Key points are not available for this paper at this time.
Temperatures measured in drillholes indicate that the amount of dissolved SiO/sub 2/ in thermal waters at depth in the low temperature hydrothermal areas in Iceland is governed by the solubility of chalcedony at below approximately 110/sup 0/. At above approximately 180/sup 0/, the solubility of quartz governs the amount of dissolved SiO/sub 2/ in the water. The factors that determine with which of these SiO/sub 2/ minerals the dissolved SiO/sub 2/ may reach equilibrium in this temperature range were not shown. Equilibrium with chalcedony appears in some instances to be established at 20/sup 0/, but most commonly cold ground water is SiO/sub 2/ supersaturated with respect to chalcedony solubility. Provided SiO/sub 2/ is the only varying component in the system, SiO/sub 2/ temperatures are minimum temperatures and represent temperatures of last equilibrium with quartz or chalcedony. If mixing with cold ground water takes place and an originally high pH of the thermal water is lowered, the estimated SiO/sub 2/ temperatures are likely to be high compared with the temperature of the mixture. There is a clear relation between the intensity of low temperature hydrothermal activity in Iceland and the age of the rocks in which this activity is located.
Stefán Arnórsson (Mon,) studied this question.