Interpretation of geochemical data from low-temperature geothermal area Fljótin, N-Iceland, compared to selected geothermal samples from Rungwe Tanzania

Abstract

The chemical analysis of geothermal water requires proper sample collection, analysis, and presentation of the data. The interpretation and evaluation of all available information regarding the geochemistry are accomplished by the methods of Na-K-Mg ternary diagram, Cl-SO4-HCO3 ternary diagram, geothermometers, WATCH programme and Suffer 12.6.963 software. Data samples from FljótinIceland are analysed pertaining to their geochemistry surface exploration and compared to selected data from Rungwe geothermal area from Tanzania. The geothermal fields differ according to volcanic activities, rock types and mineral composition. Fljótin are low-temperature geothermal field while Rungwe is classified as high-temperature geothermal field at Ngozi-Songwe (northern system) and a low-temperature field at Kiejo-Mbaka (southern system). The reservoir temperatures at Fljótin are estimated by Na-K-Mg ternary diagram in the range of 120°C -160°C and confirmed with geothermometers with temperature range; 74- 136°C (chalcedony) and 64-158°C (Na/K). The mineral saturation stated were calculated by chalcedony temperature where calcite and anhydrite are saturated but not precipitating while amorphous silica is under saturated. The estimated reservoir temperature at the Rungwe volcanic zone are 130-200°C by Na-K-Mg ternary diagram, which is in agreement with quartz and K/Mg geothermometers at a temperature range of 119-154°C and 106-252°C respectively. Detailed study of the Rungwe thermal fluid chemistry is required in order to be satisfied for direct or indirect use, due to its high concentration of CO2 which can affect the utilization of the fluid, both fields have a potential for geothermal utilization. Fljótin on the other hand can be used directly due to its low total dissolved elements and lowtemperature.