Biomineralisation in New Zealand Geothermal Areas

Abstract

Several experiments are cwently underway to investigate the role of bacteria in the formation of unique textures in sinter deposits at New Zealand geothermal areas. Preliminary results are presented from three areas: Warakei, Rotokawa, and Waiotapu. In the Main Drain at Wairakei, thermophilic filamentous bacteria are growing at -62?C at a rapid pace and are progressively sheathed or replaced by amorphous silica, building large 3-D h-shaped structures. Siliceous microstromatolites at Rotokawa, located in the outwash ftom hot springs (60 - 85"C), grow at a much slower rate maintaining a level just above the water sdkce. Growth is initiated on protrudmg pumice stones and wood hgments. At Champagne Pool, Waiotapu, siliceous microstromatolites grow on native sulphur accumulated around the pool edge or on protruding parts of the pool bottom. Their rate of growth (0.02 - 0.03 mm day-') and size is greater than at Rotokawa. Orange precipitates in the pool, previously identifed as flocculated antimony rich sulpbides and sulphur, appear to be entirely biomediated. It is not known whether the bacteria are actively metabolising sulphur or antimony or whether biominerabtion is passive. These biomineralization effects strongly increase surface areas for potential metal - mineral - microbe interactions and thus effect metal distributions in sinter deposits.