ABSTRACT
Forest-swamp terrain covers over 400,000 km2 of northeast China. Soil is poorly developed in the terrain. In contrast with A horizon soil, most elements including Cu, Pb, Zn, Ag are strongly enriched in B+C horizon. To compared with bedrock, however, these elements are enriched in both soil horizons. In the soils above the mineralization, Cu and Zn are mostly in the sulphides and crystalline iron oxyhydroxides, Pb is mainly in the sulphides and Ag is mainly in the amorphous Fe oxyhydroxides.
The drainage is not developed in the upper reaches of the valleys. The clastic stream sediments can be collected only in the low reaches of the valleys in the bottom of or sometimes near-waterline bank of streams. In the -5 mm fraction clastic stream sediments, coarse grains (+0.2mm) represent a large portion of clastic stream sediments (over 90%). Metal elements tend to increase in the fine fractions. The sequential extraction results show that the partitioning of Cu, Pb, Zn, Ag in clastic sediments corresponds closely to that of soils. Organic stream sediment (peat) can be collected at either side of streams, in which the concentration of organic carbonate is between 3-16%. In peat, both the total of many elements and the organic bound partition of Cu, Pb, Zn, Ag are markedly increased in contrast with clastic stream sediments. The study of partitioning of metals in stream sediments indicates that clastic sediment is a good medium for pinpointing the mineralization in forest swamp area..
Water plays an important role in surfacial geochemical process in the terrain and pH of water and organic matter of soil are the key control factors in migrating elements. To consider the dispersion pattern of elements in the landscape, we suggest that, clastic stream sediment (-0.9mm) at the density of one sample/4km2 is the best alternative approach for the Regional Geochemistry National Reconnaissance (RGNR) project in the forest-swamp terrain.
