Spatial analyses for copper, lead and zinc contents in sediments of the Yangtze River basin

Three kinds of spatial analysis methods (geostatistics, spatial autocorrelation and fractal) were used for Cu, Pb and Zn contents in sediments of the Yangtze River basin. The ranges of spatial correlation revealed by variograms are approximately 1000 km for Cu and Zn, while some drift has been detected for Pb. The ranges show correlation among patches, while ranges of positive spatial autocorrelation detected by spatial correlogram based on Moran's I are approximately 500 km for the three elements, showing the average size of patches in the distribution maps. Directional features of Cu, Pb and Zn have been disclosed by variogram and spatial autocorrelation index, which are in accordance with their spatial distribution maps. All of the three indices (variogram, Moran's I and fractal dimension) have shown that the spatial structure of Cu is the best among the three elements, which is mainly controlled by rock type. The spatial structures of Pb and Zn are disturbed by mineralization and possibly by human activities.