Mixing Trends and Solute Geothermometry of Borehole Waters from the Paka Geothermal Prospect, Kenya

Abstract

Borehole water in the Paka Geothermal prospect are predominantly mixed sodium bicarbonate- chloride water type with low chloride concentrations.(28-161 ppm) and could be influenced more by evaporite processes and leaching of solutes. The pH of the water from the boreholes range between (6.7and 8.5). Temperatures of the borehole waters were above ambient. Mixing trends determined from plots of chloride, boron, magnesium, sulphate, and enthalpy suggest there could have been boiling prior to mixing, oxidation processes by atmospheric oxygen in the shallower depths of the geothermal system as the hotter geothermal waters ascend to the surface. This was indicated by increase in sulphate concentrations. Boiling and mixing processes from chloride-enthalpy plot suggest waters were being diluted from the western to the eastern side of the prospect. Solute geothermometry temperatures of NaK and Na-K-Ca are relatively high and probably overestimates the actual temperatures of the geothermal system. Quartz temperatures were very low. Assumptions made for the applications of the solute geothermometry temperatures may not be valid due to high discrepancy between the NaK, Na-K-Ca and quartz temperatures.