Chemical and isotopic studies on four geothermal pospects in the Southern Afar region, Ethiopia

Abstract

Isotopic and chemical studies have been carried out in Wonji, Fantale, Dofan and Meteka geothermal prospects in the Southern Afar region, Ethiopian Rift Valley. Previous studies have mostly been overviews of a big region and not very detailed, whereas this study is focussed on a relatively small area. Deuterium, tritium and oxygen-18 proved to be most important for separating different groundwater systems. Based on the isotopic data, the following three groundwater systems are identified: 1) Wonji area, 2) Fantale and Meteka area and 3) Dofan groundwater system. Tritium results show that the waters studied are not contaminated with waters from the hydrogen-bomb tests performed during the 1950's, except for the Wonji thermal springs and the Metehara cold spring. The thermal waters in Fantale, Dofan and Meteka have very low tritium values, suggesting that the waters are pre-1950. Geothermometry indicates that the reservoir temperature is in the range 110-140°C (average). The waters do not appear to be completely equilibrated and some mixing with colder water is indicated in all fields. Future studies should give priority to the geothermal prospect of Dofan, followed by Meteka and Fantale.