Radon Emission Studies and Hydrogeochemical Investigations of Tattapani Hot springs (Kotli, Azad Kashmir, Pakistan)

Abstract

Radon Elnission Studies and Hydrogeochemical Investigations of Tattapani Hot springs (Kotli, Azad Kashlnir, Pakistan) Surface manifestation of geothermal water occurs in Tattapani town near Kotli district, Azad Kashmir, Pakistan. An integrated study focusing on radon emissions from soil gas and hydro-geochemistry of hot springs has been carried out for characterizing the subsurface geothermal system. This methodological combination of radon with hydrochemistry plays an important role in identifying the geothermal system and geologic controls on permeable zones, fluid origin and the overall flow pattern. Hot springs emerge from the carbonates ofMuzaffarabad Fonnation (Cambrian) present in the core ofTattapani anticline with Paleocene to Eocene shales and limestone on its flanks. A part of intrusion exposed on NW limb of anticline along Cambrian-Paleocene rocks contact, has been considered to be an indication of subsurface heat source. Radon sampling was carried out over 36 sampling points with 200 m spacing in a 1 km2 grid around the hot springs. Spatial distribution of radon concentration over the grid when overlapped with the surface geology, showed an anomalous zone over the Cambrian-Paleocene contact. Hydro-geochemistry data show that sodium-bicarbonate water the composition of hot spring water. The surface temperature ofthese springs is up to 60.8°C. Average reservoir temperatures based on silica and cation geothermometers are 110°C and 140°C respectively. A non-equilibrium state of fluid-rock as shown with Giggenbach ternary diagram (Na-K-Mg) suggests that a dissolution process in a low temperature condition is dominant. Data from oxygen and deuterium isotopes implies that thermal water is of meteoric origin and the source of recharge is probably rains and snow melts in the north at higher altitudes. Residence time based on tritium contents in thermal water is more than 60 years suggesting that they were recharged before thelIDonuclear testing in 1952. A conceptual model reveals that Tattapani hot springs are not associated with active magmatism. Instead a deep intrusion might generate the heat source for the hot spring waters that are recharged by.predominately meteoric water. Fluid pathways are controlled by fractures in. Cambrian carbonates. Overall, Tattapani hot springs, being immature and considered as low enthalpy system, are suitable for domestic purposes only.