Te Kopia geothermal system (New Zealand) — the relationship between its structure and extent

The Te Kopia geothermal system is one of several high-temperature systems in the Taupo Volcanic Zone (TVZ) of New Zealand. It is located along the Paeroa Fault Zone, a major active fault system trending NE in the central TVZ. Three independent studies, i.e. resistivity survey, magnetic interpretation, and detailed topographic analysis of faults and fractures, indicate the existence of another fault system, trending NW, that also signi®cantly in¯uences the Te Kopia geothermal system. Results from these studies also show that, at Te Kopia, a resistivity low and hydrothermally demagnetised rocks (both are indicators of a geothermal reservoir in volcanic rocks) clearly coincide with a zone of high fault and fracture density. Hence, the Te Kopia ®eld is a good example of the signi®cant in¯uence that geological structures (major fault systems) have on the extent of a geothermal reservoir, by creating zones of fractured rocks that provide permeable paths for thermal ¯uids. # 1999 CNR. Published by Elsevier Science Ltd. All rights reserved.