Enrichment of high field strength elements in stream sediments of a granulite terrain in Sri Lanka — evidence for a mineralized belt

Size fractions (<63, 63–125, 125–177 and 177–250 μm) of stream sediments draining high-grade metamorphic sources from the Walawe Ganga Basin located in a high-grade metamorphic terrain of Sri Lanka have been analysed for their major and trace element composition. The chemical compositions of sediments were compared with those of the probable metamorphic source rocks in the tributary basins. Rocks in the area are characterized by higher contents of some of the large ion lithophile (LIL) elements such as K, Rb, Ba, Sr, Pb and high field strength elements (HFSE) compared to similar granulitic terrains. Geochemically, the terrain is comparable to the post-Archean upper crust. The size fractions of stream sediments indicate that most of the HFSE and related trace elements are more enriched in the 63–125 and 125–177 μm size fractions compared to the <63 and the 177–250 μm fractions. Studies of elemental ratios in sediments show that the geochemistry of most elements such as Ti, Nb, Zr, Hf, Th, La and Ce in sediments is mainly controlled by the heavy mineral phases. r, geochemical data of these rocks do not correlate with elemental content in stream sediments. Only alkali, alkaline earth and some trace elements such as Cr, Mn, Co, Ni, and Y roughly correlate with the chemical composition of the probable source rocks. Nevertheless, most of the HFSE and related trace elements (e.g. Ti, V, Nb, Zr, Hf, Th, La, Ce) are highly enriched (factor of 10 or more) in sediments compared to the probable source rocks. Compared to the <63 μm fraction, other selected fractions indicate higher enrichment relative to their probable source rocks. This presumably indicates the presence of HFSE-rich mineral sources such as granitic pegmatites in the drainage area.