The fluid geochemistry of Icelandic high temperature geothermal areas

Icelandic high temperature geothermal systems are considered to number thirty three, thereof three are submarine and seven subglacial. All are briefly described but the chemistry of fluids from twenty four of them is considered. The fluid in the three submarine areas and those four on land that are closest to the sea are relatively saline but to a differing extent mixed with groundwater. The rest contain dilute fluids. The fluids of the central highland systems are mostly locally derived but may in some instances be quite old whereas those in the northerly Krafla area which is inland and the Öxarfjörður area which is close to the sea appear to be a mixture of local and central highland water, but those in the inland Hengill, Geysir, Námafjall and Theistareykir areas appear to have travelled relatively long distances from the central highlands. The gas observed is magmatic except in the northerly Öxarfjördur area close to the sea where it is apparently derived from organic sediments. •33 high temperature areas in Iceland, 200 °C temperature at 1000 m depth, 3 submarine, 7 subglacial.•9 utilized, 5 power production, 4 other purposes, 3 more explored by drilling, 1 near production.•4 terrestrial and 3 submarine with saline, rest dilute fluids.•Gas of magmatic origin except possibly in one terrestrial and one submarine organic sedimentary.