Characterization of groundwater mineralization in the eburnean coastal gneiss by geochemical modeling (South East Ivory Coast)

Fractured aquifers of gneiss are the main drinking water sources for population living in the north area of Alepe. Neglecting geochemical monitoring of such groundwater is able to deliver water consumers taking unacceptable risks. The quality of water from bedrock in terms of taste can lead people to drink surface water whose chemical quality is lower in comparison with the reference quality. The aim of this study is to estimate the major cations concentration of gneiss groundwater in which mineralization was almost due to silicate hydrolysis. To achieve the aim in view, a study of main mineral of the gneiss aquifer was carried out and a geochemical simulation through inverse modeling by PHREEQCI code was applied on water rock process. The study showed that the main silicate minerals of gneiss that contained major cations were albite, K feldspar, plagioclases and amphibole. The dissolution mean rates of minerals able to increase groundwater mineralization by hydrolysis were 1.3 x 10-5 mol L-1 for K-feldspar, 3.8 x 10-4 mol L-1 and 1.0 x 10-4 mol L-1 for oligoclase and amphibole (ferro-tshermakite), respectively. Through these results, it shown that oligoclase would be the mineral more favourable for hydrolysis among feldspars studied in the gneiss. In gneiss groundwater, sodium was mainly supplied by oligoclase, potassium was supplied by K-feldspar and ferro-tshermakite, magnesium was supplied by ferro-tshermakite only and calcium was supplied by oligoclase and ferro-tshermakite.