Abstract:
Over the last two decades, the prospecting of Rare Earth Elements (REEs) has been
extensively increased owing to their wider industrial applications. Stream sediments
which are rich in precious gem minerals are considered as one of the emerging
alternative sources of REEs with minable concentrations. Hence the present study
aimed to investigate the REE potential of gem bearing sediments of the upper reaches
of the Kalu Ganga river basin of Sri Lanka. The mineralogy and elemental composition
of eighty-one sediment samples were analyzed on X-Ray Diffractometer (XRD) and X
Ray Fluorescence (XRF) techniques respectively. The resulted XRD spectrums
revealed the presence of major quartz and ilmenite with minor gems and REE-bearing
minerals such as andalusite, chrysoberyl, enstatite, garnet, lucasite, magnetite,
monazite, pyrite, spinel, thorneite, titanite, xenotime and zircon. The mineralogy
suggests the association of gem minerals in the studied samples. The stream sediments
indicate significant amounts of Light REEs such as Ce [average 540 (286 - 4310) ppm],
La [average 178 (457 – 1670) ppm], Nd [average 120 (1140 – 1260) ppm], Y [25 (10
111) ppm] and Gd (average 0.05 (0 – 0.98) ppm] which are even above the present day
mining sites of the world. The chemical correlations demonstrated a positive correlation
between REEs with concentrations of Ti and Zr. This suggests that the REE content is
enriched within the recognized minerals such as xenotime (YPO4), monazite
[(Ce,La,Nd,Th)PO4] and lucasite (CeTi2(O,OH)6) which might be associated with Ti
and Zr rich minerals such as zircon (ZrSiO4), ilmenite (FeTiO3) and rutile (TiO2). The
REE concentration shows increased values along the river flow direction specially, after
Ratnapura town. Thus, the study concluded that the Kalu Ganga river basin is a
prospective place for REEs. Since the REEs are associated with gem minerals, it can be
suggested that the gem mining sediments may be the best source for the REEs.
