REPRESENTATIVITY OF WIDE-SPACED LOWER-LAYER OVERBANK SEDIMENT GEOCHEMICAL SAMPLING

To develop a technique of implementing global ultra-low density geoche mical sampling and as a contribution to the International Geochemical Mapping Program (IGCP Project Nd, 259), an orientation study in the us e of deep (lower-layer) overbank sediments was conducted in Jiangxi Pr ovince of Southeast China in 1989-1990. Ninety-four samples were colle cted at depths of 50 to 120 cm from overbank terraces at an average de nsity of 1 site per 1800 km(2). The total area of sampled catchment ba sins is approximately equivalent to 18% of Jiangxi Province. Most of t he samples were collected at outflow sites of catchment basins with ar eas of 100 to 800 km(2). The samples were analyzed for 39 elements. Th e representativity of wide-spaced lower-layer overbank sediment sampli ng is discussed from various perspectives; the following features have been observed: (1) Wide-spaced lower-layer overbank sediment data and the data from China's national geochemical mapping (RGNR) project sho w similar geochemical patterns for W, Sn, Pb, Cu and Zn. (2) The resul ts of wide-spaced lower-layer overbank sediment sampling demonstrate t hat catchment basins with areas of 100 to 800 km(2) are suitable sampl e site locations for the global geochemical reference network. (3) Wid e-spaced lower-layer overbank sediment sampling is a fast and cost-eff ective way to identify geochemical provinces and has strategic signifi cance in mineral exploration. (4) There is a significant correlation b etween the W content of wide-spaced lower-layer overbank sediment samp les and the presence of W mineralizations within the catchment basins. (5) The distributions of Ni, Cr and V in wide-spaced lower-layer over bank sediment samples distinctly reveals the boundary between the Yang tze sedimentary platform and the South China Caledonian fold system in Jiangxi Province. (6) Distributions of Rb and Be coincide with the Ya nshan granites, which are closely related to the major ore-forming epi sodes in Jiangxi Province.