Radioactive disequilibria and apparent ages of secondary uranium minerals from Sweden

Abstract Thorium and uranium nuclides have been measured using high-resolution alpha spectrometry in order to examine the potential of secondary uranium minerals for disequilibrium dating purposes. Mineral ages are proportional to the distance below the bedrock surface. Minerals coated on the bedrock surface are usually postglacial with apparent ages below 10 000 years. Minerals collected from cracks and fissures 3–100 mm below the bedrock surface give apparent ages from 14 000 years to equilibrium ages of more than 300 000 years. Samples from drill-cores collected more than one metre below the surface approach equilibrium. Some mineral samples have lost uranium, indicating open system conditions. The examined material does not allow the establishment of a definite relationship between glaciation and mineral ages.