Geochemical model of uranium accumulation in the semizbay riverbed (northern kazakhstan uranium ore province)

The relevance of the research is caused by the need of exploration of cheap uranium sources near potentially uranium ore bearing areas of Northern Kazakhstan based on studying modern processes of migration and accumulation of uranium. The main aim is to propose a geochemical model of leaching, migration and accumulation of uranium in the Semizbay riverbed based on determining water and bottom sediment composition of river and lake reservoirs, and composition of the Zhaman-Koytass massif and its weathering crust as a primal source of uranium.Objects: modern weathering crust of leucogranites of the eastern part of the Zhaman-Koytass massif; bed sediments of the Semizbay river and its tributary Shat river; riverbed spring, river and lake waters of the Semizbay, Selety rivers and Zhamantuz lake; bottom sediments of the Zhamantuz lake.Methods: x-ray analysis, inductively coupled plasma mass spectomerty, x-ray crystalography, classic methods of determination of cation and anion composition.Results. High concentrations of uranium in spring riverbed waters (0,32 mg/l) and artificial reservoir (0,047 mg/l) as well as elevated con-centrations of uranium in riverbed soil (8,6-13 ppm) and bottom sediments of artificial reservoir (23-24 ppm) in the upper course of the Semizbay river were found. Based on the colected data the authors have proposed the geochemical model of uranium leaching from leu-cogranites of the Zhaman-Koytass massif, its migration and accumulation in the Semizbay riverbed, the modern facies of which act as the geochemical barrier on the way of uranium migration to ecosystem of the Ishim steppe. Uranium concentrations in riverbed sediments in lower course of the Semizbay river (1,9-2, 7 ppm), as well as in water (0,0029 mg/l) and bottom sediments (4,6 ppm) of the Zhamantuz lake, which is the final discharge waterbody of the Semizbay river, represent background uranium concentrations in Western Siberia.