Putauaki (Kawerau) MT Resistivity Survey

Abstract

New magnetotelluric resistivity soundings, supplemented by Schlumberger traversing measurements, have been collected in the vicinity of Putauaki (Mt Edgecumbe) to investigate the southern and eastern extent of the Kawerau Geothermal Field. They show that this field is associated with a large area of low resistivity totalling about 22km2. Approximately 50% of this area is administered by the Putauaki and Te Tahuna Putauaki Trusts, and only a small portion has been tested with exploration drill holes. The volcanic peak of Putauaki itself (<5k yrs old) is on the southern boundary of the field. An association is inferred between the magma body feeding this vent and the heat source for the geothermal system (>300k yrs old). An area of particularly low resistivities (<5 ohm-m at lkm depth) and cold geothermal gas vents (H2/Ar geothermometry >25OoC) is located near the centre of the revised low resistivity anomaly, about 1.4 km east of the hottest existing Kawerau geothermal wells (KA26, KA29). From this data, a geothermal hydrological model is inferred: a deep upflow, with associated intense hydrothermal alteration, occurs on faults centered beneath the gas vents, and supplies lateral flows to the northwest into the area of present production at Kawerau, as well as to the northeast.