Effective exploration for uranium in South Australian palaeochannels

Abstract

Analysis of groundwater is a powerful tool for regional exploration for uranium when the target is much smaller than the potential host. Such is the case with the reduced sediments in South Australian palaeochannels. Detailed analyses of multi-element data are required to interpret the uranium data properly. Analyses by inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry can provide quality groundwater datasets and, along with commercial software and better thermodynamic databases of uranium aqueous species in saline waters, make accurate solution chemical modelling available to the exploration geochemist. Lead isotopes, measured by inductively coupled plasma-mass spectrometry, can be used to confirm the groundwater interpretations. Palaeochannels containing uranium deposits in South Australia have neutral, moderately saline groundwaters whereas others may be characterised by saline and often acidic waters. Such waters readily mobilise radium, a daughter product of the uranium, and exploration methods based on uranium-daughters such as radon at the surface or the use of down-hole gamma-logging, may be ineffective. Recent studies on reduction of U⁴⁺ by bacteria and observation of enhanced U in saline ponds suggests that bacterial reduction maybe an alternative mechanism for formation of U deposits in palaeochannels. Such a model may assist to focus exploration into more favourable areas.