Uranium numbers alert: Uncertainties associated with estimation of uranium resources

Abstract

Uranium property exploration and evaluation pose many of the challenges common to base and precious metal deposits in terms of sampling, sub-sampling, sample preparation and analysis. As always, geological interpretation plays a major role in planning sampling, selection of techniques and changing the planning as results come to hand as well as in the mechanics of obtaining numbers and their interpretation. Abnormal mineral hardnesses of both ore minerals and gangue minerals, specific gravity differentials, recovery problems in both sampling and sample preparation as well as in primary metallurgical evaluation all require consideration. Brief summaries of tricks and pitfalls in sampling of uranium deposits in Australia in the past are given, with potential and real impacts of misunderstanding the numbers. Sample preparation techniques, past and present, with recent advances to minimise problems are discussed. Analytical techniques for uranium and parts of their evolution over the last 50 years are mentioned. Simple outlines of uranium decay chains are given as an essential component in understanding modern analytical technology. While all of these factors warrant constant attention to detail, several aspects specific to uranium mineralisation are emphasised, including recovery of fine-grained minerals in sample preparation, analysis and mining and metallurgy. Radiometric disequilibrium of a sufficient degree to invalidate simple interpretation of radiation as being directly proportional to uranium content is shown by direct comparison with prompt fission neutron downhole logging. This paper is intended to be an alert to those producing and/or using uranium numbers in property evaluation.