Carbonate aquifers typically exhibit complex groundwater flow patterns, mainly due to depositional heterogeneities, faulting, fracturing and karstification. Sasan spring is a significant karst groundwater discharge point in the Kazerun area, one the most important karstic region of the southern Zagros in southern Iran. The annual precipitation, recharge coefficient and apparent catchment area of the Sasan spring are 524 mm, 37%, and 36.2 km2, respectively. On this basis, the annual discharge of the spring is expected to be 7 MCM. However, the actual measured annual discharge of the spring is 91.4 MCM, some thirteen times larger than 7 MCM. It therefore seems that a major part of the recharge source to the spring is supplied form the adjoining watershed through a fault zone and the associated fractures. To find the source of this extra water, the geometrical properties and the permeability of the associated fault zone of the local Amui fault have been analyzed. The results show that the overall setting of this fault is a conduit-barrier fluid flow system with a uniform structure. The mentioned extra recharge occurs through the carbonate rocks in the eastern part of local Salbiz and Ghandil anticlines along the Kazerun fault zone. It then reaches the Sasan spring by the Amui fault and associated fractures.