Geophysical investigations of the Ngatamariki geothermal area

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Bennie, S.L. 1983 Geophysical investigations of the Ngatamariki geothermal area. [s.l.]: [s.n.]. Report / Geophysics Division 192 35 p

Abstract: Three groups of hot springs occur at Ngatamariki about 20 km NNE of Taupo. The largest of these springs discharges water at a temperature of 88 degrees celsius and at a rate of 8.5 l/s. The total natural surface heat loss from the Ngatamariki area is estimated to be 8 MW (relative to 12 degrees celsius). Electrical resistivity traversing surveys have delineated an area of low apparent resistivity centred about 1.5 km east of the hot springs, and it is inferred that this low resistivity is caused by the presence of underlying hot mineralised water. Regional gravity and airborne magnetic surveys cover the area. The area of low resistivity lies within a zone of magnetic minima. The gravity gradient is unlikely to be related to the presence of hot water but the magnetic anomalies are not inconsistent with the exsistence of hydrothermally altered rocks in the area. Chemical analysis show that the larger springs discharge a near neutral alkali-chloride water similar in composition to that discharged by some hot springs at Orakeikorako. Silica and Na-K-Ca geothermometers suggest a deep fluid temperature in the range 180-220 degrees celsius. The results are consistent with the conclusion that Ngatamariki is an independent geothermal field, but lack of data to the north-west means a connection with Orakeikorako cannot be excluded