The boron isotope systematics of Icelandic geothermal waters: 1. Meteoric water charged systems

We have measured the boron isotope composition and boron and chloride conce ntrations of 27 Icelandic geothermal fluids from both high- and low-tempera ture systems. The delta(11)B values range from -6.7 parts per thousand in t he Krafla system, to +25.0 parts per thousand in a warm spring from the Sou thern Lowlands. In addition, we have also determined the delta(11)B values of basaltic glass from Nesjavellir (-5.3 +/- 1.4 parts per thousand) and tr avertine from Snaefellsnes (-22 +/- 0.5 parts per thousand). The B isotope and Cl/B systematics of the high-temperature systems are dominated by the c omposition of the local basalts. The lower temperature systems show evidenc e for mixing with B and Cl of a marine origin, together with some uptake of B into secondary mineral phases. The data from the Snaefellsnes geothermal system indicate that the fluids have undergone interaction with basalts th at have undergone significant low-temperature alteration by seawater. Copyr ight (C) 1999 Elsevier Science Ltd.