Economic Geology of Sri Lanka

What is economic geology?

Economic minerals are the minerals with some monitory value or provide us money by exporting or by using those to produce some valuable product.

These materials include precious and base metals, nonmetallic minerals, construction-grade stone, petroleum minerals, coal, and water.

However, the term commonly refers to metallic mineral deposits and mineral resources.

Economic geology of Sri Lanka

Geological Survey and Mines Bureau (GSMB) in Sri Lanka is one of the responsible authorities for economic minerals in Sri Lanka. GSMB evaluates the extension of the mineral reserve and conduct research on the quality of the resource.

Two sub sections

Economic minerals

Economic rocks

Economic minerals are classified into 4 major groups;

energy minerals,

ferrous and ferroalloy group,

non-ferrous group

and non-metallic group.

Economic minerals in Sri Lanka

Energy minerals

Uranium, uranite, thorite (the silicate of thorium), thorianite (the oxide of thorium) and monazite have been found in Sri Lanka.

Uranium and thorium minerals are mostly found in detrital deposits in Kalaoya area and Ratnapura, Pelmadulla areas respectively.

Monozite is found as placer deposits around Induruwa and Polkatuwa area near Beruwala along the southern beach, heavy mineral concentrates in gem bearing sediments in Ratnapura as well as in Pulmoddai as beach sands.

Ferrous and ferroalloy group

Most common ferrous and ferroalloy minerals found in Sri Lanka are magnetite, hematite and iron oxides. This deposit is considered as surface as well as subsurface reserve.

Recently found magnetite-hematite deposit at Wellawaya is one of the best ferrous and ferroalloy mineral deposits we have in Sri Lanka.

Several small magnetite reserves are found in Wilagedara and Panirendawa around Sandalanka and Chilaw respectively. These are mostly surface deposits.

Seruwawila Cu-Magnetite

The copper-magnetite deposit at Seruwawila also important.

This was discovered by the Department of Geological Survey in 1971.

Magnetite and sulphide massive sections can be found in here.

Those are about 1-10 m in thickness.

About 40% of the reserve is considered as iron while 2% is estimated as copper. However, since this reserve is located under ground, the extraction cost would be very high.

Ferroalloy serpentinite deposit

Rich in Nickel, Cobolt, Manganese and Chromium.

Most popular serpentinite deposits are found at Ussangoda and Udawalawe.

Non-ferrous minerals

Pulmoddai beach sand deposit is the most important non-ferrous mineral reserve in Sri Lanka to date.

It contains minerals which consist of one of the most expensive and important metals in the world that is titanium.

Ilmanite (FeTiO2) and rutile (TiO2) found in enormous concentrations in the Pulmoddai beach sand deposit.

This deposit extends from Nilaveli to Kokilai lagoon mouth.

The distance is about 7.5km. The average width of the sand deposit is about 60 m.

Several sand types are found in here; ilmanite (70-72%), zircon (8-10%), rutile (8%), silimanite (1%) as well as monazite (0.3%).

Geological explorations have estimated the total reserve is about 4 million tones of sand in Pulmoddai deposit while three closer deposits consist of another 7 million tones more.

Exporting sand from this deposit started on 1959. Ilmanite and rutile in this deposit are rich in TiO2.

Experiments have shown that TiO2 concentration of ilmanite is about 53% while that of rutile is about 95%.

Non metallic minerals Sri Lanka is rich in non metallic minerals

Graphite Vein quartz Apatite Dolomite Fledspar Gems Mica Clays

Kaolinite

Sands Garnet sand Silica sand

Graphite

The use of graphite in Sri Lanka has a long history, from 1675.

Sri Lankan graphite is very popular all over the world for its high purity.

There are two major mines for graphite, Kahatagaha-Kolongaha and Bogala.

The largest mine is Kahatagaha-Kolongaha close to Matale-Kurunegala road. This is deeper than 650 m.

Quartz and Feldspar

Quartz sand from Marawila-Naththandiya deposits is used for bottle industry while quartzite pieces from Galaha and Wellawaya are exported directly Metasediments aged 2000 million years

Feldspar is used as a raw material for ceramic and porcelain industries. The main feldspar mine is located at Rattota, Matale.

Apatite

One of our best economic mineral reserves is the apatite rock phosphate at Eppawala.

The reserve extents over 7 km2 and about 125 m deep from the surface. This has been proven by deep drilling.

It is estimated that the reserve consist of 60 million tones of apatite.

Apatite is being used to produce phosphate fertilizer. However, enrichment of iron and less soluble tricalcium phosphate in the reserve, fertilizer shows low solubility. Therefore the fertilizer from this reserve, triple super phosphate, is used for long term crops.

Feldspar, mica and dolomite

Feldspar, mica and dolomite are used for domestic industries.

Feldspar is used as a raw material for ceramic and porcelain industries.

The main feldspar mine is located at Rattota, Matale. Mica mining and exporting has a long history as well. It dates back as far as 1896.

Dolomite is utilized as a fertilizer in tea cultivation also as a substitute for lime from corals.

Largest dolomite mine is located at Digana, while several small scales mines are located near Badulla.

Clay Three main types of clays are used to produce domestic

as well as export goods; kaolinite, ball clay and brick clay. Borelasgamuwa and Meetiyagoda kaolinite deposits are the two main deposits for kaolinite in Sri Lanka.

Weathering of quartz-feldspar-biotite gneiss (commonly known as kalu gal in Sinhalese) results kaolinite. The depth of kaolinite clay deposit at Borelasgamuwa is about 10 m but distributed through out a large area and consists of best quality clay. Although Meetiyagoda deposit is about 30 m deep it has many impurities.

Yellow, red and blue colour ball clay is found in hill country. These are being used to make casts and used as refractory material because of their strength and high plasticity. Brick clay is found in most of the river valleys and they are used to produce bricks and tiles.

Gems

The history of gems in Sri Lanka dates back to more than 2500 years. According to gemologists Sri Lanka is the country with the highest density of gem varieties.

All minerals are not gems and all gems are not minerals either. Some organic materials are considered as gems such as pearl and amber. Only inorganic materials are considered as minerals. We are going to talk about the gems that are minerals.

Gem varietiesFamily and mineral name Colour

Corundum Blue Sapphire blue

Ruby Red, pink

Orange Sapphire orange

Yellow Sapphire yellow

Geuda White, blue and colourless

Chrysoberyl Green, red

Colorless, yellow

Topaz Green, yellow, orange, violet, brown, pink, honey colour, colourless

Tourmaline Emerald green, brown, green, black

Spinel Red, yellow, orange, violet, pink, blue, green

Garnet Hessanite Orange

Pyrope Red

Feldspar

Moonstone White

Quartz Amethyst Violet

Citrine Yellow

Gem deposits

Gem deposits in Sri Lanka can be categorized into 3 main groups.

Residual deposits - Okkampiiya

Elluvial deposits - Elahera

Alluvial deposits - Ratnapura

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