| Abstract |
Low-enthalpy geothermal resources are widely distributed in New Zealand, including (1) hot spring systems with spring discharge temperatures 3.5 km depth in abandoned oil wells in the east and west coasts of the country and (4) natural heat flow 15-20 m below the surface. Hot spring systems in New Zealand are found in four major tectonic settings characterised by: (1) Quaternary subduction-related, rifting and intraplate volcanism including deep seated magma bodies, (2) upwelling of hot mantle, (3) rapid rise of hot waters introduced along fractures in the accretionary prism of North Island and (4) rapid uplift in the Southern Alps. Within the Taupo Volcanic Zone, discharge fluids originate from two sources: arc type magmatic waters derived from subducted materials in the eastern margin, and mantle-rich volatiles in the zone of rifting and intense rhyolitic volcanism in the west. Ngawha has a large mantle component in its fluid discharges associated with intraplate basaltic volcanism. Outside the Taupo Volcanic Zone and Ngawha, most hot spring waters are derived from deeply circulating groundwaters that may bear some imprints of mantle-derived volatiles, saline formation water or metamorphic water. Within the accretionary prism in the east coast of North Island, reservoir waters originate from seawater and water from dehydration of marine clays. Although New Zealand has an installed capacity of 308 MWt, its vast geothermal resources remain largely untapped for direct utilisation of heat. |