Geophysical investigations of the Mokai geothermal area

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Bibby, H.M.; Dawson, G.B.; Rayner, H.H.; Stagpoole, V.M.; Graham, D.J. 1981 Geophysical investigations of the Mokai geothermal area. Wellington: DSIR, Geophysics Division. Report / Geophysics Division 184 41 p

Abstract: The Mokai geothermal area, about 25 km northwest of Taupo, has only minor surface thermal manifestations with a natural heat output of about 6MW. In late 1976 a bipole-dipole resistivity survey was made in the area surrounding Mokai Springs. Since then an extensive Schlumberger resistivity survey has been made using two spacings (nominally 600 m and 1200 m) covering an area of about 400 sq. km around the Mokai area. Interpretation of all the resistivity data suggests the Mokai geothermal area, below which high temperatures may be expected at depth, is about 12-16 sq. km. Low resistivities interpreted from sounds within this area indicate highly conductive (saline) geothermal fluids at a depth of about 60 m, although below this the resistivity increases, suggesting a lowering of porosity. The interpretation of resistivity measurements suggests a considerable subterranean flow of geothermal fluids northward from the Mokai geothermal area, and a further 76 MW of heat is estimated to be carried by springs and seeps into the deeply incised Waipapa Stream. A second low resistivity region occurs at the Waikato River, about 12 km north of the geothermal field, with an area of 3-4 sq. km. There are indications that this anomaly is caused by hot geothermal fluids and it is suggested here that these geothermal fluids have their origin at the Mokai geothermal field