Mineralogical and Geochemical Characterisation of Rocks and Geothermal Fluids in the Olkaria Geothermal Field, Kenya: Potential for Epithermal Deposits

Abstract

The Kenyan Olkaria geothermal field has incredibly high geothermal potential in the East African Rift, the Kenyan Rift Valley. While the Olkaria geothermal area has been primarily attributed to electricity generation and direct uses, this research investigates the potential of epithermal deposits in the geothermal systems with particular interests in base metals (Zn, Pb, and Fe) and alkali metals (Li, Na, K) in geothermal rocks and fluids. The study employed geo chemical, geological, and well-logging analyses to characterise and assess the conditions in the geothermal system suitable for forming and depositing epi thermal minerals. Rock cuttings and fluid samples were collected from geo thermal wells, fumaroles, and hot springs. Findings indicate that the mineral isation in the Olkaria wells occurs in microveins and disseminations in the rock matrix, majorly sulfides, and oxides in hydrothermal alteration zones. The reported Zn, Pb, and Fe mineralisation mainly relates to low sulphidation type from the characterised sulphur metal complexes and oxides. Fluid sam ples recorded the metals as follows: Fe (0.12 - 3.9 ppm), Zn (4.21 - 5.23 ppm), Pb (1.55 - 2.04 ppm), and lithium concentrations at ≤ 3 ppm, which is lower than extractible values in geothermal brines in the Salton Sea and geothermal fields of Europe. The economic characterisation of rocks and fluid samples in our area indicates that the concentration of base and alkali metals has not yielded economically viable values compared to other geothermal systems with economic grades. Detailed studies are recommended to quantify miner alisation in Olkaria geothermal fields and their extractability for sustainable management of the geothermal resource.