Browsing by Author "Janajeewa, W.M.C."

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    Sedimentological and Mineralogical Investigations of Heavy Mineral Sand Deposits in Mahaweli River Alluvial Fan
    (Uva Wellassa University of Sri Lanka, 2013) Janajeewa, W.M.C.
    Some places of Sri Lankan coastal stretches have high percentage of heavy mineral accumulation. There was no evidence sedimentological or mineralogical analysis many of them including Koddiyar bay alluvial sand deposit. Distribution of heavy mineral sand was observed at first visit of research area. This research was done to investigate relationship between particle size distribution and heavy mineral accumulation, sources of deposit, yield of heavy mineral in deposit and economic feasibility of the deposit. Thirty Samples were collected at thirty locations of Mahaweli river alluvial fan. Selected samples were sieved by different sizes of sieve for sieve analysis. Sieved samples were collected separately as + 0.063 mm to - 1 mm, + 1 mm to - 2 mm and + 2 mm fractions for mineralogical analysis. Composite sample was sieved using 2 mm, 1 mm, 0.5 mm, 0.25 mm, 0.15 mm and 0.063 mm sieve sizes. + 0.5 mm to - 1 mm, + 0.25 mm to - 0.5 mm, + 0.15 mm to - 0.25 mm, and + 0.063 mm to - 0.15 mm fractions were processed to investigate mineralogical details of research area. Permanent magnet was used to separate magnetite from others before the magnetic separation. Magnetic separation was done for MW samples using lift up magnetic separator. After the magnetic separation all magnetic fractions and non-magnetic fraction were collected separately. Heavy medium separation was done for Non- magnetic fractions. As final laboratory process, Grain counting was done for " all sample fractions by optical microscope. Shape of particles was observed. This research was identified type of minerals such as ilmenite, rutile, zircon, garnet, leucoxene (amorphous), quartz as major minerals and magnetite, silimenite, monazite, spinal, feldspar, mica and hornblend as minor minerals of Koddiyar bay alluvial deposit. Color of each size fraction; lower size fraction consist of very dark color minerals than other fractions. There were no any heavy minerals over + 1 mm fractions. Zircon grains were commonly rounded. Rutile grains generally were secured their crystal structure. Ilmenite particles were not regular shape and couldn't see sharp edges. Garnet particles were shaped with sharp edges. Rutile, zircon and monazite were found as nonmagnetic heavy minerals.
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    Sedimentological and Mineralogical Investigations of Heavy Mineral Sand Deposits in Mahaweli River Alluvial Fan
    (Uva Wellassa University of Sri Lanka, 2013) Janajeewa, W.M.C.; Cooray, J.T.; Jayawardana, D.T.
    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.