The La Lucette Sb-Au-(W) vein-deposit (Armorican Massif, France): new time and genetic constraints to decipher the 310-295 Ma Sb-Au metallogenic peak in the Variscan Belt

In the French Armorican Massif, La Lucette is the most important late Variscan Sb deposit with an uncommon Sb-Au-(W) ore. Detailed mineralogical investigations, fluid inclusion study in gangue and ore combined with in-situ apatite LA-ICP-MS U/Pb dating were carried out to decipher the Sb-Au-W relationships, and metallogenic processes. The mineralization consists of sigmoidal quartz lenses. Four stages of ore deposition have been identified, consisting in the following mineral assemblages: i) scheelite, ii) arsenopyrite, pyrite, iii) base-metals and iv) stibnite-Au. An initial aqueous-carbonic hot-fluid (350 to 250 °C) from a metamorphic source is involved for the early scheelite to base-metals stages, and fluid/rock interaction could be responsible for the scheelite crystallization. Cooling and mixing of the initial fluid with an aqueous cold meteoric fluid (∼200 to 130 °C), are key factors for the late Sb-Au ore-deposition. P-T conditions express a shallow emplacement level (3.5 to 6 km) in a single and progressive crystallization-deformation event. No significant exhumation, and no additional magmatic source from late Variscan felsic or early Carboniferous mafic magmatic events are needed for the Sb-Au-(W) ore genesis. Structural features and new LA-ICP-MS U/Pb apatite dating associated with a regional synthesis show that all major Sb-Au mineralizations of the Armorican Massif, and most from the European Variscan Belt districts have a relatively similar genetic model. In the French Variscan massifs those deposits have been emplaced during the same mineralizing peak, which operated at around 310-295 Ma, and was controlled by the late-orogenic Variscan post-thickening tectonic event