Geochemical Characteristics of the Mwananyamala Geothermal Prospect in the Kenyan Coast

Abstract

The Mwananyamala geothermal prospect is located outside the active volcanic Rift Valley in the Kenyan coast. A number of hotsprings occur in the area with temperatures ranging from 55-70ºC and an average flow rate of approximately 90 l/s. This paper will characterize the thermal waters; estimating subsurface temperatures define sources of solutes in the fluids and determine whether mixing with sea water exists. As the results indicates, the chemistry of the waters is variably saline for most of the springs reflecting the existence of a mixing process occurring between the infringing sea water from Indian Ocean and the locally recharged unsullied groundwater. The thermal waters from the springs are distinct from ambient borehole waters in chemistry displaying a trend where the former intercedes between the sea and the borehole waters. The Na-Li geothermometry displays a subsurface temperature that ranges between 146ºC and 164ºC. In general, the results suggests the existence of a fairly deep, moderate-temperature geothermal system recharged by shallow circulating meteoric waters related to local groundwater as well as relatively deeper sea water. Hydrochemical water types are largely Na-Cl for the thermal waters and a variation of Na-Mg-HCO3-Cl to Na-Mg-Cl for borehole water.