Timing of veining and Variscan deformation in the Stavelot-Venn Massif (Belgium)

Petrographic investigation of the Grand-Halleux boreholes identified different generations of quartz veins that were formed during different periods of fluid migration in an environment that was decreasingly influenced by compressive deformation. The 40Ar-39Ar dating of muscovite associated with shear zones crosscutting two quartz vein generations indicated an age of 318 ± 4.7Ma, which allows determining the position of the different vein generations in relation to the Variscan deformation in the Stavelot-Venn Massif. This age also determines the approximate age for the Variscan syn-orogenic metamorphism in the Stavelot-Venn Massif. Younger extension veins and prismatic quartz crystals in open spaces are associated with different generations of carbonates, associated with Pb-Zn-Cu mineralisation. This implies that this mineralisation did not form during Caledonian metamorphism or early Variscan orogenic metamorphism, but has a late to post-Variscan age. It could be linked to the post-orogenic expulsion of metamorphic fluids, but a link with the younger Pb-Zn mineralisation in the Variscan front zone is favoured based on the presence of high-salinity low temperature fluids.