New Zealand potassium-argon age list-1

Abstract The methods used at the Institute of Nuclear Sciences for the dating of rocks by the potassium argon technique are described. The potassium content of the rock is measured by flame photometry, the radiogenic argon content is determined by 38 Ar isotope dilution following vacuum extraction and the isotopic ratios measured on a Nier type mass spectrometer using digital recording and analysis techniques. The system has been calibrated both absolutely and with respect to interlaboratory standard minerals and agreement within 0.8% (S.D.) obtained. The potassium argon ages of 25 new samples from New Zealand and Antarctica are reported. In 14 samples, more than one fraction of the sample has been dated. A list of all known previously published radiometric dates for samples from New Zealand territories is given.