Evolution and origin of geothermal waters in Öxarfjörður, NE Iceland

The geothermal waters of Öxarfjördur NE Iceland have a complicated origin. They derive from effluent water from the high-temperature geothermal fields within the fissure swarms to the south, excessive groundwater flow from the mountain ranges and offshore seawater inflow into the fissure swarms. Studies of stable isotopes indicate that their origin is partly Pre-Holocene, which is supported by chemical properties. The warmest saline waters with geothermal reservoir temperatures of about 150°C show significant oxygen shift and geochemical changes due to intensive water-rock interaction. The less saline geothermal waters may originate by mixing of geothermal effluent water from the fissure swarms, fresh groundwater and a small component of Pre-Holocene water.