Geological Formations and Mineral Resources of Sri Lanka
The Wanni Complex and Other Geological Formations
The Wanni Complex is characterized by rock formations that are estimated to be over million years old. While the level of metamorphism in the Wanni Complex is generally lower than that observed in the Highland Series, there are no clearly defined structural differences between the two series. Notable geological features within the Wanni Complex include the Tonigala Granite.
Miocene rocks represent another significant geological period in Sri Lanka. In Jaffna, Miocene limestone presents as a hard metamorphic rock with a light yellow hue. In the Uva Province, specifically in the Akurukaduwa area, Miocene limestone is identified as a sedimentary rock belonging to the Tertiary period. Additionally, Jurassic rocks, which are over lakh ( million) years old, are composed of sandstone, grit, and brown or black stones. These Jurassic formations are typically found in rift basins north of Chilaw, specifically in the areas of Thambowa, Andigama, and Pallama.
Definition and Categorization of Minerals
Minerals are defined as naturally occurring substances that possess a specific chemical composition and a crystal structure. They are formed through the combination of one or more chemical elements. Minerals are broadly categorized into metallic and non-metallic types. In the context of Sri Lanka, minerals are further classified into three functional groups: Energy Minerals (Fuel), Metallic Minerals, and Non-metallic Minerals.
Energy Minerals
Energy minerals, also referred to as fuel minerals, include peat (often associated with coal), thorianite, and monazite. Peat is formed through the burial and subsequent decay of swamp vegetation. Deposits of peat can be found in the Muthurajawela swamp, the North Colombo area, and in smaller quantities within regions such as Diyatalawa, Bandarawela, and Nuwara Eliya.
Radioactive minerals like thorianite and monazite fall under the category of energy minerals due to their potential use in generating nuclear power. Thorianite is located in the Ratnapura district, while monazite deposits are found in the coastal areas of Kaikawala and Induruwa.
Metallic Minerals
Metallic minerals found in Sri Lanka include iron, copper, magnesium, nickel, chromium, tungsten, and silicon. There are two primary types of iron ore deposits in the country: Limonite and Magnetite. Limonite is typically found on the mountaintops of the Ratnapura, Matara, and Galle districts. Magnetite deposits are located in Wilagedara, Seruwavila, and Panirendawa.
Despite the presence of these deposits, the economic value of Sri Lankan iron ore is relatively low because the iron percentage is not sufficiently high and the deposits are small and scattered. However, the Seruwavila iron ore deposit is considered highly significant as it contains several other extractable minerals, such as copper. Currently, Sri Lanka imports much of its required iron because the costs associated with mining and processing local ore are prohibitive.
Mineral Sands and Clay
Non-metallic minerals include a wide variety of substances such as mineral sands, clay, gravel, salt, gems, graphite, mica, dolomite, apatite, and feldspar. Mineral sands are found in Kudiramale, Polkotuwa, Kaikawala, and Pulmoddai. The Pulmoddai deposit is the largest, stretching along the coast from Nilaveli to Mullaitivu. This massive deposit is approximately long and wide, containing roughly million tons of mineral sand. The sands are composed of ilmenite, rutile, zircon, sillimanite, and monazite. While there is minimal domestic consumption of these minerals, they are processed and exported. Ilmenite and rutile are particularly valuable as they are the raw materials needed to produce titanium.
Clay is one of the most widely distributed minerals across the island and is essential for the pottery, tile, and brick industries. Kaolin, or China clay, is found in Boralesgamuwa, Meetiyagoda, and Waskaduwa, and is primarily used for ceramics. Ball clay is distributed across the floodplains of the southwest, with the highest quality deposits located in the Dediyawala area.
Gems of Sri Lanka
Gems are the highest revenue-generating minerals for Sri Lanka, which enjoys a long history and global fame for its gemstones. Gem deposits are most abundant in the rock zones belonging to the Highland Series. They are commonly found in alluvial deposits in regions such as Ratnapura, Monaragala, and Matale. Mining techniques include extracting gems from riverbeds and traditional pit mining.
The value of a gemstone is significantly enhanced through precise cutting and polishing, a craft in which Sri Lanka possesses specialized expertise. The most important variety of gemstone in Sri Lanka is Corundum (Ruby), which is typically deep red but can also be found in yellow, orange, green, and brown. Pathmaraga is a unique variety of gemstone that is endemic to Sri Lanka.
Graphite Resources
Sri Lanka has a graphite mining history spanning approximately years and is world-renowned for the high quality of its graphite, which boasts a carbon content between and . Graphite is abundant in the southwest, northwest, and central highland regions. Well-known mines include Bogala, Dumbara, Kolongaha, and Kahatagaha.
Graphite is found in two forms: vein graphite and flaky graphite (mica). Vein graphite, which is found in rock fractures, has a higher economic value. Flaky graphite (mica) is found in layered sheets. Due to its high dielectric capacity, mica is extensively used in the electronics industry.