Présentations Colloques

    Session 8.05: Karst aquifers
    Feraga (orateur)
    Characterization and Origin of karstic thermal waters of the Northeast of Algeria.
    The northeastern part of Algeria has numerous thermal karstic springs which present an economical interest for the national office of the Algerian tourism. This organization considers the setting-up of infrastructures dedicated to the thermal tourism. The springs are located in a region of a 535 000 kmC which extends from Bejaïa to El-Kala (Tunisian border). The geological context is marked by a geological structure inherited of the alpine tectonic episodes Priabonian to Tortonian at the origin of large faults and thrust systems. **An analysis of the hydrochemical char acteristics of these waters, has be realised, at the regional scale, mainly to determine the geotectonic factors being the cause of the chemical facies and rising, but also to identify one or several deep geothermal reservoirs. Two sampling campaigns were realized on 52 sites, one during low waters (September, 2014) and the other during high waters (May, 2015). The analysis concerned major and trace elements, and isotopes (O18, H2, H3, Sr87 Sr86). **From binary diagrams and from ACP treatments, results allowed to discriminate 4 geochemical groups of waters - (1) a HCO3-Ca type, slightly mineralized and characterizing hypothermal waters with fast circulations, (2) a HCO3-Na type, more mineralized and characterizing mesothermal waters with deeper circulations, marked by phenomena of base exchange between water and clay levels, (3) a Cl-Na type, characterizing hyperthermal waters with deep circulations attested by chemical exchanges with sedimentary evaporite levels, finally (4) a SO4-Ca type having acquired its mineralization in triassic formations. Furthermore, a high percentage (75%) of hyper or mesothermal springs, with chloride or sulphate facies, are located along the large regional faults identified by geophysical investigation. These results will be clarified by the use of silicium and alkaline geothermometers and temperature estimation using saturation index. **


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