Indian Journal of Marine Sciences Vol. 29, June2000, pp. 120-127 . . I , 'J f' i

Sediment distribution and placer mineral enrichment in the inner shelf of 'Quilon, - - - - - ~ ~W coast of lndia

..- ! ~.N j> rak as h ·' /( Centre for Earth Science Studies, Akkulam, Tri vandrum 695 031 ~ /

Received 28 Febnwl)', 1999, revised 15 March 2000

G urficial sediment samples from th e innershel f off Quil on, SW coast of India have been examined for the sediment type, pl acer di stribution and titanium content. A major porti on of the in nershelf is covered with sand s and si lty clays. The southern shelf and outer-innershelf of the northern shelf are covered with moderately sorted medium sand whereas poorly sorted silty clays occur mostly in the northern shelf. The total heavy mineral content in the shelf varies from I to 12%. It is generall y seen that high percentage of heavy mineral occurs in the sandy sediments. The result s of Q-mode fact or analys is indicate the spati al distribution of factors, which renect th e grain-sorting pattern of heavy minerals in the shelf. The distribution of ti tan ium shows marked variation wi th texture of the sediments. The titanium content is higher in the southern shelf region where sandy sediments dominate. The near-innershelf of the northern shelf contains higher concentration of titanium with a decreasing tendency towards the outer-inncrshelf ind icating th e lithogenous origin . The di stribution of heavy minerals and titanium in the innershclf indicates nel sediment movement towards the northern shelf region where rich concentrations of placer minerals occur along the coast. ) 9!.. ' ( r ov l ~ The inner shelf is considered to be a sink for the Materials and Methods terrigenous sediments supplied mostly by subaerial The study area covers the innershelf zone off erosion and coastal erosion. An interestin g aspect of Quilon of area about 840 km2 with a length of 70 km the innershelf of SW coast of India is its ~arying shelf and width of 12 km (Fig. I). The she If of SW coast gradient and wave climate, which have immense India is characterised by varying wave climate and effect on the sediment distribution pattern. The coast shelf gradient. The hi ghest wave activity coincides bordering this shelf (Fig. I ) is known for beach with monsoon (June-August). This coast falls under 6 placers, which is popularly known as 'black sands'. the moderately high wave energy regime . The Commonly OCC UrrIng minerals are ilmenite, is a major river system debauching sediments magnetite, ruti le, si llimanite, zircon, monazite, garnet into Ashtamudi estuary, which opens into the sea at etc. Commercial exploitation of beach placers is . The coastal strip has lateritic cliffs, being carried out at Chavara along the Neendakara­ barrier coast and rocky headland. The shoreline coast. The heavy minerals in the shelf changes its orientation from 2900 to 3500 N at are being suppl ied by the present day rivers and from headland. This demarcates the coast south the submerged paleo-beaches (du ri ng lowered sea of Thangasseri as southern shelf and north of it as level). Though many stud ies have been carried out on northern shelf (Fig.I ). The major rock types in the the origin 1.2, mineral content in the rivers and hinterland regIOn include a Khondalite suite 3 beaches .4 and REE contentS, the distribution of consisting of garnet-sillimanite gneisses, garneti­ placer-minerals in the innershelf have not been ferous leptynite, garnet-biotite gneisses, charnockite studied hitherto. In th is paper the sediment type, and wi th a few granite and pegmatite as instrusives placer distribution and titanium content in the and a narrow strip of Tertiary sediments on the coast. innershelf, limited to a water depth of 50 m have been During the period 23-31 January 1985, usi ng a studied and the physical processes responsible for th e van-Veen grab, 77 surficial sediment samples were enrichment of placer minerals is discussed. col lected at 2.5 km interval along I J transects spaced roughly at 5 km interval (Fig. I ). T he position of the stations was fixed by theodolite. Lead sounding was *e- mail : [email protected] used to collect bathymetric data at each station . All PRA KAS H: SEDIM ENT PLACER MI NERAL EN RI CHMENT 12 1

is covered by sands and silty clays while fine-grained \ ones (clay) occur in the northern most shelf. The \ \ southern shelf is entirely covered by sand. Also, there are a few sandy patches off Chavara and in the outer­ innershelf of the northern shelf. The rest of the shelf

Km3 0 3 6 9Km is covered by silty clay interrupted by scattered I I I J I Sediment samples - occurrences of sand/silt/clay and clayey silt units. The Chavar a place r deposit" di stribution of the principal modes of coarse fracti on (Fig. 2B) demonstrates that the area is covered by fin e "-l7 0 (2-3 <1» to medium sand ( 1-2<1» category. The southern ?;> \ \ shelf is carpeted by medium sand of moderately \ \ sorted nature whereas the outer-Innershel f is dominated by moderately to poorl y sorted medium 9\ sand. The rest of the shelf is covered by poorl y sorted 0" \ , silt and clays. In general the sediments are getting ,, "- progressively fin er towards the northern side. "-, , Heavy mineral distribulioll - The total heavy \ \ mineral content in the innershelf sediment samples ranges from I to 12%. Since the heavy mineral concentrates more within the fin e grained fractions the surficial vari ati on of heavy minerals in the fi ner fracti on is given in Fig.3A whi ch shows that the high concentrati ons are fo und in the southern shelf, outer­ innershelf of the northern shelf and in the nearshore Fig. I-Locati on map zone of Chavara. Here the heavi es are mostly the surficial sediment samples were subjected to associated with the moderate ly sorted medium sand 7 sedimentological analys is ,8 . Textural parameters sediments. However, heavy mineral content was less were obtained usin g graphi c method sugGested by in the silty clay and sand-silt-c lay type of sediments. 9 . b Folk & Ward . SIxteen selected samples were The relati ve di stribution of di fferent heavy minerals subj ected to mineralogical studies. In th e laboratory in the innershelf sediments is shown in Fig.3B. The the sampl es were sieved and heavy min erals were southern shelf is characteri sed by opaques (av.36%), separated from the fractions of 1.0-0.088 mm and sillimanite (av.22%), monazite (av. 12 %), zircon 0.088-0.062 mm usi ng bromoform (sp.gravity 2.89). (av.6%), hypersthene (av.5%) and garn et (av.5%). T he heavy minerals were washed with methyl alcohol An interesting feature in this part of the shelf is the and mounted in glass slides. Nearly 300 grain s were seaward increase of relati vely stable minerals, i.e. , counted in each sli de under a petrological mi croscope zircon and monazite. T he less dense mi neral and the percentages of indi vi dual minerals were hypersthene and hornblende increased considerabl y calcul ated. T hese data are used to prepare the off Ashtamudi estuary. The di stribution of heavy distribution maps. In order to un derstand the total minerals in the outer-innershelf of the northern shel f vari abili ty of heavy min erals in the samples and to is similar to that of the southern shelf except that it group them in to assemblages, Q-mode factor analysi s had undergone hi gher degree of chemical alteration as l 2. was carried out on the heavy minera l data 10 usin g seen from the surface mi crotextural study The ll SPSS package . Factor loadin g matri x was taken distribution of heavy minera ls in the northern shelf usin g varimax rotation techn iq ue. Selected bu lk shows an average content of opaques (35%), sampl es were analysed for titanium uSll1 g atomic sillimanite ( 15%), monazite (8%), hypersthene absorpti on spectrophotometer (Perkin Elmer-4000). ( I 1%), and hornblende ( 10%). In th is part of the shelf th ere is an increase of less dense heavy mi nerals like Results hypersthene and horn blende. Sedim en t types- The distribution of the various Factor analysis- The results of Q-mode factor sediment types is shown in Fig.2A. Most of the area" analysis show three important factors, whi ch account 122 INDIAN J M AR SCI., VOL. 29, JUNE 2000

INDEX Weight pe rcen toge sond F-- -j <5 §5 -25 ~25-50 81 50- 75 ~>75

Fi g. 2-Sediment distribution patt ern (A) and di stribution of coarse fracti on sediments (8 ) for 97% of variancc. Factor loadings are shown in the epidote. High loadings off Tottapally indicate the form of isopleth maps (Fig. 4 and Table I). Factor-I occurrence of hornblende. Epidote is prevalent in the explains 86. 14% of th e total variance. Factor-I is southern and northern shelf of the study area. representative of a clustering of opaques, sillimanite, Titanium distribution-The data show marked monazite, zircon and garnet. The hi gh-density variations in the titanium content of the sediments minerals of factor-I have high loading (Table I) with the texture. The distribution of ti tanium (Fig.S) which reflects the variation between the southern indicates high content in the southern shelf and near­ shelf and the outer-innershelf suite of mineral s innershelf of the northern shelf region. Titanium in (Fig.4A). Minerals of factor-I are of higher densities the innershelf sediments ranges from 1600 to 15260 that are selectivcly entrained by waves and currents in ppm with an average value of 5327 ppm. The general the northern shelf where the beach erosion is distribution pattern of titanium shows a progressive maximum. 11" 14 an d 'It occurs as part 0 f a seasona I increase from offshore direction towards the Chavara change in wave climate. Factor-II explains 6.50 % of coast. Here the titanium value increased to as much as the total variance. This factor symbolises the 10000 ppm (1 %). The outer innershelf and the relationship of lower density minerals such as northern most shelf contain less titanium. An hypersthene and hornblende (Table I). It has shown examination of the titanium content in the sediment high loadings near the estuarine mouths (Fig.4B), indicates that a major portion of it is tied up with th e indicating their contribution from the Kallada R. and sandy sediments (silty sand and clayey sand). a tributary of Pamba river. Factor-TIl explains only 4.62% of the variance. Although it is insignificant, Discussion this factor represents monazite, which dominates in The sediment distribution in the innershelf most of the innershelf (Fig.4C). The other minerals, indicates that the southern shelf and outer-innershelf which represent this factor, are hornblende and of the northern shelf is covered with sandy sedimeni s. PRAKASH: SEDIMENT PLACER MINERAL ENRICHMENT 123

(A) (8) 7~2'

INDEX 9° 9° Weig--ht percentage20 2d JIl heavy mineral (HM) i~ r fract ion . _ 0- Opaque t...::::::::J < 5 14 C S _ Sillimanite ~ 5 10 _ M - Monaz ite t=:::J - l:-13 E 138 Z- Zircon ~ 10 -20 G- Garnet 0 ' . ' P - Pyroxene 9° 20 9 9, A - Amphibole I> >1> 10 10' 10 rn -I I E. ~ E - EPidote . L 10C L :E~" ~ 9° 9° d 0' U"lliwn L -5C • UILON

SO ~ ."~,, ':UJ..J'<"'-'.J..J 50' -3F ~ 28 -2F

Fig. 3-Heavy mineral co ntcnt of the tine fracti on (A) and relative di stribution of different heavy minerals in th e innershelf (8 )

High percentage of sa nd in the southern shelf is in heavies moved alongshore due to dominant waves attributed to the absence of estu ari es or backwater approaching from westerly and south-wes terly which trap coarser sediments and the presence of direction during most part of the year and deposited Warkalli beds which provide immediate source I S. In on to the beaches of the northern shelf. In addition to addition, the winnowing action of waves aided by th e this, wave swash on the beach face acts like miner's steep bath ymetry'6 mi ght be another reason for hi gh pan carrying the li ght minerals by water osci ll ati ons concen.tration of sand in the southern shelf region. to offshore areas leaving an enriched concentration of The innershelf sand body, which occurs as patches heavy minerals. This process might have taken place along the western continental margin , has been for many years in the beaches of the northern shelf. reporte d ear Il·er as re Ilet' 17·ryO- . M 'I cromorp hi0 og'l ca I Its formation is most favourable when the beach is study of detrital quartz grains from th e innershelf off receding as thi s all ows the li ght fraction to be carri ed central coast21 further indicated that the sand s away. On the northern shel f coast, beach eros ion is of outer-innershelf are the beach deposits of part of seasonal change in wave climate. Successive Holocene peri od. erosion of the shorelin e in most part of the yearl~ may A progress ive enrichment of placer-mineral s have led to further enri chment of heavy mineral s toward s the near-innershelf of th e north ern shelf is along the Chavara coast. The in crease of less dense observed from th e di stribution of heavy minerals minerals like hypersthene and hornblende in the shelf (Fig.3A). The seasonal variation of longs hore sediments opposite to Ashtamudi and Tottapally may currents and direc ti on I' , steepness of shelfl6 and hi gh be due to trapping of coarser particles in the e. tu ary. wave e n c r gy'~ mi ght have initi ated panning in th e The results of factor anal ys is are consistent wit h th e southern shelf sediments. Further th e differenti al interpretations made earli er based on the di stributions velociti es under wave crest and trough move th e of individual min erals. This further indicates that the li ghter coarser sili cates offshore and dense r heavier spatial di stribution of factors refl ect th e grain-sortin g 22 ones towards onshore . This panned sediments ri ch pattern of heavy min eral s in the inn ershelf. N .j:>.

30' 75°140 ( B) FAC TOR- II (C) 9° 20' F---3 +0·00 to +O · 2 5 § +0·26 to +0·50 ~ +0 · 51 to 0 ·75 §> 0·75

9 z 10' 2 » z 3: » ;>;l Conn

. ; ...... 9 o< 0' r IV \0 '- C Z tTl IVo o o ~ . . . . eO : - ~ ...... -:;::-:--(?\ == <~\ ~;~;~~=~;~~~~~=~~=~=~~~ ••••• • •••••••••• •• • I ••~, ...... ~\L --- +"~~ -76-\:30~~ - _-.,..----LJ:~}) .

Fi g. 4-Distributi on of Factor-I CAl, Factor-I! (8 ) and Factor-III (e) PRAKASH: SEDIMENT PLACER MINERAL ENRICHM ENT 125

Tab le I-Distri bution of factor loadin g in th e selected innershelf sediment samples

Sample Opaqucs Sillimanitc Garnet Zircon Monazit e Rutile Hypersth enc Hornblcndc Epidote no. % % % % % % % % %

IB 36.00 19.56 2.55 9.57 15.2 1 0.43 2.6 1 2.17 4.78 IF 32.45 32.08 5.59 6.04 13.96 1.13 1.51 2.26 4.53 2A 29.3 0 19.87 2.33 6.96 8.42 0.37 10.96 7.32 5.86 2F 46.42 21.5 1 3.30 4.53 13.2 1 1.51 1. 50 1.1 3 6.42 3A 33. 18 2 1.23 1.32 3.98 9.73 1.32 13.20 5.15 6.19 3D 38.99 19.69 3.50 5.02 16.22 0.77 3.86 1.93 4.63 4C 16.57 7. 18 0.00 0.55 4.42 2.2 1 27.62 18 .33 6.63 5A 39.66 10.78 3.39 3.88 7.76 3.88 13.93 6.47 4.3 1 7A 4S.65 18.53 3.23 5.4 1 15.44 0.77 3.09 2.32 0.00 70 43.2 1 13.2 1 1. 20 3.93 12. 14 2.86 7. 14 8.93 4.29 8E 41.54 36.15 1.92 1.15 3.85 0.38 1.1 2 2.3 1 9.61 9C 41.32 I 1. 6 1 1. 58 1.58 10.41 0. 32 5. 17 9.46 3.79 10E 40.87 16.08 2. 17 5.22 12. 17 0.00 1.35 8.26 3.48 12B 25.84 18.54 0.00 1. 69 3.37 0.56 17.41 15. 17 8.43 12E 46.35 17.52 3.29 5. 10 9. 12 1. 82 2.91 3.28 8.02 13C 8.67 2.89 0.00 0.57 5.70 0.00 31.79 28.90 2.00

Sample No. Factor-I Factor-II Factor-III

IB .927 .275 .224 IF .906 .254 . 167 2A .8 18 .533 . 160 2F .951 .268 .146 3A .827 .529 .139 3D .927 .295 .220 4C .257 .942 .208 5A .8 15 .530 . 11 4 7A .939 .227 .142 70 .863 .430 .20 1 8E .908 .303 .008 9C .863 .4 16 .191 10E .912 .328 .205 12B .621 .755 .1 39 12E .929 .325 .1 19 13C .190 . 196 .960 Rotated factor matrix: columns = factors, rows = variables

II III

Opaq ues 43.882 2.299 -.725 Sillimani tc 23008 .99 1 -4.375 Garn et 3.862 - 1. 936 -.245 Zircon 5.997 - 1.663 .100 Monazitc 6.739 -10.969 59.730 Rutil e -.179 1.242 5. 351 Hypersthcnc -6.560 3 1.844 -4.856 Horn blcndc -6.746 16 .594 30.202 Epid otc .047 2.716 27.092 Varilll

Studies carried out on the surficial sediments off 760 40' Quilon coast have brought out the di stribution

0 0 characteristics of placer minerals and titanium content 9 9 in the innershelf. The major portion of the inn ershelf 2d 20 INDEX is covered by silty clay followed by sandy sediments Ti(ppm) (s ilty sand and sand). The sediments in the southern F---1 < 3000 shelf and outer-innershelf of northern shelf have hi gh amount of denser heavy-minerals whereas in th e ~3-5 northern shelf less dense heavy-minerals dominate. ~5-9 The spatial di stribution of factors reflects the grain­ 0 .§>9000 9 sorting patterns of heavy minerals in the shelf. The 10' hi gh content of titanium in the innershelf sediments is due to th e occurrence of titanium-bearin g minerals like ru tile and ilmenite in the coastal terrain of thi s coast. The distribution of heavy minerals and titanium in the shelf suggest that the net movement of heavy minerals be toward s the nearshore zone of Chava ra where one of the wo rld 's richest placer deposits occurs.

Acknowledgement I ex press my sincere th ank s to Director, Centre for Earth Science Studies, Tri vandnllTl for the fac iliti es and kind permiss ion to publish thi s paper. Thi s study forms part of the project wo rk Marine Geological In vestigations of the Inner- continental she(f of Kerala (MSD-9). Thanks to Dr.N.P.Kurian, Head, MSD for the fruitful di scussion during the preparation of th e paper.

References Fig. S- Di stribution of titanium in the in nershelf Tipper G 1-1, Monazi te sand s or Travanco re, Rec. Ceo/. Sil l'\'. Illdia , 44, ( 19 14), 86- 196. In the western continental shelf of lndia, hi gh 2 Prabhakar Rao G, SOlli e aspec[s of [he piacer deposi[s oj percentage of titanium in the sediments is associated sO Il [h Kera/a ill relalioll [0 geolll orphic e I'O/II[iOIl oj [he II'es[ coas[ oj Ill dia. D.Sc. thes is. An dhra Un iversi ty, Indi a, 1968. \>,Ii th the hi gh percentage of si lty sand and sa ndn . However, in thi s part of shelf th e major portion of 3 Mallik T K, Vas udevan V. Verghese P A & Machado X T, The blaek sa nd deposits of Kerala beach, sou th Indi a, Mar. titanium is associated with the sand y sediments and a Ceol., 77, ( 1987), 129- 1SO . smaller content in the silty clay sediments. The hi gh 4 Prakas h T N, Raju G K & Prith viraj M, Radi o-element content of titanium in the innershelf sediments is due di stribu ti on in ri ver, beach and offshore areas and th eir to the occurrence of important titanium-bearing signifi cance to Chava ra pl acer depos it , southern Kerala coast minerals like rutile and ilmenite in th e coastal terrain of In dia, Ceo- Mar. Lell ., I I ( 19() I) 32-38. of th is coast. The covariance between titanium and 5 Thampi P K, Suchindan G K, Balasubramani an G B. iron (. 07) in the sediments indicate very poor Vasudevan V & Ramachandran K K. Eva luat ion of beach correlat ion between them and thi s may be due to th e pl acers of SW coast of In dia in te rms of rare earth elements 24 and their geochemi cal signifi cance, Tech. Rep .. (Centre for presence of excess iron unbound with titanium . The Earth Science Studies ,Trivandrum), 1990, pp . 107. distribution of heavy minerals and titanium in the 6 Kuri an N P, Wa \'e heigh[ alld spec[ret! [rall .\[or/ll(l [ioll ill [h e shelf suggest nct movement of heavy minerals shallow w{/[e rs oj Kera /a coas[ ({lid [heir predic[ioll, Ph.D. toward s the near-innershelf of th e northern shelf thesis, Cochin Un iversit y of Sc ience & Te 'hnology, Ineii a, regIon. 19 87. PRAKASH: SEDIMENT PLACER MINER AL ENRICHMENT 127

7 Ingram R L, Sieve analysis, in: Procedures ill sedimentary 16 Baba M, Wave characteri sti cs and beach processes of th e petrology, edi ted by Carver R E, (Wil ey, New York ), 197 1, south-west coast of In dia- A su mmary, in: Ocean waves and pp.49-68. beach processes, edited by M Baba & N P Kuri an, (Centre for 8 Galehouse J S, Sedimentation analys is, in : Procedures ill Earth Science Studies,Trivandrum), 1988, pp. 222-239. sedim entary petrology, edited by Carver R E, (Wiley, New 17 Nair R R & Has himi N H, Holocene climatic inferences from York), 197 1, pp . 69-94. the sedi ments of th e Western Indi an continental shelf, Proc. Indian Acad Sci., (Earth Planetary Science), 89 (1980) 9 Folk R L & Ward W C, Brazos ri ver bar: A study in the 299-315. signifi cance of grai n size parameters, J Sed. Petrol .. 27 , ( 1957), 3-26. 18 Kidwai R M, Nair R R & Has himi N H, Heavy minerals in th e sediment s on the outer continental shelf between Vengu rl a 10 Imbri e J & Van Andel Tj H, Vector analys is of heavy mineral and Mangalore on th e west coast of India, J Ceo l. Soc. In dia, data, Ceol. Soc. Amer. Blliltn., 75 (1964) 11 3 1- 1156. 22, (198 1) 32-38. II Kim J 0, Factor analysis, in : Statistical package for th e social 19 Ramana M V, Gujar A R & Rajamanickam G V, Shallow sciences, edited by N H Nic et al. (Mcgraw Hill , New York), seismic studies on the inner continental shelf off selected 1970, 468-514. beach, central west coast of Indi a, Mar. Ceol. , 9 1, (1990), 12 Prakash T N, SlIIdies on textllre, mineralogy all d 333-343 . geochemistry of different sedimentw), en virol1/'l1 ents off 20 Shankar R & Karbasi A R, Sedimentological evidence for a Paravur-Tottapally, SW coast of India with particlliar Palaeobeach ofT Mangalore, west coast of In dia, J Ceol. Soc. India , 40, (1992), 241-252. emphasis O il black salld depositioll, Ph .D. thesis , Mangalore University, India, 199 1. 2 1 Prithviraj M & Prakash T N, Surface mi crotextural study of detrital quartz rains of innershelf sediments off cent ral Keral a 13 Prakash T N & Verghese P A, Seaso nal beach changes along coast, Indian J Mar. Sci., 20, (1991 ), 13- 16. Quil on di stri ct coast, Kerala, J Ceol. Soc. India, 29 (1987) 22 Kuri an N P, Prakash T N & Felix Jose, Hydrodynamic 390-398. processes along Quil on coast, Proceedin gs of the 14 Prakas h T N, Kuri an N P & Felix Jose, Beach stability in International Conference on Ocean Engin eering, COE'96, relat ion to the nearshore wave energy di stribution along the (lIT Madras), 1996, 264-269. Quilon coast, SW coast of In dia, Illdiall J. Mar. Sci., 28 , 23 Rao Ch M & Murth y P S N, Geochemi stry of the continental (1999), 233 -239. margin sedi ment s of the central west coast of Indi a, J Ceol. 15 Hashimi N H, Kidwai R M & Nair R R, Comparative study of Soc. India. 35, (1990), 19-37. th e topography and sediments of th e western and eastern 24 Rao Ch M, Murthy P S N & Reddy C V G, Di stribution of co ntinent al shelves around Cape Camorin Indiall J. Mar. Sci., Titanium in the shelf sediment s along the west-coast of India, 10 ( 1981) 45-50. Proc. Indian Natl. Sci. Acad., 38 ( 1972) I 14-1 19