Grindley, G.W.; Browne, P.R.L. 1968 Subsurface geology of the Broadlands Geothermal Field. Lower Hutt: New Zealand Geological Survey. Report NZGS 34 52 p.
Abstract: This report describes the basic stratigraphic framework of the Broadlands Geothermal Field and provides a structural interpretation of the first eleven drillholes. The stratigraphy consists of dominantly subaqueous pumiceous pyroclastics and lacustrine siltstones of the Huka Group, interstratified with rhyolitic flows and ignimbrite ash flows, overlying non-volcanic sedimentary rocks which overlap to the greywacke basement in the southeast. Two poorly permeable aquifers have been drilled. One major subsurface fault zone- Ohaaki Fault Zone - is the main production zone so far discovered, currently averaging 12 MW/well (steam only). The minimum potential of this fault zone is estimated at 100 MW, possibly rising to 150MW if the zone extends northeast of BR3. Three additional investigation wells to 4200 ft are suggested to prospect for a feed-zone in the Broadlands thermal area, and two investigation wells to 3600 ft are suggested close to the Waikato River to search for permeable zones related to possible fault scarps in the Ohaki Rhyolite as revealed by seismic surveys. Twelve production wells and a deep well site are suggested for the Ohaaki thermal area, as the next stage in developing this area for power production. (auth/ARC)
