Mesozoic Vein Pb-Zn Mineralization in the Pyrenees: Evidence from the Aulus-les-Bains Area

The Pb-Zn deposits of Les Argentieres and Lacore are located in Devonian terranes of the Axial Zone of the Pyrenees, south of the Mesozoic Aulus basin. These Pb-Zn vein deposits display geologic setting and paragenetic characteristics clearly different from the well-known Palaeozoic sedimentary exhalative Pb-Zn mineralizations in the Axial Zone of the Pyrenees. They show an extensional setting and fluid inclusions enriched in NaCl and CaCl2 with low homogenization temperatures, consistent with basinal fluids. In addition, the (Pb-208/Pb-204)=f (Pb-206/Yb-204) ratios acquired on galena are more radiogenic than those of the Palaeozoic sedimentary exhalative mineralizations, indicating younger ages. According to the estimated model ages, their formation may be narrowed down to Middle-Late Triassic and Late Jurassic times. This underscores the role of pre-orogenic Pyrenean rifling in setting up hydrothermal fluids circulation, and indicates that the mineralized vein are related to the syn-sedimentary fault system that bounds the Mesozoic Aulus basin.