Geochemistry of the high-salinity geothermal field of Asal,Republic of Djibouti,Africa |
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| Affiliation: | 1. Department of Theoretical and Applied Sciences, University of Insubria, Via Valleggio 11, 22100 Como, Italy;2. Centre d''Etude et de Recherche de Djibouti Route de l''aéroport, Djibouti, Djibouti;3. Marine Conservation Society, Seychelles, PO Box 389, Victoria, Seychelles;1. CORDIO East Africa, 9 Kibaki Flats, Kenyatta Beach, Bamburi Beach, P.O.BOX 10135, Mombasa 80101, Kenya;2. Cousteau Society, 40 rue des Renaudes, 75017 Paris, France;3. Senckenberg Research Institute and Museum of Nature Frankfurt, Marine Zoology / Ichthyology, Senckenberganlage 25, D-60325 Frankfurt a.M., Germany |
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| Abstract: | In 1987–1988 deep exploratory geothermal wells were drilled in the Asal Rift in the Republic of Djibouti. The salinity of the brines produced in the Asal field exceeded 100 000mg/kg, with a low gas content of the order of 0.6 mmol/mol. Measured temperatures in the producing zones and at wellbottom vary from about 260 to 359°C. The sphalerite and galena scaling observed in producing wells starts at the flash level located at about 850 m depth. The calculated geochemical temperatures are close to 260°C, which is the average temperature of the main reservoir located at depths between 1000 and 1300 m. As a result of sulphide precipitation, about 90% of H2S is removed from the original fluid before discharge. The computed composition of the brine at reservoir conditions is compatible with the presence of stable phases of epidote, (MgFe)-chlorite, albite, K-feldspar, K-mica, pyrite and anhydrite. The main recharge water is seawater. |
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