Proceedings of ERE 2007
Offshore Sand Exploration Around 
Kaluthara-Beruwala Area
Gunasinghe AWDC, Chandana NHS, Ranaweera DHD, 
* Vijitha AVP and Rathnayake NP
Department of Earth Resources Engineering, University of Moratuwa 
‘Corresponding author; e-mail :vijitha@earth.mrt.ac.Ik
Offshore minerals are used as a raw mineral for various types ofAbstract:
industries around the world. The exclusive economic zone belonging to Sri Lanka 
more than eight times land area of the country, offering huge potential for extraction 
and exploitation of minerals. Industrial sector, including mining and minerals, should 
grow to achieve the development of the country. Therefore this study was carried out 
to investigate the offshore sand mineral potential around Kaluthara — Beruwela area. 
About 200 samples were collected from sea floor, from a grid of 500m, 1000m Easting 
and Northing respectively. Investigation was carried out to identify the variation of 
particle size and mineral content around the Kaluthara area by sieve analysis. For 
each sample, particle size distribution curves were plotted and mean particle sizes, 
sorting and skewness were obtained. Heavy mineral content was also determined 
using gravity separation, magnetic separation; high tension separation and 
microscopic observation. Resource maps were plotted and mineral resources areas 
were demarcated.
Key words: Offshore minerals, Particle size, Skewness, Sorting Index, Sieve analysis
environmental, social and economic 
issue in the recent past. The average rate 
of increase in demand for construction 
sand during in the last six years has 
been estimated to be round 10%. Unless 
otherwise a suitable alternative is 
introduced to the local market, building 
trade is going to face grave difficulties.
1. Introduction
Sri Lanka needs at least 9 million cubic 
meters of sand annually to meet the 
demand of the local construction 
market. This will be supplied from the 
rivers in the country. River sand known 
as "non renewable resources" is 
considered to have caused a lot of 
environmental problems during and 
after the course of mining. Therefore the 
government as well as various 
environmental lobbies do not encourage 
river sand mining due to adverse 
environmental effects. This situation has 
caused drastic shortage of sand. Hence, 
local construction is severely hampered. 
Mining of river sand for construction 
purposes has become a major
Rathnayake NP, B.Sc. (Hons) (Peradeniya), 
M.Sc(Shimane), Ph.D (Hokkaido) Senior 
Lecturer in Ddepartment of Earth Resources 
Engineering, Uuniversity of Moratuwa. 
Vijitha AVP, B.Sc. Eng. (Moratuwa), 
M.Sc.(NTNU Norway) Senior Lecturer in 
Department of Earth Resources 
Engineering, university of Moratuwa.
NHS Chandana, DHD Ranaweera, AWDC 
Gunasinghe, Final year undergraduate 
students in the Department of Earth 
Resounds Engineering
136R.E 2007
Proceedings of ERE 2007
Reference samples (50% of original) 
were kept for each analysed sample.
3. Sample analysis
As an alternative for river sand, use of 
offshore sand has been suggested since 
the use of offshore sand is now
practice, throughout the world.
The largest beach sand deposit which is 
6.5 km in length with an average width 
of 60 m located at Pulmoddai. The 
deposit is estimated to contain nearly 
4,000,000 tons of raw sands. Offshore 
mineral exploration is important 
because of the resource hidden under 
the sea bed, where can be utilized 
properly by granting prospecting and 
exploration licenses. The exclusive 
economic zone belonging to Sri Lanka 
more than eight times land area of the 
country, offering huge potential for 
extraction and exploitation of minerals. 
Industrial sector, including mining and 
minerals, should grow to achieve the 
development of the country.
a
common
All samples were subjected to sieve 
analysis and graphs were plotted for 
particle size distribution.
Mean grain size, sorting and skewness 
were determined.
Mean grain size
*16 +*50 + *84 (1)M = 3
#95 + *5 - 2(*50)*84 + #16 - 2(*50)
..(2)s = +
2(#95 #5)2(#84-*16)
In this study, we have carried out an 
exploration program to find out suitable 
sand deposits around Kaluthara- 
Beruwala area, 
existence of large minable sand deposits 
that can be used for the future demands.
Skewness
Sorting Index.Results shows,
*84 #16 + ” *s ...(3)D = +4 6.62. Methodology
267 Sand samples were collected at 12 
km x 11.5 km off the river mouth areas 
of Kaluthara-Beruwela area. Fig. 4 
shows the sampling location, 
readings of all the locations 
recorded. The collected samples 
preserved by deep freezer before 
analysis. Samples were dried at 60 °C for 
24 hours and moisture content 
calculated. Coning and quartering 
done to reduce the samples by 
considering the weight and particle size.
Where,
05- Grain size of 5% of cumulative 
weight
016- Grain size of 16% of cumulative 
weight
050- Grain size of 50% of cumulative 
weight
084-Grain size of 84% of cumulative 
weight
095- Grain size of 95% of cumulative 
weight
GPS
were
were
was
was
SR.B 2007 14
Proceedings of ERE 2007
10100
8 $ co * ♦*90
u
680 $* ♦70 4 'MW-- '•2 60 ” 2 -S 0
S -2 ,1
° -4 I
♦ ♦♦♦ ^I 50a 40
E 30 1(J 5030 4020
20
S*
10
-6 ♦—o
1500 1000 0500 0000 0 500 1 000 1 500 2 000 2500 5 000 3 500 4000 4.500 ■8 o * © ♦
Particto afe»{pht) -10J
Figure 1. Particle size distribution of 
an arbitrary sample Depth (m)
Figure 3. Variation of Mean Grain size 
with Depth4. Results
Variation of mean grain size with 
Distance to river mouth was plotted as 
shown in figure 2. It could be seen that 
coarse, medium and fine sand are 
concentrated between 6000m to 10000m 
from the shore.
According to (Kumara et al, 2006) the 
most commonly found particle size of 
the Umenite is in the range of +125pm to 
+25 Opm. Therefore heavy mineral 
concentrated areas are denoted by white 
and light ash colour in figure 5.
Mean Grain size of construction sand 
laid around medium and coarse and it 
can be identified by using Figure 5.
i
!
8 ]
6 ♦ •
4 *•» t**«. ^ f •• ♦ ♦♦ •
it * t s ?
w r r#iTiifcffitesl
mfrs&i t *? t
,'n* rrro
IOOOOO 102000 103000 104000 10*000 10*000 IP?0OO l£*#000 lOfiOCO II0O00 1iwoo
160000
" ::#v!^v2 4 * ■SUM --}0 lI5TOOO
°.20 0 2000.0 400^.0 I6&00.0 8000.0 10000.0 12000.0 ! >
A )-4 155000
-6 164000
155000
-8 * * AI44M 4frtO» * »♦ • »
163000
Distance from River Mouth
I51O00
n i
150000
14*000
Figure 2. Variation of mean grain size 
with distance to river mouth
14*000
147000
Variation of Mean Grain size with depth 
to sample point was plotted and it is 
shown below. It shows that sand is 
concentrated depths in between 0 - 10m 
and 20 - 30m.
Figure 4. Bathymetric map of 
investigated area
156R.6 2007
Proceedings of ERE 2007
However, these deposits also contains 
appreciable amount of ilmenite that 
be used for extracting Titanium metal.
can
j
J Acknowledgement
We would like to acknowledge Captain 
Y. N. Jayarathna, and Navy officers R. 
Samarweera and Jayarahal for assisting 
the offshore field program. Our sincere 
thanks also go to Mr. Suranga 
Gunathilaka of the Department of Earth 
Resources Engineering for assisting in 
the field as well as in the Lab. Finally, 
like to acknowledge 
anonymous reviewers for improving the 
quality of this paper.
j
2
J
10X00 101000 10X00 103000 104000 10X00 106000 107000 100000 109000 110000 II1000
we would
Figure 5. Grain size distribution of 
heavy minerals
5. Discussion References
Overall results of the above two charts 
and resource map we can say that sand 
deposit are located thought offshore 
around the Kaluthara area and there are 
sediment between Corel reefs and Rock 
Mountains and most are,
Herath, J. W., (1995) Economic Geology of Sri 
Lanka, Ministry of Industrial 
Development.
Kumara, H. A. N. H., Medagoda, C. J., 
Sivakala, S., Sugaraj, K., Wikrama,. M. A. 
D, M. G., Vijitha, A.V.P., Dissanayake, 
O.K. and Ratnayake N.P. (2006). 
Exploration of Ilmenite potential in and 
around Kalu and Benthara river mouths 
with special reference to the variation of 
Ti02 content along a selected stretch of 
Kalu ganga. In: Proceedings of ERE 2006 
(ed. S. Karunarthna) 
www.encydopidia.com/ doc / ilmanite 
(accessed 02/6/2007)
www.chemlink.com.au (accessed 08/4/2007) 
www.mineralzone.com(visited 
16/07/2007)
www.asincom.com/ti.htm 
16/07/2007)
1. Suitable as construction sand due its 
particle size distribution 
2. . All sand samples can contains heavy 
mineral due to most sand samples 
are suitable particle size range.
Sediment flowing path clearly can be 
identified using Mean Grain size 
Resources map. on
(visited6. Conclusion on
This study confirmed that the there are 
lot of sand deposits around Kaluthara 
area that can be used for construction 
Construction sand haspurposes.
specific particle size distribution and 
specific Mean grain size. Most of 
Experimented samples lied between this 
range and having above mean grain
size.
16ER.6 2007