The Geology, Mineralogy and Geothermometry of the Broadlands Geothermal Field, Taupo Volcanic Zone, New Zealand

Following the commissioning of the Wairakei geothermal power station, several areas in the Rotorua-Taupo Volcanic Zone were investigated for their power-producing potential. One of these was the Broadlands district, where a resistivity survey had located a sizeable area of subsurface water. The first hole, east of the Waikato River (Fig. 2), was drilled in late 1965, but although the temperature at hole bottom is 278 degrees, rock permeability is low and the bore is a poor steam producer. However, further drillholes (Br 2, 3 and 4) in the Ohaki area tapped good supplies of high temperature water and prompted a fullscale scientific and exploratory drilling programme. This was completed in mid-1971 after 25 holes had been drilled and it was estimated that the field could produce about 150 megawatts of electricity.