Stream sediment geochemistry of the Upper Mahaweli River Basin of Sri Lanka—Geological and environmental significance

Abstract

Stream sediment geochemical maps serve as a tool for mineral exploration, identifying pollutant sources and providing information on weathering and transport processes. This paper presents geochemical maps of the upper catchment of the Mahaweli River of Sri Lanka, with interpretations based on geochemistry, geology and environmental conditions. For the construction of these maps, stream sediment geochemical data of 1585 samples, collected from 05 main tributaries of the Mahaweli River, was used. Elemental concentrations of 19 major and trace elements were determined by X-ray fluorescence spectrometry. Geochemical maps were prepared and existing geological maps, discriminant analysis, factor analysis, and correlation coefficients were used to recognize the relationship between spatial distribution patterns and the geological and environmental factors. These maps and statistical analysis clearly show the identical geochemical behavior of K, Rb, Ba and Sr. Even Mg and Ca show a similar distribution in different basins, the lack of correlation with metacarbonates probably being due to dissolution of Ca–Mg bearing minerals. The anomalous concentrations of these elements observed in the Anda Oya of Belihul Oya basin may indicate the existence of a Fe–Cu ore body and a Ni–Cr deposit in the upstream tributary of Badulu Oya. This however needs further detailed geological investigations. High Al levels in some streams seem to be controlled by high silt and clay contents released due to agricultural soil erosion in the upstream areas. Similarly, Pb enrichment in the vicinity of some cities may also be anthropogenic. Na, Mn, Ti, Nb, Y, Zn, Zr distribution in the stream sediment shows a relationship with the underlying lithologies of the area.