Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(3):432-437 (ISSN: 2141-7016)

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Preliminary Geophysical Evaluation of Orin Bauxite Deposit

Southwestern Nigeria

Abel O. Talabi, Oladimeji L. Ademilua, Olusola Z. Ajayi and Simeon O. Ogunniyi

Department of Geology, Ekiti State University, Ado-Ekiti.

Corresponding Author: Oladimeji L. Ademilua ___________________________________________________________________________ Abstract Economic viability of any metallic mineral deposit depends on its areal and depth extent as well as chemical composition amongst other factors. This study was a preliminary attempt to determine the depth to and the probable areal extent of the bauxite deposit at Orin-Ekiti. As part of the methodological approach, electrical resistivity geophysical survey method involving the vertical electrical sounding (VES) technique were carried out at nine (9) points at the environment of study and seven samples picked randomly were analyzed for Al2O3 chemical content using Atomic Absorption Spectrometer (AAS). Results of these investigations revealed two main sounding curves; QH (VES 1.1, 2.4 and 4.1) and KH (VES 1.2, 1.3, 1.4, 2.1, 3.1 and 3.4). Four to six layers subsurface lithological formations of nearly similar degree of saturation were delineated. Layers 3 of the sounding curves constitute the bauxite deposit with variable thicknesses range of 7.1 14.2m. Preliminary quality assessment revealed bauxite of 25.10 61.26% Al2O3 (average 42.17% Al2O3) content. The purpose of this study therefore is to confirm the possible occurrence of bauxite of sufficient quantity and quality at Orin-Ekiti as a first indication and invitation for further investigation of a wider scope towards the exploitation for economic development. __________________________________________________________________________________________ Keywords: metallic mineral, bauxite, vertical electrical sounding, sounding curves, formation. INTRODUCTION Bauxite refers to any ore or mixture of minerals consisting of iron and aluminum hydroxides/oxides. The ore in most instances comprise of minerals such as gibbsite (Al (OH) 3), diaspore (AlO(OH)), and boehmite (AlO(OH) (Plunkert, 2000). A bauxite body which is economically mineable at present or in the foreseeable future, currently should have chemical composition of >45% Al2O3,

Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(3):432-437 (ISSN: 2141-7016)

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migmatite and charnockite especially the coarse grained type. Generally, the terrain is rugged with boulders of charnockite outcropping in few locations

Fig. 1. Location Map of Study area (Modified from Map data @2013 Google)

Fig. 2. Geology Map of Study area (Adapted from Akure sheet 61) METHODOLOGY The field study was carried out in February, 2012. The geophysical investigation was executed using the vertical electrical sounding (VES) technique of the electrical resistivity method employing the Schlumberger electrode array /configuration. This method resolves without doubt, the apparent resistivity values, thickness values, degree of formation saturation, subsurface lithological units and depth to bedrock or competent material of the area of study. The equipment used for the study was the ABEM TERRAMETER SAS 300B complete with standard cables, electrodes and modern micro processor. The electrical resistivity survey involves electrical sounding in which the potential electrodes remain fixed and the current electrodes are expanded simultaneously about the center of the spread. When the distance between the electrodes gets too large, it then becomes mandatory to increase the distance between the potential electrodes to have a measurable potential difference. For this investigation, electrodes separation varied from 2 to 260 meters thus ensuring a reasonable depth of probe of over 65 - 85meters considering the depth of penetration which ranges between 1/3 and of the total current electrode separation (David and Ofrey, 1989; Osemeikhian and

Asokhia, 1994; Mallam and Ajayi, 2000). This depth was considered adequate for the subsurface formation information needed in the environment of study. The electrodes were normally arranged along a straight line with the potential electrodes placed in between the current electrodes. Nine (9) points were fully occupied at the environment of study and the locations are shown in Fig.3, with the following GPS coordinate values VES 1.1: (Elevation 628.48m; Lat. N 070 50.9531; Long. E 0050 14.8891) VES 1.2 (Elevation 629.09m; Lat. N 070 50.9751; Long. E 0050 14.9061) VES 1.3 (Elevation624.24m; Lat. N 070 50.9901; Long. E 0050 14.9251) VES 1.4 (Elevation 626.67m; Lat. N 070 51.0001; Long. E 0050 14.9521) VES 2.1 (Elevation 640.00m; Lat. N 070 50.9721; Long. E 0050 14.8481) VES 3.1 (Elevation 623.33m; Lat. N 070 50.9851; Long. E 0050 14.8051) VES 4.1 (Elevation 617.27m; Lat. N 070 51.0211; Long. E 0050 14.7281) VES 2.4 (Elevation 632.42m; Lat. N 070 51.0681; Long. E 0050 14.9501) VES 3.4 (Elevation 631.21m; Lat. N 070 51.1081; Long. E 0050 14.9621) The vertical electrical sounding (VES) data were presented as depth sounding curves, which were obtained by plotting apparent resistivity values against electrode spacing on a log-log or bi-log graph paper. The resistivity sounding curves were interpreted quantitatively using partial curve matching and iterated computer interpretation package called WinResist version 1.0 solely used for VES data. the Partial curve matching method involved the segment by segment matching of the sounding curves with theoretical schlumberger standard curves, starting from smaller to larger electrode spacings. DATA PRESENTATION AND INTERPRETATION The field data collected from the study area was interpreted quantitatively and qualitatively. Quantitative Interpretation The quantitative interpretation involves the direct modeling using the partial curve matching and the VES interpretation package called WinResist version 1.0. Raw data obtained from the field is presented in Table 1 while the final model parameters obtained from the quantitative interpretations of the data collected is presented in the Table 2. The curve(s) of the field data collected at the VES location(s) are shown as sounding curve(s) of apparent resistivity values (m) against current electrodes separations (m) in Fig. 4 (graphs of VES 1.1 to VES 4.1).

Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(3):432-437 (ISSN: 2141-7016)

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Fig. 3: Schematic diagram of area of investigation showing the VES points The depth sounding curves were classified based on layer resistivity combinations. The curve types obtained in the study area where nine VES sounding was carried out were categorized into QH (VES 1.1, 4.1, 2.4 and 3.4), AH (VES 1.2 and VES 3.1) and KH (VES 1.3, 1.4 and 2.1). The QH- type curves were predominant in the study area constituting 44% of the total number of the VES curves. The quantitative interpretation of the points investigated showed four to six layers subsurface lithological formation of similar degree of saturation at the different locations. Qualitative Interpretation The qualitative interpretation is the geological interpretation of the quantitative data. This qualitative interpretation is further indicated in the geoelectric sections. The VES locations exhibit fairly similar geological layer systems, thus indicating that the

subsurface of environment of study is fairly homogenous. Details of the layers systems are presented below Layer system 1 (VES 1.2, 1.4, 2.1, 3.1) Apparent resistivity values = 85.3 662.4m Thickness value = 0.9 1.0 m Likely formation = Top decayed organic materials/coarse

grained/peblistic materials Layer system 2 (VES 1.1, 1.3, 2.4, 4.1) Apparent resistivity values = 1263.3 7605.7m Thickness value = 0.9 2.1m Likely formation = Top dry laterite/hardpan laterite

Table 1: Raw field data obtained from the study area Current electrode distance (AB/2)m

VES 1.1 (m)

VES 1.2 (m)

VES 1.3 (m)

VES 1.4 (m)

VES 2.1 (m)

VES 3.1 (m)

VES 4.1 (m)

VES 2.4 (m)

VES 3.4 (m)

1.0 2166.480 670.24 1106.840 483.800 694.40 96.996 4479.28 7292.400 2664.44 1.3 2684.884 588.504 1297.240 430.304 872.812 122.429 5143.76 7372.120 2933.48 1.8 2638.590 675.141 1292.064 561.522 892.050 145.826 3784.17 7211.520 3211.38 2.4 2260.686 747.792 1267.092 661.242 1083.606 170.849 3205.812 6422.010 3314.865 3.2 2039.700 825.294 1349.340 690.360 1201.854 204.283 2526.090 6128.514 3769.980 3.2 2096.695 864.796 1526.452 651.499 1105.662 242.171 2945.530 6166.75 3975.740 4.2 1921.290 909.672 1513.506 708.394 1220.738 286.494 2117.340 4671.218 4009.876 5.5 1534.730 883.619 1645.010 800.449 1383.095 329.461 1488.780 3891.965 3561.125 7.5 1198.570 753.337 1563.088 756.809 1478.901 387.951 1162.986 2846.712 2655.774 10.0 1003.040 632.926 1281.402 640.701 1404.255 471.195 1085.459 1814.801 1990.528 13.0 989.588 688.753 1023.893 591.114 1348.477 570.002 913.059 1812.92 1615.006 13.0 1038.016 702.378 965.446 536.503 1456.591 561.124 925.272 2183.591 1650.976 18.0 934.948 613.245 711.264 510.200 1163.657 733.883 562.979 1912.621 1074.184 24.0 755.218 597.952 601.097 555.722 974.872 793.824 295.606 2259.727 720.597 32.0 591.219 635.280 639.286 538.346 622.462 734.617 206.686 1105.531 410.168 42.0 454.777 471.36 635.858 439.571 429.895 632.956 174.860 1082.340 237.893 55.0 435.389 358.276 581.309 437.761 358.750 583.681 246.047 2370.317 260.284 55.0 420.660 417.115 479.742 447.838 284.772 647.533 228.881 1024.473 270.593 75.0 288.107 497.799 488.988 511.015 295.815 455.948 170.925 1592.515 292.291 100.0 402.657 533.217 448.921 770.812 328.947 530.079 281.50 1591.808 326.203 130.0 576.176 333.505 Table 2: Results of Quantitative interpretation

VES NO Apparent Resistivity Value (m) (1)( 2)( n) Depth (m); (d1); (d2)(dn-1) VES 1.1 (2592.8); (1019.0); (718.0); (247.9); (1083.9) (2.0); (8.1); (8.4); (38.4) VES 1.2 (608.1); (988.7); (539.7); (517.1); (234.0); (821.8) (1.0); (3.3); (9.8); (19.4); (17.7) VES 1.3 (1263.3); (1796.9); (439.3); (713.6); (217.9); (1365.4) (1.4); (4.5); (16.3); (23.1); (37.4) VES 1.4 (459.1); (873.8); (381.8); (625.5); (245.8); (2209.7) (0.9); (4.9); (14.2); (14.3); (16.4) VES 2.1 (662.4); (1754.8); (507.1); (200.2); (1533.6) (0.9); (7.7); (12.5); (47.2) VES 2.4 (7605.7); (1821.2); (1398.7); (708.5); (4362.6) (2.1); (7.3); (8.2); (28.0) VES 3.1 (85.3); (1053.9); (273.3); (2147.2) (1.0); (17.5); (40.8) VES 3.4 (2642.4); (4494.7); (668.7); (168.9); (662.4) (0.9); (3.7); (10.5); (30.7) VES 4.1 (5069.1); (1369.1); (348.5); (99.9); (1857.8) (1.2); (5.7); (7.0); (34.0)

Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(3):432-437 (ISSN: 2141-7016)

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Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(3):432-437 (ISSN: 2141-7016)

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Fig. 4: VES 1.1 (Traverse 1, Location 1) to VES 4.1 (Traverse 4, Location 1) Layer system 3 Apparent resistivity values = 998.7 4494.7 m Thickness value = 3.3 17.5m Likely formation = Likely the bauxite deposit layer Layer system 4 Apparent resistivity values = 348.5 1398.7 m

Thickness value = 7.0 16.3m Likely formation = Probably slightly moistured laterite Layer system 5 Apparent resistivity values = 99.9 708.5 m Thickness value = 16.4 47.2 Likely formation = Highly fractured layer/weathering from basement Layer system 6 Apparent resistivity values = 662.4 4362.6 m Thickness value = Undetermined for the depth of survey Likely formation = Probably slightly fractured bedrock Geoelectric Section The geoelectric section(s) across the point(s) investigated to show the subsurface structure of the environment down to the depth of investigation were drawn across S1, S2 and S3 (Fig.3) as presented in Figs. 5-7. Similar to the geological layering of the subsurface in the study area, geoelectric configurations exhibit fairly similar trends. In Fig. 5, the geoelectric section revealed the likely existence of the bauxitic clay in layer 3 with variable thickness of 7.1 -14.2m. In the other two geoelectric sections, Figs.6 and 7, the bauxitic clay have varied thicknesses of 6.4 10.5m and 8.4 13.2m respectively. These geoelectric sections revealed sufficient thickness of the bauxitic clay of economic significance. Preliminary Quality Evaluation Few samples (7) were analysed for Al2O3 content and the result of the analysis is presented in Table 3. The result indicates that the deposit is of sufficient grade to warrant further evaluation for economic development Table 3: Chemical analysis result

CONCLUSION Vertical electrical sounding technique of the electrical resistivity method employed in this study has proven the subsurface lithology of the study area to be likely fairly homogenous. In addition the layer of interest, which is the third layer in almost all the locations sounded, revealed thickness value of between 7.0 16.3m. This thickness is sufficient for the bauxite deposit to be considered for further economic assessment. Also, preliminary chemical analysis indicated that the deposit is of high grade to be considered for further exploration. The chemical values obtained in some of the locations sampled compared favourably with the giant Gove deposit with bauxite grading of 50.5% Al2O3 (Ferenczi, 2001) and that of Kibi deposit in Ghana with an average Al2O3 content of 46.6%

Sample No A12O3 A1 29.85 A2 32.30 A3 38.30 B1 25.10 C1 52.34 C2 56.04 C3 61.26 Mean 42.17

Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(3):432-437 (ISSN: 2141-7016)

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Fig. 5: Geo-electric section through VES 1.4 and VES 4.1 stations in the study area

Fig. 6: Geo-electric section through VES 1.1 and VES 3.4 stations in the study area.

Fig. 7: Geo-electric section through VES 1.1, 1.2, 1.3 and VES 1.4 stations in the study area REFERENCES David, L.M., and Ofrey, O. (1989): An indirect method of estimating ground water level in basement complex regolith. Water resources, Vol. 1, No. 2, pp. 34 -41. Ferenczi, P. A. (2001). Iron ore, manganese and bauxite deposits of the Northern Territory. Northern Territory Geological Survey, Report 13.http://www.nt.gov.au/d/MineralsEnergy Geoscience contents/ File/Pubs/Report/NTGS Rep.13 Gawu, S. K. Y., Amissah, E. E. and Kuma, J. S. (2012). The proposed Alumina Industry and how to mitigate against the red mud footprint in Ghana. Journal of Urban and Environmental Engineering, v.6, n.2, p.48-56 Gow, N. N. and Lozej, G. P. (1993). Bauxite; Geoscience Canada, Vol20, Number 1, pp 916. History of aluminum.combauxite.php (1999): http://www.History of aluminum.com/bauxite.php Mallam, A. and Ajayi, C. O. (2000); Resistivity method for groundwater investigation in sedimentary area. Nig. J. of Physics, 12, 34 38. Osemeikhian,J. E. A. and Asokhia, M. B. (1994); Applied Geophysics for engineers and geologists. 1 Ed. Samtos services Ltd., Lagos. Plunkert, P.A. (2000). Bauxite and alumina: U.S. Geological Survey Mineral Commodity Summaries 2000, p. 32-33. USGS: (2011): Mineral Commodity Summary. .http://minerals.usgs.gov/minerals/pubs/mcs/2011/mcs2011