Uranium in the groundwaters of the Republic of Kazakhstan

Hydrogeochemical data on uranium content in the groundwaters of Kazakhstan are evaluated and summarized for the first time. Uranium concentrations in the groundwaters of Kazakhstan vary within a broad range; according to our data, this range is 4.8∙10 −6 – 78 mg/l. The regional background uranium concentration for the groundwaters of Kazakhstan is 13 μg/l, and the anomalous level is 17 μg/l. The maximal uranium content (exceeding 10 mg/l) is detected in the acid groundwaters in oxidation zones of uranium deposits (the Kamyshovoye, Viktorovskoye, Bokayskoye, Abayskoye, Dzhusandalinskoye, etc.). Uranium concentration in near-neutral groundwaters of ore-bearing rocks ranges from 0.1 to 10 mg/l. Beyond the boundaries of deposits, uranium concentrations decrease to n∙10 −1 mg/l. Under favorable hydrogeochemical conditions, uranium has also been observed to accumulate in groundwaters outside the deposits. In this case, the formation of uranium-containing groundwater is associated with the chemically enhanced transition of uranium from rocks into groundwater and its subsequent accumulation due to complexation processes. An increase in uranium concentration occurs in alkaline waters of HCO 3 -Na, HCO 3 -Cl-Na, and Cl-HCO 3 -(CO 3 )-Na composition. With an increase in water salinity to several grams per liter (regardless of its absolute value), uranium concentration rises and can reach n∙10 −1 mg/l. With a further increase in groundwater salinity (up to n∙10 g/l), uranium concentration may increase to n∙10 mg/l, which is characteristic of Kazakhstan, with its arid climatic conditions, so that the groundwaters and surface waters are associated with closed depressions as a result of evaporative concentration. • Hydrogeochemical data on U content in the groundwaters of the Republic of Kazakhstan. • Elevated U-concentrations in groundwater are associated with the U ore deposits. • U deposits occur in both Paleozoic basement and Mesozoic-Cenozoic cover. • Highest U-concentrations occur in acidic groundwaters of U deposit oxidation zones.