| Abstract |
Active geothermal systems and related epithermal mineralization in the Djibouti Republic Abdourahman omar haga Ministry of energy, in charge of natural resources Republic of Djibouti (EAST AFRICA) bilane24@yahoo.f r ; agaboudin33@gmail.com The Djibouti republic is located in the junction of three majors extensional structures(east Africa rift, red sea rift and gulf Aden rift)forming the Afar depression(Barberi& al 1975). The Afar region is characterized by the importance of volcanic manifestation which developed since early stage of extension affecting the Afro-Arab plate (24My ago Barberi &al1973). At earlier stage of rifting, as well as in the recent volcanic centers of Afar margins, the magmatism association is mainly bimodal (basalt and rhyolite). These volcano-tectonic processes have created numerous geothermal systems in the Djibouti republic. Hot springs, fumerols, hot grounds, deeply altered basalts and hydrothermal deposits (silica, zeolites, calcite…) are found along faults lines. Geothermal explorations in the 70th (BRGM) and in the 80th (Djibouti government in cooperation with Italia and World Bank) have confirmed the potentiality of DJIBOUTI in geothermal resource. These explorations were mainly focused in geothermal resource without any consideration for possible minerals deposits from geothermal systems. Lindgren (1933) has defined different categories in hydrothermal metal deposits and among them the epithermal deposit (formed in the 200-300°C interval, in low pressure environment and low sulfidation condition. Geological, geochemical and hydrothermal alterations data’s collected during geothermal and mineral exploration programs(from 1980 to 2012) clearly show that surface expression of low sulfidation epithermal deposit linked to active geothermal systems exist in Djibouti Republic The Assal rift geothermal field drilled by the BRGM(Bureau de Recherche Geologique et Miniere) in 1975 (Assal 1 deep well) and by the Djibouti government between1986 and1988(Assal 3 and Assal 6 deep wells) have a brine reservoir( T°=260°C , P=20 bars , flow=350t/h ,TDS =130 mg/l) depositing lead and zinc sulphides in well head. A USGS(United State Geological Survey) study in the 90th demonstrate that some geothermal fields are probably depositing precious and base metals in the country(Dr Mike Foose, unpublished report). The geothermal fields of GARABAYS; OKLILA’OU and ASSALAYTA are closely associated with high surface anomalies of gold (Usgs 91, Green River 2004 and Stratex International 2012). In 2012, Stratex International (gold exploration junior) has discovered the ‘’ Pandora’’ reefs in the southeastern part of the Gaggade graben, surface samples analysis from these veins has given very high anomalies of gold (9.80 to 25.9 g/t Au,’ STRATEX International’ press release number3786B09 of 16 April 2012). Aligned in the same NW-SE structure of Pandora reef, several actives fumerols (T° ≥ 90°C) are situated to the northern part of the same area. Although surface expression of epithermal mineral deposit is widespread in some geothermal fields, until now commercially exploitable minerals deposit was not still discovered. Knowing the high risk related to any first step in exploration (geothermal or minerals) for private investors, the Djibouti government has decided to use local and regional specialists for this initial phase. Capacity building in geosciences is in progress at several state departments and at the University of Djibouti with the help of international organizations (PNUD, UNEP, UNUGTP, ICEIDA...) A new state institution fo |