Clay Science 21, 29–34 (2017)

–Paper–

KAOLIN DEPOSIT AT MEETIYAGODA, SOUTHWESTERN

a, b a Masaharu Nakagawa *, K.V. Wilbert Kehelpannala , Takahiro Manabe , b a Lalindra Ranaweera , and Ayami Nasu

a Faculty of Science, Kochi University, Kochi 780–8520, Japan b Department of Earth Sciences, Institute of Fundamental Studies, , Sri Lanka

(Received April 3, 2017. Accepted May 1, 2017)

ABSTRACT

High quality kaolin is mined at Meetiyagoda in southwestern Sri Lanka. The deposit occurs in a swampy area within the low-lying coastal region having a tropical wet . The kaolin clay beds form part of the Cenozoic fluvial sediments overlying the and pegmatite of the Highland Complex formed by the late Neoproterozoic-Cambrian orogeny. The sedimentary clays are composed mainly of kaolinite and quartz. X-ray powder diffraction and scanning electron microscopy have revealed that kaolinite is well-crystallized variety and the platy crystals are not broken in the sedimentary clay. The sedimentary kaolin is considered to have been formed by intense tropical weathering of the aluminous granulite and pegmatite, and subsequently transported and deposited into low-lying swamps or marshes near the weathering crust over the basement rock. The kaolin- ite crystals might have undergone partial recrystallization in the swampy environment.

Key words: kaolin clay deposit, well-crystallized kaolinite, weathering, sedimentation, Sri Lanka

INTRODUCTION

Clay deposits constitute one of the important mineral The island of Sri Lanka, formerly known as Ceylon, lies resources in Sri Lanka. Among various clay deposits in Sri in the to the southeast of the Indian subconti- Lanka, several important clay deposits occur in the south- nent and is located between latitudes 5°50′ and 9°55′N and western coastal belt. The clays are mostly kaolin and other longitudes 79°40′ and 81°55′E. The island comprises central similar types such as ball clay. These clays are considered to highlands, lower and low-lying coastal plains. A lot be products of tropical weathering. The occurrence of these of rivers rise in the central highlands and wind through low- clay deposits and their general mineralogical features are out- lands to the sea. lined by Herath (1985) and Fernando (1986), although detailed The island has a tropical climate. The rainfall distribu- studies have not yet been carried out. tion is influenced by topography and monsoon winds. The High quality kaolin is mined at Meetiyagoda in the south- southwest monsoon from May to September dumps heavy western coastal region. The kaolin has been designated as chi- rain on the windward slopes of the central highlands and the na clay and has been used for quality ceramic wares. Meetiya- southwestern lowlands of the island. The country has been goda has also been known for its moonstone mining since the divided into three climatic zones, the “wet”, “dry” and “inter- early 20th century. Fine quality moonstone feldspar has been mediate” zones, mainly based on annual rainfall distribution mined from kaolin clay overlying the kaolinized feldspar peg- (e.g., Panabokke, 1996; Punyawardena et al., 2003; Ministry matite. In this paper, we report the geological environments of Environment, 2011). The southwestern region including the of the kaolin deposit and the mineral associations of clays and central highlands is referred to as the wet zone receiving rela- the properties of kaolinite through laboratory investigations, tively high average annual rainfall without pronounced dry together with some genetic considerations. periods. Most of the northern and eastern parts of the island are known as the dry zone. Several clay deposits occur in nar- row coastal lowlands within the southwestern region having a wet climate (Figure 1). * Corresponding author: Masaharu Nakagawa, Faculty of Science, Kochi University, Kochi 780–8520, Japan. e-mail: mnakagaw@ GEOLOGY OF SRI LANKA kochi-u.ac.jp doi: 10.11362/jcssjclayscience.21.2_29 The geotectonic subdivision of Sri Lanka is shown in 30 M. Nakagawa et al.

Fig. 1. Locations of clay deposits shown within the generalized geological framework of Sri Lanka. The clay deposits are indicated by open circles. The geological subdivision of the basement rocks is based on Cooray (1994) and Dharmapriya et al. (2015). Three major climatic zones are shown with dashed red lines based on the agro-ecological map of NRMC.

Figure 1. Most of the Sri Lankan island is underlain by Pre- were derived from late Archean to early Proterozoic sources cambrian crystalline rocks. The northwestern coastal belt is (e.g., Milisenda et al., 1988; Kröner et al., 1991; Santosh et al., covered mainly by limestone. Quaternary sediments 2014; Dharmapriya et al., 2015). Zircon U–Pb ages show mul- and also rest on the basement rocks at the coastal areas tiple late Neoproterozoic-Cambrian high-grade metamorphic and several inland basins. events associated with the assembly of the super- The Precambrian crustal basement of Sri Lanka has been continent (e.g., Santosh et al., 2014; Dharmapriya et al., 2015; subdivided into four major lithotectonic units based on rock He et al., 2016). Numerous pegmatites are emplaced into the type, metamorphic grade, Nd model age, U–Pb zircon age metamorphic basement of the HC (e.g., Dissanayake et al., and regional structural interpretation (e.g., Milisenda et al., 2000; Fernando et al., 2011). 1988; Kröner et al., 1991; Cooray, 1994; Kehelpannala, 1997). These are the Wanni Complex (WC) to the west together with MINERAL AND CLAY DEPOSITS IN SRI LANKA the Kadugannawa Complex (KC), the Highland Complex (HC) at the middle, and the Vijayan Complex (VC) to the east Sri Lanka is endowed with mineral resources such as placer (Figure 1). Three tectonic klippens of the HC are exposed in gemstones, mineral sands including ilmenite, rutile, zircon, the southern part of the VC. monazite and quartz, clay, feldspar, graphite, mica, apatite Among the four major tectonic units constituting the Sri rock, quartzite and limestone (e.g., Herath, 1985; Fernando, Lankan basement, the HC is considered to be a part of a 1986; Jayawardena, 2004; Kuo, 2013). These minerals occur supracrustal basin, and is dominantly composed of metasedi- in granulite facies rocks, granitic rocks, pegmatites and their mentary rocks (quartzite, marble, calc-silicate rock and pelitic weathering products. Placer accumulations derived from gneiss), in association with charnockite, meta-granitoid these are common. and granitic gneiss. The HC rocks have been subjected to Kaolin (also known as china clay) and ball clay have been regional granulite facies metamorphism (e.g., Cooray, 1994, used mainly in the ceramic industry of Sri Lanka (Herath, Mathavan et al., 1999; Osanai, et al., 2006). The HC rocks 1985; Fernando, 1986). The locations of three prominent Kaolin deposit at Meetiyagoda, southwestern Sri Lanka 31

Fig. 2. Field photographs of kaolin clays at Meetiyagoda, Sri Lanka. a: Marsh in the clay mine. b: Open pit for high quality kaolin. c: Clay from the moonstone mining shaft.

clay deposits are shown in Figure 1. These deposits occur in low-lying coastal plains within the HC. Well-known kaolin deposits are located at Boralesgamuwa and Meetiyagoda. At Boralesgamuwa, kaolin occurs as lenses or beds ranging from 1 to 6 m in thickness, not deeper than 10 m, in a large swampy area (Herath, 1963). The Boralesgamuwa kaolin has already been exhausted. The deposit of ball clay having high plasticity occurs in the flood plain of a large river at Dediyawala area, although several small deposits occur in hill regions.

MEETIYAGODA KAOLIN DEPOSIT

The Meetiyagoda kaolin deposit occurs in a swampy area within the southwestern coastal plain (Figures 1 and 2a). In this area, the Cenozoic fluvial sediments, ca. 30 m thick, in- cluding kaolin clay beds are distributed overlying the granu- lite and pegmatite of the HC. In an open pit producing high quality kaolin (Figure 2b), about 10 m thick clayey sediments are exposed. Its lithostrati- graphic sequence is gray clay, peaty alluvium and peat, gray sandy clay, white clay and white pure clay from top to bottom. The white clay is massive and very fine-grained and lies in the ground at depths below about 3 m. Almost pure clay occurs as a lens or bed within the white clay bed at a depth of 5 to 7 m, near the water surface in Figure 2b. It is the most promising kaolin in this mine. The sandy clay is massive and appears to contain many quartz grains cemented with fine clay. Moonstone has been mined adjacent to the kaolin min- ing area. The colorless and almost transparent moonstone Fig. 3. X-ray powder diffraction patterns of kaolin clays from displaying a fine blue sheen is available in this mine. The Meetiyagoda. a: High quality white clay of the open pit. b: gem variety of alkali feldspar has microperthitic exsolution White clay of the marsh. c: Gray clay of the moonstone mine. lamellae of orthoclase-albite (Spencer, 1930). The kaolin clay K: kaolinite, M: muscovite, Q: quartz, G: graphite. 32 M. Nakagawa et al.

Table 1. Mineral constituents of kaolin clays from Meetiyagoda. Deposit Lithology Main constituent Minor constituent High quality kaolin Gray clay Kaolinite, quartz Peat Amorphous Quartz, kaolinite, gypsum Gray sandy clay Quartz Kaolinite White clay Kaolinite Quartz, graphite, muscovite, crandallite White pure clay Kaolinite Quartz, graphite Marshy clay Sandy clay Quartz, kaolinite Anatase, rutile Sandy clay Kaolinite, muscovite, quartz, orthoclase Gray clay Kaolinite Quartz, muscovite, graphite, orthoclase White clay Kaolinite Quartz, muscovite Moonstone Gray clay Kaolinite Graphite, quartz, muscovite, jarosite

containing moonstone feldspar as the weathering residuals of feldspar pegmatite is mined from the lowest parts of the clay beds (Figure 2c). The underground mining has been done at depths of 26 to 30 m (Spencer, 1930).

ANALYTICAL PROCEDURE

Representative clay samples were collected from both the clay and moonstone mines at Meetiyagoda during field inves- tigations. The clay samples were examined by X-ray powder diffraction (XRD) method to characterize the constituent minerals of the samples, employing a Rigaku MultiFlex dif- fractometer using CuKα radiation at 36 kV and 16 mA at the Kochi University. Morphology of kaolinite was observed with a JEOL JSM-6500F scanning electron microscope (SEM) at 15 kV accelerating voltage using gold-coated sample at the Center for Advanced Marine Core Research of Kochi Uni- versity. Fig. 4. Scanning electron micrograph of kaolinite (Figure 3a). Scale bar is 1 µm in length. RESULTS AND DISCUSSION locally found in the clays of the open pit and moonstone mine Mineralogy respectively. The representative X-ray powder diffraction patterns of the clays from Meetiyagoda are given in Figure 3. The high Properties of kaolinite quality white pure clay from the open pit is composed pre- X-ray powder diffraction patterns of kaolinites from Meeti- dominantly of kaolinite (Figure 3a). The white clay from the yagoda show sharp diffractions (Figure 3), namely, 00l basal marshy area is composed mainly of kaolinite and contains reflections near 12.4°, 24.9° and 37.8 ° (2θ), and 02l, 11l, 13l small quantities of quartz and muscovite (Figure 3b). The and 20l reflections in the range of 19.5–43° (2θ). This X-ray gray clay from the moonstone mine is composed mainly of property is characteristic of well-ordered triclinic kaolinite. kaolinite with several accessory minerals such as quartz, The kaolinites in the sedimentary clays of the Meetiyagoda graphite and muscovite (Figure 3c). mines are always well-ordered kaolinites. The sample shown The mineral constituents of the clays in the Meetiyagoda in Figure 3a is a typical example of very well-ordered kaolin- deposit examined by X-ray diffraction are summarized in ite. Table 1. High quality white pure clay which is composed al- Scanning electron micrograph of kaolinite is shown in Fig- most purely of kaolinite occurs as a lens or bed in the open pit ure 4. Good crystals of pseudo-hexagonal plates are observed (Figure 2b). Sandy clay which is composed of kaolinite and in the above very well-ordered sample. Most of the kaolinite quartz is the major component at the marsh (Figure 2a). Small crystals have the grain size ranging from 0.2 to 0.5 µm in di- amounts of graphite, muscovite, orthoclase, anatase and ameter. The thickness of the grains mostly ranges from 0.02 rutile which are considered to be the residual products from to 0.04 µm. These platy grains of kaolinite are not broken in the weathering of the original rock are locally found in these the sedimentary clay. clays. Small graphite flakes are also found sporadically in the clays of the open pit (Figure 2b) and moonstone mine (Figure Genesis of kaolin deposit 2c). In addition, trace amounts of crandallite and jarosite were The Meetiyagoda kaolin deposit occurs in a swampy area Kaolin deposit at Meetiyagoda, southwestern Sri Lanka 33 within the wet zone of southwestern Sri Lanka. The kaolin and Meetiyagoda Moonstone Mine for all their help and guid- clay beds form part of the Cenozoic fluvial sediments overly- ance in the field. We thank the editor and referee for construc- ing the granulite facies rocks of the Highland Complex (HC) tive comments. metamorphosed during the late Neoproterozoic-Cambrian REFERENCES orogeny. The kaolin clays of the Meetiyagoda clay mine are considered to be secondary (sedimentary) accumulations Cooray, P.G. 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