Bwengwa River, Zambia - Exploration of a Non-Volcanic African Geothermal System

Abstract

The Bwengwa River geothermal field is a moderate-temperature fault-based geothermal reservoir located along a northeast-trending northwest-dipping normal fault associated with prolific near-boiling hot springs and terrace deposits. Temperature gradient hole drilling has encountered a more than 100°C reservoir at the faulted contact with the Proterozoic basement. Fluid geochemistry and cation geothermometry are consistent between the well fluids and the hot springs and indicate a deeper reservoir of ~150°C. Magnetotellurics, gravity, 3D magnetic modeling, and structural mapping indicate subsidiary conjugate faults to the main fault zone. The conceptual model of the reservoir has been updated for use in exploration well targeting and for an initial resource capacity estimate. A probabilistic power density estimate of a discovered 150°C resource yields an expected power capacity of 2-93 MW (P90-P10) with a most likely value of 15 MW (P50). Further planned exploration may increase this capacity estimate and confidence level.