Constraining the Fundamental Underpinning Analogy of the Silali and Emuruangogolak Geothermal Systems Using Classical Geochemistry

Silali and Emuruangogolak are trachyte-basalt volcanic edifices located in the North Rift of Kenya. They are typically shield volcanoes with Silali having a well-defined elliptical caldera whereas the Emuruangogolak caldera is bifurcated by the eruption of Emuruapoli trachytes to the North East. Emuruangogolak is indeed located within the Suguta Valley approximately 25 km North of Silali. The two geothermal areas are punctuated by geothermal surface expressions in the form of altered grounds, quiescently weak fumaroles with outlet temperatures of upto 96°C corresponding to the local boiling point. In addition, hot springs occur majorly on the NW of the geothermal areas, for instance, Kapedo, Lorusio and Kalnangi for Silali whereas in Emuruangogolak the Kamuge, Suguta valley and Nangarabat hot springs are also located to the NW. The fundamental features of the geothermal system point to the existence of high-temperature >270°C resource. Silali and Emuruangogolak geothermal reservoirs exhibit redox conditions that are very close to those governed by the FHQ redox buffer with reservoir temperatures constrained by the chemical equilibrium temperatures above 270 °C. The deep reservoir liquid is postulated to be belonging to the Na-HCO3 hydrofacies with appreciable Cl, F, SiO2 and K as depicted from the hot springs located in the corresponding fields that is indeed reminiscent of most the Kenya rift waters. The upflow may be represented by the fumarolic activity within the summit of the two calderas. The fumarole chemistry is inherently affected by different orders of magnitude of ubiquitous air entrainment along the crevices of the lava. On the other hand, the outflow is perceived to be on the NW segment of the geothermal areas as depicted by the issuing of hot springs. The heat source and the volatiles in the two geothermal areas are proposed to be of magmatic nature as constrained by the 13C and 3He/4He isotopic signatures.
Keywords: Silali, Emuruangogolak, Analogy, Caldera, upflow, Outflow, heat source