Faure, K. 2003 Oxygen isotope analyses of nontronite from the Arapuni Dam foundation . Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 2003/26 3 p.
Abstract: Oxygen isotope analyses of nontronite from clay seams in the Ongatiti Ignimbrite, which is the rock foundation of the Arapuni Dam, indicate that they formed from meteoric water at temperatures of ~35 oC, up to ~70 oC. The cooling ignimbrite is thought to have provided the heat for the geothermal fluids from which the nontronite precipitated. No geothermal water is apparently circulating through the Ongatiti Ignimbrite at present, so nontronite precipitation in seams is probably not on-going. (auth)