Hekla cold springs (Iceland): groundwater mixing with magmatic gases.

We have analysed the chemical and stable isotope compositions of four spring waters situated just northwest of the Hekla volcano, where cold water emerges from the base of the lava flows. The stable isotope ratios of water (H, O), dissolved inorganic carbon (C) and sulphate (S) were used to determine whether magmatic gases are mixing with the groundwater. The waters can be characterised as Na-HCO(3) type. The results show that deep-seated gases mix with groundwater, substantially affecting the concentration of solutes and the isotopic composition of dissolved carbon and sulphate.