Radioactive series disequilibria in underground uranium deposits of the Singhbhum Shear Zone, Eastern India

Radionuclides of the U-238 series (Ra-226, Pb-210, Th-234 and U-234), U-235 series (Ac-227 and Pa-231) and Th-232 series (Th-228 and Ra-228) series were measured by High Resolution Gamma Spectrometry system in twenty-five uranium ore samples from underground uranium deposits in the Singhbhum Shear Zone of Eastern India. The activity concentrations were observed to vary within a wide range in most of the deposits, as is the case in most rocks of crustal origin. The uranium ore from these deposits were not of high ore grade (U concentrations ranged from 0.015 to 0.082%). Activity ratios of key daughter-parent pairs from the decay chains, viz. Ra-226/U-238, Ra-226/Pb-210, Pa-231/U-235, Ac-227/U-235, Th-230/U-238, U-234/U-238, Ra-226/Th-230 and Th-228/Ra-228 indicated migration/accumulation of uranium and radium in some samples. The Ra-226/Th-230 ARs suggested that the deposits were not closed to groundwater movement for a maximum time period of 8ky. Thiel plot of the U-234/U-238 vs. Th-230/U-238 activity ratios indicated uranium accumulation and complex processes of uranium redistribution.