Biomineralisation in New Zealand Geothermal Areas: a Progress Report

Abstract

Field biomineralisation experiments, initiated in March/April 2001, continue to be monitored and sampled. At Wairakei main drain, growth rate experiments confirmed that the fibres comprising silica precipitates are cored by filamentous microorganisms. Growth rate is -10 &day. At Waiotapu, glass slides placed in August 200 1, continue to grow and are now terminated by silica spicules up to 7 mm in length. Growth rate is -0.023 mm/day. At Rotokawa, growth rates are extremely slow (<0.001 &day) probably due to the lack of wave action and low pH values. At Tokaanu, sinter growth rate is -0.002 d d a y and encompasses appreciable amounts of green cyanobacteria and other microorganisms. At Waikite, mineralisation at the higher temperature end of the artificial terrace is dominated by calcite that appears to have no biotic characteristics (Growth rate -0.027 &day). Further along the terrace at Waikite, the decrease in temperature allows growth of considerable cyanobacteria, as well as, thick biomats in the side drain. Results from Ngatamariki and Orakei Korako are hard to interpret because of variable sinter growth due to improper positioning of the slides. A new experiment has been initiated at Ngatamariki.