Journal
CHEMICAL GEOLOGY
Volume 258, Issue 3-4, Pages 354-361Publisher
ELSEVIER
DOI: 10.1016/j.chemgeo.2008.10.039
Keywords
U-234-U-238 fractionation; Silicate weathering; Carbonate dissolution; Black shale; Groundwater input; Han River
Categories
Funding
- KBSI [N28052]
- Sustainable Water Resources Research Center of 21st Century Frontier Research [3-2-3]
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The uranium (U) content and U-234/U-238 activity ratio were determined for water samples collected from Korea's Han River in spring, summer, and winter 2006 to provide data that might constrain the origin of U isotope fractionation in river water and the link between U isotope systematics in river waters and the lithological nature of the corresponding bedrock. The large difference in the major dissolved loads between the two major branches of the Han River, the North Han River (NHR) and South Han River (SHR), is reflected in the contrasting U content and U-234/U-238 activity ratio between the tributaries: low U content (0.08-0.75 nM; average, 0.34 nM) and small U-234/U-238 activity ratio (1.03-1.22; average, 1.09) in the NHR; and high U content (0.65-1.98 nM: average, 1.44 nM) and large U-234/U-238 activity ratio (1.05-1.45; average, 1.24) in the SHR. The large spatial differences in U content and U-234/U-238 activity ratio are closely related to both lithological differences between the two tributaries and groundwater input. The low U content and small U-234/U-218 activity ratio in the NHR arise mainly from a combination of surface and meteoric weathering of the dominant silicate rocks in this branch and congruent dissolution of already weathered (secular equilibrium) materials. In contrast, the high U content and large U-234/U-238 activity ratio in the SHR are ascribed to the dissolution of carbonates and black shales along with significant inputs of deep groundwater. (C) 2008 Elsevier B.V. All rights reserved.
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