Stableisotopestudies of some lowenthalpygeothermalsystems in Kenya

Abstract

Oxygen and hydrogen isotope compositions of some lowenthalpygeothermalsystems in Kenya have been determined. Plots on View the MathML source versus δD diagrams show that the compositions do not deviate appreciably from local meteoric water values. This would indicate that local meteoric waters are heated at depth and rise to the surface without much interaction with the country rocks. This is interpreted to be the case for the geothermalsystems at Majimoto and Narosura, which have salinities of less than 350 ppm TDS and calculated reservoir temperatures of less than 110°C. The geothermalsystems at Kapedo and Homa mountain which have high salinities (> 2 000 ppm TDS) and relatively higher calculated reservoir temperatures (> 150° C) are interpreted to have been operating for long periods of time, such that the rocks through which the present day geothermal waters are circulating have attained isotopic equilibrium with local meteoric waters.