Palaeomagnetic dating of widespread remagnetization on the southeastern border of the French Massif Central and implications for fluid flow and Mississippi Valley‐type mineralization

Summary Palaeomagnetic dating techniques have been applied to determine the age of fluid migration that produced the Mississippi Valley‐type (MVT) Pb–Zn–Ba–F deposits in the Cévennes region of southern France. 15 sampling sites in two gently deformed areas around the Largentière and Croix‐de‐Pallières mines on the Cévennes border were selected for palaeomagnetic study. They yielded a very well‐defined direction of remagnetization corresponding to an Early‐Middle Eocene age. This remagnetization cannot be related to the formation of magnetite as a result of the transformation of smectite to illite because the latter has been well dated as a Mesozoic event. The magnetic overprint in this area is related to a chemical phenomenon during fluid migration. The age of remagnetization corresponds to a major uplift in the Pyrénées mountains, located to the south of the Cévennes. This implies that fluid migration occurred from the south to the north as a result of hydraulic head established in the Pyrénées orogenic belt during orogenesis and suggests that the MVT deposits in the Cévennes region formed from a gravity‐driven fluid system as described by Garven & Freeze (1984a,b).