proceedings of the 31st february 2015...

Proceedings of the 31st Technical Session of Geological Society of Sri Lanka Published Online - 27th February 2015 (http://www.gsslweb.org)

1

GSSL-2015-01

Is the Mohorovicic Seismic Discontinuity the Bed of Earthquakes?

Atula Senaratne

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

e-mail: [email protected]

The Mohorovicic discontinuity, or “Moho”, is the boundary between the crust and the mantle. It occurs at an average 8 km below the bottom of the oceans and about 32 km beneath the continents. At this discontinuity, seismic waves tend to accelerate as the material below this level seems to be of high density.

The Significant Earthquake Database of the National Geophysical Data Center of NOAA (NGDC/WDS-2015) contains information on destructive earthquakes from 2150 B.C. to the present. Earthquakes occurred since the year 1900 to date having a magnitude above 6.0 have been selected for the present study. Each event is presented with the date, the epicenter with longitude and latitude, the depth to loci and the magnitude. Statistical analyses of these data revealed that the loci of 145 earthquakes of a total of 1573 clusters at a depth of 10 km and 234 of 1573 found to occur at a depth of 33 km. This finding is in par with Mohorovicic’s (1909) interpretation of seismic waves which led to establish “Moho” at 8 km below the

surface of oceanic crust and 33 km below the surface of the continents. High seismic activity at the Moho discontinuity indicates the movements of the crust over the mantle which is not clear in available literature. This paper proposes that the “Moho” be the bed of earthquakes.

References: NGDC/WDS (2015) Significant Earthquake Database of the National Geophysical

Data Center of NOAA, USGS.

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2

GSSL-2015-02

An Electromagnetic Survey in the Area around Rangala Graphite Mine for Detecting Subsurface Graphite Veins, Sri Lanka

K.M.P.C Karunarathne* and H.A. Dharamagunawardhane

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

*e-mail: [email protected]

Graphite mining in Sri Lanka has a historical background of over one century. Although country had a great history with deep and shallow graphite mining, methods of ore exploration are still more conventional compared to other countries in the world.

Graphite veins in Sri Lanka have systematic orientations with respect to surrounding geological structures. Tracing of existing veins and exploration of new veins are the major challenges in the vein graphite exploration. Since the terrain has multiple deformations, understanding of local geology and geological structure is critical.

Rangala graphite mine is one of the graphite mines situated in the Kegalle district within the crystalline terrain of Sri Lanka. An electromagnetic survey was carried out to map probable graphite veins and estimate the graphite potential in the area around Rangala graphite mine.

A Very Low Frequency (VLF) electromagnetic survey was carried out using EM 16 handheld instrument for the field data collection. Simple numerical filtering method with low pass filtering was used to identify anomalies along survey lines that were arranged according to a pre-selected grid system. Anomalies which gave good correlation with adjacent survey lines verified the extensions of the underground conductors. Anomalies which were selected above already identified veins were the proofs for the relation between graphite veins and VLF anomalies. Anomalies which were correlated with drilling data provided further confirmations of the interpretation.

Fourteen most probable graphite veins were identified during the study. Orientation of veins was predominantly steeply dipping towards NW SE. Length of veins varies between 150 m - 20 m and located at an average depth of between 10 m - 20 m from ground level. Depending on the existing anomalies, it can be suggested that the graphite potential of the mine area is much more than what has already been extracted. Drilling, resistivity profiling and detailed geological mapping are suggested as further studies.


3

GSSL-2015-03

Vertical Cross Section of Eppawala Carbonatite Intrusion Based on Magnetic Data

W.K.D.G.D.R. Charles1, N.D. Subasinghe

1,*, Nalin De Silva

2 and H.M.T.G.A. Pitawala

3

1National Institute of Fundamental Studies, Hantana Road, Kandy, Sri Lanka.

2Geological Survey and Mines Bureau, Pitakotte, Sri Lanka.

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


Magnetic surveying is a commonly used mineral exploration method. Some rocks contain magnetic minerals such as magnetite. Magnetic minerals in the rocks can generate induced magnetic fields parallel to any external magnetic field. In addition to induced fields, there can be remnant magnetic fields in the rocks. Magnetic susceptibility values of the igneous rocks are generally higher than those of the metamorphic and sedimentary rocks, because igneous rocks usually contain more magnetic minerals. Eppawala carbonatite is an igneous rock and is comprised of magnetite as an accessory mineral and hence can produce a distinct magnetic signal. This condition was used in this work to demarcate the extent of the carbonatite body from the surrounding country rocks and to make a simple cross section for the carbonatite body using “Mathematica” software. Total magnetic intensity data were digitized from the total magnetic intensity map and digitized line was located perpendicular to the intrusion. The digitized data were plotted in Mathematica and anomaly of the cross section of the intrusion was obtained. Here, the magnetic field was considered as an induced magnetic field. Theoretical anomalies were obtained by a short Mathematica program. Horizontal and vertical components of the induced field, along the traverse were calculated using inclination, declination and the angle between traverse and the magnetic north. Horizontal length of the carbonatite intrusion was kept as infinite and vertical length was kept as finite. Cross section of the intrusion was considered as a polygon (two dimensional body) and the Talwani’s method was applied for obtaining the theoretical anomalies. The shape of the polygon was changed until it fits the observed and theoretical anomalies. Susceptibility value was kept as a variable by assigning different values during the calculation of the induced field. Digitization was done in five locations and the magnetic anomalies were plotted. Five theoretical anomalies and shape of the cross sections were obtained from the Mathematica program. The shapes of the polygons show that the shape of the cross section of the intrusion is a trapezium and it dips to north.

Financial support is provided by the National Science Foundation (Grant No: RG/2012 /NRB/03)

mailto:[email protected]


4

GSSL-2015-04

Use of Magnetic Method to Delineate the Kawisigamuwa Phosphate Occurrences

S.P. Rajapakshe1,*

, N.D. Subasinghe2, Nalin De Silva

3, U. Dahanayake

1, W.K.D.G.D.R. Charles

2

and S.A. Samaranayake2

1Department of Physical Science, Rajarata University of Sri Lanka, Mihinthale, Sri Lanka.

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



The phosphate occurrence at Kavisigamuwa is one of the smaller phosphate deposits in Sri Lanka. A limited number of geochemical and petrologic studies have been conducted on the Kawisigamuwa deposit with no detailed geophysical studies, except 1D resistivity sounding at selected locations.

A magnetic survey was conducted at locations where the phosphate is outcropped. The survey was extended to the vicinity of the area. Though the apatite is non-magnetic, it is always associated with magnetite which is a magnetically susceptible mineral producing a strong magnetic signature. The occurrence of magnetite along with apatite is a common feature in carbonatites and igneous formations. Magnetite occurs in the form of isolated crystals as well as in the coating of the apatite host. The survey area of this study was extended to a 2 km × 3 km grid covering the phosphate exposures and the close vicinity. The phosphate occurrence is margined by a N-S trending granitic gneiss rock to the east. Phosphate outcrops occur only at locations with hump-like features.

A proton precision magnetometer, GSM-19 over-Houser system with integrated GPS was used to collect field data. Magnetic mapping was done using the predefined grid. Outcome of magnetic data processing and interpretation reveal that there are four separate high anomalous regions in the study area. The highest magnetic anomaly was observed in the northern part of the survey area. In some instances, the anomalous values exceed the dynamic range of the instrument. The huge granitic body east to the survey area also reflects high magnetic anomaly probably due to iron-rich components in the granitic host.

Another area of high magnetic anomalies in the map comes from the apatite rich magnetite body located in the south.

Analysis of the magnetic results identifies that the deposit is located as a fractured antiform along the NS direction. The northern area of the deposit is rich with magnetite with a minor amount of apatite, while Southern area is enriched with an apatite rich magnetite.



5

GSSL-2015-05

Effectiveness of Ground Penetrating Radar and Electrical Resistivity Methods to Pinpoint Solution Cavities: A Case Study from Matale

A.M.T.H. Abeysinghe1,*

, Udeni B. Amarasinghe1 and M.I.D.H. Wijewickrama

2


2National Building Research Organization, 99/1, Jawatta Rd., Colombo, Sri Lanka.


Land subsidence has been a well-known Geotechnical hazard in Matale valley area since the British colonial time. It has been reported to the National Building Research Organization existence of a weak zone extending from Ukuwela to Madawalaulpatha, experiencing land subsidence. Since 2004, a new phase of land subsidence has been experienced by residents. In 2012, two sinkholes of approximately 6 m in diameter were formed in Totagamuwa where trees were vertically collapsed into them. Inhabitants in the surrounding area experienced tensional cracks along the walls and floors of their houses. This was a serious public concern and some even believed existence of an underground stream in the affected area.

The main reason for land subsidence in this area is due to subsurface cavities formed by dissolution of crystalline marble rocks. Since the urbanization in past three decades has increased the number of buildings in every possible buildable land area, these incidents have become more exposed. Therefore, it is highly necessary to locate such cavities with certainty and to plan and implement remedial measures. In this context, we conducted Ground Penetrating Radar (GPR) and Electrical Resistivity (ER) surveys as indirect geophysical methods to detect such cavities.

The study reveals that the geophysical methods were highly effective in locating solution cavities rapidly and economically. Distortions of uniform layers in GPR profiles show the existence of subsurface cavities. Clay filled cavities were characterized with resistivity values approximately between 0 and 15 Ωm and air fill cavities with resistivity values more than 5000 Ωm. Further, core drilling results confirmed the geophysical survey output. Our study recommends maintaining a good surface drainage system to decrease the infiltration of water. Furthermore, filling those cavities using mass concrete, micro piles or raft foundations to utilize the lands for the future constructions is recommended.


6

GSSL-2015-06

Gondwana Breakup and Development of Sedimentary Basins in Sri Lanka

E.K.C.W. Kularathna1,*

, H.M.T.G.A. Pitawala2, Atula Senaratne

2 and Damsith Weerasinghe

1

1PRDS, Level 06, Ceylinco House, 69, Janadipathi Mawatha, Colombo, Sri Lanka.



Sri Lanka was a part of the East-Gondwana and the breakup of the supercontinent eventually formed hydrocarbon potential basins in Mannar, Cauvery and East to South offshore (Lanka basin). The evolutionary processes of these basins have not yet been well defined. Data from seismic, wells, gravity and magnetic studies, structural maps and publications were used to interpret the development of these basins. Four major discontinuities - trending N-S, E-W, NE-SW and NW-SE directions were recognized in the offshore areas around the island of Sri Lanka. The results of this study support that the Sri Lankan landmass may have experienced at least two prominent rifting events during the Gondwana break up. First rifting phase was initiated (~165 Ma) being accompanied by possible counter-clockwise rotation during the East-West Gondwana breakup and it had resulted in the present day NE-SW and NW-SE discontinuities of the Mannar basin. The second rifting phase is more prominent and it had resulted in the initial formation of the Cauvery and Lanka basins. During this event (~142 Ma), the separation of India, Madagascar and Sri Lanka from Antarctica had taken place. During the second rifting phase, further counterclockwise rotation and subsequent strike slip movement had occurred. This had resulted in the development of the NE-SW, N-S and E-W discontinuities causing more widening and mechanical subsidence in the Mannar basin. Additional strike slip movement in Mannar may have been continued during the formation of the Kerguelen Plateau (~110 Ma to 84 Ma). Flood basalts and other intrusives in the Mannar basin seem to have had a connection with Deccan flood basalts in India. Late Cretaceous uplifting and tilting facilitated the higher erosion in the Cauvery basin. However, the erosion was not prominent in the Mannar basin. After ~84 Ma, Mannar basin had initiated to develop as a passive margin, excluding the inversion during the Eocene probably associated with the Himalayan orogeny. It can be suggested that the basins had experienced multiphase subsidence events, driven by rifting and thermal contractions. The findings of the present study are of greater importance in the development of Geo-

history models of basins; a vital requirement in hydrocarbon exploration.


7

GSSL-2015-07

Sub Volcanic Sedimentary Depositional Environment in Mannar Basin, Sri Lanka

W.A.G.K. Wickramasinghe1,*

, H.M.T.G.A. Pitawala1, Chathuranga Senevirathne

2 and

Dhamsith Weerasinghe2




Mannar basin of Sri Lanka has been identified as a hydrocarbon prospective basin associated with basaltic intrusions. Barracuda-1G-1, an exploration well in the basin, has penetrated hydrocarbon bearing sandstone beds between the depths of 4067 m to 4206 m. Previous studies revealed that multistage basaltic intrusions within the sedimentary sequences could act as a cap rock. Middle to Late Cretaceous shale that lies under the basaltic layer could be a possible source rock. The objective of the present study was to interpret petrography of the shale and to describe the depositional environment of it.

Representative, 30 drill cutting samples of shale from the depth range 4260 m to 4745 m of the well were studied using mineralogical, petrographic and geochemical analyses. Depositional setting and seismic-stratigraphy of the basin was modeled using 2-D Seismic data and drilled well data available at Petroleum Resources Development Secretariat (PRDS).

The present study revealed that calcareous shale is rich in siliceous materials and inter banded with thin sand layers. Major detrital minerals of the shale are quartz and feldspar with minor garnet, hornblende, ilmenite and zircon. Illite and smectite occur as detrital clay and chlorite and kaolinite are found as authigenic clays. Calcite is the common authigenic cement with minor authigenic apatite and pyrite. Microscopic studies and geochemical analyses suggest that the depositional environment of shale should be open marine setting due to mass movement (turbidities). Presence of pyrite and higher content of organic carbon indicate tht an anoxic environment prevailed during the depositional period. Interpretation of seismic stratigraphy suggests that the shale has formed during the Maastrichtian and Companian periods of Late Cretaceous.


8

GSSL-2015-08

A Preliminary Study on Pre-Flood Volcanic Hydrocarbon Prospectivity in the Mannar Basin, Sri Lanka

E.K.C.W. Kularathna1,*

, H.M.T.G.A. Pitawala2 and Atula Senaratne

2


2Department of Geology, University of Peradeniya, Sri Lanka.


Sri Lankan jurisdiction of the Mannar basin, which lies between Indian and Sri Lankan landmasses reaches to an area of approximately 50,000 km2 proven for hydrocarbon generation. The basin is a pre-cratonic rift basin, which has been interpreted to have evolved in four phases since the late Jurassic; Early syn-rift phase; Late syn-rift phase; Thermal sag phase and Passive margin development. Previous studies have indicated that the igneous activities in the basin had been persistent during the thermal sag phase. Both intrusive and extrusive igneous features are visible on seismic data, whereas a prominent extrusive volcanic layer exists at the top of late-Cretaceous horizon demarcating the sedimentary success-sion in the basin as “pre-flood volcanic” and “post-flood volcanic” sequences. The region that was not affected by the volcanic flood, exist as a narrow margin, close to the eastern abrupt boundary of the basin. Hydrocarbon prospectivity in the pre-flood volcanic sequence has not yet fully been understood in the Mannar basin. Therefore a scenario- based petroleum system modeling study was performed using regional and global data in order to interpret the hydrocarbon potential of this sequence.

Results demonstrate that, presently a large area of the basin for late synrift and early synrift sources are in gas window, whereas the basin margin indicates oil maturities. However, major portion of the Campanian-Maastrichtian sources are in the oil window. Paleocene and middle-Eocene sources above the flooded volcanics are at present immature. Data from Indian jurisdiction of Mannar, Cauvery and Kerala-Konkan basins show evidence for the possibility of good quality reservoir rocks in the pre-flood volcanic sequences. Flood volcanics in the Barracuda well act as a seal to the intra- volcanic gas bearing sands lead to the assumption, that possible reservoir facies beneath the pre- flood volcanic top surface would have a much higher probability of success. Furthermore, lacustrine or marine shales, which are relatively transparent on seismic, can act as top seals to the bright amplitude packages of reservoir sequences in the Cretaceous. Although pre-flood basalt imaging is challenging for prospect delineation, the interpretations pertaining to the available regional and Mannar basin data conclude that the pre-flood volcanic sedimentary section projects higher prospectivity.


9

GSSL-2015-09

Comparison between Ground Investigation Data and Actual Observed Data: A Case Study, SSDS “Tunnel F”, Hong Kong

L.H.D.D. Hasitha

Maxwell Geosystems, 135-Bonham Strand Trade Center, Sheung Wan, Hong Kong.


A geotechnical review of the Strategic Sewage Disposal Scheme (SSDS) Stage 1 –“Tunnel F” of Hong Kong was carried out as it is a great example for a deep sub-sea hard rock TBM tunneling through faulted ground conditions with heavy water inflows. Tunnel F excavation encountered very unfavorable ground conditions compared to predicted ground conditions in the ground investigation data, leading to many contractual and design amendments.

“Tunnel F” is approximately 3.5 km long and excavated through “Kawloon Granite” and it was expected to cross two major faults (Lead Mine Pass Fault and Tolo Channel Fault) in Hong Kong. However, only six boreholes were drilled along the tunnel trace to predict geological and hydrological conditions along the tunnel alignment. As a result, some assumptions have been made to predict potential ground conditions. Based on the ground investigation data, alternative tunnel was designed 40 m below the initial tunnel alignment. Tunnel excavation was started year 1995 and 3.35m diameter open shield TBM was used for excavation and it has been underground for 5 years when it removed at the end of the tunnel excavation.

Ground investigation data, geological maps, over 324 tunnel mapping records, tunnel groundwater ingress records at probe holes and grouting records of tunnel F were reviewed and used to compare with predictions.

Actual groundwater inflows were significantly higher than expected groundwater inflows which in turn demanded injection of very high grout volumes than expected grout volumes. Between Ch 920 and Ch 3500, a total 83,487 m length of drill holes was drilled for grouting and 3 million kg of cement was pumped to control groundwater inflows. Predicted rock weathering grades and predicted tunnel Q values were significantly higher compared to observed rock weathering grades and tunnel Q values. As a result, extensive temporary supports were needed to complete the tunnel excavation.

Tunneling through difficult geology and hydrogeology is not uncommon, but ground investigation data should be able to predict such situations. Therefore, ground investigation works need to be carried out until the predictions are made with very high confidence and minimum speculations.


10

GSSL-2015-10

Application of Rock Mass Classification Systems in Dyraaba Conveyance Tunnel of Uma Oya Multipurpose Development Project

W.G.P.P. Premarathne*, A.A.J.K. Gunatilake and S.W. Nawaratne



Results of two rock mass classification systems were applied to the construction of the Dyaraaba conveyance tunnel of Uma Oya multipurpose development project with the objectives of deciding the support system and obtaining a numerical relationship between Rock Mass Rating (RMR) and Rock Mass Quality (Q) Systems. The horse shoe shaped tunnel is 4.95 m high and is located within Hangiliella fault zone in the Highland Complex.

To accomplish this task, a literature survey was carried out, followed by a comprehensive field study, including the identification of geological characteristics and a detailed discontinuity survey of the rock mass along the tunnel route. Correlation between the results of the rock mass classification systems was analyzed.

In accordance with the results of two rock mass classification systems, tunnel rock mass was categorized as; (a) Poor rock mass quality with support system category 3, (b) Fair rock mass quality with support system category 3, 1 and (c) Good rock mass quality with support system category 1 according to Q system. According to RMR, the rock mass was classified as; (a’) Fair rock with support category III, (b’) Good rock with support category II and (c’) Very good rock with support category I.

As the major outcome of the study, the relationship between RMR and Q classification systems was identified as i) RMR = 1.293 Q + 63.649 (R2 = 0.0662) and ii) RMR = 11.474 ln Q + 52.509 (R2 = 0.75).


11

GSSL-2015-11

Investigation of Geological and Geotechnical Aspects for Construction of the Main Dam, Moragahakanda Reservoir, Sri Lanka

K.M.D.P. Kumara1,*

, A.A.J.K. Gunatilake1 and S.M.N.M. Senevirathna

2


2Moragahakanda-Kaluganga Development Project, Mahaweli Authority, Sri Lanka.


One of the key priorities in constructing a dam for a reservoir is building a sustainable and stable dam body and dam foundation. Geological and geotechnical aspects are the basis of determining their suitability for the construction. Layout of the dam body is of prime importance for optimizing the water storage of the reservoir. Main dam of the proposed Moragahakanda reservoir is a rock and earth fill dam having a zoned configuration that significantly enhances the stability and functionality of a dam. Soils of each borrow area from where the material for different zones of the dam is to be extracted, need to be tested for their suitability.

Under the investigation, a geological map was prepared in order to identify the lithology and geologic structures in the main dam area. Core sample interpretation was conducted to investigate the foundation and abutment conditions of the main dam. The strength of the foundation was evaluated using the previous experimental data. Soil tests, namely, sieve analysis, Atterberg limits and proctor compaction tests were performed at the Mahaweli Authority laboratory-Moragahakanda site, for the material to be employed with respect to each zone of the dam. Suitability of material was discussed using data obtained from above tests and considering the data from previous studies.

An extensive tight fault, which runs along the top of the proposed dam, was identified at the right abutment. It should be further investigated in order to apply the mitigation measures. Charnokitic gneiss possesses sufficiently enough compressive strength for the foundation. Test results for soil and rock were compared with the standards proposed for each zone of the dam and contrasted among each other. Particle size analysis revealed that the construction material for each zone meet their standard size ranges. Atterberg limits are relatively even within the clay core material and are Inorganic Clays of medium plasticity. Average optimum moisture content and respective maximum dry density are 17% and 16 kN/m3 on which the roller compaction should be performed. Triaxial compression test results denote the general cohesion and friction angle that should be involved in the construction of the core slope. Permeability test results for both borrow areas vary in between 1x10-10 – 1x10-7 ms-1 and those values generally well below the standard (1x10-7 ms-1).


12

GSSL-2015-12

Zircon U-Pb and Lu-Hf Isotope Systematics from Meta-igneous Rocks of Sri Lanka: Geochemical Evidence for Convergent Margin Magmatism

Sanjeewa P.K. Malaviarachchi1,2,*

, M. Santosh3, T. Tsunogae

4, X. He

3 and P. L. Dharmapriya

1,2


2Post Graduate Institute of Science, University of Peradeniya, Peradeniya, Sri Lanka.

3School of Earth Science and Resources, China University of Geosciences, China.

4Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan.


We present major and trace element data of whole rocks and Zircon U-Pb and Lu-Hf isotope data from a suite of meta-magmatic rocks from the Highland Complex (HC), Kadugannawa Complex (KC) and Wanni Complex (WC), Sri Lanka. These samples show distinct Nb -Ta depletion and fair-negative Zr-Hf anomalies, consistent with subduction-related tectonic settings. The meta-felsic magmatic rocks fall in the Volcanic Arc Granites (VAG) field while the meta-mafic rocks show island arc basalt affinity, suggesting their protoliths were derived from arc-related magmas in a convergent margin setting. Results of U-Pb dating on zircons by Multi collector LA-ICPMS are as follows:

Zircons in the HC charnockite display negative εHf (t) values in the range -6.7 to -12.6 with crustal model ages (TDMC) of 2039-2306 Ma suggesting magma derivation through melting of a Paleoproterozoic source. In contrast, the εHf(t) range of -11.1 to 1.6 for the metadiorite enclave in charnockite suggests a mixed source of both of older crustal and juvenile material. The εHf (t) values of -4.5 to 4.5 and TDMC of 1546-1962 Ma for the amphibolite of the KC also shows mixed sources of Paleoproterozoic components. The younger dioritic enclave has a more juvenile magma source as indicated by the mean εHf (t) value of 1.3. The associated charnockite shows a tight positive cluster of εHf (t) from 0.6 to 5.1, suggesting juvenile input. Charnockite from the WC shows clearly positive εHf (t) values of up to 13.1, and TDMC in the range 937-1458 Ma suggesting comparatively younger and depleted mantle source. The meta-diorite enclave in Charnockite has positive εHf (t) values with an average value of 8.5 and TDMC in the range of 709-1443 Ma, clearly suggesting younger juvenile sources. Thus, the studied metamorphosed suite from the three Sri Lankan crustal units can be the results of convergent margin magmatism during the period of assembly of Gondwana Supercontinent.

Sample / Rock Unit Locality Emplacement age (Ma) Metamorphic age (Ma)

Charnockite (HC) Moragahamula 565 Meta-diorite (HC) Moragahamula 576 525 Amphibolite (KC) Boyagama 973-980 Meta-diorite (KC) Boyagama 559 508 Charnockite (KC) Boyagama 962, 832, 780, 721, 661-605 Charnockite (WC) Gonagamuwa 1000 570 Meta-diorite (WC) Gonagamuwa 980


13

GSSL-2015-13

Powder XRD Study of Gem Quality Corundum (Alpha-Al2O3): A Qualitative Method to Identify Synthetic and Natural Corundum

D. Ranatunge1,2

and G.W.A.R. Fernando1, 3,*

1Postgraduate Institute of Science, University of Peradeniya, Peradeniya, Sri Lanka.

2Gem and Jewellery Authority, Galle Face Terrace, Colombo 3, Sri Lanka.

3Department of Physics, The Open University of Sri Lanka, Nugegoda, Sri Lanka.


Differentiation of synthetic and natural gemstones is a chief concern for gem dealers and major jewellery importers. Natural corundum is a precious stone and, one of the most important exports of Sri Lanka. Corundum (α – Al2O3) is known by different names depending on the colour it exhibits which in turn depends on the impurities that are present. The colour depends on the valence state of the impurity element present in corundum such as Cr3+ in ruby, Fe3+ in yellow sapphire and Fe-Ti complex in blue sapphire. There have been a number of incidences of synthetically grown corundum available in the market which cannot easily be differentiated with natural corundum with normal routine tests. Present paper deals with the X ray powder diffraction results on different colours of natural and synthetic gem quality corundum and gives evidence of an external morphology and internal growth features that reflect their formation conditions, especially disorder brought about by such synthetic treatments. This can be effectively used for diagnostic purposes for detecting the synthetic stones.

Four (04) sets of corundum samples from different origins, both natural and synthetic have been analyzed at the Industrial Technology Institute (ITI) for X ray powder diffraction (XRD). The characteristic set of d-spacings generated in a typical X-ray scan provides a unique "fingerprint" of the mineral or minerals present in the sample. The positions and the intensities of the peaks are used for identifying the underlying structure (or phase) of the material. The XRD results of both natural and synthetic corundum samples were found to be consistent with the standard international reference of corundum. Broadening of the peak was measured by calculating the Full Width at Half Maximum (FWHM) of the peak. Then, a graph was drawn as 2θ vs FWHM to find the behavior of the broadening of the peaks. According to comparison of 4 sets of different colours of corundum, it was observed that shifting of XRD peaks of synthetic corundum are considerably high and high strain could be seen in synthetic corundums than that of natural variety.


14

GSSL-2015-14

Formation of Garnet + Corundum during Isobaric Cooling of UHT Metapelites in the Highland Complex, Sri Lanka

P.L. Dharmapriya1, 2,*

, Sanjeewa P.K. Malaviarachchi1,2

, Andrea Galli3, Ben-Xun Su

4, N.D.

Subasinghe5 and C.B. Dissanayake

5

1Post Graduate Institute of Science, University of Peradeniya, Sri Lanka.

2Department of Geology, University of Peradeniya,Peradeniya, Sri Lanka.

3Department of Earth Sciences, Zurich, Switzerland.

4Institute of Geology and Geophysics, Chinese Academy of Sciences, China.

5Institute of Fundamental Studies, Hantana Road, Kandy, Sri Lanka.


In metapelite, the garnet + corundum (Grt+Crn) assemblage is generally interpreted to form during prograde heating. However, coexistence of the assemblage is rarely preserved in rocks due to subsequent break-down during retrogression. In this study, we report the occurrence of coexisting Grt+Crn in spinel- and corundum-bearing, garnet-sillimanite-biotite-graphite gneisses (metapelite) of the Highland Complex, Sri Lanka, sampled at south western part of Kandy. The studied metapelite occur as bands (2 - > 5 m thickness) intercalated with charnockitic gneisses. The studied portion of the metapelite is silica-undersaturated and encountered as patches (0.5 - >1 m) within silica-saturated domains consisting of porphyroblastic garnet (0.25 – 4 cm), ribbon quartz (Qtz, up to 5cm in length), plagioclase (Pl), alkali-feldspar (Kfs) and biotite (Bt) flakes rimming garnet. Silica-undersaturated domains are constituted of two generations of garnet (Grt1 and Grt2), sillimanite (Sil), Pl, Kfs, Crn, spinel (Spl) and Bt. Grt1 encloses rare Ti-rich Bt (up to 7 wt %) and numerous rutile (Ru) needles and apatite (Ap) rods. Grt2 contains rare Sil and/or Spl inclusions. Corundum occurs in mutual contact with Grt2, partially embedded within the rim area or as inclusions in Grt2. The presence of irregular patches of Bt are associated with feldspar- leucosomes and may have grown from melt during retrogression.

Textural evidence together with Electron Microprobe data in the silica-undersaturated domains indicate the reactions, Bt+Sil+Qtz+An poor-Pl = Grt1+Kfs+An rich-Pl+Melt and Bt+Sil = Grt1+Spl+Kfs+Melt during the prograde evolution. The peak-mineral assemblage was probably Grt-Pl-Kfs-Spl-Sil-Ilm together with melt. At retrogression, the reaction Spl+Sil = Grt2+Crn and Grt1+Fluid/Mel t= Bt have taken place. Inclusions within Grt1 indicates that during the prograde history metapelite attained a P of 10.5-11 kbar at T of ~850 °C. Pseudosections calculated in the NCKFMASHTMnO system and Ti-in-Garnet geothermobarometry suggest that peak metamorphism occurred at UHT conditions of 950-975 0C and pressures of 9-9.5 kbar. Peak T was followed by a period of isobaric cooling responsible for the formation of Crn and Grt2 at ~930 °C. Modelling of the modes of Spl, Sil, Crn and Grt confirms that Crn appears along an isobaric cooling path at about 920-930 °C and 9-9.5 kbar. This evidence implies that isobaric cooling at the base of the crust is an alternative process to form rare coexistence of Grt+Crn.

The financial support by the National Research Council (NRC) of Sri Lanka (Grant No. NRC-11-180) is thankfully acknowledged.


15

GSSL-2015-15

Reactivation of Landslides and Subsidence Threats due to Marble Band: A Case Study from Watagoda and Dodandeniya in Matale

M.M.C.U.B. Moremada1, M.I.D.H. Wijewickrema

1, Subhashini Bindusara

1, M.K.C.

Jayamali2, W.D.G.D.T. Rajapaksha

3 and H.A.H. Jayasena

3,*

1NBRO, District Office, Matale, Sri Lanka.

2Gem and Jewelry Research and Training Institute, Malambe, Sri Lanka.



During the period from 20th to 26th of December 2014, the Central Highlands of Sri Lanka

received extreme rainfall which resulted in severe landslide threats. Rainfall received at

Elkaduwa gauging station was 440 mm with daily amounts vary from 22 to 182 mm. Two

landslides initiated at Watagoda and Dodandeniya in Matale were hydrologically,

geologically and geophysically surveyed. In addition, social impacts due to landslide threat

issued to Dodandeniya residents were further investigated. The geological surveys

accompanied by desktop studies and subsequent geophysical surveys indicated two

different phenomena associated with the issuance of landslide and subsidence threat. The

first at Watagoda was the reactivation of older landslide represented by a slump within the

crown along the road and en-echelon tensional cracks developed along N65W/42N

parallel to foliation of the garnet biotite gneiss. The second at Dodandeniya, a subsidence

was initiated along with the suspected mobilized Marble band. Tensional cracks have also

developed along N60-30W in the south side of the landslide and parallel to the foliation in

the crown area, which then turning towards N80E in the north side. Major rock types of

Dodandeniya are charnockitic gneiss and mobilized marble. Charnockitic gneiss with

foliation along N10E/55W is a moderately jointed rock with two major joint planes; one

nearly horizontal and the other along N35W/90. The joint intensity vary from 3-4/m,

which geometrically support for the development of rectangular blocks. However,

colluvium spread over the adjacent marble bands cause difficulty in identification of

cavities. Therefore, resistivity and Ground Penetrated Radar surveys were conducted to

identify cavity fillings. Wells and springs indicated water table fluctuation in the range from

0-1.2 m below the ground. Bursting pore water as shown by muddy water discharge at

crown area indicated slip surface reactivation, which may have initiated the slump whereas

the middle berm and the surrounding area underlain by marble may have subsided.

Preliminary social survey of 95 household families evacuated from the area, pointed out

how they were affected due to the severity of this threat. The repercussions both to the

residents and to the government are considerable since this area falls within the

municipality limits. A detailed questionnaire based survey is planned since people expect

clear instructions and government initiatives to look after this matter at length.


16

GSSL-2015-16

Application of OSL as a Tool to Date Depositional Ages of Quaternary Deposits: A Case Study from ‘Rathnapura Beds’, Sri Lanka

Tilak Hewawasam

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


Optically stimulated luminescence (OSL) is a widely used method to date the depositional ages of sediments in Quaternary deposits. Luminescence (“pre-existing luminescence”) is developed within sediments such as quartz and feldspar when the minerals are assembled in the bedrock or regolith. Luminescence development is triggered by the absorption of the ionizing radiation produced by trace amounts of radioactive isotopes contained in surrounding materials. However, this pre-existing luminescence in the sediment is bleached upon exposure to sunlight during transportation subsequent to weathering and erosion. Therefore, at the time of deposition, the luminescence clock in the sediment should set to zero. After the sediments are deposited, radioactive isotopes in the surrounding materials in the sedimentary deposit cause more luminescence to accumulate in the sediments, which can be measured as “post-depositional luminescence” in the laboratory. Then, depositional age is simply calculated by dividing the “post-depositional luminescence (Ga)” by “annual dose rate (Ga/y)”. The annual dose rate is calculated also by measuring the radioactive content in the sphere of material (30 cm radius) surrounding the sample. However, complete bleaching of pre-existing luminescence is difficult, especially for fluvial sediments, and then deposited sediment may contain some residual signals of pre-existing luminescence thereby making the dating process more complicated. Therefore, sampling for OSL dating needs to be done carefully in support of other luminescence methods such as OSL field profiling and OSL laboratory profiling, and granulometry.

An integrated approach consisting of granulometry, OSL field profiling, OSL laboratory profiling and OSL dating on sediments from two alluvial gem pits from ‘Ratnapura Beds’ in Pelmadulla, Sri Lanka was employed. Samples were subjected to the standard OSL analysis procedures and their grain size distribution was determined by using a Coulter laser diffraction particle size analyzer. In these beds, two principal stratigraphic units were identified as; basal, gem-bearing fluvial sediments (meandering and braided channel deposits), and overlying finer-grained flood plain deposits. The OSL field and laboratory profiling investigations show an increase of several orders of magnitude in IRSL and OSL signals and higher apparent stored doses in the gem-bearing basal layer compared to the overlying alluvial fill. This suggests younger burial ages for the overlying alluvial fill, recording a break in the depositional history, and then much older burial ages for the basal gem-bearing gravels. Consistently, the OSL dating yields 250-600 years of depositional ages for the upper alluvial fill and late Pleistocene to Early Holocene ages for the basal gem-bearing layer. The OSL depositional ages of the gem-bearing sediments determined in this study coincide with the middle dynamic period in the paleo-environment records reported by the recent paleo-environmental studies of the south west monsoons of Sri Lanka.

Special thanks to Paul Bishop, Tim C. Kinnaird and David C.W. Sanderson for providing training to familiarize with the OSL technique.


17

GSSL-2015-17

Appraisal of Gem Deposits in Badalkumbura Area, Sri Lanka

R.M.R.S. Ratnayake1,*

, S.V.T.D. Raveendrasinghe2, R.M.N.P.K. Jayasinghe

2, T.S.

Dharmaratne

2

and H.M.R. Premasiri3


2Gem and Jewellery Research and Training Institute, Malambe, Sri Lanka.

3Department of Earth Resources Engineering, University of Moratuwa, Moratuwa, Sri Lanka.


Badalkumbura divisional secretariat in the Monaragala district of the Uva province, Sri Lanka is one of the major gem occurrences in the south eastern slope of the central highlands. Kumbukkan oya and Menik ganga are the main surface drainages, supported by widely distributed perennial and seasonal network of tributaries. Geologically, the study area belongs to the Highland Complex and it is located close to the boundary of Highland and Vijayan Complexes. The area consists of high grade metamorphic rocks such as calc gneiss, garnet sillimanite graphite gneiss, biotite gneiss, and chanockite gneiss. Both primary and secondary gem deposits can be found in the area. This study focused to evaluate potentiality of gem deposits in the Badalkumbura divisional secretariat.

Field investigations were carried out to identify localized gem fields. Based on textural, structural, mineralogical and geological observations, gem fields were categorized into primary and secondary gem occurrences. Furthermore, exploratory auger sampling was carried out representing each gem field for further laboratory investigations. Selected gem bearing gravel layer was thoroughly washed and sieved. Mineral identification was carried out using gemmological microscope for 125 μm, 250 μm, and 500 μm grain sizes. The extent and distribution of the identified gem fields were demarcated and the gem potential map was prepared using GIS and Remote Sensing techniques.

According to the field observations, primary gem occurrences are commonly associated with impure calc gneiss and garnet sillimanite graphite gneiss. Due to higher weathering susceptible mineralogy of these host rocks tends to form residual gem deposits rich with spinal, garnets etc. These residual deposits contribute to form secondary gem deposits due to the process of transportation and deposition following the local drainage network. Therewith, the geomorphology is a governing factor to form such gem deposits at specific localized points or regions along the stream courses. According to the laboratory studies, 0.3% of yellow sapphire, 0.1% of blue sapphire, 0.5% of geuda (low quality corundum which can be turned into gem quality corundum by heat treatment), 4% of spinal, 2% of garnet, 1% of zircon and tourmaline are the main gem minerals found in these gem fields. Considering the results of both field and laboratory analysis, Badalkumbura divisional secretariat can be recognized as a high gem potential area.



18

GSSL-2015-18

Stream Sediment Geochemistry and Mineral Potential of Walawe Basin

H.P. Marasinghe1,*

, G.R.N. Gunarathana2, P.N. Ranasinghe

3,4 and Shamalie Siriwardana

4

1Uva Wellassa University, Badulla, Sri Lanka.

2Sabaragamuwa University of Sri Lanka, Belihuloya, Sri Lanka.

3University of Ruhuna Matara, Sri Lanka.



Walawe Ganga, the third largest river located in the Southeast of Sri Lanka drains over between the Highland and the Vijayan complexes. Since this zone is known to be a mineralized belt. Walawe basin has a greater geological and environmental importance. We studied the distribution of selected major and trace (REE) elements within the stream sediments with the aim of identifying potential mineral enrichments.

A total of 78 sediment samples was collected at confluences of higher order streams (above 3rd) within the basin for chemical analysis. Element concentrations in stream sediments were measured in powdered samples using hand held X-ray Fluorescence Spectrophotometer (XRF) and totally digested samples using Atomic Absorption Spectrophotometer (AAS). Stream sediment geochemical maps were prepared by using Arc-GIS 9 software and data analysis was done using SPSS 13 software.

Major and trace element maps, prepared for each mineral, showed that the mean concentrations of Cr, Ni, Y, Pb, Ti, Zr and Zn are above the upper crustal values. Distribution of factor scores of the PCA analysis showed that they fully correlate with individual element diagrams of the constituent elements of the factors. High concentrations of Ti and Zr at certain locations could be due to the presence of heavy mineral accumulations.

The comparison of special element concentrations in the studied area with upper crustal and mean stream sediment values shows that Cr, Ni and Pb at some sampling locations are well above the upper crustal values and mean sediment levels while other elements are below the above global average values. And sampling locations suggests that enrichment of Pb in UWG5- 1, UWG-6, LWG- 1 and LWG- 2 and Cr and Ni in LWG- 20 could be due to natural sources rather than anthropogenic or hydrodynamic enrichments. Therefore, detailed high resolution sampling around these localities is suggested to identify potential mineralization.


19

GSSL-2015-19

Evidence for Pre-2004 Basin-Wide Tsunamis from Dondra Lagoon of Southern Sri Lanka

T. Ambillapitiya1, P.N. Ranasinghe

1 and C. Amarasinghe

2

1Department

of Oceanography and Marine Geology, University of Ruhuna, Matara, Sri Lanka.

2Geological Survey and Mines Bureau, Pitakotte Sri Lanka.


Tsunamis can create tremendous damage to coastal populations. The 2004 Indian Ocean Tsunami initiates active attention on tsunami studies in Sri Lanka. This study was carried out to determine the far-field signatures of Sunda-Trench palaeotsunamis and help to develop a regional palaeotsunami chronology. Three sediment cores were extracted from a landward transect in Dondra lagoon of southern Sri Lanka. Particle size and, chemical composition were measured at 1 - 2 cm intervals in the three sediment cores. X-radiograhs of the cores were used to help in identifying visible abrupt sand layers. Anomalous textural, chemical and physical properties of sediment were used to discriminate their origin either as terrestrial or marine. Ages of the abrupt events were calculated according to regional age model. Four probable palaeo-tsunami deposits date back to around 1800, 2500, 3600 and 4000 cal yrs BP were identified. Probable tsunami sand layers in the three cores stratigraphically correlate and they may represent pre-2004 large basin-wide tsunamis generated at Sunda Trench. The dates of these palaeotsunami layers correlate with recorded palaeotsunamis events elsewhere in the region.


20

GSSL-2015-20

Climate Implications on Water Stress and Selected Water Quality Parameter Variations: A Case Study from Daduru Oya Basin

E.G. Rosairo1 and H.A.H. Jayasena

2 1Post Graduate Institute of Science, University of Peradeniya,Peradeniya, Sri Lanka.



The effects of climate implications on water stress and selected water quality parameters were investigated. Water stress is quantified by taking the ratio of water demand to water availability. Few studies have been conducted to investigate development of water scarcity due to climate change in Sri Lanka. However, no study was conducted at basin level to draw inferences on how climate implications act on water stress. Forty years (from 1971 to 2010) of precipitation and temperature data from Daduru Oya basin were selected for the present study. With this long term temperature and rainfall variations, potential influence and implications of climate on water for human and ecological uses were assessed. Similarly, its influence on selected water quality parameters easily obtained from the field such as pH, turbidity, electrical conductivity, alkalinity and ammonia were also investigated. Rainfall data were analyzed with respect to seasonal as well as for the entire 40 year period to explore the trend. Statistical treatment with significant testing of rainfall trends was performed by independent two sample t-tests considering seasonal time series of average rainfall for 1991 to 2010, for which data from 1971 to 1990 was used as the reference baseline. Percentage trends were calculated for the seasonal rainfall, which indicate first inter monsoon -6.8%, SW monsoon 14.8%, second inter monsoon 15.1% and NE monsoon -3.4%. The calculated Climate Moisture Index (CMI) for the 40 year period (1971 to 2010) was used as the basis for determining water stress in the Daduru Oya basin. The results indicate that mean temperature for the 1991 – 2010 period have been

increased by 0.16 C, whereas annual mean rainfall increased by 0.6 mm with respect to the reference baseline. However, total annual water budget have not been changed since potential evapotranspiration show minor increase of 0.25 mm. It can be concluded that the Daduru Oya basin has no significant development of water stress. However, when rainfall pattern is considered together with CMI analysis, one can conclude that the alteration of climate have influenced the Daduru Oya basin to develop periods of seasonal, short term water stress during past few decades. Monthly data on selected water quality parameters were collected from Rambadagalla, Kurunegala and Nikawaratiya for three years (2009-2011) and analyzed together with the rainfall and atmospheric temperature. Moreover, this short term data base seems inadequate to reach a significant relationship with the rainfall and air temperature. Further investigations are underway.


21

GSSL-2015-21

Occurrence of Trace Fossils in Eastern Coast of Sri Lanka: Implications for Paleoenvironment

A.M.N.M. Adikaram1,*

, H.M.T.G.A. Pitawala2, H. Ishiga

3 and D.T. Jayawardane

4

1Department of Physical Sciences, South Eastern University, Sammanthurai, Sri Lanka.


3Department of Geosciences, Graduate School of Sc. and Eng., Shimane University, Japan.

4Department of Forestry and Envt. Sc., Sri Jayawardhanapura University, Sri Lanka.


Ichnological and sedimentological studies on trace fossils in coastal areas provide evidence for the paleoenvironment, paleoclimate and sea level changes. Animal burrows found in the exposed reddish crust deposits of eastern coastal areas of Sri Lanka were studied by ichnological and sedimentological methods to interpret the paleodepositional environments. Field observations, hand specimens, petrography, sieve analysis, scanning electron microscopy and energy dispersive x-ray spectroscopy are the methods used in this study. The vertical extension of the exposed fossilized animal burrows is within 50 cm depth and spatially distributed over about 1 km2. Results revealed that these animal burrows are found in fine to medium sized and poor to moderately sorted sediments. About 90% of the sediments are quartz grains having rounded to sub rounded spherical shape. The quartz sands are bound by oxidized iron to form the red crust. Ichnological identifications on the specimens indicated the trace fossil assemblages including Skolithos and Thalassinoids. These fossil assemblages are related to Skolithos ichofacies. The ichnofacies indicates the environmental conditions are typical for soft grounds in marine-littoral marginal conditions and the formation of the trace fossils is done by combinations of creatures. Intense bioturbation of the area might be an evidence for availability of the food for animals. The high iron content of the area might be due to groundwater action and tidal influence. The intermittent climate changes might be influenced for the oxidation of iron rich sediments. The oxidation is enhanced by the intense animal burrows. The textural and mineralogical characteristics of the sediments imply that they have derived mainly from the fluvial processes with minor marine inputs. The paleoenvironment of the area might be a tidal flat which was favorable for large number of organisms.


22

GSSL-2015-22

Mine Water Problem at the Bogala Graphite Mine, Sri Lanka

A.G.R.P. Weerasinghe* and H.A. Dharmagunawardhane

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


Sri Lanka has many graphite mines producing appreciable amounts of high quality graphite which has a high demand in the international market.Bogala, an underground mine located in the Kagalle District, has a special preference, since it produces high quality natural graphite with commendable annual output.

Bogala mine is situated within the highland complex basement of the country. Structural control associated with overturned refolded antiform is the major ductile deformation feature observed in the area where graphite is confined. Faulting and fracturing are dominant along NE-SW and NNE-SSW directions and graphite occurs along with these discontinuities.

As the mining activities are confined below the groundwater level,the mine has experienced water inflows ranging from a few drops to 10 liters per second at various points. The flow usually based on secondary porosities developed along fractures, joints, faults and graphite veins in the crystalline rock.

At the surface, few weak zones can be identified and they appear to be the possible agents causing the mine water problem. These weak zones are faults and joints and highly fractured quartzite rock present in the area. Most wet joints of the rock in the mine are parallel to the orientation of these main weak zones indicating that there is an interconnection between the weak zones and the underground leakage sources.

The pattern of groundwater flow distribution in the mine and the geological condition indicate the probability of arresting the leakage by external dewatering wells. Therefore, it is proposed to construct dewatering bore holes outside the mine above the leakage zones and pump water away from the area. This could support lowering the water table in the leakage zones and reduce the water pressure inside the mine.

The monthly costs for pumping from deep levels are over one million rupees. Proposed bore wells will be much shallower than the present pumping levels from inside the mine, so that water lifting cost could be reduced drastically.


23

GSSL-2015-23

Arsenic and Cadmium in Water of North Central Province of Sri Lanka:

Implications to Widespread Chronic Kidney Disease of Unknown

Aetiology (CKDu)

Bernard N. Prame*, Shamalie Siriwardana, Sanjeewa Hettiarachchi, Priyanka Jayalath and

Vindya Wanasinghe

Geological Survey and Mines Bureau, Pitakotte, Sri Lanka.


Chronic Kidney Disease of unknown aetiology (CKDu) is a major health issue in the dry zone of

Sri Lanka. And the definite causative factors for CKDu have not yet been identified. In this

context, comprehensive geochemical studies covering the affected area are highly warranted.

285 water samples from dug-wells (190), tube wells (25), reservoirs (55), canals (10) and paddy

fields (05) that representing CKDu affected area were collected and analyzed for arsenic and

cadmium content using atomic absorption spectrophotometer equipped with a vapour

generation assembly. Some selected samples (100) were further analyzed by ICP-OES and ICP-

MS instruments for the same elements for comparison. Results from three different techniques

clearly indicated that both arsenic and cadmium levels of water samples are much lower than

maximum contaminant levels for drinking water (MCL) recommended by the Environmental

Protection Agency of the United States (EPA), 10 ppb and 5 ppb respectively,

The 95th

percentile of arsenic and cadmium contents of 285 water samples were 2 ppb (against

10 ppb MCL by EPA) and 1.2 ppb (against 5 ppb MCL by EPA) respectively. These low arsenic

and cadmium values are consistent with the outcome of some of the previous studies and our

data confirms that these elements in drinking water could not be attributed to the aetiology of

CKDu.

To compliment the water analyses, 10 soil samples from paddy fields were also analyzed for

their arsenic and cadmium contents. Arsenic and cadmium levels of paddy soil samples are

below 1ppm and are well within the average levels of normal soil samples (~7 ppm and ~ 2

ppm). Thus, there is an indication that pesticides and fertilizer applied to paddy fields are not

causing a significant effect on arsenic and cadmium contents of soil.

Total hardness (mg/l, as CaCO3) and fluoride content of 1200 water samples covering CKDu

affected area and parts of Anuradhapura district were also determined. According to the

present study, hardness of the water samples were very high from which about 70% are falling

under ‘very hard’ water category (> 180 mg/l) while 15% of them fall under ‘hard water’

category (120-180 mg/l). The Mean hardness value of all samples was 350 mg/l. Mean F value

of 1200 samples were 1.1 ppm.

Analysis of 15 selected water samples from CKDu affected area for additional chemical elements

using ICP-MS indicates slightly elevated Pb, Mn, V and Br contents compared to EPA

recommended primary/secondary standard values. Further investigations on these elements,

particularly on Br are warranted as bromine can be introduced to the environment by extensive

agricultural activities. Based on the results of our study, we propose to broaden the target

elements/agents in future geochemical investigations and study other possibilities of exposure

to toxic elements/agents.


24

GSSL-2015-24

Effectiveness of Soil Conservation in Mahaweli Catchment, Sri Lanka: A Case Study from Uma Oya Sub Catchment

Saranga Diyabalanage1,*

, Sandun Illangasinghe1, K.K. Samarakoon

2, S.B. Adikari

2 and Tilak

Hewawasam3

1Department of Natural Resources, Sabaragamuwa University of Sri Lanka, Belihuloya, Sri Lanka.

2Environment and Forest Conservation Division, Mahaweli Authority, Sri Lanka. 3Department of Geography, University of Peradeniya, Peradeniya, Sri Lanka.


The Mahaweli Catchment (MC) is an important watershed in Sri Lanka since it contains a series of multipurpose reservoirs. However the longevity of those reservoirs depends on sedimentation rates. Since the soil erosion within the watershed is intense, the sedimentation rates in some reservoirs are now at alarming level. The situation in the Uma Oya Catchment (UOC), a sub-watershed of the MC is even worst with reported mean sediment yield of 1400 t/km2/per rainy season in 1994. This is the highest sediment yield measured for a catchment in Sri Lanka. In the same catchment, local rates of soil losses as measured using agricultural plots had been estimated as high as 7000 t/km2/y. Therefore, with the intention of conserving soil and water, Mahaweli Authority of Sri Lanka (MASL) has implemented Upper Mahaweli Watershed Management Project (UMWMP) and Upper Watershed Management Project (UWMP) in the UOC and operated from 1995 to 2005. Measures such as gully conservation structures, check dams, stone terraces, sloping agricultural land technology (SALT) and grass strips had been introduced through these projects. The aim of this research is to evaluate the effectiveness of such conservation measures using quantitative estimates of sediment yields.

Sediment loads in the stream, water discharge and rainfall data for the period from 1994 to 2005 were collected from Environment and Forest Conservation Division of MASL to come up with temporal variation of sediment yield. The land use pattern was identified using aerial photographs where critical areas for erosion were demarcated by generating an ArcGIS based slope maps. Syntheses of land use and slope maps indicate that rain-fed crops and vegetables are cultivated excessively along with steep slopes. During the study period, the application of mean annual rainfall of 2072 mm was resulted with 60.78 million cubic meters of discharge. Analysis of annual rainfall and runoff show no statistically significant trend, which confirms that the land use pattern has not been changed significantly over the time period concerned. The annual soil loss due to erosion from the catchment was calculated at 2686 t/km2/y whereas annual sediment load indicate statistically significant downward trend, which confirms a reduction in sediment yield. Average sediment yield of 1717 t/km2/y before implementing the projects, however reduced to 766 t/km2/y after the conservation representing 55% sediment yield reduction. The result confirms that the conservation measures were very effective over this short-period.

Research grant from the NSF (RG/2005/DMM/04) to TH is gratefully acknowledged.


25

GSSL-2015-25

Groundwater Recharge Mechanism in the Ambanganga Basin, Sri Lanka: An Assessment Based on Stable Isotope Technique

E.A N.V. Edirisinghe1,*

, H.M.T.G.A. Pitawala2, H.A. Dharmagunawardhane

2 and R.L.

Wijayawardana3

1Isotope Hydrology Section, Sri Lanka Atomic Energy Board, Wellampitiya, Sri Lanka.

2 Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka. 3Department of Physics, University of Peradeniya, Peradeniya, Sri Lanka.


Collecting baseline information on the groundwater recharge mechanism in the Ambanganga basin, spread in the Matale and Polonnaruwa districts, Sri Lanka is important to perceive the impact of proposed Moragahakanda-Kaluganga reservoirs and other irrigation schemes located in the lower part of the basin on groundwater recharge in the future. Oxygen and hydrogen isotopic compositions of groundwater (deep, shallow and flowing springs) and surface water collected (n=51) quarterly during the period from September 2012 to September 2014 in the Ambanganga basin were measured. Monthly variation of isotopic composition of rainwater collected from four meteorological stations within the basin was also studied during the same period. Laser based mass spectrometry method available with Liquid Water Isotope Analyzers was used for the isotope analysis of water.

The results revealed that the groundwater in the Ambanganga basin is recharged during the second inter monsoon (October-November) and during the northeast monsoon (December-February). However, the groundwater recharge is insignificant during the rest of the periods of the year. The groundwater regimes of Northern and Eastern lowlands of the Ambanganga basin are recharged mainly through regional groundwater flows starting from the Knuckles mountain range. Most of the groundwater regimes of the basin are not significantly recharged by the Ambanganga which is mainly fed by the water diverted from River Mahaweli at Polgolla. The diverted water of River Mahaweli affects groundwater recharge in few parts of the western valley of the basin. The irrigation canal diverted from the Ambanganga at Elehera recharges the groundwater in nearby areas of the canal in downstream of the basin. The Ambanganga is fed by both southwest monsoon rain and northeast monsoon rain while the rivers and streams starting from the Knuckles mountain range are mainly influenced by northeast monsoon rain. The distinct isotopic signatures of different water sources will be more useful in the future as the baseline values to understand any changes in the groundwater recharge mechanism in the Ambanganga basin due to future development projects.


26

GSSL-2015-26

Value-addition to Sri Lankan Impure Marbles through Synthesis of Nanomaterials

M.M.M.G.P.G. Mantilaka1,2,*

, H.M.T.G.A. Pitawala1, D.G.G.P. Karunaratne

3 and R.M.G.

Rajapakse2


2Department of Chemistry, University of Peradeniya, Peradeniya, Sri Lanka.

3Department of Chemical and Process Engineering, University of Peradeniya, Sri Lanka.


Despite marbles being very common rocks in Sri Lanka, their uses are limited as raw materials in lime, construction and fertilizer industries due to high variability of their chemical and mineralogical compositions, high rock fracture density and coarse grained texture. Therefore, identification of suitable value-added products is a timely, needed requirement on value-addition to Sri Lankan marbles as well as similar types of marbles in the world. This study focuses on synthesis of nanomaterials such as nanoparticles of Precipitated Calcium Carbonate (PCC), magnesium hydroxide [Mg(OH)2], magnesium oxide (MgO), their polymer-nanocomposites including PCC/Poly(methyl methacrylate) (PMMA), poly(acrylic acid) (PAA)-stabilized Amorphous Calcium Carbonate (ACC) and poly(acrylate) (PA-)-encapsulated Mg(OH)2; hollow PCC using impure marbles with novel economical and industrially viable techniques. All these materials have broad-range of industrial and medical applications. In the novel preparation methods of these nanomaterials, first, calcined dolomite (CaO.MgO) was added to a sucrose solution in order to prepare calcium sucrate. The MgO of calcined dolomite together with impurities were separated out from calcium sucrate as precipitate and was digested in 1 M HCl to prepare MgCl2 solution. PCC products were synthesized by adding sodium carbonate or by bubbling carbon dioxide through calcium sucrate. Nanomaterials were synthesized in the presence of additives of PAA, PMMA and Triton X-100 in each preparation medium. Hollow PCC is fabricated on novel PAA/cetyltrimethylammonium chloride template. Novel PA--encapsulated Mg(OH)2 stable colloidal composite and Mg(OH)2 nanoparticles were prepared using above MgCl2 solution. Both these nanomaterials -were heated at 500 °C to produce MgO nanoparticles. All synthesized nanomaterials were in the particle size range 20-53 nm. The synthesized PCC and Mg(OH)2 nanoparticles were modified with fatty acids to synthesize hydrophobic materials. With the devised techniques, there is a great possibility to initiate new industry in Sri Lanka for exporting magnesium-based nanomaterials and domestic production of PCC which will reduce the import cost of those. Furthermore, the findings of this research are very important to replace consumable, pure and naturally occurring calcium carbonate resources such as cockle shells, corals and pearls by impure marbles.

Financial assistance by the National Research Council (Grant 11-178) is acknowledged.


27

GSSL-2015-27

Purity Enhancement of Natural Flake Graphite in Sri Lanka

R.M.U.M. Somarathna1, H.P.T.S. Hewathilake

2,*, L.P.S. Rohitha

3, N.W.B. Balasooriya

4 and

H.W.M.A.C. Wijayasinghe2

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

2Institute of Fundamental Studies, Hantana Road, Kandy, Sri Lanka.

3Department of Earth Resources Engineering, University of Moratuva, Moratuwa, Sri Lanka.

4Faculty of Applied Sciences, South Eastern University, Sammanthurai, Sri Lanka.


Graphite is a commercially very important crystalline form of carbon. Sri Lanka is endowed with high quality natural vein graphite as well as considerable reserves of flake graphite. Flake graphite occurs as isolated, flat plate-like particles disseminated in lenses or pockets in metamorphic rocks. Most of deposits occur in the South Western region of Sri Lanka. Even though there are various studies on Sri Lankan vein graphite, limited attention was drawn to study the distribution, chemistry, origin and geology setting of flake graphite deposits of Sri Lanka. Therefore, the present study focuses to purify graphite by physical and chemical processes to evaluate for possible industrial applications. Graphite samples were collected from two abandoned mines in Pasyala area (Kaluaggala and Wawehena). After toughly washed with water, the dried graphite samples were powdered by laboratory disk mill and 215 μm sized fraction was selected for the study. 200 g of samples was subjected to froth flotation. Froth floated samples were treated with 20, 30, 40, 50 and 60 vol. % NaOH separately and roasted at 250 0C. After neutralization and drying, the residue was leached with 10% H2SO4. Carbon percentage was determined according to ASTM – 561. Initial and purified samples were characterized by Fourier Transform Infrared (FTIR) spectrophotometer (Nicolet 6700) and X-ray Diffraction (XRD) methods. The electrical conductivity measurements were performed by the d.c. four probe technique. Carbon content analysis revealed that purification of samples can be increased over 60% by the froth flotation process and it can be upgraded over 95% by alkali roasting. Further, electrical conductivity of the purified flake graphite is in the semi-conductivity range, which is comparable with the natural vein graphite in Sri Lanka.

Financial assistance by the Innovative Research Grant -2013 of University Grant Commission (UGC), Ministry of Higher Education is acknowledged.


28

GSSL-2015-28

HF Acid Digestion for Purification of Vein Graphite

H.P.T.S. Hewathilake1,*

, H.W.M.A.C. Wijayasinghe1, N.W.B. Balasooriya

2 and H.M.T.G.A.

Pitawala3

1Institute of Fundamental Studies, Kandy, Sri Lanka.

2Faculty of Applied Sciences, South Eastern University, Sammanthurai, Sri Lanka.



Sri Lanka is well known for high quality vein graphite, containing about 95-98% of pure carbon. They have been categorized into four structurally distinct varieties; shiny-slippery-fibrous graphite (SSF); needle-platy graphite (NPG); coarse striated-flaky graphite (CSF) and coarse flakes of radial graphite (CFR). Recent studies on chemical purification, such as HCl acid leaching and alkali roasting proved that the purity of Sri Lankan vein graphite can be upgraded up to 99%. Further purified graphite shows a profound effect on surface modification which was done by either thermal or chemical oxidation. Strong oxidative agents such as HNO3, H2O2 and (NH4)2S2O8 were used in chemical oxidation. Silicate rock digestion employs HF acid with HNO3 and H2SO4 acids to achieve complete digestion. Therefore, this study was focused to apply HF acid digestion method for the purification of Sri Lankan vein graphite parallel with surface modification. Ten grams (10 g) of each graphite sample (<53 μm) were treated with a mixture of 25.0 ml of 10 vol. % HF, 10.0 ml of ≥ 69% HNO3 and 10.0 ml of 98% H2SO4 at 120 0C till the evaporation has taken place. After evaporation, 25.0 ml of distilled water added and stirred for one hour at room temperature. The mixture was filtered and the residue was washed to neutral and vacuum dried. Carbon percentage was determined according to ASTM - 561 and weighing the residues. Initial and purified samples were characterized by Fourier Transform infrared (FTIR) spectrophotometer and X-ray Diffraction techniques. The electrical characterization was performed on the dense graphite pellets by the d.c. four probe technique. The carbon percentage and FTIR analysis revealed that the HF acid digestion method was able to achieve the highest purity over 99.9% and simultaneously able to modify the surface of graphite. The electrical conductivity of the treated graphite samples is in the semi-conductive stage.

Financial assistance by the Innovative Research Grant - 2013 of University Grant Commission (UGC), Ministry of Higher Education is acknowledged.


29

GSSL-2015-29

Producing Raw Silica from Sri Lankan Vein Quartz Suitable for High End Glass Industry

S.S. Pathirage1,*

, P.V.A. Hemalal1, L.P.S. Rohitha

1, Shamalie Siriwardana

2 and N.P. Ratnayake

1

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



Sri Lanka is one of the main suppliers of silica to the world market. Even the raw product has a great demand for high tech industrial applications. At present, the Sri Lankan supply mainly consists of crushed and powdered bulk products. Since investment costs are high, Sri Lanka is not in a position to venture into manufacturing high end products such as semiconductors and optical glasses. With this background, it would be prudent to make value addition to Sri Lankan raw silica through quality control before exporting to glass and semiconductor industry. Super quality glass requires high purity silica with a very low amount of iron (< 50 ppm), whereas semiconductor industry requires raw silica with a low content of aluminum (Al). Vein quartz deposits in Sri Lanka shows maneuverable but high content of secondary iron, which need to be removed for the value addition. Therefore, the production of high quality silica was investigated using raw materials obtained from vein quartz deposits in the Badulla district. Acid leaching and magnetic separation coupled with size fractionation were employed for iron removal. Three metric tons of raw quartz were processed using primary and secondary crushers before separating them into five size fractions. Atomic Absorption Spectrophotometer was used to measure Iron content before and after the processing. The acid leaching of vein quartz resulted in a reduction of 30 – 40 ppm iron from the original value of 120 ppm. Efficiency of iron removal by Magnetic separation followed by size fractionation in the production process was also investigated. Chemical analysis of quartz in the 5 size fractions shows variable iron concentrations. Markedly high reduction is observed with particle sizes above 1 mm where iron concentration is less than 40 ppm. The iron concentration is 150 ppm for particle sizes below 1 mm which is not suitable for glass industry. Therefore, it is evident that the iron containing impurities in raw quartz have added into the finer fraction during the crushing and grinding process. This is possible since fragile secondary iron coated on surface of quartz can easily be crushed into finer material. If the finer fraction can be removed as waste, a lower Iron content in raw material can also be achieved. Therefore, selecting the fraction above 1 mm to further grinding by tertiary crusher, superfine silica fractions below 300 microns with low iron content can be produced.


30

GSSL-2015-30

Chemical and Mineralogical Stability of Biotite under Acidic and Basic Conditions

A.U. Wijenayake

1,*, H.M.T.G.A. Pitawala

2, C.L. Abayasekara

3 and B.M.R.

Bandara

4

1Postgraduate Institute of Science, University of Peradeniya, Sri Lanka.


3Department of Botany, University of Peradeniya, Peradeniya, Sri Lanka.

4Department of Chemistry, University of Peradeniya, Peradeniya, Sri Lanka.


Studying of the effect of the variation of pH and temperature on the alteration in biotite mica is useful for the understanding of the chemical and mineralogical changes occurred during the traditional pharmaceutical preparation processes. Therefore an experiment was designed to interpret the effects of heating conditions and organic acids on the changes in chemical composition of mica. Two sets of biotite samples from one location were used for the experiment. Pulverized fresh mica and heated mica (artificially oxidized in muffle furnace at 1000◦C/4h) fractions passed through the 125 µm sieve was soaked in Zizipus jujubae decoction, Vinegar and Artificial Cow Urine (ACU) for periods ranging from 1 to 28 days at room temperature. Dissolved major (K, Al, Fe, Mg, Ca and Na) and trace cations (Cu, Pb, Zn, Mn, and As) concentrations of centrifuged solutions were measured on atomic absorption spectrophotometer and pH of solutions was measured with the time. Chemical concentrations of major and trace elements of acid digested treated mica samples were measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). X-ray diffraction (XRD) and Furior Transform Infar Red (FTIR) spectroscopic analysis were done to determine the mineralogical alterations in treated mica samples.

Iron, Zn, Mn , Al, Pb, Rb, Ba, and Cs concentrations of all the unheated mica samples treated with all three liquids showed clear reduction in their concentrations compared to the those of untreated mica samples. However, these reductions in cation concentrations were significantly high in samples treated with vinegar while reduction was lower in samples treated with ACU. All liquid samples showed simultaneous increment in those elements. Some of the elements such as Co, Cr, and Ti remained unchanged throughout the experiment. All the heated biotite samples showed increment in their Ca concentrations compared to the unheated biotite samples. Increasing of pH values in both vinegar and Z. jujubae decoction filtrates and the decreasing of pH in ACU filtrates further confirms the cation exchange relation between the biotite an treated liquid samples. XRD analysis of treated biotite samples revealed some defects in the structure as a result of acid and base induced alterations. As thermal oxidation has an influence to decrease releasing capacity of cation compared to the unheated biotite, oxidation state of these metals and the temperature induced for the structural alterations may have affected on the mobility of the elements.


31

GSSL-2015-31

Estimating Optimum Beach Angle for Heavy Mineral Deposition along Sri Lankan Beaches

R.B.D.L. Bandara* and Atula Senaratne



Placer deposits with different scales containing economical concentrations of Ilmenite, Rutile, Garnet, Zircon, Magnetite and Monazite are abundant along the coastal belts in Sri Lanka. In the north-eastern coastal belt deposits with high percentage of (90%) heavy minerals are present. Among them, 60-75% Ilmenite, 5-10% Rutile and Magnetite and 8% of Zircon were observed. Seasonal or intermittent harvesting can be applied to extract these minerals. The present study aimed at finding the optimum beach angle and the preferred wave conditions suitable for deposition of heavy minerals in the Sri Lankan coastal belt. A Laboratory Simulated Coastal Environmental Model (LaSCEM) was developed and simulations were conducted using controlled configurations.

Beach sand samples from Pulmoddai, Kokkilai and Nayaru were collected from berm, swash and beach face. The granulometric parameters were obtained by mechanical analyses. Heavy minerals were initially separated by heavy liquid. Then, the extract was processed through the magnetic separator for identification of different mineral groups. Optimum beach angle for each mineral was obtained by configuring the LaSCEM. A statistical model was developed to analyze heavy mineral deposition under different wave conditions, beach environments and slope angles.

A close uniformity of all of the samples was evident from the grain size distribution analysis. However, along the coastal belt, Ilmenite percentage increases from Pulmoddai to Nayaru. Rutile tends to be deposited under normal wave action in shallow water when slope angles vary between 8°-9.5°. On the contrary, under agitated wave actions with deep water Rutile deposition prefer slope angles between 12.5°- 14°. Despite the wave conditions and seasonal variation, Ilmenite deposition prefers slope angles between 8°-9.5°. Similarly, under normal wave conditions Magnetite prefers to be deposited on beach face at 9.5°-11° slope angles, whereas under agitated condition slope angles between 14°-15.5° are needed. Under stormy conditions, Garnet tends to deposit along the beach at 14°- 15.5° slope angles. Wave conditions with slope angles at 9.5°- 11° are better for Zircon deposition and Monazite tend to be deposited at very gentle slope angles under agitated wave conditions.

Results show heavy mineral accumulation on the near shore area is controlled by variation of beach slope angle. Therefore, a favorable slope angle can be artificially constructed to maximize the heavy mineral harvest on beaches of Sri Lanka.

proceedings of the 31st february 2015...

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