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Mineralium Deposita

, Volume 36, Issue 2, pp 165–176 | Cite as

Origin and evolution of high-salinity, Zn–Pb mineralising fluids in the Variscides of Belgium

  • Wouter Heijlen
  • Philippe Muchez
  • David A. Banks
ARTICLE

Abstract

High-salinity, Na–Ca–Cl-rich fluids (˜20 wt% salts) in inclusions in gangue and ore minerals from Mesozoic Mississippi Valley-type (MVT) deposits in the Verviers Synclinorium (eastern Belgium) and in Cretaceous vein calcites at the Variscan front were investigated by microthermometric and crush-leach analysis. The MVT deposits formed at temperatures of ˜110 °C while the Cretaceous vein calcites were precipitated at temperatures <50 °C. Their Cl–Br content (Cl/Br ratio between 246 and 458) suggests that the fluids probably originated by the evaporation of seawater during basin development at the southern margin of the Caledonian Brabant Massif in the Late Palaeozoic. The Na–Ca–K content (Na: 29,700–49,600 ppm, Ca: 25,700–46,200 ppm, K: 1,000–5,620 ppm) is similar to that of the mineralising fluids in other Pb–Zn districts, interpreted to be of evaporative origin (e.g. Newfoundland, East Tennessee, Polaris). Furthermore, comparison of the Na–Ca–K content of the fluids with that of an evolved evaporitic brine enables the recognition of major water–rock interactions that modified the fluid composition. It indicates that the ambient fluids participated in the early diagenetic dolomitisation of Upper Palaeozoic carbonates and also in the albitisation of plagioclase in Lower Palaeozoic siliciclastics of the Caledonian basement. Illitisation of smectites or dissolution of K-feldspar probably controlled the K-content of the fluids. A model is proposed where the bittern brines migrated down into the deep subsurface because of their density during extension. After the Variscan orogeny, these fluids were finally expelled along extensional faults, resulting in the formation of Zn–Pb deposits.

Keywords

Orogeny Rock Interaction Extensional Fault Fluid Composition Basin Development 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2001

Authors and Affiliations

  • Wouter Heijlen
    • 1
  • Philippe Muchez
    • 1
  • David A. Banks
    • 2
  1. 1.Fysico-chemische Geologie, K.U.Leuven, Celestijnenlaan 200C, 3001 Heverlee, Belgium e-mail: wouter.heijlen@geo.kuleuven.ac.be Fax: +32-16-327981BE
  2. 2.School of Earth Sciences, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UKGB

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