『Abstract
　Stream sediment geochemistry is extensively used in mineral exploration and environmental studies. However, quantitative assessments of the effectiveness of stream sediment geochemistry for describing upstream lithologies are rare, especially in high-grade metamorphic terrains. This study statistically evaluates whether stream sediment geochemistry can aid in recognizing variations in upstream geology in several high-grade metamorphic lithotectonic units having different metamorphic and tectonic histories, including the Highland Complex, Vijayan Complex, Wanni Complex, and Kadugannawa Complex of Sri Lanka. For this study, concentrations of 21 elements were measured in 2080 stream sediment samples collected from the Walawe River, Maha Oya, Gala Oya basins located on above lithotectonic units and Uma Oya, Belihul Oya, Badulu Pya basins situated adjacent to each other on the Highland Complex. These rivers flow across dry, intermediate and wet zones of Sri Lanka, with river courses having both slope (＞20゜) and flat (＜20゜) areas. Elemental concentrations, averaged over each river basin, show patterns of enrichment and depletion which may relate to localized mineralization conditions, local lithological changes, anthropogenic activities and environmental factors such as local variations in climate and morphology among river basins. Comparison of element concentrations in sediments from the four different lithotectonic units shows that enrichment - depletion patterns can be partly related to rock geochemistry of the associated lithotectonic unit. However, climate and basin morphology also seem to play an important role. Results of Kruskal-Wallis H tests show that both major and trace element levels in sediments from the four different lithotectonic units, as well as from adjacent Uma Oya, Badulu Oya and Belihul Oya basins, are significantly different. Discriminant function analysis appropriately classifies sediments into the four different lithotectonic units with an accuracy of 91.9％. This method also classifies sediments into river basins which share common lithology being situated adjacent to each other in the same lithotectonic unit with an accuracy of 89.5％. This strongly suggests that stream sediment geochemistry is capable of describing the upstream regional scale as well as local scale lithological changes at a great accuracy in complex high-grade metamorphic terrains. In both cases use of channel slope and basin climatic zone as additional variables does not significantly increase overall or individual accuracy in classification.

Keywords: Stream geochemistry; Metamorphic terrain; Discriminant function analysis』

1. Introduction
2. Geology and physiography
3. Methodology
4. Discussion
5. Conclusions
Acknowledgements
References