Lake Waikare Low Enthalpy Geothermal Resource, New Zealand: Initial Field Study

Abstract

Lake Waikare, situated within the Huntly coalfield in North Waikato, is host to a small island (Punikanae Island) where a silica sinter-depositing spring is located. This is the only sinter depositing spring known outside the Taupo Volcanic Zone. The chemical analysis from the two spring samples complimented by some geological information gathered during the short field visit and other technical data available in the literature are the sets of information used in this study. Based on the Cl-SO4-HCO3 ternary plot that was used to classify the geothermal waters with respect to major anion composition and the Na-K-Mg ternary plot to classify fluids according to the state of equilibrium at given temperatures, the origin of the geothermal system that feeds the spring is thought to be mature neutral chloride waters that probably originate from an up-flow zone beneath the Punikanae Island with the Maungaroa Fault as its main conduit. Up-flow zones are generally characterized by silica sinter deposition of hot chloride springs on the surface. The relatively high chloride concentrations of the spring that resulted in the deposition of the silica sinters possibly were derived from reservoir waters composed of marine clastic sediments of the Te Kuiti Group. These clastic sediments unconformably overlie the Mesozoic greywacke basement rocks and these basement rocks probably supply the heat to the system. One of the spring sample lies just on the boundary line of the partially equilibrated waters region suggesting reservoir temperature of about 160°C that is typical for a low enthalpy geothermal system. The Na-K and Na-K-Ca geothermometers gave comparatively similar temperatures of 160.0 and 136.0°C, respectively.