Geochemical studies on waters from the Katwe-Kikorongo, Buranga and Kibiro geothermal areas, Uganda

Abstract

Geochemical studies have been carried out in three geothermal areas in West and Southwest Uganda. They are the Katwe-Kikorongo, Buranga and Kibiro geothermal areas, all of which are located in the western branch of the East African Rift. For this report three geothermal and one or two cold ground water samples from each area have been analyzed and the results interpreted with the aid of speciation programmes, relational diagrams, chemical geothermometers and mixing models. The high carbonate concentrations of the Katwe-Kikorongo and Buranga waters apparently affect their calcium and magnesium concentrations and thus throw the validity of some conventional methods of interpretation into doubt. Taking these doubts into account subsurface temperatures of at least 150-160 C have been predicted in Katwe-Kikorongo, 120-130 C in Buranga, but two sets of geothermometer temperatures have been obtained for Kibiro, 150-160 C and 200-210 C probably reflecting equilibrium states of a different age, possibly at different depths. One of the samples from Katwe-Kikorongo was collected from an outflow on the bottom of a very saline crater lake, Lake Kitagata and is apparently mixed with a considerable amount of lake water. As this area looks a promising geothermal prospect geologically and also because the results of the chemical analysis of the sample suggested some high-temperature characteristics, it is recommended that an attempt be made to obtain a less mixed sample from the outflow and a sample of relatively pure lake water be collected to aid the interpretation of the nature of this outflow. Questions regarding the origins of the thermal water and of possible mixing patterns remain unresolved and therefore further investigations are recommended in all the three areas.