CHAPTER 1 INTRODUCTION. Placer deposits of the SW coast of India have been known for. decades and are being exploited. They are popularly known as

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1 CHAPTER 1 INTRODUCTION Placer deposits of the SW coast of India have been known for decades and are being exploited. They are popularly known as black sands and occur in modern beaches and in beach terraces of the SW coast of India. These placers are enriched in ilmenite, rutile, sillimanite, garnet, zircon and monazite. Titanium minerals predominate over the other heavy minerals. The provenance of heavy minerals has been traced to Kerala khondalite belt (KKB), charnockite and other igneous rocks of the Western Ghats. Rivers flowing over these rock types undoubtedly supplied placer minerals to the present day beaches and to submerged paleo -beaches (during lowered sea level) of Kerala. Before the demand for ilmenite as an important industrial raw material, monazite was the only mineral which was recovered in small quantities for its rare earth elements. When the demands for titanium minerals increased, regular exploitation was started on a large scale. Along the SW coast of India, two important economically viable beach placers occur at Chavara in Quilon district of Kerala and at Manavalakuruchi in Tamilnadu. They have been studied in detail by Gillson (1959) and Prabhakar Rao (1962). They believe that placer minerals must have got concentrated in the following sequence : 1. conversion of fluvial detritus into lateritic plains, 2. erosion and deposition of materials derived from laterities in the sea and the formation of offshore bars, 3. enrichment of heavy minerals in offshore bars by ocean currents,

2 2-4. emergence of bars and sorting of material by surf breaking on the bars, 5. further emergence of bars converting into a beach which was covered by dune sand, and 6. destruction of dunes by advancing waves and formation of rich black sand deposits. Beyond this general understanding of the origin and occurence of these deposits, many important aspects listed below are not clear : 1. The restricted distribution of placers along the Needakara- / Kayamkulam barrier beach complex. 2. Relationship of fluvial sediments with innershelf sediments and their dispersal in the shelf. 3. Beach and near shore processes and their significance in placer concentration at Chavara. 4. Knowledge of the processes that control mineral sorting mechanism. In order to understand these aspects, sediments from different environments such as river, beach and innershelf between Paravur-Tottapally coast (Fig.1.1) were studied in detail. Re- f suits from this study have also been used to demarcate the offshore placer mineral occurrences and to better understand the littoral transport processes along headland-bounded coastlines Background information and previous work : Placer deposits, historically called 'Black Sands' have been mined at Chavara (Fig.1.1). This deposit extends for approximately

3 -3-23 km along the Neendakara-Kayamkulam barrier beach complex. This is possibly the richest ilmenite sand in the world having an estimated ilmenite reserve of 32.8 metric tonnes (Udas et al., 1978). The chavara placer deposit has been divided into eight mining blocks of varying concentrations. The heavy mineral concentration varies from 5% to 90% and mostly present in the size grade + 80 to ASTM. Placer minerals occur in irregular / patches with alternate black and white layers. The black layers consist mostly of minerals having a specific gravity of >2.87: C ' Ilmenite (Tio %), Rutile (Tio2 : 95-97%), Zircon (Zro2 : // 63-67%), Monazite (ReO :50-70%), Sillimanite (Al2 :62%) and Garnet. Quartz and feldspars are present in white layers. Sometimes the layers are pinkish due to the presence of garnet. These placer minerals are being mined, separated and concentrated by the Indian Rare Earths Ltd., based at Chavara. High concentration of heavy minerals occuring in isolated patches along the SW coast of India was first reported by Tipper (1914). This was discussed in detail by Gillson (1959). When monazite was recognised as an important raw material for producing atomic energy, the Atomic Minerals Division of Government of India carried out systematic and extensive surveys for economic evaluation of these deposits. Subsequently, Prabhakar Rao (1962) studied these placer deposits in relation to the geomorphic evolution of the west coast of India. He suggested the contribution of minerals by three geomorphic stages viz., laterites of the hinterland, strand lines and Warkallis (sedimentary laterites).

4 -4- However, Aswathanarayana (1964) showed that the occurrence of monazite-bearing heavy mineral beach sand is a cumulative effect of geological, geomorphological and tectonic processes. Krishnan (1968) suggested that the placer minerals originate from the pegmatites and gneisses of the interior south Kerala, whereas Subramanyan and Rao (1980) opine that monazite-bearing granites are the source of heavy minerals. Later studies by Soman (1985) indicated that khondalite-mig. matitic complex of southern Kerala is the probable source for monazite at Chavara. Mallik (1986) documented the mechanical and chemical micro-features developed on the various minerals of Chavara deposit. Recently, Mallik et al.,(1987) studied the black sand concentration in rivers and adjoining beaches of Kerala and suggested a three stage depositional model corresponding to the initial, transgressive and regressive stages. The occurrence of heavy mineral placer deposits in different parts of the world have been reported by Mero (1965). Beach sand concentrations of ilmenite, rutile, zircon and monazite occurs along the coasts of E and SW Australia, Sri Lanka, S India, SE U.S.A. and Africa. Diamondiferous deposits of the west coast of southern Africa and the gold deposits of Nome area in Alaska are also important. Placer deposits of the world have been classified into two groups (Sutherland, 1985). The first is characterised by beach sand heavy mineral accumulation in moderate energy swellwave dominated coastlines, backed by terrains with moderate to low long-rate erosion rates ( and appropriate source rocks). /

5 -5- Typical examples are the eastern coast of Australia, the SE U.S.A, Sri Lanka and southern part of India. The second is an association between auriferous beach placers and glaciated coast. This is observed in Alaska,Canada, Chile and New Zeland. Detailed studies have been carried out on the placer deposits of Australia (Connah, 1961), Sri Lanka (Meyer 1983; Wickremaratne, 1986) and Oregon coast, USA (Komar and Wang, 1984; Peterson et al., 1985; Clemens and Komar 1988). Compared to the world placer deposits the Indian ones are rich, extensive and easy to mine (Udas et al., 1978) Study area : The area of investigation is confined to the coastal terrain of Quilon district in southern Kerala between Paravur and Tottapally (Fig.1.1). The area of study is drained by two rivers, namely Kallada and Ittikara. Kallada is a major river that drains into the Arabian sea through the Asthamudi estuary at Neendakara. The Asthamudi back waters has eight branches and is the second largest estuary of Kerala. The coastal strip has lateritic cliffs (Fig.1.2), barrier beaches (Fig.1.3 ) and rocky headland at Neendakara (Fig.1.4). The well exposed laterite cliffs (Fig.1.2) of Mio-Pliocene age are seen at Varkala to the south of Paravur. The coast changes its orientation from 290 Deg. to 350 Deg.N at the Neendakara headland (Fig. 1.4) which brings about considerable variation in beach processes. Considering this, the area has been demarcated into the southern sector (stations: CES-74 to 88) and

6 -6- northern sector (stations: CES-97 to 115). Beaches along this coast have been classified into sandy backshore beach (CES and ), barrier beach (CES-70-74, and ), cliffed beach (CES-74-77) and pocket beach (CES-92); Prakash and Aby Verghese (1987). A view of the seawall being constructed at station 101 is shown in Fig.1.5. Placer minerals are being mined in the barrier beach complex. The shelf gradient is fairly steep at Quilon and decreases towards north. 1.3 Geology and Physiography : The Kerala region is characterised by Precambrian crystallines and coastal Tertiary and Quaternary formations (Fig. 1.6). Precambrian crystallines are the dominant rocks consisting chiefly of the charnockitic suite of pyroxene granulites, hypersthenediopside gneisses, migmatites and hypersthene-bearing gneisses that are distributed in the northern and central parts of Kerala (Narayanaswamy, 1976). The khondalite suite with garnet-sillimanite gneisses, garnetiferous leptynite, garnet-biotite gneisses and migmatites occupies nearly 75% of southern Kerala, where the study area is located. Sometimes, garnet biotite gneisses are intruded by granite and pegmatite (Soman et al., 1983). Mineralogically, these pegmatites were classified into simple and complex types (Soman and Nair, 1985). The simple one consists of quartz, feldspar, biotite,garnet, apatite,monazite and the complex one essentialy contains beryl, muscovite, tourmaline, sillimanite and chrysoberyl. The other rock type exposed in large patches is

7 Fig.1.6 Geology map of Kerala (after GSI, 1976)

8 -7- charnockite,consisting of garnet,hypersthene, hornblende, biotite and plagioclase with opaque and zircon as accessory minerals. The coastal Tertiary formations are essentially composed of Warkalli and Quilon beds. The former has sandstones, variegated clays and lignite ban s and is considered to be littoral facies. / Ilmenite, magnetite, zircon, sillimanite, garnet, biotite are some of the commonly occuring heavy minerals in Warkallis (Raha et al.,1983). They partially overlap the Quilon limestone. A Mio- Pliocene age has been tentatively assigned for them (Poulose and Narayanaswamy, 1968). The raised beaches and sand dunes of the coastal strip constitute Quaternary formations. Based on the distinct landscapes, the Kerala region has been classified into three geomorphological provinces, namely highlands, midlands and lowlands. The highlands comprise the hill ranges of the Western Ghats ranging in altitude from 2450 m to 600 m above MSL. This is the watershed divide between the east- and west- flowing rivers. Midlands, consisting of foot hills and pediment zones, exist between 600 m and 300m above MSL. Lowlands at 300 m to 30 m have a subdued topography. They consist of areas of moderately high relief, surrounded by lateritic pediment Climate: Western Ghats form the water shed of the Peninsula and play a critical role in the climate of the country. The areas on either side of the Western Ghats have contrasting climate. The area, in

9 -8- general has an average temperature of 30 Deg.C with an annual rainfall of 3000 mm. The SW monsoon sets in towards the end of May and is active for three to four months. The general atmospheric circulation shows a seasonal reversal. The northerly winds of pre-monsoon change to west during monsoon with an increase in speed. But in post-monsoon ( Oct-Nov), the wind direction slowly changes towards south with a progressive decrease in speed ( Ananthakrishnan et al., 1979) Hydrography: Coastal current: The coastal circulation off Kerala shows seasonal reversal. The surface current flow from November to January is towards north. By the end of January, a sudden reversal towards south is noted. In the study area, the northerly oriented current prevails, with the velocity ranging from 0.05 to 0.40 m/sec and 0.06 to 0.05 m/secy during pre- and post-monsoon seasons respectively. But during monsoon a complex current has been observed. Details of the longshore current pattern observed in the study area are given in Chapter Waves: The wave regime along Kerala coast is controlled by the meteorological conditions in the Arabian sea. The highest wave activity coincides with monsoon. The direction of wave approach is from west-southwest during most part of the year. The wave period

10 -9- ranges from 11 sec. in fair weather season to 8.5 sec. during monsoon (Baba et al.,1983a). Wave height changes seasonally from 0.5 m to 1.9 m. Tides are diurnal with a range of < 1 m. Offshore southern Kerala is characterised by varying shelf gradient and wave climate.(fig.1.7). A decreasing nearshore wave energy regime from south (Trivandrum) to north (Alleppey) has been reported by Baba et al. (1983 a,b). The shelf profile off Trivandrum is characterised by steep inshore shelf gradient, whereas, off Alleppey ( situated 20 km north of Tottapally), a flat inshore profile is present. The southern most part (Trivandrum) is a high energy coast compared to Quilon and Alleppey ( Baba et al a, b). During monsoon (May-Oct) the significant wave height exceeds 2 m at Trivandrum and 0.9 m at Alleppey. But in fair season ( Nov- Apr), wave height exceeds 1 m at Trivandrum and 0.6 m at Alleppey (Kurian and Baba, 1987). The maximum wave height reported during at Trivandrum and Alleppey are 6 m and 3.8 m respectively.

11 WAVE POWER (KW/n) CM QUILON (4-56,6-25,5-26,2-82 ) J FMAMJ JASOND TRIVANDRUM ' ,40,7-5,4-54) Fig.1.7 Wave power and shelf gradient off southern Kerala. Shelf gradient (x 10^) at 10,20,30,50 m water depths are given in parantheses (after Baba, 1988).

Fractal dimensions of selected coastal water bodies in Kerala, SW coast of India - A case study

Indian Journal of Marine Sciences Vol. 36(2), June 2007, pp. 162-166 Fractal dimensions of selected coastal water bodies in Kerala, SW coast of India - A case study *Srikumar Chattopadhyay & S. Suresh