Gallium and germanium distribution in geothermal water

Abstract

The geochemistry of gallium and germanium was studied in geothermal waters from the low-temperature fields in the Southern Lowlands and the Geysir hightemperature field in Iceland. Germanium concentrations in waters with temperatures below 225°C were in the range <0.05-24 ppb whereas those of gallium lie in the range of <0.01-21 ppb. Both elements show positive relationships with temperature, in particular Ge. Based on aqueous speciation studies, the dominant forms of Ge and Ga in the water are H4GeO4 0 and Ga(OH)4 -, respectively, but H3GeO4 - and Ga(OH)3 0 are also important. The mobility of Ge relative to Si and of Ga relative to Al is much higher than the respective primary rock ratios. The cause of this is considered to be either non-stoichiometric dissolution of the primary basalt rock-forming minerals with respect to Ge and Si and Ga and Al and/or exchange of Ge into silicates and Ga into aluminium silicates in ratios that differ from those of fresh basalt. An example of such an exchange is given for Si and Ge.