Snapshot of hot-spring sinter at Geyser Valley, Wairakei, New Zealand, following anthropogenic drawdown of the geothermal reservoir

From the 1950s, extraction of thermal fluids to generate electricity at Wairakei, Taupo Volcanic Zone, New Zealand, heralded a rapid transformation of surface manifestations at nearby Geyser Valley, 1 km NW of the power station. Active geysers and hot-springs fed by alkali-chloride waters ceased by 1968, replaced by acidic steam-dominated conditions. Field relationships indicate geothermal features are fault-controlled. Siliceous hot-spring (sinter) deposits represent spring-vent to distal marsh settings. The dominant mineralogy is opal-A, with some minor clay alteration. Some textures show silica dissolution and re-precipitation. Thus, only minor alteration and diagenesis has occurred, with vegetation overgrowing the extinct sinter.