| Abstract |
The three main Ugandan geothermal fields namely, Kibiro, Katwe and Buranga are located in East African Rift System (EARS) particularly in its western arm the Albertine Rift. The general strike of the Albertine Rift is NE-SW. Geophysical surveys indicate 2500 to 3000m thickness of Pleistocene sediments in the rift floor. The Kibiro geothermal prospect, which is located at the Eastern escarpment of Albertine Rift, comprises of hot springs that emerge at the base of the escarpment at the intersection of three oblique faults. The escarpment forms a boundary between the old basement rocks (to the east) and the young sedimentary formation of the rift (to the west). The basement consists of Precambrian acidic granites, granitic gneisses, gneisses and N-S striking basic amphibolite intrusives. Mylonitic gneisses characterise the fault-controlled valleys. The NE striking faults in the area are oblique to main rift fault and crosscut E-W striking faults. All rocks are heavily fractured with crosscutting joints. The geothermal manifestations include; hot springs, solfatara, extinct clayey alterations and secondary hydrothermal minerals that include gypsum and calcite filling joints in altered mylonitic gneisses on escarpment among others. The maximum temperature of hot springs is 86.40C. The Katwe volcanic field is on the SE of Rwenzori massif and consists of 78 randomly distributed craters of which seven have water. The volcanics are deposited on Pleistocene sediments. Precambrian rocks of Toro system lie on the western side while on the eastern side; the sediments are underlain by Karagwe-Ankolean (K-A) meta-sediments. In the southeastern side of Katwe field, there is Bunyaruguru volcanic field that consists of tuffs mixed with K-A rock fragments. The Katwe volcanics are mainly phreatomagmatic pyloclastic deposits consisting of ash, tuff, lapilli, volcanic bombs and xenoliths of basement rocks. Basaltic lava flows and ejected lava blocks occur around Kyemengo and Kitagata craters. The volcanic material pile rises up to 420m above surrounding sediments. NE-SW striking faults in the same strike as the main rift fault characterize the field. The carbon dating puts the age of volcanism as Pleistocene to Holocene. The Katwe geothermal manifestations include travertine deposits that indicate extinct hot springs, warm springs (300C) at L. Katwe and hot springs (700C) at L. Kitagata. The Buranga field is located at the NW end Rwenzori massif near the base of Bwamba escarpment. The hot springs emerge through Pleistocene sediments. Precambrian rocks underlie the sedimentts. The main rift fault strikes 450 and dips 600-650. The three hot spring areas namely Mumbuga, Nyansimbe and Kagoro lie on a line striking 400 parallel to main rift fault. Precambrian rocks form northern half of Rwenzori massif that strike 100-300 and consists of migmitites and gneisses. The sediments consist of fine to medium-grained, poorly consolidated sands and clays, some of which are coated with calcareous material. The geothermal manifestations of Buranga field include three hot spring areas with a maximum temperature of 980C, travertine cones and some sulphur deposits at Kagoro spring area. The area is seismically active and frequent earthquakes in the region reactivate and create new manifestations like new hot springs near Nyansimbe pool. |