。海洋钻探计划 (ODP) 1256D 孔穿透了上洋地壳的完整原位部分，为研究热液蚀变期间金属的行为提供了独特的样本套件。使用低检测限方法分析了一组代表性样品的金、砷、锑、硒和碲，并通过与新鲜的大洋中脊玄武岩 (MORB) 玻璃数据库进行比较，进行了金属迁移率的质量平衡。质量平衡显示，片状岩脉和深成杂岩中的 Au、As、Se、Sb、S、Cu、Zn 和 Pb 的消耗量为 -46 ± 12、-27 ± 5、-2.5 ± 0.5、-27 ± 6、-8.4 ± 0.7、分别为-9.6 ± 1.6、-7.9 ± 0.5和-44 ± 6%。由于海水衍生的流体循环，火山剖面中砷和锑富集。计算表明，大量金属从洋壳中被释放出来，但只有一小部分最终被 VMS 矿化所捕获。 Au 的动员量以及 Au 与贱金属的比例与镁铁质 VMS 相似，需要 10 倍的 Au 富集才能形成富 Au VMS。镁铁质 VMS 矿床的富铜亲和力可以通过上部片状岩脉中和 VMS 矿床形成过程中的贱金属分馏来解释。
Volcanogenic massive sulphide (VMS) deposits are commonly enriched in Cu, Zn and Pb and can also be variably enriched in Au, As, Sb, Se and Te. The behaviour of these elements during hydrothermal alteration of the oceanic crust is not well known. Ocean Drilling Program (ODP) Hole 1256D penetrates a complete in situ section of the upper oceanic crust, providing a unique sample suite to investigate the behaviour of metals during hydrothermal alteration. A representative suite of samples was analysed for Au, As, Sb, Se and Te using low detection limit methods, and a mass balance of metal mobility has been carried out through comparison with a fresh Mid-Oceanic Ridge Basalt (MORB) glass database. The mass balance shows that Au, As, Se, Sb, S, Cu, Zn and Pb are depleted in the sheeted dyke and plutonic complexes by −46 ± 12, −27 ± 5, −2.5 ± 0.5, −27 ± 6, −8.4 ± 0.7, −9.6 ± 1.6, −7.9 ± 0.5 and −44 ± 6 %, respectively. Arsenic and Sb are enriched in the volcanic section due to seawater-derived fluid circulation. Calculations suggest that large quantities of metal are mobilised from the oceanic crust but only a small proportion is eventually trapped as VMS mineralisation. The quantity of Au mobilised and the ratio of Au to base metals are similar to those of mafic VMS, and ten times enrichment of Au would be needed to form a Au-rich VMS. The Cu-rich affinity of mafic VMS deposits could be explained by base metal fractionation both in the upper sheeted dykes and during VMS deposit formation.