Geochemical Study of Hanle Geothermal Field, Djibouti

Abstract

The Republic of Djibouti is located in East Africa, in the Great Rift Valley and Afar Triple Junction. From a geological point of view, Hanle lava plateau is composed of basaltic lava layers called the Afar Stratoid Series. Faults or fractured systems were formed in the NW-SE direction in the plateau. Hydrothermal activities are found as fumaroles with temperatures higher than 98°C and a hot spring. Using the chemical compositions of the fumaroles and hot spring, reservoir temperature was estimated to be180°C–260°Cwith gas geothermometers. Also, temperature of the hot spring aquifer was estimated to be 125°C with a solute geothermometer. The major solute components of the hot spring suggest that the spring water is created by mixing of groundwater and heated fossil seawater or dissolution of evaporate by heated groundwater. Results from geochemical, geological and geophysical studies indicate that a geothermal reservoir lies below the central area of the Hanle lava plateau. In that area, geothermal steam discharges most vigorouslyat Garabbayis and Goros. These zones can be a prospect for subsequent exploration including test drilling.