Geochemical characteristics of the greater Olkaria geothermal field, Kenya

Abstract

Aquifer fluid compositions and aqueous species distribution have been calculated for samples from nineteen wells in the greater Olkaria high-temperature geothermal field, Kenya, with the aid of the WATCH-speciation program. It is concluded that overall mineral-solution equilibrium is closely approached at quartz equilibrium temperature with respect to most hydrothermal minerals occurring in the aquifer. The minerals involved are in alphabetical order: albite, anhydrite, calcite, epidote, fluorite, microcline, prehnite, pyrite and pyrrhotite. The solute geothermometers indicate temperatures similar to anticipated aquifer temperatures. However, the gas geothermometers give temperatures either higher or lower than measured aquifer temperatures. The chemical composition of the alteration minerals of the buffer participating in the gas equilibrium is required to formulate new calibration that will be suitable or appropriate for the Olkaria geothermal field discharges. The stable water isotopes indicate that the fluid discharged in the eastern and western fields has different sources.