Structural, geochemical, and mineralogical investigation of active hydrothermal fluid discharges at Strýtan hydrothermal chimney, Akureyri Bay, Eyjafjörður region, Iceland

A submarine hydrothermal fluid discharge structure in Akureyri Bay, Eyjafjörður region, Iceland, was investigated by means of structural, geochemical, and mineralogical methods. Thermal and chemical gradients between the hydrothermal fluid and the subarctic seawater lead to an ongoing mineral precipitation. This process builds up hydrothermal chimneys of dozens of meters in height and they are still growing. The structural analysis reveals an internal stratification of the mineral precipitates at various scales from sub-micrometers to several decimeters. This stratification indicates random changes in the depositional system during the formation of the hydrothermal cones. Some mineral layers are characterized by a dominance of Si, Mg, and O. In contrast, others are dominated by Ca and O. However, the results of XRD analysis proved that the material consists mainly of a trioctahedral phyllosilicate of the smectite group, presumably saponite or stevensite. Additionally, aragonite and hisingerite could be present. The material is built up of numerous parallel tubes, which act as conductors in the hydrothermal chimneys. Consequently, a large amount of available pore space with pore volumes of up to 6 mm 3 was detected in the sample by the porosity analysis.