A contribution to the pre-Cambrian chronology of Australia

Abstract

The results of quantitative chemistry combined with isotope analyses by mass speotrometry have been used to compute a number of mineral ages by the U-Pb method. The ages of uranium minerals from various parts of Australia have in most cases been in agreement with the previously accepted geologic interpretations. Two periods of uranium mineralization have been confirmed in the Northern Te Titory uranium mining fields (Late Archaean and Upper Proterozoic), and at Crocker's Well in South Australia (Archaean and Upper Proterozoic). Two periods of mineralization have been postulated for the uranium mineralization at Radium Hill (Archaean and Proterozoic) and for the lead mineralization at Broken Hill (Archaean and Cambrian). The uranium mineralization at Myponga, South Australia, and Hart's Range, Central Australia, has been dated as Upper Proterozoic, and at Woodstock, Western Australia, as Archaean. Where suitable samples were available potassium-argon ages have been used to provide additional evidence as to the correctness or otherwise of the U-Pb determinations. A “concordia” diagram did not satisfactorily resolve discordant ages, and it is concluded that radon losses may generally be expected to vitiate this method. A set of four figure tables is presented for conversion of isotopic ratios to geological ages.