Comparison, characterization, and interpretation of geothermal fluid geochemistry in the sedimentary environments of Kibiro, Panyimur, and Öxarfjördur

Abstract

Geochemical data interpretation of representative chemical, analytical, and isotopic results for geothermal waters and gas in sedimentary environments obtained by standard analytical methods were studied in this research work. Techniques like chemical geothermometers (silica and cation geothermometers) and gas geothermometers were used in predicting the variation in temperatures in three geothermal systems, i.e. Kibiro and Panyimur in the East Africa Rift System, and Öxarfjördur in Iceland. The speciation programme WATCH was used to calculate the activity of the different species of anions and cations, Na/K, Quartz and Chalcedony temperatures, a Ternary diagram for Na/1000-K/100-√Mg based on the equilibration conditions for these cations in these waters at particular temperatures, and a Cl-SO4-HCO3 ternary plot were constructed. Different mixing models and plots of different constituent relationships were used in the comparison, characterization and interpretation of the geochemistry of these different geothermal areas. The geochemistry of magmatically driven geothermal systems may be used to develop effective exploration techniques for the geothermal systems that are driven by temperature gradients like the East African Rift System (EARS), the western branch of which Kibiro and Panyimur are part. The chemical and isotopic composition of the water samples from Kibiro, Panyimur and Öxarfjördur, suggest mixing of cold groundwater with geothermal waters. Major ions and isotope parameters were used to characterize the waters from Kibiro and Panyimur as Na-Cl-HCO3 waters, and water from Öxarfjördur as Na-Cl water. The main processes affecting the geothermal system in the sedimentary geological environment are: dilution and conductive cooling.