Assessment of the Kiejo-Mbaka geothermal field by three-dimensional geophysical modelling

Description

High-resolution magnetotelluric and gravity data have been collected over the Kiejo-Mbaka geothermal field, located along the NW–SE trending Mabka fault, in the Karonga Rift basin (East Africa Rift System). Such resolution allowed to reconstruct the field structure with unprecedented detail. Resistivity modelling has been obtained by three-dimensional finite-differences inversion of MT data, while density modelling has been accomplished by surface-oriented inversion of gravity data. Geophysical modelling has identified two sedimentary sub-basins separated by the Mbaka fault ridge, exposing the basement; these previously unknown sedimentary fills have a maximum thickness of ca. 1.5 km. The estimation of the clay cation exchange capacity (CEC) from magnetotellurics identifies a layer of low-temperature smectite alteration in the south-western sub-basin sediments, interpreted as a clay cap. The resulting updated conceptual model of the Kiejo-Mbaka geothermal system is therefore a fault-controlled system with lateral leakage into the sediments, expectably implying a larger reservoir volume than previously estimated.

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