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. (C) 2017 Elsevier Ltd. All rights reserved.