Dating of groundwater using uranium isotopes disequilibrium in Siwa Oasis, Western Desert, Egypt
Résumé
Abstract Data on the recent migratory history of radionuclides as well as geochemical circumstances can be obtained from the disequilibrium of the uranium series, which is often brought on by groundwater flow and host rock. Groundwater from the Siwa Oasis is a vital source of water for many uses, and it is distributed widely throughout the Western Desert. Groundwater in Siwa Oasis was dated using measurements of uranium in the water. In water samples that exhibited disequilibrium behavior, the activity concentrations of radionuclides from the 238 U, 235 U and 232 Th series were measured. Therefore we conclude that the measured waters are rich in the 234 U and 230 Th. The secular equilibrium between 234 U and 230 Th indicates that colloidal transport could be the mechanism for the mobility of 230 Th in groundwater. Higher 230 Th levels in the samples show that the aquifer is deep and may have a large amount of thorium-bearing minerals. The lake and groundwater estimated ages showed that the time of uranium migration happened between 60 and 130 ka ago. This aquifer is rich in mineral deposits, as evidenced by the extraordinarily high content of radionuclides. The 230 Th/ 232 Th activity ratio of the samples, indicating pure carbonate minerals, ranged from 12.58 to 20.86.
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