716 RODINIA, GONDWANA AND ASIA

Mineralization of Highland Rocks of Sri Lanka: A Case Study in the Kandy - Matale Area S.W. Nawaratne and C.B. Dissanayake Department of Geology, University of Peradeniya, Sri Lanka

The history of mining for minerals in Sri Lanka can be dated back to more than 2000 years. Mining has been done through all this time for gemstones, gold, iron and copper, clay, sand and phlogophite. Several mineral deposits in Sri Lanka are of economic importance even to the present day standards and the others being too small in size to be used in the large or medium scale industries. The mineral deposits that are being exploited in the commercial scale include graphite, phosphate, feldspar, quartz, gemstones, clays, limestone, dolomite and mineral sands. Although these mineral deposits are scattered throughout the country some economically highly valuable mineral deposits in the Kandy and Matale areas, which include feldspar, quartz and mica deposits. In addition gemstones mainly topaz but also large crystals of aquamarine have also been found. However, genesis of gemstones has not yet been studied in detail.

The primary mineralizations are mainly fracture controlled vein type or localised within shear zones. Graphite is one of the major economic minerals that occur in large quantities in a fracture controlled vein systems in Sri Lanka. However, many other fractures and shears in the Highland rocks are occupied by other types of mineralization. The mineralization in the Kandy-Matale area include intrusive formations such as quartz veins with high purity SiO, and pegmatites bearing high quality K-feldspar, fluorite and muscovite, some of which make important economic mineral deposits of the country. Some pegmatites carry considerable amounts of gem minerals, which include tourmaline, topaz and beryl. Quartz of gem-quality occurs in vugs and fissures of the country rock, quarz veins and pegmaties as secondary developments. Some zones of the ductile and brittle shear fractures are filled with disseminated sulphides, sulphide veins and pockets of various sizes bearing principally pyrite, chalcopyrite and pyrrhotite.

Among the major mineralizations in the Matale area, are the Kaikawala, Owala and Rattota K-feldspar deposits, Rattota vein quartz deposits, Kaikawala muscovite deposits, Kaikawala fluorite deposits and Polwatte topaz deposits which also occassionlly with large crystals of aquamarine (a gem variety of beryl) of several kilograms in weight. The sizes of the pegmatites vary widely from small ones to extremely large deposits and the

large deposits are made of mainly K-feldspar with minor inclusions of quartz, fluorite and biotite. All the minerals occur in in-situ primary deposits but topaz have been found up to now only in the sediments in low lying parts of the area.

In the Kandy area several minor mineralizations such as chalcopyrite, pyrite, pyrrhotite?, phlogophite, spinel occur at several locations such as garnet at Digana (good dodecahedra1 almandine crstals) and beryl at Gatambe. Occurrence of fluorite also has been known from Gatambe. The Matale-Kandy pegmatitic and related gemstone mineralizations which postdates the last deformational event known as D,, (Almond, 1992) as D,, D, and D, being the earlier ones, are therefore clearly late stage derivatives of a extensive granitic magmatism of the Pan-African tectonics. The placement of pegmatites, quartz veins and other fracture and shear controlled mineralization in the Kandy-Matale area can be attributed to an intensive pegmatitic and pneumatolitic stage of the magmatic activity during the D,. The active components of the mineralizing agents have been rich in S, CO,, B, F and Be which gave rise to tourmaline, carbonate and sulphide minerals and more importantly fluorite and topaz. It must also be noted that some minor alteration zones associated with those fractures have been dated to be younger than 450 Ma (Yoshida et al., 1990). The Kandy-Matale mineralization is of post-metamorphic nature, which is younger than 550 Ma could well be related directly to Pan-African magmatic event. Therefore in view of the recent findings that Sri Lanka was geologically closely associated with Southern India and Madagascar during a period of Pan-African mineralization, the above observations have important implications in the study of mineralization in Gondwana.

References Almond, D.C. (1992) Structural Implications of a new geological map

of Kandy sheet, Central Sri Lanka, J. Geol. SOC. Sri Lanka, v. 4,

Yoshida, M., Kehelpannala, K.V.W., Hiroi, Y. and Vithange, P.W. (1990) Sequence of deformation and metamorphism of granulite facies rocks of south to southwestern Sri Lanka, Proceedings of the NIPR symposium on Study of Geologic correlation between Sri Lanka and Antarctica, pp. 71-106.

pp. 48-56.

Gondwana Research, V. 4, No. 4,2001