| Abstract |
Korosi geothermal prospect is a shield volcano located in Baringo County within the Kenyan Rift Valley closely edged by Paka volcano to the north and Baringo geothermal prospect to the south. Korosi volcano is positioned in the inner trough of the rift and is marked by quaternary volcanism and sedimentation. A fault zone separates Korosi with a smaller volcano- Chepchuk to the northeast. GDC field surveys reveal that a geothermal system with reservoir temperatures of over 250 ̊C exists. The volcano is uniquely characterized by geological features each of which has been instrumental in the geological buildup of the area. These features in probable chronological order include a tuff ring, shield volcano, normal faults and fissures, pyroclastic cones, a crater, volcanic domes and a lava tube. These features are each associated to the major lithological units in Korosi which include pumice, lower Korosi trachytes, basalts and mugearites, pyroclastics, upper trachytes and the young Adomeyon basalts respectively. The Kolobochon tuff ring is generally unaltered and exhibits bedding of pumice material or material of pyroclastic density. Based on its characteristics, it was formed around a volcanic vent located in a lake or an area of abundant groundwater. Pyroclastic deposits are exposed on the western lower flat plains of the Korosi volcano and are presumed to be the oldest rock unit associated with the volcano. The lower trachytes are perceived to be the Korosi shield forming rocks whose main edifice which is also well preserved is hypothesized to be Kotang as it forms the summit of the volcanic complex. The rocks are intensely faulted and weathered and exhibit fissility particularly in the northern zone of the prospect. The NNE-trending faults and fissures, which highlight horst-graben topography and alignment of cones, are evident in the Korosi prospect. This main phase of faulting was accompanied by the voluminous eruption of fluid basalt and basaltic trachyandesite lavas which exhibit strong structural orientation. Pyroclastic cones associated with this phase of faulting are also present which is also show alignment with the major hydrothermal alteration activity. The Kinyat Crater is a feature of importance as it signifies an underlying large volcanic vent. This feature is associated with the formation of the upper trachyte rocks as are the gently sloping mounts of trachytic lava that form domes within the prospect where most of the surface alteration occurs. The lava tubes encountered in Korosi are formed by the youngest rocks, the Adomeyon basalts. Although these basalts have not been dated, they are considered very young judging from their unaltered and unvegetated state |