Radon and helium as pathfinders of fault systems and groundwater evolutionin different Italian areas

Groundwater surveys in some Italian areas with different geological and geo dynamical features were performed in order to evaluate dissolved pare gases (Rn-222, He and Ar) as potential tracers of fault systems and groundwater evolution (fluid origin, water-rock-gas interaction, fluid migration and mi xing phenomena). The obtained results showed that the highest values of Rn and He were found along important fault systems cutting the investigated ar eas, where the fault-related permeability increases deep-seated fluid circu lation. However, dissolved-radon anomalies may be due to: a) a rapid ascent of Rn-bearing fluids, equilibrated with lithologies richer in U than outcr opping formation; b) a local enrichment of U due to the action of low-entha lpy groundwater or strong carrier gas (CO2) discharges usually occurring al ong the fault systems.