proceedings of the 34 technical session of geological

Proceedings of the 34th Technical Session of Geological Society of Sri Lanka, 2018

1

GSSL-2018-A01

HEMATITE NANORICES DEPOSITED MUSCOVITE SURFACES: NOVEL APPROACH ON VALUE ADDITION TO SRI LANKAN

MICA

Anoja Senthilnathan1,2*, D.M.S.N. Dissanayake2,3, G.T.D. Chandrakumara4, M.M.M.G.P.G. Mantilaka2,3, R.M.G. Rajapakse1,5, H.M.T.G.A. Pitawala3,6 and

K.M.N. de Silva2,7

1Academy of Sri Lanka Institute of Nanotechnology, Nanotechnology and Science Park, Mahenwatte, Pitipana, Homagama, Sri Lanka

2Sri Lanka Institute of Nanotechnology, Nanotechnology and Science Park, Mahenwatte, Pitipana, Homagama, Sri Lanka

3Postgraduate Institute of Science, University of Peradeniya, Peradeniya, Sri Lanka

4Department of Science and Technology, Uva Wellassa University,Badulla, Sri Lanka

5Department of Chemistry, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka

6Department of Geology, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka

7Department of Chemistry, Faculty of Science, University of Colombo, Colombo 3, Sri Lanka

*Corresponding Author Email: [email protected]

Industrially important mica mineral deposits are widespread in many parts of Sri Lanka such as Matale, Talatu Oya, Badulla, Maskeliya, Halmadulla, Kabitigollawa and Balangoda. However, industrial applications of mica minerals in Sri Lanka are limited to production of paints, plastics, lubricants and traditional medicinal ingredients even though there are advanced technologically important materials from mica minerals available in the world. Therefore, this study focused on the synthesis of iron oxide nanoparticles on the surface of thin sheet of natural muscovite mica. In this study, 75 mL of 0.37 M ferric chloride solution and 25 mL of 1.11 M urea were mixed together and heated at 90 °C under reflux conditions for 30 min to synthesize iron oxide nanoparticles. Cleaved thin sheets of 0.5 cm × 0.5 cm natural mica were suspended in the colloidal solution of iron oxide nanoparticles and stirred for 24 h using a magnetic stirrer to synthesize iron oxide nanoparticles deposited on muscovite material. Synthesized iron oxide nanoparticles and advanced material of mica was characterized using Scanning Electron Microscopy (SEM) and revealed that iron oxides are in rice grain-like morphology (nanorices) with average particle size of 50 nm and the nanoparticles are uniformely deposited on mica. Fourier Transformed Infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) patterns showed that the final product is comprised of hematite nanoparticles and muscovite. X-ray Florescence (XRF) and Energy dispersive X-ray spectroscopy (EDS) showed the elemental destributions of the synthesized material which contain the composition of muscovite and hematite material. Thermo Gravimetric Analysis (TGA) confirmed that the final product is thermally stable even at 1000 ᴼC. The synthesized advanced synthesized material is having the potential applications in water purification, photocatalytic processes and thermal insulation process.

Keywords: Nanorices, Nanoparticles, Muscovite, Water Purification,Thermal Insulation


2

GSSL-2018-A02

PURIFICATION AND WHITENESS ENHANCEMENT OF KAOLIN FROM A TROPICAL IN-SITU DEPOSIT

G.T.D. Chandrakumara1*, H.P.T.S. Hewathilake1, K.R. Kudahetty2 and A.N.B. Attanayake1

1Department of Science and Technology, Uva Wellassa University, Badulla, Sri Lanka

2Lanka Ceramics PLC, Colombo 03, Sri Lanka


Whiteness of kaolin is considered as a significant optical measurement which is used for grading kaolin in the industry. The main contaminating elements contained in kaolin are iron and titanium which cause reduction of the whiteness values. Enhancing the whiteness values of kaolin to higher levels makes it more suitable for high whiteness applications such as porcelain, paint and paper. Meetiyagoda Kaolin (MK) deposit located in the Southwestern part of Sri Lanka is a result of intense tropical weathering of pegmatitic rocks rich in feldspars. It has been intensively exploited by Sri Lankan ceramic industry. Whiteness of MK has been significantly affected by iron and titanium contaminants. This work aims at enhancing the whiteness of refined MK by purification using potassium persulfate treatment followed by phosphoric acid leaching method. Five hundred micrometer size refined MK was dispersed with sodium silicate in a slurry and treated with potassium persulfate. The resultant powder obtained from the filtration was oven dried and leached for 2 hours by various concentrations of phosphoric acid solutions. Reflectance spectrophotometer analysis, FTIR and AAS were used to characterize the treated and untreated kaolin. Reflectance spectrophotometer analysis results of the fired kaolin pellets revealed that the “L” value can be improved from 89.8 % to 94.5% at the 2 mol dm-3 phosphoric acid concentration while the optimum “a” value of +6.1 and optimum ”b” value of +3.4 were recorded in 3 mol dm-3 phosphoric acid concentration after 2 hour reaction time. The maximum iron leaching capacity was recorded as 77.4 mg L-1 in the 2 mol dm-3 phosphoric acid concentration with 2 hour treatment time. The experimental results suggest that the tested purification method can significantly improve the quality of kaolin in industrial point of view.

Keywords: Kaolin, Impurities, Whiteness, Purification


3

GSSL-2018-A03

VALUE ADDED PRODUCTS FROM SRI LANKAN LATERITES

D.M.S.N. Dissanayake1,2*, M.M.M.G.P.G. Mantilaka1, H.M.T.G.A. Pitawala3, K.M. Nalin de Silva1, R.T. De Silva1 and G.A.J.

Amaratunga1

1Sri Lanka Institute of Nanotechnology, Nanotechnology and Science Park, Mahenwatte, Pitipana, Homagama

2Postgraduate Institute of Science, University of Peradeniya, Peradeniya

3Department of Geology, Faculty of Science, University of Peradeniya, Peradeniya


Laterites are widely distributed in various localities of Sri Lanka. Locations such as Colombo, Kaluthara and Rathnapura districts and most parts of the south western coastline consist of iron-rich laterites with less aluminium content in large minable quantities, although Al –rich laterites are uncommon in Sri Lanka according to the literature. However, based on the preliminary studies, it was noted that Al-rich laterite deposits are found in the Matale district. Current application of laterite is limited to small-scale production of bricks. Nevertheless, such laterite deposits could be used to manufacture value-added products such as oxides and metallic forms of iron, aluminium and silicon, and their nanomaterials which have a large global need and demand. This research focuses on producing value added products from Sri Lankan laterites and their applications in various industries. In a typical extraction procedure, a 3-step continuous procedure was applied for orderly extraction of Fe, Al and Si. First, laterite samples were powdered and sieved after which Fe extraction was done by acid leaching using HCl. The supernatant (S-1Fe) was Fe rich and the residue was Al and Si rich. In the second step, the resulted residue was allowed to react with concentrated NaOH solution in a high-pressure reactor under high temperature to extract Al components by dissolving it as (AlO2)-

(aq). The second supernatant (S-2Al) was used to synthesize value added chemical products of Al including Al2O3 and Al(OH)3. The second residue was rich in Si which was used to synthesize value added high purity SiO2 product. However, further purification methods are needed to get high purity products from these extractions. Iron oxide nanoparticles of various morphologies, were synthesized using extracted iron components of laterites. The purity and the chemical properties were characterized by X-ray fluorescence, X-ray diffractrometry, Scanning electron microscopy, Fourier transform infrared spectrometry. Therefore, this study assures an innovative route for the preparation of industrial Fe, Al and Si based products from Sri Lankan Laterites

Acknowledgement: Financial assistance by the National Research Council Grant no. 16-123 is highly appreciated.

Keywords: Value added products, Laterite, Metal extraction, Nanomaterials, Sri Lanka


4

GSSL-2018-A04

FIELD SURVEY ON MAGNETIC SUSCEPTIBILITY OF SRI LANKAN BASEMENT ROCKS: A USEFUL TOOL FOR CHARACTERIZATION OF CRUSTAL DOMAINS AND

PROCESSES

Bernard Prame1*, S. Samarakoon2, S.N.B. Thaldena4, A.G.S.R. Perera and C.H.E.R. Siriwardana4

116/27, Maligawa Road, Ethulkotte Sri Lanka, 2Deptartment of Physics, University of Sri Jayawardanapura, Sri Lanka, 3Quantec Geoscience Ltd., Toronto, Canada. 4Geological

Survey and Mines Bureau, 569, Epitamulla Road, Pitakotte, Sri Lanka.


Magnetic susceptibility is a measure of the extent to which a substance can be magnetized when it is placed in an external magnetic field. On rock out crops, it is an easily measurable petrophysical parameter. Main magnetic carriers in rocks are magnetite, pyrrhotite and maghematite. As these phases belong to accessory minerals that are often sensitive indicators of geological processes and conditions, the magnetic susceptibility is useful in characterizing the host rocks containing them. During present study magnetic susceptibility of Sri Lanka Precambrian was measured at 632 locations using Exploranium KT-9 Kappameter (Table 1) to identify different susceptibility domains and postulate indications for protolith characteristics and geological processes involved.

Table 1 (*Magnetic susceptibility in SI units)

Highland Complex (HC) including central highlands and former SW Group forms a domain with very low magnetic susceptibility values. This low susceptibility domain is mainly composed of acidic charnockites, quartzo-feldspathic granulites, quartzite and marble. Distinctly uniform weak total magnetic signals of the SW Sri Lanka identified in a previous airborne study are compatible with low and uniform susceptibility readings from SW area. This part of the Sri Lanka Precambrian is identified as a domain of distinctly low oxygen fugacity. Rare high susceptibility values within this area are from rocks of tonalitic to trondhjemitic composition. Towards West, rocks of low susceptibility change to hornblende gneisses and hornblende bearing migmatitic gneisses (including Kadugannawa gneiss) and cordierite bearing pelitic gneisses of Wanni Complex (WC) which have higher susceptibility values. Markedly different histogram patterns of HC and WC are noteworthy. It is noted that magnetite produced at the expense of garnet by cordierite-forming decompression reactions has given rise to very high susceptibility values. Magnetic susceptibility transition from extremely low values to higher values coincides with HC-WC boundary defined by Nd model ages. If this transition manifests the boundary area between HC and WC, present data favours the existence of WC much extended easterly and southerly. Vijayan Complex (VC) displays a distribution pattern similar to HC but its susceptibility values are somewhat higher than those of HC. Further detailed susceptibility measurements combined with magneto-petrology would enhance our understanding on these different crustal units.

Keywords: Magnetic susceptibility, Crustal domains, Magneto-petrology, Sri Lanka


5

GSSL-2018-A05

P-T- t EVOLUTION OF PELITIC AND MAFIC ROCKS AROUND DELPITIYA, IN THE HIGHLAND COMPLEX, SRI LANKA

R.M.D.M. Ratnayake* and L.R.K. Perera Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka


Delpitiya area East of Gampola in the central Highland Complex has received attention due to local occurrences of cordierite and ultra-high temperature (UHT) mineral assemblages in pelitic rocks. This study investigated (a) the distribution of UHT pelitic assemblages, (b) possible indicators of prograde very-high pressure (VHP) /high pressure (HP) metamorphism in pelitic, semi-pelitic and mafic rocks, in Delpitiya area. P-T-t evolution of the area was inferred based on petrography and mineral reactions textures.

The assemblage hypersthene + sillimanite + quartz is rare, but coarse hypersthene + sillimanite, and fine-grained intergrowths of hypersthene + sillimanite after garnet + quartz are relatively common in pelites. Tiny garnet ± quartz within some fine-grained intergrowths of hypersthene + sillimanite and along their rims suggests that the reaction garnet + quartz → hypersthene + sillimanite has been reversed during progression to peak T. However, garnet formation after biotite + plagioclase suggests an isobaric cooling (IBC) path after peak T, and garnet breakdown reactions leading to cordierite + hypersthene and spinel + cordierite symplectites suggest isothermal decompression (ITD) from high to low P following the IBC path. Relic sillimanite needles observed in the core of porphyroblastic garnet in a semi-pelitic rock suggests garnet growth in the sillimanite stability field. Sapphirine + quartz association is very rarely found as inclusions in garnet, and isolated sapphirine inclusions associated with spinel occur in garnet too. Spinel + quartz association is present in the matrix of pelitic rocks. A mafic rock intercalated with the pelitic layers contains porphyroblastic garnet with crystallographically oriented exsolved ilmenite/rutile needles. According to available natural and experimental data, exsolution of ilmenite/rutile from garnet happens during decompression from VHP. Mafic rocks around Delpitiya also show garnet formation and breakdown textures during IBC and ITD, respectively, following peak T. Although unavailability of mineral chemical data hinder a proper metamorphic analysis of our observations from a P-T-t point of view, decompression from a VHP as the area progressed towards peak T, and isobaric or near-isobaric cooling and near-isothermal decompression following the peak of metamorphism can be suggested. Further studies are necessary to decipher VHP/HP metamorphic conditions in the Highland Complex of Sri Lanka.

Keywords: Highland Complex, High Pressure, Decompression, P-T-t path, Sapphirine


6

GSSL-2018-A06

CHANGE OF COLOUR & CLARITY OF SRI LANKAN ZIRCON BY HEAT TREATMENT

U.G.A.M.P. Abewardana* and Sanjeewa P.K. Malaviarachchi

Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka


Among the various value addition methods for gemstones heat treatment is one of the popular methods which can enhance the colour and clarity of gems. In Sri Lanka, different colour varieties of Zircons are found in many locations as semi-precious gemstones. The main objectives of this study are to find the appropriate temperatures for the best colour enhancements under different conditions and to identify structural, compositional and surficial changes due to heat. green, greenish brown and honey brown colour zircons were subjected to heat treatments under oxidizing and reducing conditions by charcoal, coal and muffle furnaces from 8000C-11000C with 500C of temperature increments. Under reducing conditions more significant colour changes were observed, producing light blue and pink colour zircons than the oxidizing conditions for maximum 2.5 hours of heating. From green Zircons, light green colour was produced around 9000C and light blue colour was produced at around 9500C-10000C. The greenish brown Zircons gave light brown colour around 8000C-9000C and produced light blue verities at around 9500C-10500C. From honey brown Zircons, bright pink colour was produced at around 9000C and produced pinkish brown varieties at around 10000C. Colourless varieties were produced by above all three zircon-types above 11000C of heating. In addition to the enhancement of colours, clarity of Zircons was also improved. Only under the oxidizing conditions, the samples were broken into few pieces during heating above 9000C. According to the FTIR spectrums, reducing conditions have decreased the amount of OH- stretching groups while the oxidizing conditions have increased the amount of OH- stretching groups in the zircon structure during heating. ED-XRF analysis gave elemental intensities and the spectrums of heated zircons under reducing condition do not show significant variations compared to the unheated samples while the oxidized samples show much variations like decreasing of the intensities of trace elements. According to the SEM analysis the heated samples at reducing conditions do not show surficial changes while the oxidized samples show some development of surface cracks and fractures. XRD patterns of reduced samples do not show variations compared to the unheated samples concluding the reducing condition is the most suitable environment for heat treatment.

Acknowledgement: The National Research Council (NRC) Grant No. 15-089 is highly appreciated.

Keywords: Zircon, Heat treatment, Color enhancement, Oxidizing-Reducing, Sri Lanka


7

GSSL-2018-A07

PETROLOGY, MINERALOGY AND GEOCHEMISTRY OF ARANGALA GRANITE, SRI LANKA

W.M.R.R. Wickramasinghe* and H.M.T.G.A. Pitawala



Granite is one of the main intrusive rock type in Sri Lanka. Post-tectonic felsic intrusives are found along the South-west coast of Sri Lanka at Induruwa area in the Galle district. In this study, in order to understand their characteristics and evolutionary history, field observations, geological mapping and petrological analysis were carried out. Further, major and trace element compositions of selected rock samples were measured by XRF. A model for the emplacement of intrusions is developed based on detailed mapping of each plutons and their wall rocks and characterization of their internal structures and compositional variation. The plutons were intruded into charnockitic gneiss and biotite hornblende gneiss. Petrological and geochemical analyses suggest that the intrusives are in granitic to syenitic composition. Field relations indicate multiple intrusion episodes in this rock association. According to the mineralogy and textural characteristics four type of intrusives have been identified. Coarse grained pink coloured granitic rocks with porphyritic texture is the most common rock in the area. The next common rock is also porphyritic however, it is a dark coloured medium-grained uniform rock which occurs within the coarse-grained granite. The rock is syenitic in composition and is lacking coarse-grained hornblende. Light coloured medium to coarse grained rocks with syenitic composition and fine-grained pink coloured rocks with granitic to syenitic composition have intruded into the above two plutons and to the host gneisses. According to the aluminum saturation index, studied rocks can be categorized as metaluminous and peralkaline rocks. Highly variable trace element contents of studied samples indicate different genetical history for the intrusives.

Keywords: Sri Lanka, Arangala, Granite, Magmatic intrusion, Post tectonic


8

GSSL-2018-A08

SOURCE OF IMPURITIES ASSOCIATED WITH SRI LANKAN VEIN GRAPHITE: IMPLICATION FROM GANGUE MINERALS

T.C. Senevirathna1*, H. P. T. S. Hewathilake2, P. L. Dharmapriya3, N. W. B. Balasooriya3, H. M. T. G. A. Pitawala3 and H. W. M. A. C. Wijayasinghe1

1Nanotechnology and Advanced Material project, National Institute of Fundamental Studies, Kandy, Sri Lanka


3Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka


Possession of highly pure and crystalline vein graphite of Sri Lanka is well-known all over the world. Further, purification can increase the demand of vein graphite usage in high tech applications. Hence, proper identification of impurities present in graphite is much important before selecting a suitable method of purification. The occurrence of vein graphite is caused due to the transportation of carbon-bearing hydrothermal fluid through fracture system of a host rock. When this fluid is uplifted, the impure graphite could be formed due to wall rock interaction and impurities incorporated with the hydrothermal fluid. Therefore, this study focuses to identify the source of impurities incorporated with Sri Lankan vein graphite by employing both chemical and petrographical investigations. The graphite samples were collected from Kahatagaha-Kolongaha mine at 1132ft and 2000ft depth levels. Samples were collected as a series from host rock to middle of the graphite veins. They were crushed using a laboratory disk mill and <53 μm size fraction was separated by using a sieve. Thin sections of wall rock and graphite-wall rock boundary were prepared from selected samples for petrography. The carbon percentage was determined according to the ASTM - 561 by weighing the residue method. Moreover, geochemical analysis of the graphite samples, was carried out by Inductively Coupled Plasma (ICP) technique followed by aqua regia partial extraction and lithium metaborate/tetraborate fusion. The carbon content of the graphite samples collected from the middle and at both boundaries are 99.08%, 96.29% and 98.01%, respectively, indicating that the purity of graphite decreases from the middle of the vein towards the wall rock. The major gangue minerals found in the samples are pyrite, quartz, chalcopyrite, calcite, dolomite, feldspar, kaolinite and chlorite. Further, petrographical studies show that the wall rocks, which were collected about 5 m away from the graphite veins, contain quartz, feldspar, garnet, biotite and orthopyroxene as major mineral phases while disseminated graphite, zircon, ilmenite and apatite as accessories. In contrast, the graphite-wall rock boundary shows a highly altered zone with the formation of secondary minerals such as biotite, titanite, calcite, pyrite and feldspars. This may be due to the transportation of hydrothermal fluid through the fracture system of the wall rock or mineral grain boundaries. Therefore, this study reveals that the most of the impurities associated with the graphite were derived from the wall rock itself due to the fluid-wall rock interaction and only a minor amount of impurities may have come along with the hydrothermal fluid.

Acknowledgement: The financial assistance by NRC Research Grant 15-007, Ms. D.R.T.L. Harishchandra in Earth Resources and Renewable Energy project at NIFS and Staff at Kahatagaha/Kolongara mine are gratefully acknowledged.

Keywords: Wall rock, Vein Graphite, Hydrothermal fluid, Impurities, Gangue minerals


9

GSSL-2018-A09

QUALITY DEGRADATION OF SRI LANKAN VEIN QUARTZ DUE TO POOR INDUSTRIAL PRACTICES

S.S. Pathirage1*, P.V.A. Hemalal1, L.P.S. Rohitha1, Y.P.S Siriwardhana2 and N.P. Ratnayake1

1Department of Earth Resources Engineering, University of Moratuwa, Sri Lanka

2Geological Survey and Mines Bureau, Sri Lanka


Applications of high purity quartz in the high-tech industry are numerous. A few of them includes semiconductors, microchips, industrial integrated circuits, high temperature lamp tubing, telecommunication devices, optical fibers, chemically reinforced glass and solar silicon cells. Sri Lanka is rich in quartz mineralization with an abundance of major vein-quartz deposits located in many parts of the island with purity levels over 99.5% of SiO2. Non-industrialized countries, including Sri Lanka export raw quartz with enforced size reduction of the run-of-quarry quartz in grit and powder forms to industrialized countries without further value addition. Due to draw-backs in quartz mining and processing, its natural quality is reduced with subsequent increase in impurity levels in the end product. Soil contamination, handling with bare-hands, contamination in the transportation process due to the presence of rust along with waste materials such as dolomite dust in the trucks/tractor trailers and addition of Fe in crushing and, Ni in sieving respectively degrade the natural purity of quartz. In this study, quality variation taking place due to above poor industrial practices were investigated with respect to a vein quartz quarry and a quartz processing plant with state of the art facilities located in Badulla, Sri Lanka. Samples taken in the process, step by step from mining to packing of the final product were subjected to chemical analysis using Atomic Absorption Spectrophotometer (AAS) and Inductively Coupled Plasma (ICP) techniques for elemental composition. Results of the chemical analysis showed a considerable presence of Fe, Mn, Cr and Ni levels of 394 ppm, 6010 ppb, 935 ppb and 766 ppb respectively due to soil contamination, Na, K, Ca, Mg levels of 78 ppm, 64 ppm, 17 ppm and 9 ppm respectively due to handling with bare-hands, Fe level of 164 ppm due to contact with rust layer forming in the conveyances and Ca and Mg levels of 3314 ppm and 3368 ppm respectively due to contamination in trucks used for dolomite transportation. In the crushing process with jaw and roller crushers, analysis shows an addition of Fe level up to 55 ppm. An increase of Ni level up to 135 ppb is shown in sieving using SUS 304 mesh. Methods and techniques to be adopted to ensure strict quality control to prevent quality degradation are proposed.

Keywords: Vein quartz, Sri Lanka, Quality degradation, Value addition


10

GSSL-2018-A10

PURELY CHEMICAL METHOD TO SYNTHESIZE PRECIPITATED CALCIUM CARBONATE NANOPARTICLES FROM IMPURE

DOLOMITIC MARBLES

V.C.M. Somarathna1*, R.M.G. Rajapakse 1,2, M.M.M.G.P.G. Mantilaka3 and H.M.T.G.A. Pitawala4

1Postgraduate Institute of Science, University of Peradeniya, Peradeniya

2Department of Chemistry, Faculty of Science, University of Peradeniya, Peradeniya

3Sri Lanka Institute of Nanotechnology, Nanotechnology and Science Park, Mahenwatte,

Pitipana, Homagama



Precipitated calcium carbonate(PCC)-nanoparticles have gained attention in recent years due to their applications as fillers, extenders, and pigments in industries such as paint, textile, rubber, plastics, cosmetics, drug coatings in medicine, paper and foodstuffs. PCC nanoparticles are mainly synthesized using pure calcite and dolomite-rich rocks. However, there are many drawbacks in the existing process due to higher energy cost at calcination steps, the inclusion of impurities of the rock in the final PCC product. Therefore, in this study, a novel pure chemical route without using high energy calcination step was developed. In this method, dolomitic marble (40g) sample was digested in 1-M hydrochloric acid (100 ml). The same amount of sucrose and 2M sodium hydroxide (100 ml) were added to the mixture in order to separate calcium ions of the rock as calcium sucrate solution while Mg(OH)2 as a precipitate. The filtered calcium sucrate solution was used to synthesize high purity PCC by adding NaCO3 drop wise, while Triton X-100 surfactant were used to prevent the aggregation of CaCO3 particles. The size of PCC nanoparticles were determined using scanning electron microscope (SEM) and showed that it was in the range 30-50 nm. The X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy analyses showed that the PCC product is comprised of crystalline form of calcite. Atomic absorption spectroscopy (AAS) studies confirmed that the final product is in over 99% purity which is suitable for industrial applications. Therefore, the devised chemical method is successful in the synthesis of high purity PCC nanoparticles using impure dolomitic marbles.

Keywords: Calcium carbonate, nanoparticles, dolomitic


11

GSSL-2018-A11

SYNTHESIS OF REDUCED GRAPHENE OXIDE FROM SRI LANKAN VEIN GRAPHITE USING SODIUM HYDROXIDE AS AN

ECO-FRIENDLY ALTERNATIVE

J.N. Kanagaratnam1*, T.H.N.G. Amaraweera2, H.W.M.A.C. Wijayasinghe1 and N. W. B. Balasooriya3

1Nanotechnology and Advanced Materials Project, National Institute of Fundamental Studies, Kandy, Sri Lanka

2Department of Science and Technology, Uva Wellassa University, Badulla, Sri Lanka 3Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka


Sri Lankan vein graphite, being renowned for its high crystallinity and high natural purity (95-99 of C%), has a very high potential to synthesize into graphene with comparatively low cost. Chemical reduction of Graphene Oxide (GO) is the most efficient way to produce graphene on large scale, starting with graphite. However, this chemical reduction process has severe limitations as far as the toxicity of the presently used reducing agents are concerned. Hence, an eco-friendly approach of using sodium hydroxide to reduce GO into reduced Graphene Oxide (rGO) was investigated in this study. GO was synthesized by modified Hummer’s method and reduced with sodium hydroxide to produce rGO. The prepared GO and rGO were characterized by X-ray Diffractometry (XRD), UV-visible spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy. The XRD results showed that the reducing agent used in this study (NaOH) was highly effective to produce rGO from GO. Further, the FTIR analysis confirmed the successful reduction of oxygen functional groups in rGO. Moreover, the UV absorption peak present at 236 nm in GO had shifted to 263nm as the reduction proceeded. Therefore, this study unravels a successful synthesis of reduced graphene oxide out of Sri Lankan natural vein graphite by chemical reduction using NaOH as the reducing agent. Moreover, it reveals this approach is a simple, easily controllable and alternative eco-friendly method with a great potential for production of rGO in large scale.

Keywords: Sri Lankan vein graphite, Graphite oxide, Chemical reduction, Reduced graphene oxide


12

GSSL-2018-A12

PETROGRAPHY OF ROCKS OF KAHATAGAHA- KOLONGAHA GRAPHITE MINE, WANNI COMPLEX, SRI LANKA

N. H. M. C. Nawarathna* and L. R. K. Perera



Present study is a field and petrographic analysis of lithologies of the Kahatagaha-Kolongaha graphite mine, located 32 km NNW of Kandy in the Wanni Complex (WC). Emphasis has been placed on mineral assemblages, reaction textures and mineral inclusions in order to understand, (a) the metamorphic conditions and P-T-t evolution of the area and their relation to the neighbouring Highland Complex (HC) and (b) the timing of graphite mineralization in relation to P-T-t evolution. Lithologies encountered in the mine mainly belong to the granulite- to amphibolite- facies and are represented by charnockitic gneisses and the garnet biotite gneisses, where quartzite is found interlayered with the host charnockitic gneiss. Peak metamorphic mineral assemblages of the gneisses observed in the area are as follows: Hypersthene–garnet–biotite–plagioclase–quartz±diopside (Charnockitic gneiss) and garnet–biotite–plagioclase–quartz±K–feldspar (Garnet biotite gneiss). Sillimanite inclusions inside garnet porphyroblasts in garnet biotite gneisses is the only evidence representing prograde metamorphic evolution of the study area. However, retrograde evolution is represented by three garnet formation reactions involving iron–ore + plagioclase, diopside + hypersthene + plagioclase, and hypersthene + plagioclase suggesting near-isobaric cooling, and by garnet breakdown reaction (garnet + quartz = hypersthene + plagioclase) suggesting near-isothermal decompression. Another cooling stage after the isothermal decompression is indicated by retrogression of hypersthene and clinopyroxene to form biotite, and by exsolution of alkali feldspar to form perthite. D3 deformation has resulted in the formation of the Maduragoda antiform and the E-W striking cracks within its core are hosting the Kahatagaha-Kolongaha vein graphite mineralization. The host rocks of the veins, which metamorphosed during D1 and D2 have been decompressed during D3, and the decompressional reaction textures close to graphite veins have been completely altered during the crystallization of graphite.The garnet formation and breakdown reaction textures and evidence for a later cooling period mentioned suggest that the rocks in the study area in the WC have had a post-metamorphic peak P-T-t evolution similar to the HC. This is the first time garnet formation and breakdown reaction textures have been reported from the WC. Field relations and petrography suggest that the graphite veins are post-D3 or late stage D3.

Keywords: Wanni Complex, Garnet, Kahatagaha, graphite


13

GSSL-2018-A13

TONIGALA GRANITE IS NOT POST-TECTONIC

M.L.G.N.T. Jayatilaka* and L.R.K. Perera



A Km wide and ~13 Km long sheet-like body trending ENE and concordant with the lithologies of the northwestern Wanni Complex occurs at Tonigala, Sri Lanka. It is a rock often referred to as pink granite due to predominance of microcline. It consists of quartz (35-40%), microcline-microperthite (50-55%), plagioclase (10-12%) and biotite hornblende (5-8%) and appears massive when poor in biotite and hornblende, but is foliated whenever the latter minerals are high in abundance. Presence of a biotite-rich foliation, biotite schist lenses and boudins, stretched quartz, large-scale boudins (~3m), pinch and swell structures, tight-folds, and evidence of shearing within the rock suggest that it has been deformed, perhaps in several episodes. Occasional rigid, rotated and disrupted mafic bands contain an internal foliation which is oblique to the foliation of the granite sheet.

The granite is cross-cut by numerous dykes/veins, which according to their field relationships appear to have three modes of origin, namely, intrusive, replacement, and in-situ melting. There are two types of intrusive dykes/veins, they are intrusive pegmatites and layered dykes. Based on field observations and cross-cutting relationships the order of emplacement of dykes was found to be, first the replacement dykes, then intruded pegmatitic dykes followed by intruded layered dykes and finally irregular in-situ melt patches. Intrusion of pegmatitic dykes has occurred after a minor folding event in the granite but before a shearing event in it. Intrusion of layered dykes has post-dated almost all deformational events in the granite. Despite the diversity in mode and chronology of emplacement, all dykes/veins are mineralogically similar to the granite.

Tonigala granite, although referred to as a post-tectonic granite, has a foliated fabric that is visible in outcrop and in thin-section, and evidence of stretching, flattening, folding and shearing within it clearly indicate that its protolith has been subjected to several episodes of deformation. In addition, the history of dyke/vein emplacement suggests that (a) the granite has been residing in the Wanni Complex for a long period of time despite the ~550 Ma age assigned to it based on U-Pb zircon dating, (b) the sources of dykes (and the granite itself) have been re-activated during later tectono-metamorphic events. Present-day it is a granitic gneiss and its protolith has been metamorphosed at least to the amphibolite-facies, and blue-green hornblende that has been retrograded to form actinolite indicate that the granite passed through the 3rd sub-facies of the greenschist-facies during retrogressive P-T-t evolution.

Keywords: Post-tectonic, intrusion, pegmatites, protolith, boudins


14

GSSL-2018-B01

GROUNDWATER DYNAMICS AT THE BOUNDARY BETWEEN HARD ROCK AND SEDIMENTARY TERRAIN IN THE PUTTLAM

DISTRICT: ANALYSIS OF AVAILABLE DATA

G.S.S. Karunarathne1*, G.R.R. Karunarathne2 and H.A.D. Dharmagunawardhane1

1Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka

2Water Resources Board, 2A, Hector Kobbekaduwa Mawatha, Colombo, Sri Lanka


Groundwater dynamics along the boundary between Wanni Complex and the Sedimentary sequence of Sri Lanka have not been understood clearly. The study area selected in the Puttalam Divisional Secretariat consists of Miocene sedimentary rocks and Pleistocene sedimentary sequences. The study was conducted as a desk study collecting and analyzing the primary and secondary records obtained mainly from the unpublished data of the Water Resources Board. Geological features within the limestone and the discontinuity along the boundary of Wanni Complex inherit specific groundwater dynamics which would affect the water supply scheme of the Puttlam Town. Thus, the main objective of the current study was to understand the groundwater dynamics in the area across the crystalline and sedimentary rock boundary. Limestone aquifers had higher yields (100-3000 liters per minute) than the crystalline rocks (60- 500 liters per minute). The water quality of the aquifers was relatively poor with respect to salinity and total dissolved solids and could be due to pollution, dissolution of minerals from host rocks possibly over long residence time and salt water intrusion. Negative groundwater elevations too were observed in some areas probably as a consequence of heavy abstractions. Overflowing wells were also observed closer to the coast in Seguwantivu area. As a whole, the area consisted of complex unconfined and confined aquifer system which is mainly recharged from the crystalline terrain to the east.

Acknowledgement: The staff of Water Resources Board are acknowledged for providing necessary data and support to carry out the study.

Keywords: Groundwater dynamics, Aquifer boundaries, Sedimentary sequence, Sri Lanka


15

GSSL-2018-B02

STRATIGRAPHY AND MINERALOGY OF GEM DEPOSITS

IN PELMADULLA, SRI LANKA

C.R. Welikanna, N.W.B. Balasooriya* and K. Dahanayake



Gem deposits in Sri Lanka are concentrated in a broad belt known as Highland Complex which is underlain by high grade metamorphic rocks. Gems are obtained from three main formations such as, eluvial, alluvial and residual formations. This study is focused on the evaluation of gem deposits in Pelmadulla area. More than 60 gem pits were observed in the Denawaka valley area in the Sabaragamuwa Province and five of them were selected for sampling. Literature survey and a direct field reconnaissance survey were carried out to obtain information and to select suitable locations for study. This study is focused on the evaluation of gem deposits in Pelmadulla area. The stratigraphy of the deposits, grain size distribution, texture of grains, heavy mineral distribution and the clay mineralogy were investigated in this study. Soil samples were taken from the ground and the weathered bed rock called “malawa”. Various laboratory testing techniques were carried out on the samples such as sieving followed by analysis by laser particle size analyzer for fine particles analyze in sediments. FTIR analysis and magnetic separation of grain sizes below 125 microns were used to evaluate heavy mineral concentration in the gem gravel bed called “illama”. Based on the obtained data, the detailed stratigraphy of gem beds was constructed. Three types of gem deposits varying from valley to hill slope were identified as alluvial, sub- alluvial and eluvial in that order. Corundum is the main gem mineral obtained from the area indicating the presence of gemstones such as ruby and sapphires. Garnet, monazite, spinel, zircon, topaz, tourmaline and quartz are the other gem minerals in the area present in variable concentrations. Kaolinite, montmorillonite and illite are the main clay minerals associated with gem beds. In addition, a characteristic organic clay layer with plant debris was encountered in alluvial deposits. Further, FTIR analysis proved the occurrence of high concentration of quartz and sheet silicate minerals in the sediments. Texture and maturity of grains indicate that they have not been transported very far from their origin.

Keywords: Gem deposits, Corundum, Ruby, Sapphire, Malawa and Illama


16

GSSL-2018-B03

HYDROCARBON SOURCE ROCK POTENTIAL OF THE LATE CRETACEOUS TO YOUNGER SEDIMENTS IN THE NORTHERN

PART OF THE MANNAR BASIN, OFFSHORE SRI LANKA

Ridma Boralugoda1, Chaminda Kularathne2 and Upul Premarathne1*

1Department of Oceanography and Marine Geology, Faculty of Fisheries and Marine Sciences and Technology, University of Ruhuna, Wellamadama, Matara, Sri Lanka

2Petroleum Resources Development Secretariat (PRDS), Level 06, Ceylinco House 69, Janadhipathi Mawatha, Colombo 01, Sri Lanka.


Mannar Basin, which is located between India and western offshore areas of Sri Lanka (6°-9° N latitude and 78°-80° E longitude), covers approximately 45,000 km2. It developed due to multiphase breakup of Gondwana during the Mesozoic. Stratigraphic thickness of the Late Jurassic to recent sediments overlain by Precambrian metamorphic rocks ranges from about 4 km in the northern part of the basin to more than 10 km in the southern part. Existence of an active petroleum system in the basin was confirmed for the first time in 2011 with the discovery of natural gas bearing Late Cretaceous (Campanian) sandstones by the Dorado-91H/1z well. Later in the same year, CLPL-Barracuda-1G/1 well also penetrated natural gas bearing late Cretaceous (Maastrichtian) sandstones. Though, petroleum system of the Mannar Basin has been unraveled by several previous studies, source rock potential of the northern part of the Mannar Basin is little known. Hence, the objective of the present work was to study the hydrocarbon source rock potential and thermal maturity of Late Cretaceous to younger sediments in the northern part of the Mannar Basin, based on Rock-Eval pyrolysis, vitrinite reflectance (VR) seismic data and basin modeling techniques. PetroMod 1D software (Version 2012.2) was used to model the burial and thermal history and petroleum generation and expulsion timing of the entire stratigraphic section at the Barracuda well. Though the Barracuda well has not penetrated the entire stratigraphic section up to the crystalline basement, seismic data were used to deduce the stratigraphic section below the total depth of the well. The model was standardized against the present day geothermal gradient and kerogen maturation profiles for the Barracuda well. The results of the study showed that the northern part of the Mannar Basin has recovered a highest heat flow of 129 mW/m2 at the peak rifting period around 115 Ma. The heat flow has then gradually diminished during the post rift period to the present-day heat flow of 60 mW/m2. Sediments in the Late Cretaceous section penetrated by the Barracuda well has entered the oil window, while the Early Cretaceous and older sediments have entered the gas maturation window. The Late Cretaceous (Maastrichtian to Campanian) fine grained sediments penetrated by the Barracuda well has good hydrocarbon source potential for both oil and natural gas.

Keywords: Mannar Basin, Basin modeling, Barracuda, Source rock


17

GSSL-2018-B04

GEOCHEMICAL BEHAVIOR OF ARSENIC IN COASTAL AQUIFER SYSTEMS OF MANNAR ISLAND, SRI LANKA

A.V.U.P. Amarathunga* and R.L.R. Chandrajith



Elevated concentrations of arsenic (As) in groundwater exceeding the World Health Organization (WHO) permissible levels have only recently been documented from Mannar Island, Sri Lanka. In this study, probable sources and release mechanisms of As in to groundwater were evaluated under laboratory condition using water and sediment samples obtained from critical regions in the Mannar island. Water samples analyzed with ICP-MS showed As concentrations ranging from 6.49 µg/L to 43.80 µg/L. Moreover, field measurements indicated that all the water samples with pH between 7.2 and 7.6 have higher As concentrations (>25.00 µg/L). Fe and Ba concentrations of groundwater also indicated their coexistence with As complexes, having correlation coefficients 0.78 and 0.87 respectively. Sediment analysis showed that very high concentrations of both As and Fe, particularly in the finer fraction of the aquifer material. Treating the original aquifer material with solutions with pH between 4.0-8.0, showed that the highest levels of As and Fe were released into the solution at pH 5.0 and 6.0. The organic content of the aquifer material was 13%. The FTIR data indicated the changes in metal-OH bond vibrations due to the formation of As-mineral complexes. When rain water percolates into the water table, oxygen becomes depleted at or near the surface due to the decay of organic matter, hence, dissolution of carbonate minerals in water may increase. This helps to dissolve iron rich coatings in sand grains under reducing conditions, releasing As into groundwater.

Keywords: Arsenic, Coastal Aquifer Systems, Sri Lanka, Groundwater


18

GSSL-2018-B05

MODELLING OF THE BURIAL AND HEAT FLOW HISTORY OF THE CAUVERY BASIN, SRI LANKA

Upul Premarathne

Department of Oceanography and Marine Geology, Faculty of Fisheries and Marine Sciences and Technology, University of Ruhuna, Wellamadama, Matara, Sri Lanka


Cauvery Basin is located in southeast onshore and offshore areas of India and northwest onshore and offshore areas of Sri Lanka. It is a pericretonioc failed rift basin evolved due to multiphase breakup of the East Gondwana. The basin has been divided into several sub basins/ depressions by basement ridges. The Sri Lankan sector of the Cauvery Basin extends over 15000 km2, which encompasses the Pesalai-Palk Bay depression and a part of the Ramnad-Palk Bay depression, separated each other by the Mandapam-Delft ridge. Six exploration wells, Pesalai-1, 2 & 3, Pedro-1, Palk Bay-1 and Delft -1, were drilled in the Sri Lankan sector of the basin during 1975 to 1981 period. Whether an active petroleum system exists in the Sri Lankan sector of the basin is not certainly known. However, the Indian sector of the basin is now producing both oil and natural gas from its onshore and offshore fields, located mainly in the Ramnad-Palk Bay depression. The objective of this research was to understand the burial and the heat flow history of the Sri Lankan sector of the basin, using PetroMod 1D basin modeling software (Version 2012.2). Input data were obtained from the Pesalai-1, Palk Bay-1, Delft-1, and Pedro-1 wells. The Bottom Hole Temperatures and Vitrinite Reflectance (VR) data from the wells were used to optimize the modelled present day and Paleo heat flows, respectively. Backstripping method was used to estimate the stretching (β) factor corresponding to each well. The synrift period of the Cauvery Basin was considered to be from the late Jurassic to the end of the Aptian age. The resulting burial history plots for the Delft-1 and Pedro-1 wells have unconformities with larger hiatuses from Cenomanian to Late Eocene and Late Albian to Middle Eocene, respectively. The β factors estimated for the Pesalai-1, Palk Bay-1, Delft-1 and Pedro-1 wells are 1.20, 1.17, 1.14, and 1.10, respectively, while the optimized present-day heat flows in the wells are 48, 39, 40, and 72 mW/m2, respectively. The peak synrift heat flow in the Pesalai-1, Palk Bay-1 and Delft-1 wells, estimated by the McKenzie model, was 49 mW/m2, while it was 48 mW/m2 for the Pedro-1 well. The present day Geothermal Gradients (GTG) and kerogen maturation profiles, modeled for the Pesalai-1, Palk Bay-1 and Delft -1 wells using the Makenzie heat flow model, reasonably match with the those measured experimentally. Though the kerogen maturation profile modelled for the Pedro-1 well using the McKenzie heat flow model reasonably match with the measured VR data, the modelled present day GTG is significantly (~13oC/km) less than the GTG (36oC/km) calculated from the BHT data. The relatively high present-day heat flow in the Pedro-1 well may be due to a more recent tectonic event.

Keywords: Cauvery Basin, Heat Flow, Basin Modeling, Mc Kenzie model


19

GSSL-2018-B06

RESOLVING HOLOCENE SEA LEVEL CHANGES IN COASTAL SEDIMENTS USING GROUND PENETRATION RADAR (GPR)

METHOD

L. Palamakumbure1, *, H. M. R. Premasiri1, N. P. Ratnayake1, A. S. Ratnayake2, Jinadasa Katupotha3, W. A. P. Weerakoon1, N. P. Dushyantha1,

D. S. M. Weththasinghe 1, J. D. S. U. Jayakodi1 and Rohana Chandrajith4



3Department of Geography, University of Sri Jayewardenepura, Sri Lanka

4Department of Geology, University of Peradeniya, Sri Lanka


Sea level have fluctuated throughout the geological history, intermittently inundating or retreating coastal plains. Analysis on changes of such sea level oscillations recorded in the coastal plains are important to predict future global sea level trends. Inland coral is one of the most reliable proxy which provide clear evidence for Holocene sea level change, since corals thrive in many low- latitude coastal environments, in the intertidal zone. Several inland coral beds and beach rock submerged by surface soil layers existing in southern coastal belt of Sri Lanka can be used to identify paleo-sea level height and paleo-coastal position of the area. GPR survey along selected traverses in Walgama area in Matara district were carried out to identify the extension and the distribution of the submerged coral beds. Digital Elevation Modal (DEM) created using Light Detection and Ranging (LiDAR) data was used to identify the coastal geomorphology and to infer the paleo-sea level height and paleo-coastal position. Processed GPR images indicate that the submerged coral beds and beach rock extend up to 0.5 km towards inland and approximately 1.0 - 3.5 m in depth. These results were confirmed in the field by using observations made at the wells and abandoned coral mining pits in the vicinity. Further, GPR survey indicates that these submerged coral beds do not extend as a continuous bed, however they appear as pockets. Using the developed DEM, the paleo sea level was identified existing along the 5 m contour line. For further confirmation, cross sectional profile sampling and measuring dielectric properties are needed to be carried out in addition to constructing a detailed map combined with chemical data as the next step of the research.

Acknowledgment: Funding for the project through University of Moratuwa Senate Research Capital Grant (Grant No: SRC/LT/2017/28) is gratefully acknowledged.

Keywords: Coral, Beach rock, GPR, Sea level change


20

GSSL-2018-B07

PRELIMINARY INVESTIGATIONS OF INLAND CORAL DEPOSITS TO RECONSTRUCT HOLOCENE SEA-LEVEL

CHANGES

W. A. P. Weerakoon1*, H. M. R. Premasiri1, N. P. Ratnayake1, A. S. Ratnayake2, Jinadasa Katupotha3, L. Palamakumbure1, N. P. Dushyantha1,

D. S. M. Weththasinghe 1 and Rohana Chandrajith4



3Department of Geography, University of Sri Jayewardenepura, Sri Lanka

4Department of Geology, University of Peradeniya, Sri Lanka


Coral reefs are related to contemporary processes and sea-level changes over the geological time. Although corals can be dated from late Cambrian to Present, most modern reefs date approximately 5000-7000 years BP. Several Holocene inland coral reefs are preserved in the southern coastal belt of Sri Lanka as pocket deposits. These deposits can be used effectively as proxies to determine the paleo-sea level and environmental changes in Sri Lanka. Well preserved coral samples collected from the southern coastal area were investigated by X-Ray Imaging to identify the skeleton structure. Scanning electron microscope (SEM) combined with EDX and X-ray diffractometer (XRD) were used to identify the external morphology and elemental composition. Chemical composition of samples was analyzed using an inductively coupled mass spectrometer (ICP-MS). Samples were selected based on annual growth bands recognized by X-Ray imaging. SEM and XRD and analyses indicated the presence of aragonite crystal structure suggesting the growth of the skeleton at a deep ocean environment. Ratios of Mn/Ca, Fe/Ca and Pb/Ca indicated the sedimentation of the coral surface occurred after being exposed or at the termination of the coral colony. Mg/Ca (1.45 x 10-3-1.58 x 10-3), Sr/Ca (21.31-21.79) and Ba/Ca (10.93 x 10-3-47.25 x 10-

3) ratios indicate 6 different ocean temperature variations. Therefore, inland corals of Sri Lanka can be used to identify sea level changes and detailed mapping combined with chemical compositional variation can be used to predict paleo-sea level changes.

Acknowledgement: Funding for the project by University of Moratuwa Senate Research Capital Grant (Grant No: SRC/LT/2017/28) is gratefully acknowledged.

Keywords: Coral, ICPMS, Holocene, Sea level change, Sri Lanka


21

GSSL-2018-B08

RECONSTRUCTION OF WINTER MONSOON VARIABILITY USING GEOCHEMICAL PROXIES IN A SEDIMENT CORE FROM

POTTUVIL LAGOON, SRI LANKA

B.P.G.A.M.K. Dharmarathna* and R.L.R. Chandrajith

Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka.


Understanding the northeast (winter) monsoon system in the Indian Ocean is essential for reconstructing past climate in the region. Although the southwest monsoon variability is known comprehensively, behavior of the winter monsoon is still in argument. The present study focused to reconstruct the paleo-climatic record in the eastern coast of Sri Lanka that is heavily influenced by the winter monsoon using geochemical proxies, from which sub-samples were selected from each 20 cm depths for the detailed study. Lithological and granulametric characteristics, and mainly major, trace and rare earth elements as geochemical proxies were studied in detail. Elemental analyses were

performed using ICP-MS. In addition, organic matter (450 C) content and the loss on

ignition (1000 C) were also determined. Major, trace and rare earth element variations are well matched with the loss on ignition and the grain size variation. The results suggest seven possible major climatic events that depict the behavior of the winter monsoons. These events possibly represent high rainfall and enhanced productivity in the terrain and appear in depths of 5.00 – 4.00 m (zone 1), 2.40-1.60 m (zone 4) and 0.80-0.40 m (zone 6), while Zone 2 (4.00-3.00 m), zone 3 (3.00-2.20 m), zone 5 (1.60-0.80 m) and zone 1 (from 0.40 m – surface) suggest a possible dry climatic event. Holocene marine transgression event was represented by the Zone 3 that continued up to ~360cm depth followed by subsequent marine regression. Paleo climatic evidence suggest a cycling variation of weak and strong winter monsoon periods that was followed by long term marine transgression that possibly submerged coastal low lands. However, ages of layers need to be established using 14C dating methods in the future.

Keywords: Winter Monsoon, Indian Ocean, Paleo-climatic record, Geochemical proxies


22

GSSL-2018-B09

ATTRIBUTE ANALYSIS FOR PALEO-DEPOSITIONAL ENVIRONMENT PREDICTION IN THE ALBIAN SECTION OF THE

MANNAR BASIN, SRI LANKA

T.M. Munasinghe1, Damsith Weerasinghe2 and Upul Premarathne1*

1Department of Oceanography and Marine Geology, Faculty of Fisheries and Marine Sciences and Technology, University of Ruhuna, Wellamadama, Matara, Sri Lanka

2Petroleum Resources Development Secretariat (PRDS), Level 06, Ceylinco House 69, Janadhipathi Mawatha, Colombo 01, Sri Lanka.


The Sri Lankan sector of the Mannar Basin, which extends over 45,000 km2, is located between 6o-9o N latitudes and 78o-80o E longitudes. It is a pericratonic failed rift basin evolved due to crustal extension between the Indo-Sri Lanka landmasses triggered by the breakup of the Gondwana. The sediment thickness of the basin ranges from about 4 km in the northern part to more than 10 km towards the southern part of the basin. The northern part of the Mannar Basin is one of the targeted frontier areas for hydrocarbon exploration in Sri Lanka. Yet, only five exploration wells have been drilled in the basin to date. CLPL-Dorado-91H/1z and CLPL-Barracuda-1G/1 wells drilled in SL-2007-01-001 exploration block in the northern part of the Mannar Basin, encountered natural gas bearing sandstones in 2011. These have been the only two instances where hydrocarbon deposits encountered in the country. Geology, evolution and petroleum system of the basin have been addressed in several previous studies. However, the reservoir potential of the Cretaceous and older sections has not been adequately studied. This study focusses on understanding the depositional environment and sediment facies of the Albian section using 1750 km2 three dimensional (3D) marine seismic data acquired in the SL-2007-01-001 exploration block. RMS (Root Mean Square) amplitude analysis was performed to identify the paleo-depositional environment of the Albian section using the IHS Kingdom Seismic and Geological Interpretation software. Data from the exploration wells and sequence stratigraphic principals were used to interpret the key horizons in the 3D seismic volume. In addition to RMS amplitude maps, velocity maps and seismic facies characterization were used to understand the dispersal patterns and paleogeography of the northern part of the Mannar basin. The results of the study showed the existence of multi-level Albian depositional geomorphologies including a turbidite fan system emerging from East-to-West trending deep-water channels, which are thought to be paleo-rivers that were draining from the western part of the island. These features are expected to have a good quality reservoir faces capable of accommodating economically viable hydrocarbon deposits, which should be the potential targets for hydrocarbon exploration in the Mannar Basin in the future.

Keywords: Mannar Basin, Seismic data, Albian, RMS Amplitude


23

GSSL-2018-B10

MINERALOGY, GEOCHEMISTRY, AND GENESIS OF LATERITES IN KAWUDUPELELLA AREA OF THE

MATALE DISTRICT, SRI LANKA

W. K. G. V. Weligepola1*, D.M.S.N. Dissanayake2,3 , H.M.T.G.A. Pitawala1,2 and M.M.M.G.P.G. Mantilaka2,3


2Post-graduate Institute of Science, University of Peradeniya, Peradeniya

3Sri Lanka Institute of Nanotechnology, Nanotechnology and Science Park, Mahenwatte, Pitipana, Homagama

Lanka Institute of Nanotechnology, Nanotechnology and Science Park, Mahenwatte, Pitipana, Homagama


Lateritic formations are very common in many areas of Sri Lanka. Present study, we report the chemical and mineralogical characteristics of lateritic occurrences in Kawudupelella area of Matale district to elucidate their anatomy and genesis. Geological mapping and geomorphological analysis of the area were carried out to understand the distribution of basement high-grade rocks and lateritic exposures in the overburden. Geochemistry and petrology of selected samples of lateritic formations and saprolites were studied.

The major rock types of the area are khondalite and marble. Lateritic formations are characterized by presence of gibbsite, kaoline, goethite, hematite, limonite, boehmite and chert and relicts of iron-oxide minerals and garnet. Out of the studied samples, dark brown and reddish-brown laterites contain higher amounts of Fe. In contrast, the yellowish variety consists of relatively higher amounts of Al and Si. In general, lateritic bauxites are common in the area.

Concentric laminations are common feature of the studied samples and they are made up with goethite, chert and kaoline with minor amounts of MnO2, Cr and P. Formation of hematite nodules as well as Fe and Al enriched matrix may have taken place through chemical weathering of almandine garnet and sillimanite of the basement with removal of some amounts of Si and other elements. Higher concentrations of Si in studied samples compared to many lateritic formations in other parts of the world suggest that during the formation of laterite kaolinisation process has taken place predominantly than that of lateritisation process. Results of the study indicate that weak structural setting of the bedrocks has facilitate to infiltrate water to subsurface for intense weathering of the bed rock. Presence of large number of laterite bodies towards the valleys imply us that formation of lateritic occurrences is many due to the groundwater fluctuation.

Keywords: Sri Lanka, Matale, Lateritisation, Lateritic bauxites, Hematite nodules


24

GSSL-2018-C01

OUTCOME OF CONSTRUCTION DEWATERING ASSOCIATED

WITH GLACIAL AND HARD ROCK TERRAINS: NEED OF A

REGULATORY FRAMEWORK FOR FUTURE MEGACITY

DEVELOPMENT

H.A. Hemachandra Jayasena1, 2*, Kourosh Mohammadi2, Riffat Shamsi2,

Hafiz Muneeb Ahmad2 and Bhanuka Hettiarachchi2

1Department of Geology, University of Peradeniya, Peradeniya 20400, Sri Lanka

2Orbit Engineering, Unit-9 1900 Clark Blvd., Brampton, ON L6T 0E9, Canada


Construction dewatering has been a routine requirement, however, constricted by the

regulatory-driven megacities such as Greater Toronto Area (GTA) in Canada. The

hydraulic conductivities (K) obtained through experimental approach; percolation,

infiltration and slug tests and empirical approach; particle size distribution (PSD) based

formulae, resulted in providing necessary guidelines and directives to prospective

buyers, developers or authorities in terms of completing their due diligence. The

following K’s obtained by Orbit for glacial terrains in Ontario resulted in a range of

arithmetic averages. For aquifers of sand and gravel; 4.4E-02, sand to silty sand; 3.8E-

04, sandy silt/silty sand till; 1.03E-04, clayey silt/silty clay with fine sand; 4.70E-05 and

for aquitard of clayey silt till; 4.52E-06 cm/s, which clearly follow the observed trend in

GTA. However, the results of the PSD output gave somewhat higher average ranges,

4.72E-02 to 6.16E-02 for sand and gravel; 1.8E-03 to 3.3E-04 cm/s for sandy silt till with

some clay. The respective guidelines adhered by GTA to allow discharge permits

consider horizontal flow with the highest applicable point K. The recent collapse of high

rising buildings in Megacities and excessive dewatering along with Uma Oya tunnel

highlights the dire need for Sri Lanka on implementing similar regulations to those in

GTA and other parts of the world in order to cope up with the environmental quality and

safety issues. The K (Transmissivity (T)/assuming 30m aquifer thickness) and Storage

Coefficient (S) data acquired from tunnel construction, dam building and pumping tests

within the fractured basement resulted with ranges from 3.24E-05 to 2.8E-02 cm/s and

0.0001 to 0.5 respectively. These values assume homogeneity and isotropy which are

not coherent with reality as observed in the fractured rocks and marble formations in Sri

Lanka. As the Sri Lankan basement consists of regolith (10m thick) progressing towards

highly transmitting semi weathered rock over to the subsurface fractured network (30m

thick), the proposed infrastructure confined at such depth levels should expect scale

effect. Therefore, to obtain satisfactory K would be a difficulty. However, reasonable

assessments on individual cases should be available to the decision maker. Since the

guidelines for extraction, discharge and conveyance have not yet been codified in Sri

Lanka, the consequence will clearly result in difficult social outcome unless the

government authorities or accredited institutes intervene to implement a regulatory

framework.

Keywords: Construction dewatering, hydraulic conductivity, Transmissivity, Sri Lanka,

Canada


25

GSSL-2018-C02

PALEOTSUNAMI RESEARCH ALONG THE COAST OF SRI LANKA

K. Goto1, T. Haraguchi2 and N. P. Rathnayake3*

1International Research Institute of Disaster Science, Tohoku University, Japan

2Graduate School of Science, Osaka City University, Japan



Tsunami geology is undoubtedly useful to clarify paleotsunami histories. Paleotsunami researches have been conducted after the 2004 Indian Ocean tsunami in Indian Ocean countries such as at Sri Lanka, Indonesia, Thailand, and India. However, unified view of paleo-tsunami scenarios across the Indian Ocean countries has not been understood well. This study reviews the previous studies on paleo-tsunami research in Sri Lanka and other Indian Ocean countries in order to discuss problems and future directions in reconstruction of tsunami histories in this region. During the literature survey, it was found that since the occurrence of Indian Ocean Tsunami in 2004, only approx. 20 peer-reviewed papers have been published in line with the paleotsunami research in the Indian Ocean countries, which is surprisingly few. In our paleotsunami research in Sri Lanka from 2007 along the south to southeast coast including Dikwella, Hambantota, and Kirinda, possible tsunami deposits as old as ~7000 years BP were identified. However, sedimentary records of past 2000 years were not well recovered similar to the case of previous studies, possibly due to the hiatus. In addition, we performed transoceanic correlation of event age among Indonesia, Thailand, India, Maldives, and Sri Lanka as well. Although there are several difficulties such as tsunami deposit identification and dating, previous researches suggested that possible Tsunami might have occurred ca. 500-600 years BP based on the evidence other than those from Sri Lanka. Thus, it is critically important to find geological evidence of this event in Sri Lanka in order to prove possible occurrence of transoceanic tsunami.

Keywords: Tsunami, Sri Lanka, Deposit, Indian Ocean countries


26

GSSL-2018-C03

SAND MINING IN BOLGODA LAKE: A POSSIBLE THREAT TO GROUND STABILITY IN URBAN AREA AROUND BOLGODA

C N B Wijeratne

Geological Survey and Mines Bureau, Epitamulla Rd. Pitakotte

Author Email: [email protected]

Damage to sensitive infrastructure and ecosystems particularly in urban areas due to uncontrolled mining activities has become an issue with adverse impacts. Therefore controlling mining activities within highly populated and geologically unstable land should be strictly monitored or prohibited. Bolgoda Lake is a shallow brackish water body in the Bolgoda watershed, located between the southern border of the Kalu Ganga basin and the northern border of the Kelani river basin in the wet zone of Sri Lanka. It is categorized as a semi-closed lagoon, as it is not connected to the sea throughout the year. Sand mining area of Bolgoda Lake is located on the left bank where southward mining site is located 500m away from Panadura Bridge (new bridge) and extends 2.5 km northwards upstream. The right bank is a relatively narrow (300m – 600m) dune sand bar and the left bank is a coastal sand stretch. The bridge of old Galle road had been constructed avoiding this narrow sand bar. Bolgoda Ganga catchment area is relatively small (374 km2) and comprised of mainly laterites and charnockitic rocks hence the sand amount which would be derived from this terrain is considerably less. Slow or unmoving water flow has no potential of transporting sand from upper areas of the catchment. Therefore the low generation and low transportation rates of sediment hardly provide considerable sand to the existing sediment layer in the bottom of the lake, compared to other systems. It is evident that the sand percentage of the sediment layer is gradually lessening compared to last decade. Although sand mining is carried out in Bolgoda Lake continuously, the sediment layer thickness remains almost constant over the years (2-3m). The possible explanation for such character is that the sediment layer of the flood plain gradually release sand into the river compensating the vacuum created by extensive sand mining. Depletion of sand accumulation of the flood plain potentially destabilize the river banks threatening urban structures of the area including critical infrastructure such as A2 main road and southern railway.

Keywords: Bolgoda Lake, Sand Mining, Ground Stability


27

GSSL-2018-C04

FRACTAL ANALYSIS ON RIVER NETWORKS BASED ON REMOTE SENSING DATA: AN EXAMPLE FROM KELANI RIVER

BASIN, SRI LANKA

S.B.A.D.Y. Jayawardena and N.D. Subasinghe*

National Institute of Fundamental Studies, Hantana Road, Kandy, Sri Lanka


River networks are important components of basin geomorphology and have impacts on various natural phenomena such as river flow, sediment transport and flood. Therefore, an accurate description of river network geomorphology is crucial for investigating patterns and correlations in these natural phenomena. Traditional morphologic methods can only investigate the simple geometric configurations and poorly describe natural features of complex river networks. Fractal geometry method includes river shapes characterized by irregularities. Recent applications of models based on fractal geometry have shown the ability to describe complex geomorphologic characteristics of river networks and other hydrological variables. Hence, this initial study provides a valuable approach to quantify the river network complexity. This study employs a natural river network extracted using ASTER Global Digital Elevation Models (GDEM s – 30m resolution). Study area is located between 7ᴼ 13′ 29.5″ - 6ᴼ 47′ 20.5″ North latitude and 79ᴼ 58′ 22.5″ - 80ᴼ 25′ 47.5″ East longitude (about 2,428 km2). Five sub – watersheds of Kalani basin were selected for the study: 1) Ambalanpiti oya, 2) Gurugoda oya, 3) Pugoda oya, 4) Pusweli oya, 5) Wak oya. 250 pixels were set as threshold and extracted network upto threshold includes a river network of six orders according to the Strahler ordering scheme. Fixed - size box counting algorithm was applied to obtain fractal measures. Box counting method was applied to the same river network twice; allocating weighted lines (pixel width) for different orders and allocating non-weighted line for all tributaries to check which one gives the better explanation on complexity. Both fractal and multifractal analyses were conducted. Goodness of fitted regression line (R2) is greater than 99% for all river networks when weighted lines were used, while some of the non-weighted textures are below 99%, indicating that weighted lines are the best for analyzing the river network orders. Fractal dimension of selected sub – watersheds varies from 1.42 to 1.55 in weighted order textures and 1.39 to 1.53 in non – weighted order textures. Generalized fractal dimension obtained from multifractal analysis varies from 1.48 to 1.63 in weighted order textures and 1.47 to 1.60 in non–weighted order textures. In this study, Gurugoda oya has the highest fractal dimension and the most complex geomorphologic shape. Smallest value obtained from Pugoda oya displays the least complexity. Multifractal spectra f(α) are index of the river network geometric complexity. A detailed investigation is required (considering lithological and structural features of the basin) to link f(α) to the physical characteristics of a river network.

Keywords: Fractal Analysis, Geomorphology, Complexity, Kelani River Basin


28

GSSL-2018-C05

SOME HYDROGEOLOGICAL ISSUES IN HYDROPOWER TUNNELS IN SRI LANKA: A CASE STUDY COVERING FOUR

TUNNELS IN THE CENTRAL HIGHLANDS

E.P.S. Pathirana* and H.A. Dharmagunawardhane

Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka.


Hydropower tunnels convey water from reservoirs to power houses. Underground hydropower tunnels have shown some hydrogeological problems during and or after their construction. Present study discuss encountered hydrogeological problems during construction of four hydropower tunnels; Castlerieigh, Polgolla, Kotmale and Victoria in the central highlands of Sri Lanka. Encountered hydrogeological issues in tunnels could be related with the geological environment and therefore by studying the geological conditions in selected tunnels, it is possible to explain in to a certain extent, the causative factors of the problems. Under the present study, tunnel traces were plotted on orographic, topographic, geologic and structural maps. In addition, an effective catchment area which can create groundwater inflows in to each tunnel was also demarcated on the topographic maps. The associated geological environment was then compared with the encountered hydrogeological problems. The study revealed that the encountered problems in the tunnels are water ingresses and debris flows in to the tunnels. They could be related to the weak zones developed along the trace of the tunnels due to truncation of lineaments, fracture or fault zones, folds, weathered zones and certain rock types. The size of the effective catchment area and the length of the tunnel also positively correlate with the incidences of the encountered problems. The findings suggest that the length of the tunnel as far as possible should be short, and tunnel need not be always straight. Identification of the effective catchment area as a part of preliminary investigation can be immensely helpful to have an idea about the magnitudes of potential water ingresses during Excavation of the tunnels.

Keywords: Hydropower tunnels, water ingresses, central high lands, Sri Lanka


29

GSSL-2018-C06

FINDING SUITABILITY OF BIO ENGINEERING APPLICATIONS IN SLOPE STABILIZATION IN SRI LANKA: SPECIAL

REFERENCE TO BADULLA DISTRICT

A.D.H. Balasuriya1*, Pathmakumara Jayasingha2 and W.A.P.P. Christopher1

1Uva Wellassa University, Badulla

2Landslide Research and Risk Management Division, National Building Research Organization, Colombo 05


Bioengineering is the application of engineering technology to biological systems or vice versa. It is the combination of biological, mechanical, and ecological techniques to reduce or manipulate erosion, preserve soil, and stabilize slopes using vegetation or a combination of living things, such as plants, and non-living materials. Vegetation can be used to enhance slope balance in a number of ways such as by mechanical reinforcement, controlling erosion, increasing the infiltration ratio, decreasing runoff, and soil moisture adjustment. According to Mohr–Coulomb theory plants’ root, increases soil cohesion, so the Factor of Safety increases, in a slope. Objective of this research is to identify the most suitable plants in Sri Lanka that would provide sufficient root support to increase the slope stability with a view to apply them in future slope stabilization work. Using Landslide Hazard Zonation Maps provided by National Building Research Organization of Sri Lanka, 15 sites of high hazard and medium hazard landslides on steep slopes of Badulla district were selected for investigating the types of soils and identifying the suitable plants with bioengineering characters. Plants were chosen based on their power of mechanical reinforcement, controlling erosion, increasing the infiltration ratio, decreasing runoff, and soil moisture adjustment. The results were compiled using Arc GIS 10.2 software. Identification of the plants with special root systems and specific morphological characters were scientifically done in the laboratory. Geotechnical analysis of soil (i.e. Sieve analysis) was carried out to identify the soil types in order to select the most suitable plants for each soil type. According to the results, most of the selected slopes are steep (>45o) and most of the soil types are clayey and well graded. Imperata cylindrica , Mimosa pudica, Wedelia trilobata, Bouteloua dactyloides, Arachis pintoi, Gleichenia linearis, Desmodium Sp., Microstegium vimineum, Digitaria sanguinalis ,Lunularia cruciate, Sporobolus heterolepis, Asplenium sessilifolium, Miscanthus sinensis, Poa labillardierei, Strobilanthes Sp., Pteridium aquilinum, Bouteloua dactyloides, Juncus prismatocarpus, Ageratina riparia, Hemerocallis fulva, Lamiaceae, Austroeupatorium inulifolium, Ageratina riparia, Osbeckia octandra. Agave Sp., Chrysopogon zizanioides, Artemisia argyi, Cymbopogon nardus, Adenanthera pavonina, Calliandra calothyrsus, Juncus usitatus, Juncus prismatocarpus, Indocalamus, Oclandra, Osbeckia lantana, Bambusa guangxiensis, Aundinaria densifolia, Gliricidia sepium, Paspalum dilatatum, Rhododendron arboreum, and Symbplocus Sp., were identified as the bio engineering applicable plants from the study area. These plants will be tested by applying them on unstable slopes in future, in order to prevent slope failures.

Keywords: Fractal Analysis, Geomorphology, Complexity, Kelani River Basin


30

Author Index

Abewardana, U.G.A.M.P. 6

Ahmad, Hafiz Muneeb 24

Amarathunga, A.V.U.P. 17

Amaratunga, G.A.J. 3

Amaraweera, T.H.N.G. 11

Attanayake, A.N.B. 2

Balasooriya, N.W.B. 8,11,15

Balasuriya, A.D.H. 29

Boralugoda, Ridma 16

Chandrajith, R.L.R. 17,19,20,21

Chandrakumara, G.T.D. 1,2

Christopher. W.A.P.P. 29

Dahanayake, K. 15

De Silva, K.M. Nalin 1,3

De Silva, R.T. 3

Dharmagunawardhane, H.A.D. 14,28

Dharmapriya, P.L. 8

Dharmarathna, B.P.G.A.M.K. 21

Dissanayake, D.M.S.N. 1,3,23

Dushyantha, N.P. 19,20

Goto, K. 25

Haraguchi, T. 25

Hemalal, P.V.A. 9

Hettiarachchi, Bhanuka 24

Hewathillake, H.P.T.S. 2,8

Jayakodi, J.D.S.U. 19

Jayatilaka, M.L.G.N.T. 13

Jayasena, H.A. Hemachandra 24

Jayasingha, Pathmakumara 29

Jayawardena, S.B.A.D.Y. 27

Kanagaratnam, J.N. 11

Karunarathne, G.R.R. 14

Karunarathne, G.S.S. 14

Katupotha, Jinadasa 19,20

Kudahetty, K.R. 2

Kularathne, Chaminda 16

Malaviarachchi, Sanjeewa P.K. 6

Mantilaka, M.M.M.G.P.G. 1,3,10,13

Mohammadi, Kourosh 24

Munasinghe, T.M. 22

Nawarathna, N.H.M.C. 12

Rajapaksa, R.M.G. 1,10

Palamakumbure, L. 19,20

Pathirage, S.S. 9

Pathirana, E.P.S. 28

Perera, A.G.S.R. 4

Perera, L.R.K. 5,12,13

Pitawala, H.M.T.G.A. 1,3,7,8,10,23

Prame, Bernard 4

Premarathne, Upul 16,18,22

Premasiri, H.M.R. 19,20

Rajapaksa, R.M.G. 1,10

Ratnayake, A.S. 19,20

Ratnayake, N.P. 9,19,20,25

Ratnayake, R.M.D.M. 5

Rohitha, L.P.S. 9

Samarakoon, S. 4

Senevirathna, T.C. 8

Senthilnathan, Anoja 1

Shamsi, Riffat 24

Siriwardana, C.H.E.R. 4

Siriwardhana, Y.P.S. 9

Somarathna, V.C.M. 10

Subasinghe, N.D. 27

Thaldena, S.N.B. 4

Weerakoon, W.A.P. 19,20

Weerasinghe, Damsith 22

Weligepola, W.K.G.V. 13

Welikanna, C.R. 16

Weththasinghe, D.S.M. 19,20

Wickramasinghe, W.M.R.R. 7

Wijayasinghe, H.W.M.A.C. 8,11

Wijeratne, C.N.B 26

proceedings of the 34 technical session of geological

Documents