HYDROCHEMISTRY OF THERMAL SPRINGS IN THE COULOIR SUD RIFAIN REGION, NORTHERN MOROCCO

The Couloir Sud Rifain extends eastward from the Atlantic coast of northern Morocco along the valley of the river Sebou. In the eastern part of the region, which includes the Saïss and Fès-Taza basins, groundwater is recharged on the limestone plateau of the Middle Atlas. Groundwater flows northward following the topographic gradient and stratigraphic dip within two carbonate aquifers, the confined Liasic and the surficial Plio-Quaternary, which are separated by marl. Discharge occurs from springs at the margin of the pre-Rif hills and from wells.

Nine springs and a flowing well in the eastern Couloir Sud Rifain were sampled for field parameters, major and minor solutes, and ²H and ¹⁸O. With the exception of one spring (Moulay Yacoub, 54 C) and the flowing well (Ain Allah, 45 C), water temperatures ranged from 25 to 34 C. By comparison, the mean monthly air temperature was 17.6 C. Values of pH ranged from 6.7 to 7.2. TDS values were < 2,000 mg/L except for Moulay Yacoub (29,300 mg/L). Hydrochemical facies for the springs were primarily Na-Cl and Ca-HCO₃, whereas hydrochemical facies for upgradient Liasic wells were primarily Mg-Ca-HCO₃, Mg-HCO₃, and Na-Cl. The only pronounced relationship among major ions for the springs was between Na and Cl (r² = 0.98). Spring waters were near saturation with respect to calcite and dolomite, and undersaturated with respect to anhydrite, gypsum, and halite. Activity-activity diagrams indicate that spring waters were stable with respect to kaolinite. Values of d²H plotted versus d¹⁸O for spring waters fell along a local meteoric water line for Fez (d²H= 7.0d¹⁸O + 6.9) generated using IAEA data. Dissolution of carbonates and Triassic evaporites by meteoric water appears to be the main control on spring-water chemistry.