Mixing of metamorphic and surficial fluids during the uplift of the Hercynian upper crust: consequences for gold deposition

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• 作者：Boiron ; Marie-Christine ; Cathelineau ; Michel ; Banks ; David A. ; Fourcade ; Serge ; Vallance ; Jean
• 关键词：Gold ; Fluid chemistry ; Stable isotopes ; P&ndash ; T conditions ; Uplift ; Variscan belt
• 刊名：Chemical Geology
• 出版年：2003
• 出版时间：March 15, 2003
• 年：2003
• 卷：194
• 期：1-3
• 页码：119-141
• 全文大小：787 K

文摘

A detailed geochemical study of fluids from representative quartz-sealed faults hosting late Hercynian gold concentrations shows that fluids percolating the mineralised faults had two main distinct reservoirs: one was a quite shallow and the other rather deep-seated. Both fluids have lost a great part of their original geochemical signature through interactions with host metamorphic formations. Early fluids, present during the primary sealing of the faults by quartz, are considered to have effectively equilibrated with the metamorphic pile and then predominantly flowed upwards along the faults. They are characterised by CH₄/CO₂/H₂O ratios rather typical of fluids equilibrated with graphite, and moderate to medium chlorinities with a high Br/Cl ratio. The striking feature of the gold-bearing quartz is that gold is not synchronous within any quartz deposition, and appears located in late microfractures and associated with Pb–Bi–Sb sulphosalts and sulphides. These late stages are characterised by fluids whose salinities decrease to very low values indicating their progressive dilution by waters of more surficial origin in the fault system.