Journal of Information and Computational Science ISSN: 1548-7741 SPATIAL DISTRIBUTION OF COASTAL PLACER DEPOSITS BETWEEN MARAKKANAM AND MANDAPAM, CENTRAL TAMIL NADU, INDIA. J.S. John Wilson1*, N. Chandrasekar2 1Centre for Geotechnology, Manonmaniam Sundaranar University, Abishekapatti, Tirunelveli – 627012, Tamil Nadu, India. 2Dean – Research, SCAD Group of Institutions, FX Engineering College, Tirunelveli – 627003, Tamil Nadu, India. 1*[email protected], [email protected] ABSTRACT The main objective of the research is to investigate and understand the spatial variation of heavy minerals along the Tamil Nadu coast between Marakkanam and Mandapam. Placer heavy minerals such as garnet, zircon, topaz, kyanite, opaque, rutile, monazite, are identified. The total heavy mineral percentage (THM %) varies from 34.23% to 0.27%. Concentration of heavy mineral in the study area with an average of 39.08% in top, middle layer 31.51% and bottom 29.40%. The average weight percentage is 12.21% in backshore, 5.97% in berm and 4.83% in mid-tide region. The average weight percentage of opaque mineral was 16.24% and non-opaque minerals were 83.76%. Higher concentration of heavy mineral is seen in the northern region of the study area and lower in the southern region. This is due to the high-low wave energy system and sediment transport in the region. The heavy minerals are derived from Mio-Pliocene, Cretaceous sediments, khondalites, kyanite schist, amphibolitic gneisses, and green schist facies. Keywords: Heavy mineral, Coastal placer deposits, Opaque and non-opaque, Sediment transport, Tamil Nadu. 1. INTRODUCTION Heavy minerals are those mineral having specific gravity of more than 2.89. Placer heavy minerals such as garnet, zircon, topaz, platinum, kyanite, magnetite, ilmenite, rutile, monazite, are more economically valuable. For these accumulations of mineral is based on the nature of specific gravity, chemical stability in the zone of oxidation and physical strength of the respective mineral. The heavy heavy mineral (HHM) with specific gravity more than 6.8 generally occur in stream beds within less than 15km from source, whereas light heavy minerals (LHM) with specific gravity 4.2 – 5.3 travel long distance and deposit on beach with high energy. [1] The total value of light heavy minerals produced from placer is only 7% less than that of heavy heavy minerals. Volume 9 Issue 9 - 2019 908 www.joics.org Journal of Information and Computational Science ISSN: 1548-7741 Indian coastline has different types of placer accumulation along its mainland of 6100 km stretch surrounded by Arabian Sea in the west, Bay of Bengal in the east, and Indian Ocean in the south. The narrow coastal regions of India, both east and west coast are deposited with Quaternary sediment. Many researchers have studied certain patches of coastal Quaternary formation and many regions is yet to be studied for coastal geomorphology, grain size, heavy minerals, geochemistry. The concentration of mineral deposits is seen at most of the beaches. These heavy mineral are generally classified as black sands. In India the occurrences of placer deposits have been reported [2]. [3] Noticed deposits between Quilon and Kanyakumari on along the southwest coast and between Tanjore and Kanyakumari along the southeast coast of Tamil Nadu. Detailed study on placer deposits have been studied by [4]. [5][6][7][8][9] Along east and west coasts of India. Placer deposits have been reported in Ramanad, Tirunelveli and Thanjavur in Tamil Nadu [10] [11] [12]. The potential offshore ilmenite deposits of Ratnagiri were evaluated [13]. [14] Highlighted the provenance and economic potential resource of beach placer of central Tamil Nadu coast. Many literature studies of previous work have shown that major placer deposits such as Garnet, Ilmenite, Rutile, Zircon, Monazite and Sillimanite are present in the Central Tamil Nadu coast [15][16][17][18][19][20][21]. This coastal region is subjected to high sensitive of hydrodynamic processes, sediment source and beach dynamics morphology and the status of heavy mineral deposition along the central coast of Tamil Nadu. 2. STUDY AREA The present study area extends over central coast tract of Tamil Nadu, between Marakannam – Mandapam extending over a distance of about 430 km in length. The study area located between latitude 9° 16’ to 12° 11’ N and longitude 79° 08’ to 79° 56’ E (Figure.1), covering seven coastal districts from Viluppuram to Ramanathapuram and including Puducherry a Union Territory. The study area occupies a major portion of the Cauvery drainage system. The study area can be classified into the a region representing a high energy oceanographic condition facing Bay of Bengal, a mixed wave energy of both Bay of Bengal and Palk Strait, the rest is typical Palk Strait with very low energy condition associated with low energy flat beach condition. This coastal stretch which has been formed under different landform an area facing open ocean and other is enclosed by Palk Bay, which led to variation of sediment deposits. Volume 9 Issue 9 - 2019 909 www.joics.org Journal of Information and Computational Science ISSN: 1548-7741 Figure.1 Study Area Map 3. MATERIALS AND METHOD 3.1 Sampling Method Forty sampling points have been located with help of hand held GPS and samples are collected from different coastal geomorphologic features. Each station with approximate 10km interval each has been fixed. Depending upon the river confluence, delta mouth and swamp, the sites have been varied but do not exceed an interval of 1 km. Sample collected from backshore, berm and mid-tide region with the help of hand auger to a depth of 1m which is sub sub-sampled to top, middle and bottom along the beach transect. Care is been taken for the collected samples which is transferred to polyethylene bag with labeled. Area with strong lithological variation due to granulometry and heavy mineral deposition if present that location too was observed and sampling was done. 20 stations have been taken for heavy mineral studies. 3.2 Laboratory Method Collected samples were dried in hot air oven at 600c to remove all moisture. The bulk sample had been reduced by coning and quartering to get equal mixing of the sediment content. Representative of 100gm from the sample is taken and treated with 1:10 HCl, 30% by volume H2O2 and SnCl2, to remove carbonates, organic matter and ferruginous coatings from the samples by treatment. After this pre-treatment, the samples were again dried and weight of the sample is noted. The dry samples are sifted at 0.25 ø intervals through ASTM sieve sets using a Ro- Tap sieve shaker for 20 minutes. The sieved materials were collected and weighed. Heavy mineral separation was done by following the method [22] using bromoform which has the specific gravity of 2.89 and separating funnel. The heavier minerals settle at the bottom and the lighter minerals float at the top which has lower specific density. The separated minerals Volume 9 Issue 9 - 2019 910 www.joics.org Journal of Information and Computational Science ISSN: 1548-7741 are washed with acetone to remove the bromoform from the minerals surface. Each fraction samples are dried and weighed. Heavy fraction is them mounted on glass slide with the help of Canada balsam with about approximately around 300 grains were in the slide for mineral counting. Following, [23] line counting method is done with the help of polarized light using a Letiz Orthoplan Microscope and mineral count percentage is calculated for different minerals present in the sample. 4. RESULT AND DISCUSSION The heavy mineral distribution in the study area shows mineral are enriched varying from medium to fine grain in nature in some location and in some location light minerals are dominant over heavy minerals. The concentration of heavy minerals variation is seen in vertical depth also. This variation in the mineral concentration is mainly dominated by the location near to river mouth influences, wind action and direction of wave action. Each mineral identified under the microscope is captured for future studies (Figure.2). Figure.2 Heavy Minerals under Microscope. 4.1 Distribution of Heavy minerals The weight percentage distribution of heavy mineral is classified based on four fractions - 35 to +50, +60 to +80, +100 to+140 and +170 to +230, given in (Table.1) for each location. Station wise separate weight percentage distribution both vertical and horizontal variation of heavy mineral from backshore to mid-tide is inferred. The bulk heavy mineral weight percentage concentration (Table.2) is high in the top layer along the study area with an average of 38.79%, Volume 9 Issue 9 - 2019 911 www.joics.org Journal of Information and Computational Science ISSN: 1548-7741 middle layer 31.39% and bottom 29.82%. The concentration of heavy mineral is high in the backshore region with 61.11% and minimum of 0.30%. berm region concentration ranges from 23.78% to 0.28%, mid-tide region varies from 19.67% to 0.23%. Table: 1 Heavy mineral in different fraction ASTM Sample No. Sieve Opening In Mesh ASTM -35 to +50 +60 to +80 +100 to+140 +170 to +230 st.1 5.78 26.60 51.55 16.07 st.3 6.53 44.32 39.16 9.99 st.5 5.95 14.86 50.58 28.61 st. 8 7.72 49.50 35.12 7.67 st. 10 7.03 58.27 28.47 6.23 st. 11 7.94 57.94 27.37 6.75 st.12 8.50 54.78 31.66 5.05 st.15 8.65 33.98 41.14 16.24 st.18 0.76 5.44 43.52 50.29 st.20 0.13 1.72 26.02 72.12 st.22 0.80 4.54 43.25 51.41 st.24 1.16 21.45 55.62 21.77 st.26 4.47 38.90 48.94 7.69 st.29 1.54 29.91 62.92 5.63 st.31