Geochemistry of thermal waters from Morocco

Thermal waters from the Rif (Northern Morocco) have temperatures in the 31±528C range, near-neutral pH (6.3±7.0), variable redox conditions (from ÿ0.2 to 0.5 V) and a wide range of total dissolved solids (<1±27 g/l). The D/H and 18O=16O isotopic ratios of the water suggest a meteoric origin for the thermal waters. The main chemical composition is sodium-chloride, resulting from the interaction of water with marine sediments. High- salinity waters show high concentrations of B, Li, and Sr, while other minor components and metals (e.g., Fe, Mn, Zn, Cd, Pb, Cu, Co, Ni, As, Sb and Hg) are usually very low. At Oulmes (Massif Central) the water shows 428C, a pH of 5.9, TDS of 1.5 g/l, sodium- bicarbonate chemical composition, and high P-CO2. This water ¯ows out of granite rocks and is characterised by high concentrations of SiO2, Li, Rb, Cs, Fe, Mn, Be and As. Chemical equilibrium studies show that the thermal waters are close to equilibrium with respect to calcite, dolomite, chalcedony and kaolinite, while equilibrium with respect to gypsum and barite occurs in the sulphate-rich waters. Chemical geothermometers suggest deep temperatures close to 1008C for the warmest water in the Rif (My Yacoub: 528C at the emergence), and about 1308C at Oulmes. 7 2000 CNR. Published by Elsevier Science Ltd. All rights reserved.