| Title | Isotope Hydrology Studies of Katwe, Buranga and Kibiro Geothermal Systems, Uganda |
|---|---|
| Authors | Godfrey Bahati |
| Year | 2008 |
| Conference | ARGeo |
| Keywords | Isotopes; Recharge; Geothermometry; Salinity; Katwe; Buranga; Kibiro; Uganda |
| Abstract | Isotopes hydrology investigations have been carried out on three geothermal areas in western Uganda, namely Katwe, Buranga and Kibiro. The three geothermal areas have reached advanced stages of surface exploration for geothermal energy and will soon be subjected to exploratory drilling. The aim of the study was to upgrade the geothermal models with hydrological information on the movement of the fluids from recharge areas to the reservoirs and hot springs. 118 water samples from hot and cold springs, dug wells, rivers, lakes and 13 rock samples from surface outcrops have been collected and analyzed for chemistry and isotopes of hydrogen (ä2HH2O, 3HH2O), oxygen (ä18OH2O, 18OSO4), carbon (ä13CDIC, 14CDIC), sulphur (ä34SSO4), and strontium (87/86SrH2O, 87/86SrRock). The results suggest a meteoric origin of the geothermal water. Based on isotope data, Katwe and Buranga are recharged from the Rwenzori Mountains while Kibiro is recharged from high ground represented by the Mukihani-Waisembe Ridge in Kitoba Sub-county 20 km to the southeast. Oxygen isotope geothermometry based on aqueous sulphate and water equilibrium fractionation, indicates a subsurface temperature of 200°C for Buranga, which is higher than that inferred from chemical geothermometry (120-130°C), but lower temperatures (140-160 °C) for Katwe and Kibiro that are similar to the results of chemical geothermometry. Tritium concentrations indicate some involvement of modern cold water close to the surface at Kibiro but not at Buranga and Katwe, where hot springs discharge tritium-free waters. Sulphur isotope ratios (34SSO4) of hot water suggest magmatic contributions of sulphate in all the three areas, confirming results of earlier geochemical investigations. Strontium isotope ratios in water and rock samples (87/86SrH2O, 87/86SrRock) allow a preliminary identification of rock types that may have interacted with the thermal waters. |