Abstract: The floodplain sediments were systematically collected from the major tributaries and mainstream of the Changjiang River to investigate their rare earth elements ( REEs) compositions. In this study, 1M HCl was used to separate the acid-leachable REE from the residual REE in the bulk samples. The analytic results suggested that the residual fraction enriches REE with a proportion up to 70% of the bulk concentration. Different REEs show variable leaching proportions and the leached fraction mainly contains middle REEs, which are predominantly sourced from the dissolution of phosphate minerals such as apatite and partly from Fe-Mn oxide minerals. Light REEs primarily reside in clay minerals and exhibit similar leaching proport ions; whereas heavy REEs generally concentrates in some heavy minerals demonstrate regular leaching proport ions. The HREE-enriched heavy minerals significantly influence the REE compositions between two different fractions of the sediments from different tributaries. Overall, the variat ions of REE composit ions in the tributaries sediments are larger than those in the mainstream sediments, reflect ing the control of provenance rocks on REE compositions in river sediment s. The UCCnormalized REE patterns in the bulk samples and the residual fractions from the major tributaries and the main stream are similar, basically representing the average compositions of the weathered upper continental crust within different catchments. Our study suggested that the REE compositions in the residual fract ion of the Changjiang mains tream sediments sampled from the lower reaches near the estuary reflect the average compositions of the fine-grained Changjiang sediments into the sea, although the REE compositions in s ome floodplain sediments from the upper mainstream may be altered by the nearby local tributaries. The main research result from this study will be helpful for the reconstruction of sediment source-to-sink patterns in the marginal seas.
Key words: Changjiang River; sediment; rare earth element; cont rolling factor; speciation
*Corresponding Author, E-Mail: syyang@tongji.edu.cn
Bulletin of Mineralogy, Petrology and Geochemistry Vol. 30, No.1, 2011, page 31-39
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