Characterization the Gem Bearing Sediment Deposits Using GIS Technique in Kalu-Ganaga River Basin, Sri Lanka

B. A. S. Kumara, H. M. R. Premasiri


Sri Lanka iswell known for supply of most valuable of gemstones in the world,and dominated by varieties of corundum; spinel, garnet, beryl, tourmaline, topaz, andzircon. The most popular and main gem mining fields fall in Rathnapura and Elaheraareas. In most localities, gem minerals are recovered from residual alluvial and eluvialdeposits, though deposits of hybrid origin are also common.The gem deposits arepredominantly associated with river flood plains and paddy fields. There are masses ofgravel and other residual or detrital materials that have been concentrated by weatheringand mechanical processes. The gem bearing beds in the Rathnapura areas are mostlyalluvial in origin and thesequaternary gravelsbeds are inter-layered with site, claysandand lateritic beds. Angular rock Fragments are also present in the gravel and in residualdeposits. The gem deposits of Sri Lanka have been studied by many previous workers(Adams, 1929; Coates, 1935; Wadia and Fernando, 1945; wells, 1956; Cooray andKumarapeli; 1960; Cooray; 1967; Katz, 1969, 1972 a ; Silva; 1976; Dahanayakeetal.,1980). Most of these studies were mainly focused on to determine mode of occurrenceand sedimentary environment. But the present study was mainly aimed to characterizedgem bearing beds with respect to source and distribution within the basin. In this study,present gem deposits/ beds were mapped and collected data on characteristics of gembearing gravel layers, their association and gem potentiality etc. Finally spatial data basewas formed using GIS tools and model the distribution and characteristics of gembearing layers. The results show number to layers have gem bearing layers. Mainlyconfined to Pelmadulla area gem bearing layers are located in special variation pattern.

Key words: Gem beds, Alluvial gem deposits, spatial data base, Modeling

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