Use of Radon and Carbon Dioxide in Geochemical Exploration of Menengai and Silali Geothermal Prospects, Kenya

Abstract

Anomolous concentrations of indicator gas components in subsurface air are related to the geological structures and geochemical environments of the regions under consideration. Intensity of gas flow, its composition and isotope ratio of some of its components radically change in periods of seismic activity. Gas surveying in combination with other geochemical, geophysical and geological methods can be applied to fulfilling a number of needs in geological prospecting. High values of Radon//CO2 ratios were detected in the Menengai caldera and towards the north and north western parts out of the caldera, coinciding with high 222Rn (cpm) and somewhat elevated CO2 values (% v/v), indicating good permeability. In the Silali geothermal prospect, high carbon dioxide concentrations in the soil gas were observed around the south, south east, north and north-eastern flanks of the caldera, areas that coincide with the deep seated faults where the source may be a magmatic body. A NE-SW and N-S trend emerges in areas of high radon distribution. Soil gas survey values are consistent with surface manifestations showing a permeable area with somewhat elevated soil gas concentrations on the south eastern side of the Silali caldera.