Sedimentological and Mineralogical Investigations of Heavy Mineral Sand Deposits in Mahaweli River Alluvial Fan
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Date
2013
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Uva Wellassa University of Sri Lanka
Abstract
Most of the economically important offshore heavy mineral sand deposits in Sri Lanka
including Koddiyar bay is not fully investigated and there are very limited studies available in
literature. Koddiyar Bay is the Mahaweli River discharging area. Detailed investigation on
heavy mineral sand deposits is vital before extracting them. This paper presents the results of a
sedimentological and mineralogical investigation of Koddiyar Bay heavy mineral sands deposit
with the view of identifying its economic potential.
More than ninety percent of Sri Lankan terrain is underlain by metamorphic rocks with meta -
sedimentary or meta-igneous origin. Meta-sediments consists of quartzites, quartz schists, fine
to medium grained acidic gneisses and granulites, calc gneisses, crystalline limestones,
dolomites, sillimanite gneisses and silimanite-garnet-graphite rocks (Fernando, 1986). During
the ice age, the present inner harbor area of Koddiyar Bay might have had the normal ridge and
valley topography as we find in present day inland. With the rise of the sea level the present
inner harbor area has submerged gradually and it has opened up rapidly due to wave and current
actions with time (Wijayananda, 1985).
Rock fragments are flown to Mahaweli River mainly during rainy season from catchment areas.
Heavy mineral particles are derived from these detrital materials. Heavy mineral grains are
subjected to abrasion during this transportation. Grains with higher hardness like ilmenite, rutile
and garnet do not change their shape during the course of transportation. Moderately hard grains
like magnetite are changed slightly their shape and they tend to form round grains. Low
hardness grains like monazite and zircon are changed slightly their size and shape also tend to
well roundness. Then this heavy and light mineral grains move with combination of sea waves
and tidal forces. Then sedimentation occurs along coastal stretch in Koddiyar bay. This
processes are not continue throughout the year. During monsoon period deposition layer
thickness is higher than dry season.
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Keywords
Mineral Sciences, Mineral, Science and Technology, Materials Sciences, Biodiversity – Sri Lanka