La grotte-mine du Piei (Lagnes, Vaucluse), paléokarst hypogène à remplissage de minerai de fer oxydé

Abstract

The Piei mine-cave (Lagnes, Vaucluse, France), a hypogene iron-ore paléokarst. The Piei mine-cave is siutated at the contact of the Vaucluse Mounts and the Carpentras basin, close to the Fontaine de Vaucluse spring. It develops in Cretaceous limestone (urgonian fades) on a main regional lineament, the Salorl-Cavaillon fault. The cave was mined in the 19th Century, giving access to passages previously completely filled with diverse neogene sands and massive iron crusts. The miners mainly followed the natural passages. The origin of the cave is related to hypogenic flow rising along deep fissures or hydraulic breccia pipes, depositing iron at the contact or on top of the neogene sand fillings. Microbial activity was present during that time, and is associated to the iron deposition. This cave probably was active in the Neogene, when the Vaucluse plateau was uplifted. The Piei mine-cave records the position of the corresponding base level and thus the progressive tilting of the plateau, as do other similar caves located around the western edge of the Vaucluse Plateau.