Browsing by Author "Wijesinghe, W.A.D.T.L."

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    Application of Geology and GIS in the Exploration of Gem Deposits in Haldumulla Divisional Secretariat Division, Badulla District, Sri Lanka
    (Uva Wellassa University of Sri Lanka, 2019) Wijesinghe, W.A.D.T.L.; Jayasundara, J.M.C.K.; Jayasinghe, R.M.N.P.K.; Francis, P.
    Sri Lanka has a very long history for gem industry. Geologically, ninety percent of the Sri Lankan rocks are high grade metamorphic type and higher percentage of them has attributed for many of the gem deposits. These gem minerals are found as either primary or secondary deposits. Application of GIS based analysis and predictions of mineral potential areas have attracted huge attention for its versatility of mapping and making predictions of mineral potential areas. Haldumulla Divisional Secretariat in Badulla District was selected as the study area covering 39 GN divisions and 183 villages. This area lies on both Highland and Vijayan complexes and chiefly underlain by Biotite Hornblende Gneiss, Marble, Chanockitic Biotite Gneiss, Charnockitic Gneiss, Garnet Sillimanite Biotite Gneiss and Quartzite. In addition, geological structures like Bintenna Synform, Koslanda Fault and Shear zones were identified within the area. Based on field experience and literature, eight parameters were recognized as causative influences for occurrences of gem deposits, namely; geology, mineralogy, distance to geological structures, distance to internal drainage system, elevation, slope, paddy area, and flood area. Distribution of each factor within the study area was obtained as raster layers (referred to as factor maps). Overlay Method and Weights of Evidence Method (WOE) were used to integrate the factor maps to produce a gem potential map in GIS environment. Kotabakma gem field, Gampha gem field, Weli oya gem field and Nikapotha gem field were identified as high gem potential areas in the area studied. Confirmatory field visits on selected areas of the identified gem fields were made to confirm the information on the map. The final gem potential map will help gem miners to extract gem deposit in Haldumulla DS area and it will upgrade gem industry in Sri Lanka.
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    Introducing a Simple Heat Treatment Method for Natural Topaz in Matale as an Alternative to the Irradiation
    (Uva Wellassa University of Sri Lanka, 2019) Jayasundara, J.M.C.K.; Wijesinghe, W.A.D.T.L.; Jayasinghe, R.M.N.P.K.; Francis, P.
    Most of the Topaz found in Sri Lanka has low commercial value due to their yellow to colourless appearance. The pale colour Topaz can be converted in to blue by irradiation and it is stable at ambient or normal temperature and light. After the irradiation atoms become radioactive whenever there is an excess of energy in their nuclei. This radioactivity generates gamma radiation which can course health problems for those who wear them. Therefore, some countries have issued acceptable radiation level for handling irradiated Topaz. However, Sri Lankan government’s policies on the handling and distribution of radioactive irradiated Topaz to the public are still in infancy. This study is conducted to analyses the radioactivity of irradiated Topaz and to introduce a law cost simple harmless heat treatment method for colour enhancement of Topaz. Natural and irradiated Topaz of Polwatta was analyzed using gamma ray emission detector and radionuclides were identified using Gamma Spectrometry measurements. Mineralogical constituents and composition were confirmed by X-ray diffraction and Energy Dispersive X-ray Fluorescence. Natural topaz samples were subjected to heat treatment and exposure the treatment of temperature ranging 430 °C to 440 °C using electric furnace. Based on the results natural Topaz contained chromium (Cr) Thorium and Uranium series isotopes of 212 Pb, 214 Pb, 214 Bi, 228Ac, 40K and 208Tl other than Al. After the irradiation process long levied radionuclides, 182Ta, 88Kr and 46Sc were generated. Radioactivity of the irradiated samples is high with compared to the natural samples. The reported dose rate of irradiated Topaz was 107.34 mS v h-1. It was able to obtain Pinky color by heat treatment of pale yellow Topaz. This was due to the presence of chromium in trace amount and it has been incorporated in to the crystal structure during the heating process in brown stones.