Geochemical studies on the thermal brine from Reykjanes (Iceland)

Chemical and isotopic (D and ¹⁸O) analyses are presented for thermal brines from three springs and two boreholes on the Reykjanes peninsula. They suggest that the discharge waters are formed mainly by the penetration of local meteoric water into brine-bearing formations followed by evaporation of this brine. As postulated by Björnsson et al. (1970), this evaporation probably occurs relatively close to the surface in the thermal area during the convectional cycling of the brine. The ionic composition of the original seawater is probably modified by equilibria involving secondary minerals; thus, sulphate and fluoride concentrations are probably controlled by the solubility of anhydrite and fluorite, respectively.