Ngatamariki Geothermal Field, New Zealand: Geology, geophysics, chemistry and conceptual model

Abstract

Ngatamariki Geothermal Field is the most recently developed field (2013) in the Taupo Volcanic Zone (TVZ) New Zealand for electricity generation. This paper summarises the geological, geophysical and chemistry findings of the last 30 years, and states the current knowledge and understanding of the field.The field, located 17km northeast Taupo, extends on an area of 7km2, where 12 geothermal and 15 monitor wells have been drilled since 1984. Ngatamariki comprises a deep, hot (260–285°C) geothermal reservoir overlain by two separate groundwater aquifers. Host rocks are predominantly similar to most of TVZ geothermal systems, rhyolitic pyroclastic and lava, with volcaniclastic sediments and deep buried andesitic units, but differ in the North part of the field where an intrusive complex has been intercepted by drillings. The fluid chemistry is consistent with near-neutral pH reservoir conditions dominated by meteoric waters. Shallow steam-heated waters mixed with deep chlorine water above clay caps. The extent of the clay alteration has been assessed by several electrical and magnetotelluric surveys, along with gravity and magnetic, defining a North–South elongated resource area.Results from exploration and surveys for the last 6 years are presented and integrated together to present an overall conceptual model of the field.