Geochemical investigation of geothermal power potential exploration of hot springs in South-western Tanzania
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Date
2010
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Abstract
Geochemical investigation of the power potential of Songwe geothermal prospect in south-western
Tanzania within the East African Rift Valley was carried out. The thermal geochemistry was studied by
collecting and analysing samples from 14 hotsprings. The maximum discharge of thermal water occurs
at the northern part of the prospect, at the bottom of a travertine cliff, 35 km above River Songwe level,
at a rate of 26 kg/s (T = 80°C, pH = 6.7). The southern springs are discharging between 30 to 50 m above
river level. Degassed thermal water (CO2 and H2S) discharges at the river level and cause an increase of
about 0.2 to 2°C above the ambient river water temperature (25°C in November), with a maximum spring
temperature of 81°C (pH = 6.9). The lowest is Bwana Hutu (3 to 5 m above river level) thermal area where
springs are degassing carbon dioxide gas with maximum temperature of 81°C (pH = 7.6). All springs in
Songwe are depositing travertine except one spring degassing at (46.7°C, pH = 6.8). The total discharge
rate of thermal fluid is between 45 to 75 kg/s with a median temperature of 60.5°C, and an estimated
heat transfer of 10 MW. The results showed that the waters are of sodium-bicarbonate type, formed by
steam heating below water table at the periphery of a geothermal system. The low predicted subsurface
temperature of maximum 152°C (SiO2 no steam loss geothermometer), compared to the earlier
prediction of 270°C (unknown geothermometer) is due to great dilution of the deep fluid by percolating
rainwater and encroaching ground water (July). This was indicated by high magnesium concentration in
the samples of over 8 mg/l compared to deep fluid magnesium level of less than 1 mg/l and also by the
chloride-enthalpy plot in which most of the data plotted along the dilution line. The total usable power
potential is estimated to be 107 MWe.
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Keywords
Geochemistry, Geothermometer, Mbeya prospect, Geothermal power potential
Citation
Mnzava, L.J. and Mayo, A.W., 2010. Geochemical investigation of geothermal power potential exploration of hot springs in South-western Tanzania. ABOUT IJWREE, 601.