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Continental J. Earth Sciences 5 (1): 1 - 7, 2010 ISSN: 2141 – 4076 ©Wilolud Journals, 2010 http://www.wiloludjournal.com

FAULTS AND PROMINENT LINEAMENTS: MIGRATORY ROUTES OF WATER FROM LAKE CHAD

TO THE BENUE TROUGH

Nkereuwem, O. T., Mijinyawa, M. U. and Yusuf, S. N. Department of Geology, University of Maiduguri, Borno State, Nigeria.

ABSTRACT Comprehensive studies of groundwater resources in Lake Chad region have been embarked upon by several workers. The contribution of faults and other prominent lineaments to the dwindling resources of Lake Chad water and its movement are vital issues that must be addressed. Based on recent land satellite and shuttle images, prominent lineaments trending NE-SW were delineated. Five controlled source audio-frequency magnetotelluric profiles made, perpendicular to the general trend of the observed lineament, revealed deep seated faults with similar orientation. This clearly suggests that the said faults might be potential migratory routes of water from Lake Chad to the Benue Trough. KEYWORDS: Lake Chad, Lineaments, Routes, Migratory, Satellite Images, Benue Trough.

INTRODUCTION Lake Chad, an extensive inland Lake with a large body of fresh water in this Sahel region, is considered a vital source of potable water by dwellers of that region. However, the shortage of potable water in this region is often aggravated by drought and desertification. According to Isiorho (1989), Lake Chad has on occasions completely or almost completely dried up, as evident from prehistoric sand dumes found on the Lake bottom. Located in a semi-arid region with a low annual rainfall of 30mm and a high evaporation rate of 2mm/year (Rouche, 1980; Carmouze, 1983) coupled with its proximity to the Sahara desert, the southern part of Lake Chad shrinks during periods of low annual rainfall. Lake Chad is not only the main source of water in the region, it also recharges the underlying aquifers through seepage from the lake bed (Isiorho and Matisoff, 1990). Several workers (Cratchley, 1960; Cracthley et al, 1984) have mapped structural features around Lake Chad. Durand (1982) observed that many of the structures around Lake Chad, covered by thick sediments of the Quaternary Chad Formation, may be visible at the surface. Observations of Land satellite and shuttle images made by Isiorho et al (1991) in the south west portion of the Lake Chad Basin revealed the presence of linear features. A further study of the area by Isiorho and Nkereuwem (1996) resulted in the delineation of several prominent lineaments the least of which was twenty kilometers long. RESISTIVITY PROFILING The existence of at least one of the said prominent lineaments observed from the land satellite and shuttle images was later confirmed by geophysics. A 14km long N-S resistivity profiling perpendicular to the said prominent lineament was conducted across it (the profile is shown as a broken line in fig 1). The Wenner configuration was adopted with a 30m electrode separation. Both the terrameter SAS 300C and the strata scout resistivity meter were used for data acquisition. A segment of the resistivity profile (about 3km long and lying between the 9th and 12km of the said 14km long profile), with lowest resistivity values was observed to correspond to the inferred lineament (fig 2). The prominent lineament was suggested in that work to be a basement fracture.

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NKEREUWEM, O. T et al.,: Continental J. Earth Sciences 5 (1): 1 - 7, 2010 TDS Several water samples were collected within the study area. The depth of sampling varied from 0.6 to 1.6m. It was observed that total dissolved solids (TDS) in the groundwater tended to increase with distance from the Lake. It was further observed that TDS values were generally low in the vicinity of the inferred lineament (fig 1, labelled Z), suggesting that the lineament is indeed a fracture which acts as a Local recharge zone. This is because groundwater recharge by direct rainwater through the fracture zone would have lower TDS values because of the short distance travelled by the said groundwater, relative to groundwater in the surrounding areas (Ishiorho and Nkereuwem 1996). THE PRESENT STUDY This work seeks to utilize the CSAMT method to establish whether or not there is a relationship between inferred lineaments established by Isiorho and Nkereuwem (1996), the Benue Trough and the diminishing size of the lake water.

Fig. 1. Map showing the prominent lineaments visible on all the Landsat images, the resistivity profile

(indicated as a broken line), and the TDS values of some groundwater and lake water samples (After Isiorho & Nkereuwem, 1996.)

CONTROLLED SOURCE AUDIO-FREQUENCY MAGNETOTELLURICS (CSAMT) The CSAMT method is a frequency-domain electromagnetic technique which utilizes a fixed grounded dipole as an artificial signal source. This technique is similar to the natural-source magnetotellurics (MT) and audio frequency magnetotellurics (AMT) techniques; the main differences centre around the use of the artificial CSAMT signal source at a finite distance. The source provides a stable, dependable and repeatable signal resulting in higher precision and economical measurements than are usually obtainable with natural source measurements in the same spectral bands (Zonge and Hughes, 1993). Since its introduction in the mid-1970s, CSAMT has been used in exploration for petroleum, geothermal resources, massive sulfides, base and precious metals, structures, lithologies and sources of groundwater contamination. The CSAMT is a relatively new geophysical technique. Not much is known about CSAMT interpretational skills and case histories as such are still being held as proprietary by CSAMT contractors and exploration companies. Apart from the CSAMT work done by the author for FES (NAPIMS) in Magumeri and Ladi Bida sectors of the Chad Basin, no similar work has been reported in Nigeria so far. This paper is in part an attempt to highlight the technical capabilities of the CSAMT method and to encourage its usage as it possesses positive implications in structural delineation as well as petroleum, solid mineral, geothermal and groundwater prospecting.

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NKEREUWEM, O. T et al.,: Continental J. Earth Sciences 5 (1): 1 - 7, 2010

Distance in Kilometers from New Marte

Fig. 2. Resistivity profile along the New Marte-Kirenowa road. The lowest resistivity readings correspond to the lineament (fracture zone) position (After Isiorho & Nkereuwem, 1996.)

INSTRUMENTATION The equipment used in the execution of the scalar (2-D) CSAMT survey in the South-western part of Lake Chad were made up of the Turbo Universal V4 console, magnetic sensor coil, porous pots, cables and peripherals, on the receiver line (Rx). On the transmission line (Tx), we had the MG-3 generator which generated the current signal used in the survey, an IPT-1 transmitter console which introduced the current into the ground, cables and two sets of grounded bipoles (fig. 3a). The CSAMT method measures electric field (E-field) and magnetic field (H-field) induced by electromagnetic field transmitted from electrical current through grounded bipoles. The CSAMT measurements with V4 receiver can be achieved at a maximum of 34 frequencies ranging from 8192Hz to 0.25Hz producing sounding from the ground surface to several kilometers deep. Any combination of E-field and H-field from the 8 channels, for an example 6 Ex’s Hy and Hz, can be simultaneously measured to perform multi-soundings, thus maintaining a high survey production. The electric field (E-field) which is parallel to the receiver line and the orthogonal magnetic field (H-field) are measured at a specified frequency. The magnitudes of the E-field, the H-field, relative phases, apparent resistivity and phase difference are calculated using the following Cagniard equation. ρa = 1/5f (E/H)2, = E - H ……………………………….(1) Where ρa is apparent resistivity in ohm-m; f is frequency in Hz; E is the E-field magnitude in mv/km; H is-field magnitude perpendicular to the E-dipole in gammas; is phase differences in radians; E and H are E-field and H-field phases respectively. Field Strength At a given receiver location, the field strength depends upon various factors: locations of measuring point (relative to transmission bipole), earth resistivity, and measuring frequency. For optimum survey results, it is important to know the approximate expected field strength in order to plan the transmitter location properly.

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NKEREUWEM, O. T et al.,: Continental J. Earth Sciences 5 (1): 1 - 7, 2010 Apparent Resistivity The apparent resistivity is calculated from the ratio of orthogonal electric and magnetic fields using the well known Cagniard equation (1) for Magnetotelluric method (MT). It should be noted that this equation is valid in the plane wave region of the electromagnetic field; that is, when the distance between transmitter signal source (Tx) and receiving location (Rx) is sufficiently large. The effective survey area, trapezoidal in shape, indicated in (Fig. 3a) is thus optimised by the maximum possible field strength and by avoiding areas that are too close to the transmitter bipoles. Far-Field and Near Field In a CSAMT survey, the distance between the transmitter and receiver locations is constrained, in general, by the requirement that the magnetic and electrical fields be strong enough to permit useful measurements. The paradox is that where the “plane-wave” assumption is valid, the signal may be weak; and where the signal is strongest (near the transmitter), the “plane wave” assumption is no longer true (Yamashita et al, 1985).

Fig. 3. Illustration of the CSAMT survey configuration and grid (a) and equipment layout (b). At some distance from the transmitter bipoles, where the transmitted electromagnetic field becomes a “plane-wave”, it is called “far-field”. (The region between 4-8km in fig 3a). Cagniard equation is valid in the “far-field” to calculate the apparent resistivity. The “far-field” distance, Lf, is given approximately by the following equation:

Lf > 3 skin depth = 1509 √ρa/f …………………..…………. (2)

Where Lf is in m, ρa is resistivity of the homogeneous earth in ohm-m and f is frequency in Hz. This Lf estimate is much more complicated in general field cases where the earth is not homogeneous. If the distance between transmitter and receiver is much less than Lf, the transmitted field is not “plane-wave” in character. It is referred to as the “near field” (region between 2-4km in fig 3a) and the Cagniard equation over estimates the actual resistivity. CSAMT Field Work in Dikwa The site map (fig 4) displays the CSAMT profiles spaced 2km apart and survey configurations used in Dikwa area. The distance between the transmission bipoles varied from 100m during CSAMT calibrations to 1400m during actual survey in Dikwa code-named “TEST 2008”. Three aluminium foil electrodes were grounded at both ends of

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NKEREUWEM, O. T et al.,: Continental J. Earth Sciences 5 (1): 1 - 7, 2010 the transmission line. Currents ranging from 3.8 to 4.2 amperes were transmitted through the grounded bipoles depending on the values of contact resistances encountered at various transmitting stations. At all times,

the magnetic sensor was placed at right angles to each receiver line during CSAMT data acquisition in Dikwa area. The E-dipole separation was fixed at 200m, while the transmitter-receiver distance varied from 2 to 8km. Recordings were made beginning with the highest frequency number, 13 (F-high=8192 Hz) and reduced one step at a time after a time interval of 3 minutes to the lowest frequency number, -2 (F-low=0.25Hz). All data were automatically recorded and stored in the Turbo V4 receiver which had to go back to Maiduguri on daily basis at the end of each day’s field work for data transfer. RESULTS The results of the CSAMT investigations in Dikwa area are presented in the form of a coloured Bostick section (apparent resistivity versus depth) fig. 5. GEOELECTRICAL INTERPRETATIONS Five CSAMT profiles (A, B, C, D and E) were sounded and processed to generate five Bostick sections. Each of the five Bostick sections revealed a pattern interpreted as three parallel faults (Zonge et al, 1986) similar to the ones on profile A presented in fig. 5, where the fault planes are indicated by three arrows. A complete interpretation of the five Bostick sections obtained on the profiles A, B, C, D, and E with a view to establishing the actual positions of the three parallel faults on each profile has been presented in figure 6. Figure 6 shows a set of three parallel faults oriented in a northeast-southwest direction. These faults have the same orientation as the inferred lineaments observed on land satellite and shuttle images and confirmed with resistivity profiling by Isiorho and Nkereuwem (1996). This work has thus confirmed the well established trend of basement fracturing in northern Nigeria by previous workers (Daniel, 1999; Bassey et al, 2000; and Kamureyina, 2007 etc.) CONCLUSION The study has delineated three parallel deep-seated faults using the CSAMT technique in Dikwa area about 25km North of New Marte in the North western sector of lake Chad. Based on the Bostick section (Fig. 5), the faults are as deep as 10km. This fact tends to support the suggestion by Isiorho and Nkereuwem (1996) that the inferred lineament were indeed bedrock fractures. The work has equally established the fact that the inferred lineaments

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NKEREUWEM, O. T et al.,: Continental J. Earth Sciences 5 (1): 1 - 7, 2010 detected by Isiorho and Nkereuwem (1996) and the parallel faults obtained in this study have the same NE-SW orientation towards Benue Trough. We strictly believe that recharging the underlying Chad Formation aquifers through seepage and high rate of evaporation are not the only reasons for the disappearance of water from the Mega Lake Chad which ancient shoreline extended to Bama, a distance of over 130km from the present Lake. Only gigantic basement fractures acting as migratory routes have the capacity to drain such a colossal amount of water from Lake Chad.

Fig. 5. BOSTICK INV. APP. RESISTIVITY (Ex/Hy) (CORRECTED)

Resistivity in ohm-m

RECOMMENDATION We wish to suggest that further remote sensing and geophysical works be carried out in areas between South of Dikwa and the Benue Trough to establish the continuity or otherwise of those basement fractures.

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NKEREUWEM, O. T et al.,: Continental J. Earth Sciences 5 (1): 1 - 7, 2010

REFERENCES Bassey, N. E., Nur, A. and Obiefuna, G. I. (2000): Analysis of aerial photographic data over Guyuk area, Northeastern Nigeria Journal of Mining and Geology V.36 (2):145 - 152 Carmouze, J. P. (1983): Hydrochemical Regulation of the Lake: in Lake Chad ecology and productivity of a shallow tropical system. Junk Publishers, Boston, p. 95-123. Cratchley, C. R. (1960): Geophysical survey of the Southwestern part of the Chad Basin. Conference on geology, Kaduna, Northern Nigeria: Kaduna, Nigeria Geological Survey, Pub. 35:21 Cratchley, C. R., Louis, P. and Ajakaiye, D. E. (1984): Geophysical and geological evidence for the Benue Chad Basin Cretaceous rift valley system and its tectonic implications: Journal of Africa Earth Sciences; V.2 (2): 141 150. Daniel, E. (1999): Interpretation of Aeromagnetic map of Shani area (sheet 154), N. E. Nigeria, unpublished B. Tech Thesis. Department of geology, Federal University of Technology Yola, p 94. Durand, A. (1982): Oscillations of Lake Chad over the past 50,000 years: New data and new hypothesis: Palaeogeogr. Palaeoclim; Palaeoecol; V.39: 37-53. Isiorho, S. A. (1989): Remote sensing applications in Chad Basin (Abstract): Geological Society of America Abstracts with Programs, V. 21(4):16. Isiorho, S. A. and Matisoff, G. (1990): Groundwater recharge from Lake Chad: Limnology and Oceanography V. 35(4):931-038. Isiorho, S. A. and Nkereuwem, O.T. (1996); Reconnaissance study of the portion of the Lake Chad. Journal of Environmental & Engineering Geophysics, V. 1(1):47-54. Isiorho, S. A., Taylor-Wehn, K. S. and Corey, T. W. (1991): Locating groundwater in Chad Basin using remote sensing technique and geophysical method (Abstract): EOS (Transactions of the American Geophysical Union), V.72 (44):220-221. Kamureyina, E. (2007): Analysis of aeromagnetic data over Garkida and Environs, Northeastern Nigeria. Unpublished M.Sc. thesis. Department of geology, Federal University of Tech. Yola, p.67. Roche, M. A. (1980): Tracage natural salin et isotopique des eaux du system hydrologique du lac Tchad: Cah. I office de la recherché scientifique et technique outré-Mer (ORSTOM) Publ. #117, p.375. Yamashita, M., Hallof, P. G. and Pelton W. H. (1985): CSAMT case histories with a multi-channel CSAMT System and near-field data correction, 55th Ann. Intern. Mtg., Soc. Expl Geophysics, Expanded Abstracts 276 278. Zonge, K. L. and Hughes L. T. (1993): Controlled source Audio Frequency Magnetotellurics (in Electromagnetic methods in applied Geophysics) Vol. 2 Application, Part B. pp 713-809, Soc. of Expl. Geophysics. Zonge, K. L. and Hughes, L. T. and Emer, D. F., (1986): The use of IP, CSAMT and TEM in mineral exploration. 2nd Symp. on Expl. Geophysics, Absorts, Xian. Received for Publication: 23/09/08 Accepted for Publication: 12/04/09 Corresponding Author NKEREUWEM, O. T., Department of Geology, University of Maiduguri, Borno State, Nigeria.

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Continental J. Earth Sciences 5 (1): 8 - 13, 2010 ISSN: 2141 - 4076 ©Wilolud Journals, 2010 http://www.wiloludjournal.com

PRELIMINARY INVESTIGATION OF THE ORIGIN AND QUALITY OF BARYTES IN THE TSARETA-

TUNGAN KUDAKU AREA, NORTH WESTERN NIGERIA BASEMENT COMPLEX, NIGERIA.

Daspan, R. I. and Imagbe, L.O Department of Geology and Mining, University of Jos, P.M.B. 2084, JOS, NIGERIA.

ABSTRACT A preliminary study of the baryte occurrence in the Tsareta-Tungan Kudaku area, Northwestern Nigeria shows that it is hosted by low- grade metamorphic rocks mainly Phyllites, in veins of about 1.5km wide and 4m deep. It is a fissure filling vein type deposited in fissures running parallel-sub parallel to the Anka fault system. The barytes has variable specific gravity ranging between 3.8 for surface occurrences and 4.3 at deeper levels. This quality meets the specification of specific gravity of 4.2 for use as drilling mud in the oil industry. Chemically, the baryte has BaSO4 concentration between 79.1%-95.8%. The presence of an inclusion of pyrite and leached capping (gossans) which is typical of sulphides suggests that the hydrothermal fluids that formed the gold mineralization in the Anka region could be responsible for the formation of the baryte in the area. KEYWORDS; Baryte, Tsareta-Tungan, Anka Fault, Vein, hydrothermal.

INTRODUCTION Baryte, as an industrial mineral, is a major type of inert volume and weight filler in drilling mud used in the oil industry, in the chemical industry, as a constituent in lithophone paint as well as in the glass and paper industry. Most of the baryte mineralizations in Nigeria are reportedly found as vein occurrences within the middle Benue Trough with most concentration in the Azara, Awe and Keana areas, McCurry(2000), Offodile,(1980). The baryte deposits are usually found to be closely associated with Lead and Zinc and can be related to the same mineralizing activity. Baryte mineralizations have also been reported in Akpet area, Oban Massif in Southeastern Nigeria (Akpeke at al ,2006). Other occurrences are found in Gombe, Zurak, Akwana, Abakaliki and Ishiagu. It is significant to note that it is only in the middle Benue Trough that vein mineralization includes fluorite and baryte, Omada and Ike, (1996) This paper reports on preliminary investigation on the origin, geochemistry and quality of a new baryte occurrence found within the metamorphic rocks of Anka Schist belt of the Basement complex of Northwestern Nigeria in contrast to the occurrences reported within the Cretaceous Benue Trough. The quality of the barite is here studied based on international specifications such as concentration of BaSO4 (between 92-95%), degree of whiteness and reflectance, Specific gravity (4.2 and above), and concentration of iron oxide minerals, moisture and other foreign elements (less than 2-3%) (Dawson, 1985) GEOLOGIC SETTING Tsareta-Tungan Kudaku area falls within the Anka Schist belt in the Basement Complex of Northwestern Nigeria. (fig.1) The Basement Complex includes all rocks older than the late Proterozoic metasediments. The geology of the Basement Complex in Nigeria have been described and reviewed by various authors including Ajibade,(1980),McCurry and Wright,(1976); Oyawoye,(1972) ;Rahaman (1976); Reyment (1976). The Tsareta Tungan Kudaku area, however comprises of the mafic-ultramafic rocks(Diorites,Syenite,Gabbro); Molasse-type clastic sedimentary rocks, (unmetamorphosed greywackes and conglomerates); Older Granites ; Metasediments and Granite –gneiss. The Serpentinites are however the most extensive rocks in the study area. METHOD OF STUDY A total of twenty samples of baryte, and five each of host Phyllite and Serpentinite rocks were collected during the field work. The baryte samples were collected at various depths in veins which follows a structural trend of N180E

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Daspan, R. I. and Imagbe, L.O: Continental J. Earth Sciences 5 (1): 8 - 13, 2010 corresponding to the major structural control exhibited by the Serpentinites emplaced at the margins of the Anka fault system, Ogezi (1977). The specific gravity of the baryte was also determined. However , only six representative samples of the baryte and one each of serpentinite and Phyllite were pulverized and analyzed for preliminary assessment of some of their major and trace element compositions using the energy dispersive X-rays fluorescence method at the Centre for Energy Research and training Zaria, Nigeria.

RESULTS Mode of Occurrence The baryte mineralization in the area is hosted by the country rock (Phyllites) in veins of about 1.5m wide and 4m deep. The veins follow a general structural trend of N180E which corresponds to the major direction of the serpentinite in the area and falls within the Anka fault system (AFS). They can therefore be described as fissure filling deposit type where hydrothermal solutions deposited or precipitated the baryte minerals in the fissures running parallel to the major Anka fault system (AFS). The baryte veins occur approximately two Kilometers from the serpentinite bodies. At the time of this study, two veins were being mined and the veins appear on the surface as dykes occurring in close association with quartzites which also occur in the area. There were observed leached cappings (gossan) around the veins which is typically associated with sulphide mineralisation on top of the baryte veins. Table 1. Specific Gravity of the Tsareta -Tungan Kudaku barytes.

Sample No. Specific Gravity TB1 3.80 TB2 4.10 TB3 4.40 TB4 4.35 TB5 4.30 TB6 4.25 AVERAGE VALUE 4.20

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Daspan, R. I. and Imagbe, L.O: Continental J. Earth Sciences 5 (1): 8 - 13, 2010 Chemical Properties The baryte in the area has variable specific gravity ranging from 3.8-4.3. The least specific gravity of 3.8 was found at the top most regions of the trench where it was observed to be mostly weathered. However, those found at the deeper levels of the trench gave specific gravity values of between 4.1- 4.4. This falls within the specification in the oil industry (Table 1) required for use as drilling mud which is 4.2. Pyrite was observed as an impurity in the baryte. The specific gravity of baryte is of considerable importance in determining its quality and use in the oil industry. Barytes with specific gravity values of 4.5 and above is considered pure while barytes with specific values from 4.2 satisfies the weight requirements of most oil industries. Apart from the barytes found at the top-most region of the trench, which gave specific gravity value of 3.8, those that occur at the deeper levels of the trench gave average values 4.20 which confirms good quality and thus suitable for use as a drilling mud.

Table 2. Chemical composition of the Tsareta -Tungan Kudaku barytes. Sample no. Concentration

(%) Chemical compound

VEIN A VEIN B VEIN C

TB1 TB2 TB3 TB4 TB5 TB6

Al 2O3 0.94 0.54 1.06 0.90 1.36 0.87 SiO2

1.00

1.09

0.97

1.20

1.18

2.1

Fe2O3 2.85 0.52 0.25 0.21 6.27 3.97 CaO 0.12 1.82 1.69 0.11 1.28 0.12 MnO ND ND ND ND ND ND BaSO4 88.02 83.0 92.4 95.8 79.1 89.2 TiO4 1.30 0.87 1.56 1.40 1.98 1.07 SrO 0.54 0.99 0.23 0.23 1.00 0.39 As2O3 0.01 0.03 0.03 ND ND 0.01

Table 3 Results of geochemical analysis of host rocks of the baryte mineralization.

ELEMENTS CONCENTRATIONS % Major oxides SERPENTINITE PHYLLITE K2O 1.494 2.591 Ca O 0.979 0.90 TiO2 0.756 0.923 MnO 13.82 0.067 Fe2O3 7.08 7.460 Trace Elements

Conc. in ppm Conc. in ppm

Ba 4.05 X 104 1.12 X 104 Ce 5.12 X 101 3.9 X 101 Zn 2.75 X 102 1.16 X 102 Pb 3.47 X 102 6.78 X 101 Br 2.05 X 101 1.84 X 101 Rb 1.58 X 101 6.37 X 101 Sr 2.76 X 102 7.5 X 101 Y 2.97 X 101 1.41 X 101 Zr 1.14 X 102 1.31 X 102 Nb 1.02 X 101 7.95 X 100

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Daspan, R. I. and Imagbe, L.O: Continental J. Earth Sciences 5 (1): 8 - 13, 2010 The results of the chemical analyses of the baryte samples and the host rocks are presented in tables 2 and 3 respectively. The concentrations of BaSo4 in the six samples preliminarily investigated ranged between 79.1 to 95.8% (Table 2). The SIO2 and Al2O3 concentrations also varies between 1.0-2.1 and 0.54-1.36 % respectively while the Fe2O3 varied between 0.21-6.27%. However , it should be noted that the barytes with high BaSo4 concentration tend to have low Fe2O3. Chemically, the analyzed baryte gave a composition of between 79.1 to 95.8% BaSO4. (Table 2). Also, texturally, in terms of colour, it was observed that most of the barytes is off-white especially the ones occurring close to the surface of the trench while those at the deeper levels where almost whitish in colour. This suggests that the pure Baryte samples occur at the deeper levels ORIGIN The baryte deposits in the Tsareta-Tungan Kudaku area is best described as vein or fissure filling deposit type where hydrothermal solutions precipitated the baryte minerals in the fissures running parallel-subparallel to the major Anka fault system (A.F.S). Previous studies of the origin of the Pan-African mesothermal gold mineralization of Bin Yauri, Garba, (1996) using isotopes showed that sulphur isotopes have positive values of δ345 which is considered to be consistent with a crustal sedimentary sulphur source. Also, carbon isotopic studies, Garba and Akande, (1992) gave values of δ13C to be in the order of –7+ 2% which reflects the average crustal carbon(C) value of –7%[8] . Garba and Akande, (1992), Obtained values in the order of 13+ 1.4% for hydrothermal carbonates at Bin Yauri. These values fall within the range for metamorphic water, Craw and Chamberlain, (1996) and are markedly different from the δ180 associated with magmatic or normal meteoric waters. Thus, from isotopic studies, it could be inferred that a reservoir confined to the clastic sedimentary rock may be the source of the mineralizing fluids generated through large scale metamorphic process along an active transcurrent Anka fault during the waning stages of the Pan-African event, Hoefs, (1987). The heat of the metamorphism which resulted in the regional metamorphism of the entire area and the intrusion of the Pan-African granitoids could have provided the heat needed for the generation of the mineralizing fluid. The host rock (Phyllite, Schist) and the surrounding basement rocks are possibly the source from which these elements were leached. This is attested to by the high barium concentration of 1.12 x 104 and 4.05 x 104 in the phyllites and serpentinites respectively (Table 3). The baryte has a barium concentration of 4.5 x 105 to 5.5 x 105 showing that only a concentration factor of 10 is needed for a barite deposit to form using these rocks as source. Fairly noticeable concentrations of lead and Zinc in the serpentinites and phyllites as well as baryte shows a possibility of the mineralizing fluids carrying sulphur species of lead-Zinc hence the area has the potentials of Pb-Zn mineralization which is common with most of the barite occurrences in Nigeria. The probable pathway for the fluids is the major Anka fault system. This fault system has been severally been described as a possible crustal suture ,Ajibade, (1980) ; McCurry and Wright, (1976) These fluids are believed to be transported through the late tectonic fault zone into smaller suture or fissures formed as a result of the brittle fault zone within the Phyllites. These fluids moved through these faults to the near surface which is characterized by low temperatures and pressures thus favouring precipitation. CONCLUSIONS From the discussion above the following conclusions can be drawn: The baryte in the Tsareta-Tungan Kudaku area can be described as a fissure filling deposit type formed by deposition of hydrothermal solutions in the fissure running parallel-subparallel to the major Anka fault system. The baryte is of high quality and is suitable for use as drilling mud.

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Daspan, R. I. and Imagbe, L.O: Continental J. Earth Sciences 5 (1): 8 - 13, 2010 Daspan, R. I. and Imagbe, L.O: Continental J. Earth Sciences 5: 8 - 13, 2010 The source of the ore elements could be from the leaching of these elements from the surrounding basement rocks. Future research would be on isotopic studies of the barytes to confirm deductions on the origin.

ACKNOWLEDGEMENT Enoch Ejurkurlem is gratefully acknowledged for sample collections while the center for Energy research and Training Zaria is acknowledged for the analysis. The comments of the reviewer are highly appreciated.

REFERENCES Ajibade, A.C.,1980. Geotectonic Evolution of the Zungeru region , Nigeria PhD dissertation ,University of Wales, Aberystwyth Ajibade, A.C.and Wright,J.B.,1989. The Togo-Benin-Nigeria Shield;Evidence of crustal aggregation in the Pan-African belt, Tectnophysics,165 125-129. Akpeke, G. B.; Ekwueme, B. N. and Ephraim, B. E., 2006. The nature and origin of the Barite mineralization in Akpet area, Oban Massif, Southeastern Nigeria. Journal of Geological Sciences, Vol.4 No.2 139-146 Craw, D.and Chamberlain,C. P., 1996. Meteoric incursion and oxygen fronts in the Dalaradian metamorphic belt, southwest Scotland: a new hypothesis for regional gold mobility. Mineralium Deposita 31,365-373 Dawson, K.R. 1985. Geology of Ba, Sr, and Fl. Deposits in Canada. Geological Survey of Canada, Econ. Geol. Rept., 34. 1-30 Garba, I., 1996. Tourmalinization related to late proterozoic Early palaeozoic lode gold mineralisation in the Bin Yauri area, Nigeria mineralium Deposita.31,201-209 Garba, I. and Akande ,S.O, 1992. The origin and sinficance of non-aqueous CO2 fluid inclusions in the non aqueous veins of Bin Yauri, northwestern Nigeria. Mineralium Deposita 27,249-25 Hoefs, J., 1987. Stable isotope Geochemistry. Springer-Verlag, New York, 241p. Kogbe, A.C. 1989. Geology of Nigeria. Elizabethan Publishing Company Lagos Nigeria Mangs, A.D. 2000.The viability of setting up a Bartye processing Pilot plant in Mabudi Langtang south L.G.A Plateau State. Unpublished M.Sc Research Seminar University of Jos. McCurry, P., 2000. The geology of the Precambrian to Lower Palaeozoic rocks of northern Nigeria- a review, in: Kogbe, C.A(ED), Geology of Nigeria. Elizabethan Publication Company Lagos. McCurry, P. and J.B.Wright,J.B., 1976. Geochemistry of calc- alkaline volcanics in Northwestern Nigeria, and a possible Pan-African suture zone. Earth Planetary Science Letter 37, 90-96. Omada, J. I. and Ike, E. C., 1996. On the economic appraisal of the barite mineralization and saline springs in the middle Benue trough, Nigeria. J. Min. Petr. Econ. Geol. 91, 109-115 Offodile, M.E., 1980. A Mineral Survey of the Cretaceous of the Benue Valley, Nigeria. Cretaceous Research 1, 101-124 Ogezi, A.E., 1977. Geochemistry and geochronology of basement rocks from Northwestern Nigeria. PhD dissertation, University of Leeds.

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Daspan, R. I. and Imagbe, L.O: Continental J. Earth Sciences 5 (1): 8 - 13, 2010 Ogezi, A. E., 1978. Geochemistry and Origin of ensialic Alpine type Serpentinite Associations from Mallam Tanko (Shemi) and Ribah (Wasagu), NW Nigeria. In Dessuvgie et. al (Eds), African Geology ; Nigeria. 67-99 Onyeagocha, A. C., 1979. The Mallam Tanko Serpentinite Petrology and Economic Implication, Jour. Mining and Geology 16(1)37-40 Oyawoye, A., 1972. The Basement Complex of Nigeria. In Dessuvagie et. al (Eds). African Geology ; Nigeria. 67-99. Rahaman, M. A. 1976. Review of the Basement Geology of S-W Nigeria. in C.A. Kogbe, Elizabethan Publishing Company Lagos Nigeria 42-58 Reyment, R. A. 1976. Aspects of the geology of Nigeria Ibadan University press. Wright , J.B., 1976. Fracture systems in Nigeria and initiation of fracture zones in the south Atlantic, Tectnophysics 34 43-47 Received for Publication: 03/03/10 Accepted for Publication: 02/04/10 Corresponding Author Imagbe, L.O Department of Geology and Mining, University of Jos, P.M.B. 2084, JOS, NIGERIA.

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Continental J. Earth Sciences 5 (1): 14 - 19, 2010 ISSN: 2141 - 4076 ©Wilolud Journals, 2010 http://www.wiloludjournal.com PRELIMINARY ASSESSMENT OF THE RARE EARTH ELEMENT COMPOSITION OF SHALES OF THE

GONGILA FORMATION, GONGOLA BASIN NIGERIA.

1Imagbe, O. L, 2Piwuna , R.M. and 3Egbon , W.E 1&2Department of Geology and Mining, University of Jos, Nigeria.

3Raw Materials Research and Development Council, Maitama district, Abuja , Nigeria.

ABSTRACT This preliminary study was carried out on the Shales of the Cenomanian-Turonian sedimentary sequence representing the Gongila Formation of the Gongola Basin as exposed in the Ashaka Cement quarry in Gombe, northeastern Nigeria. A total of ten shale samples were collected from the outcropping sections, out of which five representative samples were subjected to instrumental Neutron Activation Analytical (INAA) methods. The results of the analysis of the shale samples shows the average composition values; La (57),Ce (89.4), Nd (34), Sm (6.94), Eu (1.52),Tb (0.66),Lu (0.42).This result however show slightly high LREE (light rare earth elements) enrichment and relatively low HREE (heavy rare earth elements) when compared to the Post-Achean Australian Standard (PAAS).The provenance of the Shales thus may be ascribed a granitic source rock with a high proportion of plagioclase feldspars. KEYWORDS: Rare earth, Shales, Gongila Formation, Provenance.

INTRODUCTION Gongila formation is one of the many sedimentary formations in the Gongola sub basin of the Benue Trough (fig.1). The type locality of the Formation is well exposed in the limestone quarry of the Ashaka Cement Factory at Ashaka village in Gombe state, north eastern Nigeria (Obaje et al, 1999a) (fig.2). The Formation was first named by Carter et al (1963) to distinguish it from the almost similar Pindiga Formation on the ‘Zambuk Ridge’. It lies conformably on the Yolde formation and is one in a series of marine calcareous units deposited in the Gongola Basin during the Mid- Cretaceous worldwide transgression. The Formation is lithologically characterized by dark carbonaceous limestones and shales, intercalated with pale limestones and shales and minor sandstones. Popoff et al., (1986), Zarboski et al., (1998, 2000), Obi (1998), Obaje et al (1999, 2000) and Imagbe and Davou (2007) have variously carried out studies on aspects of the stratigraphy, origin, depositional environment and geological significance of the Gongila formation. However, despite these studies, none has focussed on the trace and rare element geochemistry which tend to create a lacuna in the multidisciplinary approach of investigating the formation. Trace and rare element Geochemistry as a tool for rock provenance, depositional environment, facies and diagenetic changes has been used by many authors (Elderfield et al 1981; Glasby et al 1987; Adekeye et al 2007). This preliminary study presents the rare earth element occurrence and distribution patterns in shale of the Gongila formation to provide an understanding of the environment of deposition as well as determine their source rock. GEOLOGICAL SETTING The Gongila Formation is located within the Gongila-Gombe Sub basin of the Gongola Basin of the Upper Benue Trough, Nigeria (Popoff et al., 1986). The Upper Benue Trough was first investigated by J.D Falconar, (1911) who described some of the Cretaceous and Tertiary sedimentary formations. Stonely, (1966) and J.B Wright (1968) proposed a graben genesis related to the Cretaceous opening of the Gulf of Guinea. Burke et al, (1972) suggested a sea floor spreading model for the

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Imagbe, O. L et al.,: Continental J. Earth Sciences 5 (1): 14 - 19, 2010 Southern Benue Trough. Grant, (1971) characterized the Benue Basin as an aulacogen based on a triple arm rift model. All these subsequent methods imply a continental rifting for the genesis of the Benue Basin. An outline of the major stratigraphical subdivisions of the Cretaceous to Tertiary Sedimentary formations of the Benue Trough was reported by Peters (1982), fig 2.

Fig 1; Simplified geological map showing the location of the Benue trough, its subdivisions and the Ashaka Limestone quarry

Fig 2: Major stratigraphic subdivisions of the Cretaceous to Tertiary sedimentary formations of the Benue Trough, Nigeria. (Modified from Petters, 1982; Grandstein et al., 2004.)

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Imagbe, O. L et al.,: Continental J. Earth Sciences 5 (1): 14 - 19, 2010 MATERIALS AND METHODS Initial fieldwork involving vertical in situ outcropping sedimentary sequence description, measurements and sampling in the Gongila Formation has earlier been carried out and reported in Imagbe and Davou (2007). Ten shale samples were collected from the outcropping sections, out of which five representative samples were subjected to Instrumental Neutron Activation Analytical (INAA) methods. This method was chosen because of its high sensitivity and efficiency. All the analysis was carried out at the Activation Laboratory, Canada. This method involves weighing a 30g sample into specially fabricated small polyethene vials. The sample was then irradiated with control international reference material CANMET WMS – 1 and Ni-Cr flux of 7x1012 ncm-1 s-1 in the McMaster Nuclear Reactor. Following 7 day decay, the sample was measured and the Canberra Series 95 Multi-channel analyzer under computer controls (Hoffman, E. L., 1992). The detection limit for the rare earth elements is between 0.1 and 5ppm. RESULTS AND DISCUSSION Field Occurrence of Shales The Gongila Formation is lithologically characterized by dark carbonaceous limestone, calcareous shale, intercalated by pale limestone and grey shale and minor sandstones reaching a collective thickness of nearly 12 meters above ground level as observed at the type locality of the formation exposed in the limestone quarry at Ashaka. The limestone is massive and contains well preserved sections, highly fossilized with evidence of mega fossils including ammonites, bivalves, and gastropods which are abundant in the lower part of the section. Thick grey shale beds were however observed to cap the limestone sequence and thus were susceptible to varying degrees of chemical weathering, as typified by the reddish-brown iron stains on the surfaces of the shales. The shales are fissile and friable in nature. The proportion of clay, silt and carbonaceous material vary within the shale resulting in different types of wavy laminated microfabric. Diagnostic sedimentary structures within the top shales of this formation include desiccation cracks, laminations and joints. Chemical Analyses The results of the analysis of the five representative shale samples shows rare earth elements concentration value ranging from 0.5 to 103ppm (Table 1).The average elemental composition values are ; La (57),Ce (89.4), Nd (34), Sm (6.94), Eu (1.52),Tb (0.66),Lu (0.42).This result however show slightly high LREE (light rare earth elements) enrichment and relatively low HREE (heavy rare earth elements) when compared to the Post-Achaean Australian Standard (PAAS). Table 1: Rare Earth Elements Composition (ppm) of Shales in the Gongila formation

Element W1 W2 W3 W4 W5 PAAS La 52.5 50.5 65.1 55.7 61.2 38 Ce 84 81 103 91 88 80

32 Nd 28 30 43 37 32 Sm 6.5 6.3 8.3 7.1 6.5 5.6 Eu 1.3 1.2 1.9 1.7 1.5 1.1 Tb 0.5 0.5 0.5 1.3 0.5 0.77 Lu 0.4 0.33 0.48 0.41 0.44 0.43 ΣREE 176.1 172.43 225.25 197.11 206.24 160.7

In ΣREE content, the REE content in the shales ranges from 172.43 and 225.68. The bulk REE normally reside in the clay fraction (silt or clay) and it has also been inferred that trivalent REE readily accommodated in most clay minerals enriched with alumina and ferric iron. The REEs were compared to the Post-Achaean Australian Standard (PAAS). The shales show slightly high LREE (light rare earth elements) enrichment and relatively low HREE (heavy rare earth elements).

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Imagbe, O. L et al.,: Continental J. Earth Sciences 5 (1): 14 - 19, 2010

Norm: SUN

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

1 1

1 10

1 100

1 1000

1 1

1 1000W1 W2 W3 W4 W4

Fig.3 Chondrite-normalised rare earth element plot for Shales of the Gongila Formation (normalising values after Sun and Mcdorough , 1989).

Norm: PRIM

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

1 1

1 10

1 100

1 1000

1 1

1 1000W1 W2 W3 W4 W4

Fig.4 Primitive Mantle normalised rare earth element plots for Shales of Gongila Formation. The REE patterns of europium anomaly in sedimentary rocks provide important clues regarding source rock characteristics (Taylor and McLennan, 1985). Higher LREE/HREE ratios and negative Europium (Eu) anomalies are generally found in felsic rocks, where as the mafic rocks exhibit low LREE/HREE ratios and none or small Eu anomalies (Cullers, 1995). The positive Eu anomalies are generally found in Precambrian rocks (tonalite-tronjhemite-gneiss (TTG), granitoids, and quartz diorite). The TTG rocks exhibits very high LREE/HREE ratios and no or small positive positive Eu anomalies, and the positive anomaly resulted from hornblende-melt equilibria.

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Imagbe, O. L et al.,: Continental J. Earth Sciences 5 (1): 14 - 19, 2010 Table 2: Range of Elemental Ratios of Shales in the Study Area compared to Ratios in Similar Fractions Derived from Felsic Rocks, Mafic Rocks and Upper Continental Crust. (n=number of samples)

Range of Sediments Range of Shale (n=5) Elemental Ratios

Felsic Rocks Mafic Rocks UCC

Th/Sc Th/Co Th/Cr Cr/Th La/Sc

1.35-1.51 1.25-1.91 0.23-0.27 3.17-4.29 2.84-3.68

0.84-20.5 0.67-19.4 0.13-2.7 4.00-15 2.5-16.3

0.05-0.22 0.04-1.4 0.018-0.046 25-500 0.43-0.86

0.79 0.63 0.13 7.76 2.21

The shales of the Gongila Formation shows slightly high LREE/HREE ratios which suggests that they were mainly derived from Intermediate granitic source rocks. Ratios such as La/Sc are significantly different in felsic and basic rocks. The La/Sc ratios in the studied samples range between 2.84 and 3.68 and compared with those of the sediments derived from felsic and basic rocks (fine fraction) as well as the Upper Continental Crust (UCC). SUMMARY AND CONCLUSION This study have shown from the REE pattern, as well as other geochemical parameters like the La/Sc, Th/Sc, Th/Co, Th/Cr, and Cr/Th ratios, and La/Sc vs Th/Co plot, that the shales of the Turonian- Cenomanian Gongila sedimentary sequence were mainly derived from felsic source rocks. The REE patterns also suggest that these shales may be from intermediate granitic source rocks. REFERENCES Adekeye, O. A. ,Akande, S.O. and Abimbola, A.F(2007); Preliminary Investigation of Rare Earth Element(REE) Composition of shales in the Oshoshun Formation exposed at the Shagamu quarry, Eastern Dahomey Basin, Southwestern Nigeria, Journal of Mining and Geology, .43(2) pp105-108 Benkhelil, J., (1986); Benue Trough and Chain, Geological Magazine 119: 155-168. Carter, J.D., Barber, W., Tait, E.A., Jones, G.P., (1963). The Geology of part of Adamawa, Bauchi and Borno Provinces in the North Eastern Nigeria. Bulletin 30, Geological Survey of Nigeria, 30:1:108. Cullers, R., Lowe, D.R., Cox, R.L., (1995). The influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern United States: Geochimica et Cosmochimica Acta, 59(14), 2919-2940. Cratchley, C. R., and Jones, J. P., (1965). An Interpretation of the Geology and Gravity Anomalies in the Benue Valley, Nigeria. Overseas Geol. Seiru. Geophysics. Paper 1, 1-26. Elderfield, H., Hawkesworth, C.J., Greaves, M.J., and Calvert, S.E., (1981). Rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments, Geochem. Cosmochem. Acta, 45: 1231-1234. Falconer, J. D., (1911): The Geology and Geography of Northern Nigeria. Macmillan Press. 295p Glasby, G.P., Gwozdz, R., Kunzendrof, H., Friedrich, G., and Thijssen,T.(1987). The distribution of rare earth and minor elements in manganese nodules and sediments from the equatorial and S.W. Pacific, Lithos. 20: 97-113.

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Imagbe, O. L et al.,: Continental J. Earth Sciences 5 (1): 14 - 19, 2010 Gradstein, F., Ogg, J., Smith, A., (2004); A Geological Time Scale 2004. Cambridge University Press, United Kingdom .589pp. Grant, N. K., (1971): South Atlantic, Benue Trough and Gulf of Guinea Cretaceous Tripple Junction. Bulletin of the geological Society of America. 82: 2295-2298. Guiraud, M.,(1993):Late Jurassic rifting-Early Cretaceous rifting and Later Cretaceous transpressional inversion in the Upper Benue Basin (NE Nigeria) Bulletin des Centres de Recherches Exploration-Production ELF Aquitaine 17 pp 371-383. Hoffman, E. L.,(1992). Instrumental Neutron Activation in Geo-analysis; Journal of Geochemical Exploration, 44:297-319. King, L. C., (1950): Outline and Distribution of Gondwanaland. Geological Magazine, 87:353-559. Imagbe L.O and Davou, D.D.(2007); Sedimentary and Geochemical Characteristics of the Cenomanian –Turonian Carbonates of the Gongila Formation, Gongola Basin, Upper Benue Trough Nigeria. Nigerian Journal of Applied Science 25:91-98 Obaje N.G; Peason, M.J; Suh, C.E. and Dada, S.S (1999b); Organic Geochemical characterization of the Potential Hydrocarbon source Rocks in the Upper Benue Trough. Journal of Mining and Geology, 35 (2): 137-152. Obaje, N.G; Ulu, O.K; Maigari, S.A and Abubakar, M.B. (2000); Sequence Stratigraphic and Paleovenvironmental Interpretations of Heterohelicids from the Pindiga Formation Northeastern Benue Trough, Nigeria. Journal of Mining and Geology, 36 (2) 191 – 152. Obi, G.C. (1998). Upper Cretaceous Gongila Formation in the Hawal Basin, North Eastern Benue Trough: A storm and wave dominated regressive shoreline complex. Journal of African Earth Science. 26 (4), 61-63. Petters, S.W. (1982); Central West African Cretaceous-Tertiary Benthic Foraminifera and Stratigraphy. Paaecongraphica A. 179 1-104 Poppof, M., (1986); The Upper Cretaceous Gongila and Pindiga Formations, Northern Nigeria Subdivision, Age, Stratigraphic Correlation and Paleogeographic Implications. Echope Geol. Helv. Besel, 79. 263-343.

Wright, J. B., (1981); Review of the origin and evolution of the Benue Trough in Nigeria. Earth Evolutionary

Science. 2, 9. Zarboski, P.M. (1997); A Review of the Cretaceous System in Nigeria, Africa Geoscience Reviews 5 385-483 Zarboski, P.M. (2000). The Cretaceous and Paleocene transgressions in Nigeria and Niger. Journal of Mining and Geology 36, 155-175. Zarboski, P. Ugodunlunwa, F. Idornigie, A., Nnabo, P and Ibe, K. (1998). Stratigraphy and structure of the Cretaceous Gongola basin, Northeastern Nigeria. Bulletin des Centres de Recherches Exploration-Production. ElF-Aquitaine 21 (for 1997), 153-185. Received for Publication: 03/03/10 Accepted for Publication: 02/04/10 Corresponding Author Imagbe, L.O Department of Geology and Mining, University of Jos, P.M.B. 2084, JOS, NIGERIA.

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Continental J. Earth Sciences 5 (1): 20 - 31, 2010 ISSN: 2141 -4076 ©Wilolud Journals, 2010 http://www.wiloludjournal.com

GEOTECHNICAL EVALUATION OF SOILS IN NUMAN AND ITS ENVIRONS, NORTH EAST NIGERIA.

G.I Obiefuna1,M.O. Oreagbune2 and C. David1

1Department of Geology and 2Department of Building, Federal University of Technology, Yola, Nigeria

ABSTRACT: A geotechnical evaluation of some soils in Numan, Adamawa, North –East, Nigeria has been carried out. This was done to determine the suitability of the soils for use as sub-grade/filling, sub-base and base course materials for road construction. The samples were collected from five different areas, at surface and sub-surface levels. The areas are New Demsa, Farei, Dowaya, Numan Town and Imbru. The soil samples were subjected to laboratory investigations in conformity with the American Association of State Highway and Transportation (AASHTO) and the Bristish Standard Institution (BSI) Standard specifications. Results of the geotechnical tests indicate that the proportion passing the BS sieve NO.200 ranges from 20. 92% to 39. 02% whereas plasticity index and consistency index ranges from 14.05 to 22. 01 and 1. 42% to 2. 16% respectively. The compaction test result revealed an optimum Moisture Content (O.M.C) Value of 11. 60% and a maximum Dry Density (M.D.D) Value ranging from 91g/cm3 2.08g/cm3 The California Bearing Ratio Values ranges from of 8% to 24%, whereas the plastic limit values ranges from 30% to 51%. Soils at New Demsa, Farei, Numan Town and Imbru are thus considered suitable for use as sub-grade/filling materials, while the soil at Dowaya is unsuitable for use as sub-grade/filling and sub-base material. This is probably why the road at this area failed after construction. KEYWORDS: - Geotechnical evaluation, sub-grade/filling, sub-base, base course, laboratory.

BACK GROUND INTRODUCTION In highway design and construction, careful attention is not only given to sampling and testing of the aggregates which are required to provide a pavement that will be sound and durable; but also to the subsoil materials which will provide support for the pavement (Okagbue and Uma, 1988). In selecting the route for the highway, one of the important factors considered is the geotechnics of the subsoil. At least a casual study of the subsoil through which the highway must pass is exceedingly helpful. From it the general stability of the area can be determined. Furthermore experience has shown that sub-soil conditions along a highway route can be a crucial factor in the serviceability and good performance of the highway (Weinert ,1968; Earquhar, 1980). It is therefore very crucial to determine the geotechnical properties of soils in order to establish whether a particular soil is suitable for use as fill, grade or sub-base materials. Some of the roads in Numan area have failed and hence constitute potential hazard to pedestrian and motorists alike because of lack of informed geotechnical data on the sub soil conditions. Most of the previous work done in the study area are mainly regional (Falconer, 1911) and have described the geology of the Upper Benue Trough in terms of sedimentary and stratigraphic aspects. Subsequently, (Carter et al, 1963) gave some details on the geology, geological structure, hydrology and water quality of the old Northern Nigeria in which the study area is included. Offodile (1976) wrote on the origin of the Benue Trough and Geology of the cretaceous of the valley. Braide (1992) studied the sedimentation and tectonics of the Yola arm of the Benue Trough with emphasis on facies architecture and their provenance significance. Offodile (1976), also gave some details on the sedimentation, tectonics and hydrolithological characteristics of part of the Benue Trough. Head (1988) indicated the various methods to be employed in the treatment of expansive soils and gave out the procedure to be adopted in the laboratory. Obiefuna et al., (1999), gave detailed account of the geological and geotechnical evaluation of selected gully sites in Yola area of Adamawa, north–east, Nigeria and recommended on how to tackle the environmental hazards.

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G.I Obiefuna et al.,: Continental J. Earth Sciences 5 (1): 20 - 31, 2010 The objective of this study is to determine the geotechnical factors responsible for the suitability of some soils in Numan and its environs. To achieve the objective of this research, the result of the various tests have been analysed and used to proffer ways geared towards constructing durable roads. STUDY AREA The study area falls within the savannah belt of the Northern Part of Nigeria. It is located between latitude 9o25’N and 9o30’N and longitude 12o 00’E and 12o09’ with an areal of about 172. 05 km2. The area is bounded to the east by the Ngurore Town to the North by the Benue River and to the South by the Chabbai hills. The Southern part which is underlain by the Bima Formation is characterized by high relief. The Northern part constitutes the flood plain of the Benue River, and is characterized by river course alluvium consisting of dark muds which show prominent desiccation cracks during the dry season. The topography thus slopes uniformly from hilly south towards the flood plains in the north (see Fig 1)

Soil types of the area are composed predominantly of sandy loam and sandy clay, which vary from the high lands to low lands. The sandy loams are continuously encountered on the southern portion underlain by the Bima Formation. The sandy clays are the main soil type in the northern part consisting of the flood plain of the Benue River.

The study area lies within the tropical semiarid climatic region and hence consists of wet and dry seasons. The wet (rainfall) season starts in April and end on October. The mean annual rainfall in the area is 1003.5mm. The dry season commences on November and ends in March. The average maximum recorded temperature is 39. 9oC, while the hottest months are March and April. The trees, rocks and soil in the area have been affected by physical and chemical weathering (denudation). The entire area is mostly covered with weathered materials of residual soils which is underlain by Bima Formation. This means that the strength of the sandstone has been greatly reduced by weathering (Fig.2).

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G.I Obiefuna et al.,: Continental J. Earth Sciences 5 (1): 20 - 31, 2010

GEOLOGY OF THE AREA For the purpose of stratigraphic correlation, the Benue Trough was divided by Cratechley and Jones (1965) into an Upper Benue Trough, Middle Benue Trough, and Lower Benue Trough. The area falls within the Yola Arm of the Upper Benue Trough which is believed to have been formed by wrenching faults tectonics and filled with cretaceous sediments. Stratigraphical Sequence of the Yola Arm. According to Carter et al., (1963), the stratigraphic sequence of the Upper Benue Trough begins with Albian to Cenomanian epochs. It has a varied thickness from 0.5km to about 4.6km (Offoegbu, 1988). Overlying this is a transitional deposit named the Yolde Formation showing both marine and continental characteristics. Cenomanian Yolde Formation which shows intercalation of sandstone, limestone and shale is overlain by Dukul, Jessu, Sekule and Numanha Formations which are thought to be lateral equivalents of the Pindiga Formation in the Gombe Sub-basin. The Dukul Formation is a limestone shale sequence which marks the beginning of a wide-spread shallow marine transgression during Turonian and coincides with the lower end of the Pindiga Formation in Gombe Sub-basin. The Jessu Formation is the continental equivalent (regression) of the Pindiga Formation. it consist of sandstones, sandy mudstones, shales and lime-stones. Numanha Formation is dominantly marine and is composed of shales mudstones, sandstone and limestone. The lower part consists of grey to black shales with nodular mudstones and contemporaneous lava flows. The Maastrichtian witnessed the deposition of the carbonaceous Lamja Sandstones in the Yola Arm, a lateral equivalent of the Gombe sandstone intercalated with siltstone and shale with poor quality coal in the Upper Part. Thus, capping the Yola Arm, are the Paleocene basaltic flows with the Kerri-kerri Formation terminating the stratigraphy of the Gombe Sub-basin. The Bima Formation. The Bima Formation which is at the base of the stratigraphic sequence in the Yola Arm and currently the most highly studied underlies the study area. It consists essentially of two sedimentary units. These are the Albian Bima Formation found largely in the Southern part and the Quaternary River course alluvium, which dominates in the Northern part of the area. The Bima Sandstone has been weathered in places to loose sands deposits. The river course alluvial deposits are characteristised by sands, clays silty-clay and pebbly sands.

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G.I Obiefuna et al.,: Continental J. Earth Sciences 5 (1): 20 - 31, 2010 According to Braide (1992), the Bima Formation in the Yola Arm, form a coarsening upward (fining upward) sequences. The coarsening upward sequence is more common in the conglomerates on the margin of the basin and range in thickness between 20-30m. The coarsening upward sequence and fining upward sequence is interpreted as an alluvial fan system which reflect fan –lobe, caused by vertical movements of the basin floor, while the fining –upward sequence are thought to be due to the auto cyclic shifting. The Bima Sandstone comprises of solely clastic sediments laid down under non-marine conditions and according to Offoegbu (1988), varies in thickness from about 0.5km to 4.6km. It can be divided into three members. Bima 1, Bima 2, and Bima 3, but Bima 1 member out-crops only in the core of the Lamurde Anticline South of Kaltungo in-lier (Braide, 1992). According to Offodile (1976) however, the thickness varies from 100m-3000m with its maximum development at the Lamurde Anticline, where the thickness exceeds 3000m. The Bima 1 member is said to be comprised of about 400m of sandstone and argillaceous rocks. The Bima 2 is made of 800m of coarse sandstones interbedded with clays and shales, while the Bima 3 which is at the top has a thickness of about 1700m and comprised essentially of coarse sandstone.

Field observation in the area shows that the Bima Sandstones outcrops in many locations in the southern portion. The rock outcrops do not show clear sections which hindered determination of thickness of deposits. The rock appear light brown to pink in colour Both primary and secondary sedimentary structures abound in the area. The rocks indicate cross stratification or beds which are mainly tabular structures consisting of planer beds having regular contacts with basal surfaces. Results of petro-graphic analysis indicate that sandstone is composed essentially of orthoclase feldspar, quartz with iron oxides occurring as cementing materials. The iron cement gave the rocks their characteristics pinkish colour. The percentage of orthoclase in the rock is greater than that of quartz, thus indicating lack of maturity of the sediments.

Yolde Formation The Yolde Formation is a variable sequence of sandstone and shale which mark the transition from continental to marine environments. The base of the Formation is defined by first the appearance of marine shale and at the top, the disappearance of sandstone and the commencement of limestone shale deposition. The type of section occurs in Dadiya anticline and is exposed in the stream at Yolde, where 166m thick sedimentary deposits were exposed. In this section, the Bima Sandstone is overlain by bedded sandstone which is followed by alternating sandy mudstone and Shelly limestone. To the east around Jessu, the Formation is represented by about 80m thick sandstones and mudstones with occasional shales and oyster beds. To the west of Yolde and Cham, soft cream massive sandstone with thin shale beds are present, where as Mona marked the occurrence of about 210m thick well bedded sandstone which is overlain by sandy mudstone with thin Shelly limestone. The Yolde Formation in the study area is believed to be in continuity with those of Bambam and Gombe area. The limestone member of the Yolde Formation is highly fractured and fossiliferous. The Formation consists of a succession of alternating flaggy fine to coarse-grained sands and sandstone, which are intercalated with clays, silts and shales. The beds dip gently to the west beneath younger rocks.

In Numan area, the Yolde Formation consist of cyclically bedded shale limestone-siltstone and sandstone units with each cycle beginning with shale of the base passing upword through siltstone to sandstone. The shales and sandstone unit are best developed in the sampled Numan boreholes which attained a total thickness of about (210m). The lower 25m consist of course to medium grained poorly sorted Bima Sandstone which is overlain by cyclically bedded shale, lime-stone, siltstone and sandstone facies of the Yolde Formation. HYDROGEOLOGY. The area consists of two Formations namely; the Yolde and Bima Formation. The Yolde Formation overlies the Bima sandstone and consists of 150m of thinly bedded sandstones, followed by alternating mudstones and Shelly lime-stones. The Yolde Formation is a more promising water bearing formation than the Bima sandstone. Aquifers of the Yolde Formation have given better and reliable yields than those of the Bima Sandstone. Yields of up to 4 lit/sec have been obtained at Gombe and Numan. The water normally occurs under water table condition. However in some places clay beds provide confined artesian or sub-artesian conditions.

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G.I Obiefuna et al.,: Continental J. Earth Sciences 5 (1): 20 - 31, 2010 In the Lau Sedimentary basins, a number of successful boreholes have been drilled into the Yolde Formation, (Offodile, 1992). The Bima Sandstone host aquifers that occurs mainly under water table to semi-confining conditions. Most lithologic logs reveal clays and shales or sandy shale horizon, in a predominantly sandstone lithology. These clays or sandy clay horizon occur as lenses. The saturated thickness of the aquifers ranges from 3m to 206m with mean value of 140.9m. The depth to static water level in the aquifer range from O.61m to 16.93m in the hand dug wells during the rainy season and between 1.06m and 24.50 during the dry season (IShaku and Ezeigbo, 2000)

The hydraulic conductivity (k) values of the aquifers ranges from 1.63x10-4 cm/s to 9.6x10-2 cm/s whereas transmissivity (T) Values range from 8.13x10-6m-2 to 3.23x10-3m-2 in boreholes in the area (Ishaku and Ezeigbo, 2000). METHODOLOGY This research work started with a field reconnaissance survey at point where road failures were noticed. This was achieved with the aid of a topographic map of the area. Pictures of the failure portion or point were taken. Soil samples were collected at grade, sub base and base levels, with the use of geologic equipments such as geologic hammer, measuring tape, chisel and sample bags for carrying the samples. Five samples were collected at five different pits at sub-surface levels. Before taking the samples, the faces of the soil were scrapped to remove long exposed Oxidized materials to enable the collection of fairly fresh samples. Soil samples were collected at base, sub base and grade levels, which were taken to the laboratory for geotechnical analysis. These include the Atterberg limit test, California Bearing Ratio test, compaction test and particle size distribution test. All samples were air dried and lumps broken using a rubbered pistle. This was done to stimulate as much as possible the field condition especially as it affects the use of soil in road construction. Table 1 indicates (a) Sieve analysis test result for Numan and its environs (b) Atterberg limit test result, (c) California bearing ratio test result and (d) Compaction test, for the various places in Numan area where the samples were collected. RESULTS AND DISCUSSION For Numan Town, the result indicated the proportion passing BS Sieve No.200 of the sieve analysis to be 36.4%. The BS sieve, indicate a plastic limit value of 29.0% and liquid limit value of 51%, giving a plasticity index value of 21.10 and consistency index of 2.16. A California bearing ratio value of 8% was revealed where as at the optimum moisture content of 11.6%, a maximum dry density of 1.91g/cm3 was recorded as shown in Table 1. These results are indicative of sub-grade/filling material. Figures (3a &3b).indicate the plotted graphs of CBR and compaction tests for Numan Town. At Imbru site, the grain size analysis indicates that the proportion passing the BS sieve No 200 was 39.0%. The AtterBerg limit results indicate the plastic limit value of 15.5% with a liquid limit value of 30%, giving a plasticity index of 14.5 and consistency index value of 1.6 respectively. The CBR test indicate a value of 14%, where as at the optimum moisture content of 9.9%, the maximum dry density value of 1.96g/cm3 was recorded (Table 1). These results are indicative of sub-grade/filling material. For New Demsa, the results indicate the proportion passing BS Sieve NO 200 of the sieve analysis to be 29.44%. The same area indicate plastic limit value of 23.7% and liquid limit value of 43%, giving a plasticity index of 19.3 and consistency index of 1.87 respectively A California Bearing Ratio value of 16% was revealed, whereas at the optimum moisture content of 8.6%, the maximum dry density of 1.97g/cm3 was recorded (Table 1). Therefore based on the recommendation of American Association of State Highways and Transportation (AASHTO), the soil in New Demsa site is suitable for use as sub-grade/filling material.

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G.I Obiefuna et al.,: Continental J. Earth Sciences 5 (1): 20 - 31, 2010 For Farei site, the grain size analysis results indicate that the proportion passing the BS sieve No 200 was 20.92%. The Atterberg limit result indicate a plastic limit value of 23.3% with a liquid limit value of 44%, giving a plasticity index of 20.4 and consistency index of 1.91 respectively. Thus, at the optimum moisture content of 7%, the maximum dry density value of 20. 08g/cm3 was recorded. The average California Bearing Ratio (CBR) was 24% (Table 1). These results are indicative of a soil that is suitable for use as sub-grade/filling materials according to the American Association of State High ways and Transportation Official (AASHTO). The result of sieve analysis at Dowaya site, indicate the proportion of samples passing Bs No 200 to be about 38.04%. The Atterbrg limit result indicate the a plastic limit value of 24.9% with a liquid limit value of 47%, giving a plasticity index of 2.2 and consistency index value of 1.46. Furthermore at the optimum moisture content of 11%, a maximum dry density value of 1.96g/cm3 was recorded. The average California Bearing Ratio value was 16% (Table 1). These results are thus not indicative of sub-grade/filling material and sub-base material according to AAHTO and BS recommended limit. The tests result indicate that the soil at Numan town, New Demsa, Farei and Imbru are suitable for use as sub-grade/filling while the soil at Dowaya site is not suitable for use as sub-grade filling and sub-base material. However some parts of the roads at the three sites (Numan town, New Demsa, Farei and Imbru failed probably because of poor work done during construction. The road at Dowaya site failed probably because the values of result exceed the Bristish standard Institution (BS) and (AASHTO) recommended limits (Pictures 1,2,3,4 and plotted graphs (Figures 3a,b, 4, 5a,b, 6a, b) CONCLUSION AND RECOMMENDATION. Geotechnical analyses of some soils in Numan area were carried out. The soils were sampled at grade, sub-based and base levels at New Demsa, Farei, Dowaya, Numan Town and Imbru respectively. The study area is underlain by river course alluvial deposits, the Yolde Formation, and the Bima Formation. Geotechnical test such as Atterberg limits tests, grain-size distribution, compaction test and California Bearing Ratio test were carried out and used to analyse the soil in the study area. This was done to determine their suitability for use as sub-grade/filling material and sub-base material for road construction. The results of the analysis indicate that soil of New Demsa, Numan Town and Imbru are suitable for use as Sub-grade/filling materials, while that of Dowaya is not suitable for use as sub-grade/filling and sub-base material. This is probably the cause of the failed road at Dowaya. The importance of soil laboratory test/quality control test cannot be relegated to the background. This is because they serve as a means for the Engineers, Geologist and scientists to determine the suitability of various soils for construction purpose. Experts such as Geologists and Engineers should be involved or employed as consultants for the determination of soil nature and properties during construction. This is because soils should under-go various tests according to laid down procedures. Finally professional Engineers should always supervise the construction of roads in order to make sure that proper and specified materials are used. REFERENCES Braide, J.P (1992): Sedimentation and tectonics of the Yola Arm of the Benue Trough, Facies Adritecture and their provenance significant. Journal of mining and Geology. 28(1):23-32 Carter J.B; Barber, W.T. and Jones,G.P (1963): The Geology of part of Adamawa, Bauchi and Borno Province in North Eastern Nigeria, Geological Survey Nigeria Bull. 30 p109. Cratchley, C.R and Jones, G.P (1965): An interpretation of the geology and gravity anomalies of the Benue Valley, Nigeria. Overseas Geological surveys. Geophysical paper1 PP26 Earquhar, O.C (1980): Geologic Processes affecting the stability of rock slopes along Massachusetts highways. Eng. Geology 16:133-145

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G.I Obiefuna et al.,: Continental J. Earth Sciences 5 (1): 20 - 31, 2010 Eziegbo H.I and J.I.Ishaku (2000): On the longevity of Boreholes/water wells in Yola Area North- Eastern Nigeria. Journal of Nigerian Association of Hydrogeologists 11(2):39-48 Falconer, J.D. (1911): The Geology and Geography of Northern Nigeria. McMillan Publishers London P.295. Head, K.H (1988): Manual of soil laboratory testing, vol.2, Plymoth Devon. pp747. Obiefuna, G.I, A.Nur, A.U. Baba and N.E. Bassey (1999): Geological and Geotechnical Assessment of selected gully sites in Yola Area, North –East Nigeria, Journal of Env. Hydrology San Antonio. Vol.7 paper 6. Offodile M.E (1976): A Review of Geology of Benue Trough Inc. C.A.Kogbe, (Ed) Geology of Nigeria, Elizabeth Press Lagos pp315-330 Offoegbu, C.O. (1988): A review of the geology of the Benue Trough of Nigeria Journal Afr. Earth Science 15: 283-291 Offodile, M.E (1992): Approach to Groundwater study and Development in Nigeria. Mecon Services Limited PP 74-77. Okagbue, C.O and Uma, K.O (1988): The impact of geology on the performance of a bituminous surfaced pavement; a case study from southeastern Nigeria Journal of African Earth science (17) (1)157-164 Weinert H.H. (1968): Engineering petrology for roads in South Africa Eng. Geol. 2 (6) 363-395.

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G.I Obiefuna et al.,: Continental J. Earth Sciences 5 (1): 20 - 31, 2010

TABLE1: SUMMARY OF RESULTS OF SOIL TEST MIN THE STUDY AREA

S/N Location Sieve Analysis Result (proportion passing BS sieve No 200) (%)

ATTERBERG LIMIT COMPACTION

Plastic limit (%)

Liquid limit (%)

Plasticity index

Consistency index (%)

Califonia bearing ratio (%)

OMC (%)

MDD g/cm3

1 Numan 36.7 29.9 51 21.1 2.16 8 11.6 1.91 2 IMBRU 39.02 15.5 30 14.5 1.66 14 9.9 1.96 3 NEW

DEMSA 29.44 23.7 43 19.3 1.87 16 8.6 1.97

4 FARAI 20.92 23.3 44 20.4 1.91 24 7.0 2.08 5 DOWAYA 38.04 24.9 4.0 22.1 1.46 16

11.0 1.96

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G.I Obiefuna et al.,: Continental J. Earth Sciences 5 (1): 20 - 31, 2010

Fig. 3a: A PLOT OF CBR FOR NUMAN TOWN

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G.I Obiefuna et al.,: Continental J. Earth Sciences 5 (1): 20 - 31, 2010

FIG. 3B: A PLOT OF COMPACTION FOR NUMAN TOWN

FIG 4: A PLOT OF COMPACTION FOR NEW DEMSA

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G.I Obiefuna et al.,: Continental J. Earth Sciences 5 (1): 20 - 31, 2010

FIG 5A: A PLOT OF CBR FOR FARAI

Fig 5B: A PLOT OF COMPACTION FOR FARAI

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G.I Obiefuna et al.,: Continental J. Earth Sciences 5 (1): 20 - 31, 2010

FIG 6A: A PLOT OF CBR FOR DOWAYA

FIG 6B: A PLOT OF COMPACTION FOR DOWAYA

Received for Publication: 30/01/10 Accepted for Publication: 02/04/10 Corresponding Author G.I Obiefuna

Department of Geology, Federal University of Technology, Yola, Nigeria

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Continental J. Earth Sciences 5 (1): 32 - 41, 2010 ISSN: 2141 - 4076 ©Wilolud Journals, 2010 http://www.wiloludjournal.com

ASSESSMENT OF GEOTECHNICAL PROPERTIES OF MIGMATITE-DERIVED RESIDUAL SOIL FROM ILORIN, SOUTHWESTERN NIGERIA, AS BARRIER IN SANITARY LANDFILLS

Olusegun O. Ige

Department of Geology and Mineral Sciences, University of Ilorin, P.M.B 1515, Ilorin, Nigeria. Email: Vickyige2002@Yahoo.Com

ABSTRACT This study investigates the geotechnical properties of a migmatite - derived soil from southwestern Nigeria for its potential use as barrier in sanitary landfill. The required parameters for soils to be considered as barrier such as grain size distribution, Atterberg consistency limits, maximum dry density (MDD) and the coefficient of permeability were determined. Results obtained show that the hydraulic conductivity is lower than the suggested limit (1 x 10-7cm/s) of the various waste regulatory agencies. In addition, it has adequate basic geotechnical properties, strength and the shrinkage potential upon drying. These properties suggest the potential suitability of the soil as a barrier in containment facility for disposal of waste material. KEYWORDS: Barrier, Hydraulic conductivity, Residual soil, Unconfined shear strength

INTRODUCTION Waste material in waste containment facilities are made isolated from the surrounding environment by providing liners barriers. The barrier is to control or restrict the migration of pollutant into the environment. Commonly use barriers are composed of natural inorganic clays or clay soils. The low hydraulic conductivity of the compacted clayey soils combined with their availability and relatively low cost make them potential materials to use as barriers in sanitary landfills for environmental protection. Since it is desirable for containment system to achieve its purpose at minimum cost; careful consideration should therefore be given to the choice of materials for the construction of the barrier. The environmental and health hazards associated with “unengineered” landfills are well known (Ige, 2003; Asiwaju-Bello and Akande, 2004; Onipede and Bolaji, 2004, and Fred and Anne, 2005). In the U.S.A, Fred and Anne (2005) asserted that 75% of unengineered landfills pollute adjacent water body with leachate. This is because deposited waste undergoes degradation through chemical reaction thereby contaminating usable surface and subsurface water supplies. In addition, the produced leachate forms complexes with the sesquioxides of lateritic soil (Orlon and Yeroschicheva, 1967) thereby weakening their in-situ geotechnical properties (Ogunsanwo and Mands, 1999). Migmatite-derived residual soils, like other soils of basement complex origin, are widely distributed over the country. Its traditional geotechnical properties have been studied (Alao, 1983; Ogunsanwo, 1988, 1996, Adeyemi, 2002). The potential use of the soil will reduce cost of construction of sanitary landfills and encourage friendly environment. However, for soil usefulness as barrier, certain recommendations have been proposed by several previous investigators (e.g ÖNORM S 2074, 1990; Daniel, 1993; Bagchi; 1994, Benson et al, 1994,Benson and Trust, 1995 and Ogunsanwo, 1996). See Table 1 for the list of some of the required geotechnical parameters with the recommendations. Also minimum unconfined pressure of 200kPa (Daniel, 1993) and volumetric shrinkage upon drying of less than 4% was proposed (Daniel and Wu, 1993; Tay et al, 2001). This study aims at assessing the geotechnical properties of a migmatite-derived residual soil for potential usage as barriers in landfills. The typical tests that are generally used to investigate soil proposed as barriers in landfill such as the grain size distribution, Atterberg limits compaction, unconfined compressive strength; volumetric shrinkage and hydraulic conductivity were conducted on sample of the compacted migmatite residual soil. If on the basis of these tests, the soil proves to have properties desirable for a barrier material, then it should be considered as a potentially suitable material for the isolation of waste material in sanitary landfill.

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Olusegun O. Ige: Continental J. Earth Sciences 5 (1): 32 - 41, 2010 BARRIER IN SANITARY LANDFILLS Barriers are natural clayey soils or artificial (geomembrane) impermeable materials used in sanitary landfills to prevent migration of waste leachate into groundwater body. The barrier is placed within the top sealing system to prevent percolation of run-off and precipitation into the waste column and within the bottom sealing system to prevent migration of generated leachate into the groundwater bodies (Fig. 1). Different types of seals such as clayey soils, synthetic membranes (artificially manufactured mixtures: bentonite, asphalt, cement) have been extensively studied by Bagchi (1994). The choice of residual migmatite-derived soils is emphasized in this report because of its natural occurrence and abundance at the studied locality. MATERIALS AND METHODS The material used for this study was migmatite-derived residual soil. The soil was obtained from the bottom of a waste disposal landfill, 2.4km along Ita-Amo/Peke road in Ilorin, Nigeria. The already excavated surface for the purpose of waste disposal prevents the interaction of humus soil, plant roots with the sampling depth and provides good access for soil sampling. The sample was collected into a plastic bag and transported to the soil laboratory of the Yaba college of Technology, Yaba, Lagos. The basic test such as specific gravity, particle size distribution and Atterberg limits of the soil were performed according to British Standard (BS 1377:1990). The data of these index properties were used to classify the soil following the Unified Soil Classification System (USCS) classification.

SAMPLE PREPARATION The soil was air dried and crushed into small pieces. The crushed sample was then sieved through 4.75mm opening. The sieved soil was wetted with tap water (PH= 7.4) then the moistened soil was sealed in a plastic bag and stored for 3 days to allow moisture equilibration and hydration (BS 1377, 1990). The soil was later used for other geotechnical tests. The tests were conducted in duplicate for each particular soil condition to ensure the reliability of the test result. The average result of the two tests is presented in this report. The soil was compacted with two different Proctor energies (modified and standard) which represent the commonly used energy of compaction on the field as recommended by Daniel and Benson (1990) and Daniel and Wu (1993). The hydraulic conductivity was measured using the rigid-wall permeameter under falling head condition as recommended by Head (1994). Compaction was carried out on the soils at two different energies under different water contents within the permeameter moulds. The permeant liquid was tap water and hydraulic gradient was 15. Permeation was conducted on the sample until steady condition was achieved. The volumetric shrinkage upon drying was measured by extruding compacted cylindrical specimens from the compaction mould and allowing the cylindrical specimen to dry on the laboratory table on an air-condition room (Daniel and Wu, 1993). Everyday the diameter and the height of samples were recorded with a digital caliper (accuracy 0.01). At each reading a minimum of three heights and three diameter measurements for each height at interval were recorded. The average diameter and height were used to compute volume, and the measurements were continued until the volume seized to change further. The unconfined compression test was performed in accordance with the BS 1377: 1990 procedures. The tests were performed on cylindrical specimens having a diameter and length of 50mm and 100mm respectively, which were trimmed from the larger compacted cylinders.

RESULTS AND DISCUSSION Several limits have been proposed by various researchers with respect to the geotechnical properties of soil to be useful as barrier. Such limits are presented here along with the results obtained from this study. Grain Size Distribution The specific gravity of the granite residual soil is about 2.73. The particle size analysis shows that the soil contains 53% clay (<0.002mm), 70% fines (<0.075mm), 35% sand. Moreover, the results of Atterberg limits reveal the liquid limit (LL) is 68%, the plastic limit (PL) is 35% and the plasticity index (PI= LL- PL) is 33%. On the basic of these data, the migmatite residual soil is classified as CH (Inorganic clay with high plasticity) according to the USCS. Inorganic clay with high plasticity (CH) is recommended for landfill liner (Oweis and Khera, 1998). The soil has similar properties to cohesive soils, and therefore is likely to have desirable characteristics to minimize hydraulic conductivity. The hydraulic conductivity value of the liner material is used as the principal indicator of its

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Olusegun O. Ige: Continental J. Earth Sciences 5 (1): 32 - 41, 2010 containment potential. Hydraulic conductivity behaviour of soil barrier is greatly influenced by the particle size distribution because the relative proportions of large and small particle sizes affect the size of voids conducting flow (Kabir and Taha, 2006). Barrier soils should have at least 30% fines (Daniel 1993b; Benson et al; 1994) and 15% clay (Benson et al, 1994) to achieve hydraulic conductivity ≤ 1×10-7 cm/s. Thus, the migmatite-derived residual soil can be used as barrier to achieve a hydraulic conductivity ≤ 1×10-7 cm/s, as it possesses suitable amount of clay and fine fractions. Moreover, the soil contains adequate amount of sand, which may offer notable protection from volumetric shrinkage and impart adequate strength as well. Liquid limit is an important index property since it is correlated with various engineering properties. Soils with high liquid limit generally have low hydraulic conductivity. Benson et al (1994) recommended that the liquid limit of the liner material be at least 20%. However, soils with very high liquid limit have poor volume stability and high shrink-swell potentials (Kabir and Taha, 2006). Most of the specifications for soil liners proposed by various researchers or waste regulatory agencies do not generally prescribe any limit (maximum value) for their liquid limit. As long as it does not create any working problem, soils with high liquid limit are generally preferred because of their low hydraulic conductivity. Thus, the migmatite residual soil with liquid limit of about 68% appears to be promising for use as barrier. The plasticity index is one of the most important criteria for the selection of soils as barrier in sanitary landfill construction. It is the key property in achieving low hydraulic conductivity. Literatures suggest that the plasticity index must be more than 7% (Daniel 1993; Benson et al; 1994; Rowe et al, 1995). However, extremely high plasticity soil becomes sticky when wet and then becomes difficult to work with in the field. Also high plasticity soil forms hard lumps when they are dry and are difficult to break down during compaction. The hard lumps, if not properly compacted, form zones of higher hydraulic conductivity. Moreover, a high plasticity soil tends to be more susceptible to desiccation cracking. For plasticity index value greater than 65, excessive shrinkage can be expected (Daniel, 1991). Thus, the migmatite residual soil has suitable plasticity property (PI is about 33%) to minimize hydraulic conductivity and shrinkage susceptibility as well. The activity (PI/% clay fraction) of migmatite residual soil is about 0.62. Thus, according to Skempton’s classification it is inactive clay. Inactive clayey soils are the most desirable materials for compacted soil barrier (Rowe et al, 1995). In order to achieve a hydraulic conductivity ≤ 1×10-7 cm/s for the soil barrier, soil with an activity of > 0.3 has been specified (Benson et al, 1994, Rowe et al, 1995). An activity is an index of the surface activity of the clay fraction. Soils with higher activity are likely to consist of smaller particles having larger specific surface area and thicker electrical double layers (Kabir and Taha, 2006). Therefore, hydraulic conductivity should decrease with increasing activity. However, soils with higher activity are more readily affected by chemical pollutant if they are used in containment structures (Oweis and Khera, 1998). Thus, the comparison between the index properties of migmatite-derived residual soil and the index properties as recommended by various researchers for a good barrier material shows that the investigated migmatite residual soil has suitable properties to use as barrier material. COMPACTION PROPERTIES. In the construction of barriers, compaction is done to achieve a soil layer of improved engineering properties. Compaction of soil results in homogenous mass that is free of large, continuous inter-clods voids; increase their density and strength, and reduce their hydraulic conductivity. Hydraulic conductivity is the key design parameter when evaluating the acceptability of a barrier material. Low hydraulic conductivity is achieved when the soil is compacted close to its maximum dry density and corresponding optimum water content for a soil under a specific compactive effort. The compaction curves for the migmatite-derived residual soil are shown in Fig 2. The compaction curves clearly illustrate that the dry density is the function of compaction water content and compactive effort. For each compactive effort, at the dry side of optimum water content, the dry density increases with the increasing water content. This is due to the development of large water film around the particles, which tends to lubricate the particles and makes them easier to be moved about and reoriented into a denser configuration (Holtz and Kovacs, 1981).

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Olusegun O. Ige: Continental J. Earth Sciences 5 (1): 32 - 41, 2010 Whereas, at the wet side of optimum water content, water starts to replace soil particles in the compaction mould and since the unit weight of water is much less than the unit weight of soil, the dry density decreases with the increasing water content. The curves (Figure 2) are single peaked and parabolic in shape, which is typical of most clayey soils (Kabir and Taha, 2006). This is expected since the liquid limit of the soil is between 30% and 70% (Lee and Suedkamp, 1972). The peaks represent the maximum dry density and corresponding optimum water content for a given compactive effort. The maximum dry density and the optimum water content obtained from these tests are given in Table 2. An increase in compactive effort increases the maximum dry density but decreases the optimum water content (Daniel, 1994). Because higher compactive effort yields a more parallel orientation to the clay particles, which gives a more dispersed structure, the particles become closer and a higher unit weight of compaction results (Das, 1998). Hence, a high compaction energy is preffered. Hydraulic Conductivity The relationship between hydraulic conductivity, water content and compactive effort is shown in Fig. 3. The hydraulic conductivity decreases with the increasing compactive effort because increasing compactive effort decreases the frequency of large pores and can eliminate the large pore mode (Acar and Oliveri, 1989). These changes in pore size yield lower hydraulic conductivity. The hydraulic conductivity also changes with the change of compaction water content. Soils compacted at dry of optimum water content tend to have relatively high hydraulic conductivity whereas soils compacted at wet of optimum water content tend to have lower hydraulic conductivity. Increasing water content generally results in an increased ability to breakdown clay aggregate and to eliminate inter aggregate pores (Mitchell et al, 1965; Benson and Daniel, 1990; Garcia-Bengochea et al, 1979). Moreover, increasing water content results in reorientation of clay particles and reduction in the size of inter particle pores (Lambe, 1954; Acar and Oliveri, 1989 and Benson and Trust, 1995). The hydraulic conductivity is the key parameter affecting the performance of most landfill barriers and covers (Daniel 1987, 1990 and Elsbury et al, 1990), thus great attention is generally focused on ensuring that low hydraulic conductivity is achieved. Therefore, it is usually preferred to compact the soil wet of optimum. Barriers should have a hydraulic conductivity of at least 1×10-7 cm/s. Figure 3 shows that the two different compaction efforts caused hydraulic conductivity less than 1×10-7 cm/s. The minimum hydraulic conductivity and corresponding water content at various compactive efforts is represented in Table 3. In the case of each compactive effort the minimum hydraulic conductivity is obtained at water content of slightly (0.5 to 1.7%) wet of optimum water content. Generally the lowest hydraulic conductivity of clayey soil is achieved when the soil is compacted at water content slightly higher than the optimum water content (Mitchell et al, 1965; USEPA, 1989; Daniel and Benson 1990). This characteristic makes the soil suitableas barrier in sanitary landfill. Volumetric shrinkage Compacted soil barriers are subject to frequent desiccation due to evaporative water losses. Desiccation leads to the development of shrinkage. Cracks provide pathways for moisture migration into the landfill, which increases the generation of waste leachate, and ultimately increases the potential for soil and groundwater contamination. Thus, the soil barrier significantly losses its effectiveness as an impermeable barrier. Literature suggested that cracking is not likely to occur in clay barrier when compacted cylinders of the same soil undergo less than about 4% volumetric shrinkage strain upon drying (Daniel and Wu 1993; Tay et al, 2001) In this study compacted cylindrical specimens were used to determine shrinkage potential of the soil. In the field, the soil shrinks under the overburden pressure. Soil shrinks simply due to water loss, which is independent of the pressure if water and soil particles are considered incompressible. Much information is not available on the relationship between overburden pressure and volumetric shrinkage of compacted soil. However, in this study, shrinkage tests were performed by allowing the specimen to dry at approximately 27˚C (the mean temperature in Nigeria) temperature to stimulate the slow rate of drying that occurs in the field (Briad et al, 2003). The cylindrical specimens began to shrink into smaller cylinders with volume changes occurring as the water surrounding the individual soil particles of the specimens is removed and the soil particles move closely together. During drying, the sides of the specimens were open to the atmosphere, which does not replicate the field condition. Nevertheless, the

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Olusegun O. Ige: Continental J. Earth Sciences 5 (1): 32 - 41, 2010 relative effects of soil type on volumetric shrinkage are supposed to be preserved. The result of volumetric shrinkage test is presented in Figure 4. Test results indicate that shrinkage strains are influenced by compaction conditions. Shrinkage increases with increasing compaction water content, but the relationship between compactive effort and shrinkage strain is less clear. At low compaction water contents, shrinkage decreases with increasing compactive effort. No clear trend is apparent at higher water contents. Similar results have been reported by other researchers (Klepe and Olson, 1985; Daniel and Wu, 1993). In this study, each of the two different compactive efforts shows little volume change behavior of less than 4%, which is typical maximum permissible limit for compacted clay soil barrier. Thus, if drying takes place, the compacted soil will undergo minimal shrinkage and desiccation cracking. Unconfined Compressive Strength. The result of unconfined compression test against compaction water content is shown in Figure 5. The strength of compacted soil decreases with increase of compaction water content. As the amount of water increases the electrolyte concentration is reduced, leading to an increase in diffused double layer. Expansion takes place at a distance between the clay particles as well as the distance between the aluminiosilicate unit layers increases, resulting in a reduction of both the internal friction and cohesion. Other researchers (Seed and Chan, 1959; Daniel and Wu 1993; Taha and Kabir, 2003) observed the same effect. Compactive effort has also a great influence on soil strength. At low compaction water content, unconfined compressive stress increases with increasing compactive effort. But at higher water content no clear trend is noticed: e.g at 24% compaction water content, modified Proctor effort results the lowest unconfined compressive stress among the two compactive efforts. An isolation barrier used in waste containment system is supposed to sustain certain amount of static load exerted by the overlying waste materials. In this regard, the barrier material must have adequate strength for stability. The bearing stress act on the barrier system depends on the height of landfill and unit weight of waste. Thus, the minimum required strength of soil used for compacted soil barrier is not specified. Daniel and Wu (1993) arbitrarily selected them, to support the maximum bearing stress in a landfill. They mentioned that soil used as barrier material should have minimum unconfined compression strength of 200KPa. Test result shows (Fig.5) that the soil possesses higher strength than the recommended minimum strength of 200KPa for all the three compactive efforts. CONCLUSIONS The following conclusions can be drawn form the investigation of migmatite-derived residual soil: (1) The residual soil is inorganic clay with high plasticity. Generally, this type of soil possesses desirable characteristics to minimize hydraulic conductivity, and is frequently used for the construction of compacted soil barriers. (2) The index properties (liquid limit, plastic limit, % clay content, % fines, activity etc) of the soil satisfy the basic requirements as a liner material. (3) It is inactive clayey soil. Thus, the soil will be less affected by waste leachate and less susceptible to shrinkage. (4) The soil has hydraulic conductivity of equal to or less than 1×10-7 cm/s, when it is compacted with both modified and standard Proctor compaction efforts. (5) Moreso, the soil has average strength in the range of 200KPa and volumetric shrinkage strain of less than 4%. Thus, it is concluded that the migmatite-derived residual soil can be used as a suitable barrier material for isolating waste in sanitary landfills. Its potential use as isolation barrier will enhance the waste management programs in Nigeria since migmatite derived soils are locally readily available Although the soil meets all the basic requirements as a good barrier material, it would be hard to work with due to its high plasticity. Therefore, during liner construction great attention should be focused on soil preparation. The soil should be properly blended and homogenized to achieve a mixture of relatively small clods with reasonably uniform moisture distribution.

37

Olusegun O. Ige: Continental J. Earth Sciences 5 (1): 32 - 41, 2010 ACKNOWLEDGEMENT The author is very grateful to Prof. O. Ogunsanwo, Department of Geology, University of Ilorin, for reading through the draft of this paper. REFERENCES Acar, Y. and Oliveri,.I. (1989). Pore fluid effects on the Fabric and Hydraulic Conductivity of Laboratory Compacted Clay. Transportation Research Record, 1219, 144-159. Alao, D. A. (1983): Geology and Engineering Properties of laterites from Ilorin, Nigeria. Journal of Engineering Geology. 19, 111-118. Asiwaju-Bello, Y. A. and Akande, O. O. (2004). Urban groundwater pollution: Case study of a Disposal site in Lagos metropolis. Journal of Water Resources. 12, 22-26. Bagchi, A. (1994). Design, Construction, and Monitoring of landfills. 2nd Edition. Wiley-Interscience Publication, New York, U. S. A, 361p Benson, C.H., and D.E Daniel (1990). Influence of clods on Hydraulic conductivity of compacted clay. Journal of Geotechnical Engineering ASCE, Vol.116, (8), 1231-1248. Benson, C. H. and Trust, J. M. (1995). Hydraulic Conductivity of Thirteen Compacted Clays, Clays and Clay Minerals, vol. 43, (6), 669-681. Benson, C. H; Zhai, H. and Wang, X. (1994). Estimating Hydraulic Conductivity of clays liners. Journal of Geotechnical Engineering, vol.120, 2, 366-387. Benson, C.H., D.E. Daniel, and G.P. Boutwell (1999). Field performance of Compacted clay Liners, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 125, No. 5, pp 390-403. Briad, J.L., X. Zhang, and S. Moon (2003). Shrinkage test – Water Content Method for Shrink and Swell Predictions, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, vol. 129,(7), pp 590-600. BS1377 (1990). Method of Testing soil for Civil Engineering purposes. British Standard Institute, London. Daniel, D. E. (1987). Earthen Liners for Land Disposal Facilities. Geotechnical Practice for Waste Disposal. vol.87, (13), (R.D Woods, Ed), New York, USA, ASCE, pp21-39. Daniel, D. E. and Benson, C. H. (1990). Water Content – Density Criteria for Compacted soil liners Journal. of Geot. Eng. ASCE, 116, 12, 1811- 1830. Daniel, D.E., (1990). Summary Review of Construction Quality control for Earthen Liners, in waste containment systems: Construction, Regulation, and performance, GSP, No. 26, (R. Bonaparte, Ed.), New York, ASCE, pp175-189.

Daniel, D.E., (1991). Design and Construction of RCRA/CERCLA final covers, Chapter 2: Soils used in cover systems. EPA. /625/4-91/025, US EPA,Cincinnati, Ohio. Daniel, D.E., (1993). Clay Liners, in Geotechnical Practice for Waste Disposal, (ed. David. E Daniel) Chapman & Hall, London, UK, pp 137-163. Daniel, D.E., Y.K, Wu (1993). Compacted Clay Liners and Covers for Arid sites, Journal of Geotechnical Engineering ASCE, vol. 119,(2), pp 223-237.

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Olusegun O. Ige: Continental J. Earth Sciences 5 (1): 32 - 41, 2010 Das, B.M., (1998). Principles of Geotechnical Engineering, 4th Edition, PWS Publishing Company, USA. Elsbury, B.R., D.E. Daniel, G.A. Srader, and D.C. Anderson (1990). Lessons learned from Compacted Clay Liner, Journal of Geotechnical Engineering, ASCE, vol. 116, (11), pp1641-1660. Fred, L and Anne, J. (2005). Flawed technology of subtitle D. Landfill Municipal Solid Waste. Http. www.gfredlee.com.64p. Garcia-Bengochea, I., C. Lowell, and A. Altshaeffi (1979). Pore Distribution and Permeability of Silty Clays, Journal of Geotechnical Engineering, ASCE, Vol.105, (7), pp 839-856. Head, K.H., (1994). Manual of Soil Laboratory testing- Volume 2: Permeability, Shear Strength and Compressibility Test, Halsted Press, New York, USA. Holtz, R.D. and W.D. Kovacs (1981). An Introduction to Geotechnical Engineering, Prentice-Hall, New Jersey. Ige, O.O (2003). Impact of cultural and Industrial waste on surface and shallow groundwater along Asa River, Ilorin metropolis, Kwara State, Nigeria. University of Ilorin, M.Sc., thesis, unpublished, 108p. Kleppe, J.H. and R.E. Olson (1985). Desiccation Cracking of Soil Barriers, Hydraulic Barrier in Soil and Rock, Special Technical Publication No. 874, ASTM, Philadelphia, PA, pp 263- 275. Lambe, T.W., (1954). The Permeability of Compacted fine grained soils, Special Technical Publication, No. 163, American Society of Testing and Materials (ASTM), Philadelphia,USA, pp56-67. Lee, D.Y. and R.J. Suedkamp (1972). Characteristics of Irregularly Shaped Compaction Curves of Soils, Highway Research Record, No. 381, pp 1-9. Mitchell, J.K., Hooper, D., and R. Campanella, (1965). Permeability of Compacted Clay, Journal of Soil Mechanics and Foundation Division, ASCE, Vol. 91, (4), pp41-65. Ogunsanwo, O. (1988). Basic Geotechnical Properties, Chemistry and Mineralogy of some Laterite soils from Southwestern, Nigeria. Bullettin of IAEG. 37, pp131-135. Ogunsanwo, O. (1996). Geotechnical investigated of some soils from southwestern Nigeria for use as mineral seals in waste disposal landfills. Bulletin of I.A.E.G. 54, 119-123. Ogunsanwo, O. and Mands. E. (1999): The role of geology in the evaluation of waste disposal sites. Journal of Mining and Geology vol. 33, 1, 83-87. Onipede, M. A. and Bolaji, B. O. (2004). Management and disposal of industrial wastes in Nigeria. Nigerian Journal of Mechanical Engineering. 2, 1, 49-63. ONORM S 2074 (Teil 2), (1990). Geotechnik in Deponiebau-Erdarbeiten. Osterrichisches Normungsinstitut, Wein. Orlov, D. S and Yeroshicheva, N. L. (1967): Interaction of humic acids with the cations of some metals . Soviet Soil Science. vol. 12, 1799-1806. Oweis, I.S., and R. P. Khera (1998). Geotechnology of waste management, 2nd Edition, PWS Publishing Company, USA. Rowe, R.K., R.M. Quigley, and J.R. Booker (1995). Clayey barrier systems for waste disposal facilities, E & FN Spon, London, pp 404.

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Olusegun O. Ige: Continental J. Earth Sciences 5 (1): 32 - 41, 2010 Seed, H.B., and C.K. Chan (1995). Structure and Strength Characteristics of Compacted Clays, Journal of Soil Mechanics and Foundation Division ASCE, vol. 85, (5) pp87-128. Taha, M.R., and M.H. Kabir (2003). Sedimentary Residual Soil as a Hydraulic Barrier in Waste Containment Systems, In: Proceedings of the International Conference on Recent Advances in Soft Soil Engineering and Technology, 2-4 July 2003. Putrajaya, Malaysia. Tay, Y.Y., D.I. Stewart, and T.W. Cousens (2001). Shrinkage and Desiccation Cracking in Bentonite-Sand Landfill Liners. Engineering Geology, Elsevier Science, Vol. 60, pp 263-274. U.S. Environmental Protection Agency (1989). Requirements for Hazardous Waste Landfill Design, Construction, and Closure, Publication No. EPA-625/4-89-022, Cincinnati, Ohio. TABLE 1: REQUIRED GEOTECHNICAL CRITERIA AND RECOMMENDATIONS FOR SOILS AS BARRIER

KEY: SP= Standard Proctor LL= Liquid Limit, MP= Modified Proctor, IP= Index of Plasticity Ac= Activity of clay

PARAMETERS AUTHOR(S) RECOMMENDATIONS GRAIN SIZE ANALYSES

Oeltzschner (1992) Bagchi (1994) ONORMS 2074 (1990) ONORMS 2074 (1990) Daniel (1993b), Rowe et al 1995

Clay fraction <20% Largest Grain Size ≤63mm Silt/clay fraction ≥15% Largest grain size <25mm, %Gravel <30, % fine ≥30

ATTERBERG CONSISTENCY LIMITS

Daniel (1993b); Rowe et al(1995) Seymour & Peacock (1994) Oeltzschner (1992)

LL ≥30%, IP≥15% LL ≥30%, IP≥10% LL ≥30%, IP≥15% LL ≥25%, IP≥15% LL ≥30%, IP≥15% Inorganic Clay of low –medium plasticity(CL-CI) and Ac of <1.25

MOISTURE CONTENT- DENSITY RELATIONSHIPS

ÖNORMS 2074 (1990) Kabir and Taha (2006)

MDD ≥ 1.71t/m3

MDD ≥ 1.74t/m3

COEFFICIENT OF PERMEABILITY (k)

Murphy and Garwell (1998) Mark (2002) Joyce (2003) Fred and Anne (2005)

≤1x10-9m/s ≤1x10-9m/s ≤1x10-9m/s ≤1x10-8m/s ≤1x10-9m/s

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Olusegun O. Ige: Continental J. Earth Sciences 5 (1): 32 - 41, 2010 Table 2. Maximum dry density and corresponding optimum water content.

Compactive efforts optimum water content (wopt%) max.dry density, γ(KN/m3)

Modified Proctor 20.7 16.33

Standard Proctor 26.2 14.51

Table 3: Minimum hydraulic conductivity and corresponding water content at various compactive efforts.

Compactive Efforts

Minimum hydraulic conductivity (cm/s)

Water content(%)at minimum hydraulic conductivity

Optimum water content (%)

Modified Proctor 2.2×10-8 22.2 20.7

Standard Proctor 1.4×10-7 27.9 26.2

Top Sealing System

BaseSealing System

Geotextile

Gravel Layer with dra inage

Geotextile

Polyethylene Foil

Mineral Seal

Natural underground

Recultivated soil layer

Gravel Layer with dra inage

Geotextile

Polyethylene Foil

Mineral Seal

Geotextile

Geotextile

Fig.1: Section through a waste disposal sanitary landfill (Ogunsanwo, 1996).

(Excluding Nuclear, liquid Hospital and Domestic waste)

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Olusegun O. Ige: Continental J. Earth Sciences 5 (1): 32 - 41, 2010

20

18

16

14

12

1014 16 18 20 22 24 26 28 30 32 34

Dry density (kN/m3 )

Water Content (%)

Figure 2. Compaction curves

Modified Standard

1.0E-05

1.0E-06

1.0E-07

1.0E-08

1.0E-09

14 16 18 20 22 24 26 28 30 32 34

Water content (%)

Modified Standard

Hydraulic conductivity (cm

/s)

Figure 3: Hydraulic conductivity versus compaction water content

16

141210

86

420

Volumetric shrinkage (%)

14 16 18 20 22 24 26 28 30 32 34

Water content (%)

Figure 4: Volumetric shrinkage strain versus compaction water content

Modified Standard

1000

800

600

400

200

0

14 16 18 20 22 24 26 28 30 32 34

Water content (%)

Modified Standard

unconfined com

pressive

strength (kPa)

Figure 5: Unconfined compression strength versus compaction water content

XX

X

XX

X

X

Received for Publication: 30/01/10, Accepted for Publication: 02/04/10

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Continental J. Earth Sciences 5 (1): 42 - 55, 2010 ISSN: 2141 - 4076 ©Wilolud Journals, 2010 http://www.wiloludjournal.com

THE PRINCIPAL SOURCE ROCKS FOR PETROLEUM GENERATION IN THE DAHOMEY BASIN, SOUTHWESTERN NIGERIA

Olabisi A. ADEKEYE and Samuel O. AKANDE

Department of Geology and Mineral Sciences, University of Ilorin, P. M. B. 1515, Ilorin, Nigeria.

ABSTRACT The Upper Cretaceous (Maastrichtian) Araromi Shale formation in the Nigeria sector of the Dahomey basin has been investigated for its petroleum generation potential. From three exploratory wells, Araromi, Bode Ashe and Gbekebo in the eastern end (west of Niger Delta), source rock potential has been evaluated for over one hundred (100) drill core and ditch cutting samples. The investigated shallow marine shale facies have Total Organic Carbon (TOC) value range of 0.50-4.78wt% and Hydrogen Index (HI) value range of 1-327mgHC/gTOC with the maceral composition of liptinite (av. 26.0%) and abundance of vitrinite (av. 38.1%) plus inertinite (av. 35.9%) in all the samples investigated. Vitrinite reflectance values vary from 0.51-0.68%Ro. The Tmax values vary from 398oC-437oC and the kerogen Types include type II, II/III, III, and IV in all the samples. The Source Potential (SP) values range from 0.01-14.56kgHC/ton of rock. Biomarker analysis of the shale samples generally reveal a bimodal n-alkane envelope with maxima between (nC16 and nC18) and (nC27 and nC29) suggesting that the source organic matter were derived from a variable mixture of algae and higher plant materials with q relative higher input from marine algae as reveal by the presence of the C30 24-n-propyl cholestane (%C30 sterane range from 0.45 to as high as 5.23%). The presence of organic matter of marine algae (%C27 sterane av. 52% and positive detection of C30 sedimentary n-propyl cholestane av. 3.7%) suggest that the control on the HI as an indication of source rock quality in varying level of organic matter preservation. The source rocks have predominantly gas prone with lesser oil prone organic matter ranging from immature to marginally mature at shallow levels but reaching proven mature levels in the subsurface. Hydrocarbons in the basin would be predominantly gas dominated, generated from deeper Cretaceous source rock (marine shale) in the subsurface levels with greater chances of heavy oils and tars at shallow levels. KEYWORDS: Upper Cretaceous, Hydrogen Index, sedimentary rock, petroleum generation

INTRODUCTION The search for hydrocarbons in the Cretaceous source rocks in the Nigerian in land sedimentary basins has been a major task for many decades now. The efforts were to bust the oil and gas exploration and production activities and also adequately tap the natural resources in the country. Geoscience research in the aspects of hydrocarbon search in the Nigeria sector of the Dahomey basin has been so few for many years. In the last decade, there have been considerable interest and geosciences researches in the aspects of hydrocarbon search in the basin. Recent exploration and prospect re-evaluation efforts in the Nigeria segment of the basin have been encouraged following oil discovery and production in the neighboring Benin republic sector west of the basin and the social unrest in the prolific Niger Delta, east of the basin. The Dahomey basin is an extensive sedimentary basin in the Gulf of Guinea. It extends from southeastern Ghana through Togo and Benin Republic on the west side to the Okitipupa ridge/Benin Hinge line on the west of Niger Delta. Shale samples (drill cores and ditch cuttings) for this study came from the Araromi and Gbekebo wells drilled in the eastern part of the Dahomey basin, southwestern Nigeria (Fig. 1). The drill core samples were collected from Geological Survey of Nigeria Agency (GSNA), Kaduna main office. This work is to contribute to the geosciences research and data generation activity by assessing and documenting the organic geochemical parameters and hydrocarbon generation potential of the Araromi shales in the Nigeria sector of the Dahomey basin. This paper will also throw more light on the possibility of Cretaceous sourced oil in the overlying prolific Tertiary Niger Delta which is at the eastern side of the basin.

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010 Geological setting The break-up of the Gondwanaland as a result of “continental drift” led to the subsequent opening of the South Atlantic Ocean during the Mesozoic Era (Stoney, 1995; Mpanda, 1997). This event is also connected to the evolution of the Dahomey Basin. Several hypotheses have been developed as to the origin and evolution of the basin. The rift hypothesis is widely supported, on the basis of several salient features characterising the basin. During the rifting stage in the Lower Jurassic – Early Cretaceous, there was basement fracturing and initial separation between the African and South American plates. At this time, several marginal basins developed consequent to block faulting, fragmentation and subsidence on the central Paleozoic basement rock (Asmus and Ponte, 1973; Ojeda, 1982; Omatsola and Adegoke, 1981). The early movements were in the Early Cretaceous when there was transcurrent movements on the oceanic fracture systems especially the Romanche, Chain and Charcot fractures during the drifting stages of separation of South America from Africa in the Campanian to Tertiary times. Consequent to the opening of the South Atlantic Ocean, there was landward extensional and transtensional movement (drift stage) during the Upper Cretaceous to Tertiary. Horizontal movements along the oceanic fracture zones were translated to vertical movements leading to block faulting and subsequent development of horsts and grabens (Omatsola and Adegoke, 1981). Adediran and Adegoke, 1987 proposed a four stage evolutionary model for the Gulf of Guinea basin (Dahomey Basin inclusive); as follows: Stage 1 – The deposition of thick clastic sediments mostly immature sandstones and fresh water shales in the intracratonic basin. Stage 2 – Reworked sands and silts intercalated with shales of fluviatile – lacustrine origin deposited within the grabens during a period of tectonic activity, erosion and sedimentation. Stage 3 – Paralic sequence (in the northern basins) and evaporitic deposits (in the southern basins) marking the beginning of marine incursion into the basin after the separation of South America from Africa. Stage 4 – Marine sediments rich in fauna and flora marking the final stage of the development of the Gulf of Guinea basins. The stratigraphic setting of the Dahomey Basin has been described in detail in the works of Adegoke, 1969; Ogbe, 1970; Kogbe, 1974; Billman, 1976; Omatsola and Adegoke, 1981; Ako et al., 1980; Okosun, 1990; Adekeye, 2005 and Adekeye et al., 2006. These authors reported five lithostratigraphic formations covering the Cretaceous to Tertiary ages. The formations from the oldest to the youngest include: Abeokuta Group comprises of Ise, Afowo and Araromi formations (Cretaceous), Ewekoro Formation (Paleocene), Akinbo Formation (Late Paleocene-Early Eocene), Oshosun Formation (Eocene) and Ilaro Formation (Eocene) Fig.2. Substantial amount of sediments were deposited in fault-controlled depressions in the Dahomey Basin during the Late Cretaceous. Post Santonian marine transgression accompanied the subsidence and drowning of continental margins, which brought about the deposition of very thick sequence of continental grits and pebbly sands over the entire basin (Lehner and Ruiter, 1977). In some places, mudstones and shales with thin limestone beds were formed. This lithostratigraphic formation is referred to as Abeokuta Group comprising Ise, Afowo and Araromi formations (Omatsola and Adegoke, 1981). A continuation of the marine transgression during the Paleocene led to the deposition of shallow marine limestones of the Ewekoro Formation and the shales of the Akinbo Formation (Ogbe, 1970; Okosun, 1990). On top of the Paleocene sequence is the Eocene shales of the Oshosun Formation and the sandstones of the Ilaro Formation (Okosun, 1990; Idowu et al., 1993).

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010 Sample Material and Laboratory Analyses

A. Hydrocarbon Source Rock Potential Representative core samples of the Late Cretaceous Araromi Formation in the Dahomey Basin, SW Nigeria were collected from the Araromi and Gbekebo wells (Fig. 1) drilled on the eastern margin of the basin where it shares a border with the western Niger Delta. The samples were analysed for their total organic carbon content (TOC) and hydrocarbon source quality by Rock-Eval Pyrolysis using standard experimental techniques. Bitumen extracts from selected organic rich source rock samples were analysed for their biomarker and stable carbon isotope composition of n-alkanes using the GC, GC-MS and GC-MS-MS techniques described below. Selected shale samples were crushed to less than 2mm and impregnated in epoxy for qualitative reflected light microscopy. Where organic constituents are sparse, kerogen concentrates were prepared, mounted and polished. Organic petrology studies were carried out on a Reichert Jung Polyvar Photomicroscope equipped with halogen and HBO lampa, a photomultiplier and computer unit at the Zentraleinrichtung fur Elektronemikroskopie (ZELMI), Technische Universitat Berlin, Germany. Mean random reflectance of vitrinite in oil (Ro%, cf. Bustin et al., 1983) was calculated from the reflectance of at least 30 grains of vitrinite measured in random orientation using monochromatic (546nm) non-polarised light in conjunction with a x40 oil immersion objective. Calibration of the microscope photometer was achieved using standards of known reflectance (1.23 and 3.16%). Measured Rom values of reflectance standards confirmed the photomultiplier to be consistently linear within the range of the measurements. Data collection and evaluation were done using the coal programme by Reichert Jung and macerals were identified through the use of white light and blue light excitation at 546 and 460nm respectively. The mean reflectance as compared to the median or modal reflectance appear to be an adequate measure of thermal maturity in this study (Tissot and Welte, 1984; Pollastro and Barker, 1986). The rock Eval pyrolysis was carried out at the Organic Geochemistry Laboratory of the Department of Mineralogy, Geochemistry and Petrology, University of Szeged, Hungary following the standard procedure of Rock Eval pyrolysis experimentation on Rock Eval II machine. The Rock-Eval II pyroanalyses has the ability of measuring the total organic organic carbon (TOC) content on the pulverized samples at elevated temperatures of ca. 600oC (Espitalie et al., 1977). Pyrolysis of 10-40mg of samples at 300oC for 4mins was followed by programmed pyrolysis at 25oC/min to 550oC in an atmosphere of helium.

B. Biomarker Gas chromatography was performed on the saturated hydrocarbon fractions in order to obtain n-alkane and isoprenoid data as well as to determine sample concentration and complexity before GC-MS and gas chromatography-isotope ratio mass spectrometry (GC-IRMS) analyses. An HP 5890 series II gas chromatograph equipped with an HP-5 coated capillary column (60m x 0.25mm, 0.25µm film thickness) was used. The GC oven was initially set at 50°C for 2 min. and then the temperature was ramped from 50°C at 4°C/min to 300°C and held at final temperature for 20 minutes with hydrogen as the carrier gas (flow rate approx 2ml/min and initial pressure of 100kPa). Gas chromatography-mass spectrometry (GC-MS) and gas chromatography-mass spectrometry-mass spectrometry (GC-MS-MS) analyses of saturated hydrocarbon fractions were performed on a Varian CP3800 GC split/splitless injector (280C) linked to a Varian 1200 triple quadrupole mass spectrometer (electron voltage 70eV, filament current 50uA, source temperature 230°C, quad temperature 40°C, multiplier voltage 1400V, interface temperature 300°C). After addition of 5β-cholane internal standard, the samples were analysed in scan mode (50-550 amu/sec) or selected ion monitoring mode (SIM) for 30 ions (dwell 35ms per ion) or in MS-MS mode where up to 8 parent/daughter transitions could be monitored, using argon as the collision gas at a pressure of 2mTorr and with a collision energy of -10ev. The sample (1µl) in dichloromethane was injected by a Varian CP8400 autosampler and the split opened after 1 minute. Separation was performed on a fused silica capillary column (60m x 0.32mm i.d) coated with 0.25um methylsilicone (HP-1). The GC was temperature programmed over 3 ramps from 4°C-300°C ( 40°C-75°C at 10°C/ min, held for 1min at 175°C, followed by 175°C-225 °C at 6 °C/min and held for 1 min at 225 °C, and 225-300 at 4 °C/min) and was held at final temperature for 20 minutes with helium as the carrier gas (flow approx 1ml/min, initial pressure of 30kPa, split at 30 mls/min).

45

Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010 RESULTS AND INTERPRETATIONS Organic Matter Richness The quantity of organic matter (OM) in a rock is a direct measure of the Total Organic Carbon content (TOC). The analysed Araromi shale samples have a value range of 0.5-4.78wt% (Tables 1 and 2), which indicates variable source rock organic carbon quality from poor to excellent. There is an overall trend of increasing TOC values down the well (Fig. 3) suggesting better source rock quality in deeply buried intervals. Most of the samples have TOC >0.5wt% which is the minimum threshold value for hydrocarbon generation in siliciclastic source rock (Tissot and Welte, 1978, Hedberg et al., 1979). The TOC values suggest that Araromi shales have adequate organic matter constituents for hydrocarbon generation. Hydrogen Index (HI) The hydrogen index (HI) values vary from 1-327mgHC/gTOC (Tables 1 and 2) thus, suggesting source rock quality that spans from non-source potential through to gas/oil and oil generating potentials. In general, the OM is considered to be a mixture of Type II and Type III and a downhole profile of increasing HI concomitant with the TOC trend is apparent in the well logs. Deeper sections of the formation seem to be more organic rich and thus presumably have greater potential to generate liquid hydrocarbon. Additionally as shown in Fig. 3, two organic rich intervals (A and B) are obvious from the geochemical log and some core samples within the interval B contain HI values as high as 327mgHC/gTOC suggesting that more organic rich sections in the deep offshore equivalent of the strata may have greater potential to generate liquid petroleum. Samples with HI value range of 1-45mgHC/gTOC having kerogen Type IV indicate a highly reworked terrestrially derived OM perhaps in a highly oxic depositional environment. They form inert source which have no potential for hydrocarbon generation. The samples with HI values of 45-132mgHC/gTOC with kerogen Type III suggest woody or herbaceous organic matter origin having gas prone characteristics. Those samples with in the range of 151-327mgHC/gTOC consisting of kerogen Type II and Type II/III usually at the basal part of the wells contain oil and mixture of oil and gas prone kerogens. Thermal Maturation The thermal maturation (Tmax) measured from the Rock Eval pyrolysis varies from 398oC to 437oC while the vitrinite reflectance values vary from 0.50 to 0.68%Ro. These values suggest that the source rocks are thermally immature to marginally mature for hydrocarbon generation. The plots of Rock Eval Tmax against hydrogen index also show thermally immature to early mature source rocks with respect to hydrocarbon generation and dominance of a mixture of oil prone Type II and gas prone Type III kerogens (Fig. 4). Source Potential The source potential (SP) values vary from 0.01-14.56kgHC/ton of rock (Tables 1 and 2). The SP values are generally lower than the 2kgHC/ton of rock expected for good source rock (Dymann et al., 1996), suggesting little or no oil source rock potential but some potential for gas. Samples with higher SP values ranging from 3.01kgHC/ton of rock to 12.88kgHC/ton of rock suggest a moderate source rock with fair oil potential. Maceral Analysis The organic petrological study of the disseminated organic matter in the shale samples was carried out using the techniques in studying optical characteristics of finely dispersed organic matter particles in coals, coaly shales and carbonaceous shales. Terminologies of Stach et al., 1982 modified in Teichmuller, 1987 were used here. Selected shale samples were polished and observed under organic petrological microspcope. The different macerals of vitrinite, liptinite and inertinite were observed. Photomicrographs of representative macerals are shown in Fig. 5. In general, the maceral composition include liptinite (av. 26.0%), vitrinite (av. 38.1%) and inertinite (av. 35.9%) in all the samples inverstigated. The dominance of vitrinite and inertinite macerals suggests terrestrially derived, reworked and oxidized organic matter in the shale sediments. There is no particular maceral variation pattern or zonation down deep in all the wells.

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010 Biomarker compositions of the shales Core samples analysed by Gas Chromatography (GC) display a bimodal n-alkane GC fingerprint envelope with maxima between nC16 – nC18 and nC27 – nC29 (Fig. 6), suggesting variable inputs from both terrigeneous and non-terrigeneous (probably marine algal) organic matter. However, some samples display a unimodal n-alkane GC fingerprint typical of dominantly normal marine algal contribution (maximizing between nC16 and nC18). There is a relatively high input from alga-bacterial precursors indicated by the abundance of the low molecular weight relative to high molecular weight n-alkane derived from terrigeneous higher plants (Bray and Evans, 1961). Additionally pr/ph ratios vary from 0.78-2.02 reflecting anoxic to sub-oxic source rock depositional environment (Didyk et al., 1978, Volkman and Maxwell, 1986). Steranes in the saturated hydrocarbon fractions of the bitumen extracts of the Araromi shale samples analyse by GC-MS and GC-MS-MS show the C27-C29 distributions to be nearing a ratio of 1.1:0.9:1.0, with higher C27 and C28 compounds on occasions relative to the C29 sterane homologues for the 5α(H),14α(H),17α(H) 20R configuration isomers. Figs. 7 and 8 show the sterane distributions of the bitumen extracts from the Araromi shales. The above observation suggests a relatively higher input from the marine red algae and a low level of land plant contribution to the source organic matter (Goodwin, 1973). Additionally, the presence of the C30 24-n-propyl cholestane (detected by GC-MS-MS m/z 414-217 parent to daughter ion transition), confirms the relatively high marine algal contribution to the organic matter in the Araromi shales, as values of %C30 sterane range from 0.45 to as high as 5.23%, even in oleanane rich intervals in “Zone B” (Figure 3). CONCLUSION Rock Eval pyrolysis data from this study suggest that the organic rich core samples of Late Cretaceous Araromi Formation in the Dahomey Basin, southwestern Nigeria contain predominantly gas prone with lesser oil prone organic constituents ranging from immature to marginally mature at shallow levels but reaching proven maturity in the subsurface. Hydrocarbons in the basin will be predominantly gas dominated generated from deeper Cretaceous source rock in the subsurface levels with greater chances of heavy oils and tars at shallow levels. Gas chromatographic analyses of the bitumen extract show bimodal and unimodal n-alkane distributions, suggesting elevated contributions of marine relative to terrigenous higher plant matter to the source organic matter. The source rock organic matter accumulations probably occurred under anoxic to sub-oxic conditions (pr/ph ratios range from 0.78-2.02). Sterane distributions in the shale extracts are dominated by C27 relative to C28 and C29 carbon homologues and the presence of significant C30 24-n- propyl cholestane concentrations are both diagnostic of marine algal inputs. These biomarker characteristics are comparable with the deepwater oil. Araromi bitumen extracts have nearly flat n-alkane CSIA stable carbon isotopic profiles that suggest derivation from organic carbon from a uniform δ13C composition marine algal source. REFERENCES Adediran, S. A. and Adegoke, O. S. 1987. Evolution of the sedimentary basins of the Gulf of Guinea. In: Current Research in Africa Earth Sciences, Matheis and Schandeimeier (eds). Balkema, Rotterdam., p. 283-286. Adegoke, O. S. 1969. Eocene stratigraphy of Southern Nigeria. Mem. Bur. Rech. Geol. mins., p. 23-46. Adekeye, O.A. 2004. Aspects of sedimentology, geochemistry and hydrocarbon potentials of Cretaceous-Tertiary sediments in the Dahomey Basin, south-western Nigeria. Unpublished Ph.D thesis, University of Ilorin, 202p. Adekeye, O.A., Akande, S.O., Erdtman, B.D., Samuel, O.J. and Hetenyi, M. 2006. Hydrocarbon Potential Assessment of the Upper Cretaceous-Lower Tertiary Sequence in the Dahomey Basin Southwestern Nigeria. NAPE Bulletin. v. 19 No 1, p.50-60. Ako, B. D., Adegoke, O. S. and Petters, S. W. 1980. Stratigraphy of the Oshosun Formation in South-Western Nigeria. Jour. Min. Geol. v. 17, p. 97-106.

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010 Asmus, H. E. And Ponte, F. C. 1973. The Brazillian marginal basins: In: Naim, A. E. M and Stehli, F. G. (Eds). Ocean Basins and margins: The South Antlantic, The Plenum Press, v. 1, 250p. Billman, H. G. 1976. Offshore stratigraphy and paleontology of the Dahomey embayment. Proc. 7th Afri. Micropal. Coll. Ile-Ife, p. 27-42. Bray, E.E. & Evans, E.D. 1961. Distribution of n-paraffins as a clue to recognition of source beds. Geochimica et Cosmochimica Acta, 22, p.2-5. Bustin, R. M., Cameron, A. R.., Grieve, D. A. and Kalkreuth, W. D. 1983. Coal petrology: its principles, methods and applications: Geology Association of Canada Short Course Notes, v. 3, 230p. Didyk, B. M., Simoneit, B. R. T., Brassell, S. C. & Eglinton, G. 1978. Organic geochemical indicators of paleoenvironmental conditions of sedimentation. Nature, 272, p.216-222. Dymann, T. S., Palacos, J. G., Tysdal, R. G., Perry, W. J. and Pawlewicz, M. J. 1996. Source Rock Potential of Middle Cretaceous Rocks in Southwestern Montana: AAPG Bulletin, v. 80, p. 1177-1184. Espitalie, J., Madec, M., Tissot, B. P., Menning, J. J. and Leplat, P. 1977. Source rocks characterization method for exploration. Offshore Technology Conf. Paper 2935, 11th Annual OTC, Houston, v. 3, p. 439-444. Goodwin , T.W., 1973. Comparative Biochemistry of Sterols in Eukaryotic Micro-organisms. In: Erwin , J. A. (ed.), Lipids and Biomembranes of Eukaryotic Micro-organisms, Academic Press, New York, p. 1-40. Hedberg, H. D., Moody, J. O. and Hedberg, R. M. 1979. Petroleum prospects of deep offshore. AAPG Bull. v. 63, p. 286-300. Idowu, J. O., Ajiboye, S. A., Ilesanmi, M. A. and Tanimola, A. 1993. Origin and significance of organic matter of Oshosun Formation south-western Dahomey Basin Nigeria. Jour. Min. Geol. v. 29, p. 9-17. Kogbe, C. A. 1974. Paleo-ecologic significance of vertebrate fossil in the Dukamaje and Dange Formations (Maastrichtian and Paleocene) of northwestern Nigeria. Jour. Min. Geol.(Nigeria). v. 8, p. 49-55. Lehner, P. and de Ruiter, P. A. C. 1977. Structural history of the Atlantic margin of Africa.AAPG Bull. v. 61, p. 961-981. Mpanda, S. 1997. Geological development of East African coastal basin of Tanzania: Acta Universities Stockholmiensis, v. 45, 121p. Ogbe, F. A. G. 1970. Stratigraphy of strata exposed in the Ewekoro Quarry Western Nigeria. In:(Dessauvagie, T. F. J. and Whiteman, A. J. (eds). African Geology University of Ibadan Press, Nigeria. p.305-324. Ojeda, H. A. 1982. Structural framework, stratigraphy, and evolution of Brazilian basins. AAPG Bull. v. 66, p.732-749. Okosun, E. A. 1990. A review of the Cretaceous stratigraphy of the Dahomey Embayment, West Africa. - Cretaceous Research, v. 11, p. 17-27. Omatsola, M. E. and Adegoke, O. S. 1981. Tectonic evolution and Cretaceous Stratigraphy of the Dahomey Basin. Jour. Min. Geol. v. 8, p. 30-137. Pollastro, R. M. and Barker, C. E. 1986 . Application of clay mineral, vitrinite reflectance and fluid inclusion

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010 studies to the thermal and burial history of the Pinedale anticline, Green River basin, Wyoming. SEPM Special Publication. v.28, p. 73-83. Stach, E. M., Mackowsky, T. H., Teichmuller, M., Taylor, G., Chandra, D. and Teichmuller, R. 1982. Stach‘s text book of coal petrology. Gerbruder Borntaege, Berlin. 535p. Storey, B. C. 1995. The role of mantle plumes in continental break up: case history from Gondwanaland – Nature, v. 377, p. 301-308. Teichmuller, M. 1987, Organic material and very low grade metamorphism. In: M. Frey (ed). Low temperature metamorphism. Blackie and Sons Pub. London, p.114-161. Tissot, B. P. and Welte, D. H. 1978. Petroleum formation and occurrence., Springer-Verlag, New York, 538p. Tissot, B. P. and Welte, D. H. 1984, Petroleum Formation and Occurrence, 2nd ed. Spinger Verlag, Berlin 699p. Volkman J.K. & Maxwell, J.R 1986. Acyclic isoprenoids as biological markers. In: Johns, R.B. (ed.) Biological markers in sedimentary record, Elsevier, New York, pp. 1-42.

Fig. 1: Map showing the sedimentary basins of Nigeria. The arrow points to thelocation of the Dahomey Basin on the western margin of the Niger Delta. The map to the right is an enlarged outline geological map of Dahomey basin showing the location of the Araromi and Gbekebo wells (red ring) on the eastern margin of Dahomey (west of the Niger Delta). Map modified after Adekeye et al. (2006).

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010

Fig. 2: Generalised stratigraphic setting of the Dahomey Basin in the southwestern Nigeria (modified and redrawn from Idowu et al., 1993)

Figure 3: Geochemical log of the Gbekebo well. Two organic rich intervals are apparent (A and B). Only one sample within the interval A contains oleanane whereas most samples in the interval B contain oleanane, with oleanane index values as high as 0.21, despite the high marine algal biomarker composition of interval B.

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010

Figure 4: Plot of Rock-Eval HI against Tmax indicating the kerogen types and their respective hydrocarbon potentials in the analysed Araromi Formation sediments. Overlay field after Integrated Geochemical Interpretations Ltd P: IGI 2.7 geochemical interpretation software.

Figure 5: Photomicrographs of the macerals observed in the shale samples from the Araromi Formation in the Araromi borehole.

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010

Caption to figures

1.A large huminite grain within mineral matter matrix normal white light observation, sample number Ar-140; Araromi borehole; bar scale 50µm. 2. Same field of observation as in 1, now in blue light excitation showing threads of sporinites and resinites with

yellowish fluorescence intensity, sandwiched within the huminite cell structure; bar scale 50µm.

3. Discrete euhedral to subhedral grains of pyrite distributed within mineral matter and clouds of amorphous organic matter: normal white observation; sample number Ar-145; Araromi borehole; bar scale 50µm.

4. Same field of observation as in 3 now during blue light excitation; showing thin walled sporinite with yellow

fluorescence in the clouds of organic matter and the non-fluorescensing pyrite grains in black colour; bar scale 50µm.

5. Irregular grains of huminite within mineral matter matrix; normal white observation; sample number Ar-146;

Araromi borehole; bar scale 50µm. 6. Same field of observation as in 5 now during blue light excitation showing non-fluorescensing huminites in black colour associated with threads of sporinite in the lower bottom and yellowish fluorescensing pollen grain ? in the upper sector of the huminite grain; bar scale 50µm.

Figure 6: A bimodal peaks n-alkane envelope of sample Ar-149 maximizing at n C16 and nC29 typical of source rock whose organic matters have been derived from a variable mixture of algal and Pr; Pristane , and Ph; Phytane.

GC mass chromatogram of Sample Ar-149

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010

Figure 7: Figure 9. Gas chromatograms of representative saturated hydrocarbon fractions of the Araromi shale (samples GB314 and GB 307) extracts showing how n-alkane and isoprenoid distributions in the Araromi shale. Figure 8: m/z 217 mass chromatograms showing the distribution of C27-C29 steranes in representative intervals within the Araromi. Note the downhole variation in the sterane distributions within the Araromi shale extracts.

m/z 217 mass chromatograms

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010

Table 1: Rock Eval pyrolysis data of the Araromi (Maastrichtian) and Imo (Paleocene) formations in the Araromi borehole. Sample Number

Depth (m)

Location Forma tion

S1(mgHC/g rock)

S2 (mg HC/g rock)

SP (kg/t)

Tmax PI %Ro TOC wt%

HI(mgHC/g rock)

Kerogen Type

Ar-46 256.03 Araromi BH

Imo Shale 0.19 0.44 0.63 417 0.31 - 0.75 58 III

Ar-53 277.37 Araromi BH

Imo Shale 0.16 0.38 0.54 399 0.30 0.45 0.63 60 III

Ar-60 298.70 Araromi BH

Imo Shale 0.09 0.09 0.18 427 0.50 0.64 0.39 23 n.d

Ar-68 329.18 Araromi BH

Imo Shale 0.07 0.09 0.16 391 0.44 - 0.34 26 n.d

Ar-74 350.52 Araromi BH

Imo Shale 0.09 0.13 0.22 399 0.41 0.55 0.50 26 IV

Ar-81 371.86 Araromi BH

Imo Shale 0.09 0.35 0.44 420 0.20 0.55 0.58 60 III

Ar-88 393.19 Araromi BH

Imo Shale 0.08 0.31 0.39 419 0.21 - 0.74 41 IV

Ar-91 405.38 Araromi BH

Araromi FM

0.02 0.01 0.03 403 1.00 0.51 0.65 1 IV

Ar-97 435.86 Araromi BH

Araromi FM

0.05 0.10 0.15 419 0.36 - 0.61 16 IV

Ar-100 454.46 Araromi BH

Araromi FM

0.05 0.10 0.15 412 0.36 - 0.75 13 IV

Ar-105 463.29 Araromi BH

Araromi FM

0.04 0.05 0.09 410 0.50 - 0.66 7 IV

Ar-110 475.49 Araromi BH

Araromi FM

0.17 0.95 1.12 424 0.15 - 1.69 56 III

Ar-114 487.68 Araromi BH

Araromi FM

0.11 0.57 0.68 428 0.16 - 1.05 54 III

Ar-119 495.30 Araromi BH

Araromi FM

0.15 0.75 0.87 422 0.17 - 1.77 40 IV

Ar-124 505.36 Araromi BH

Araromi FM

0.18 0.54 0.72 420 0.25 - 1.19 45 III

Ar-132 518.16 Araromi BH

Araromi FM

0.08 0.26 0.34 409 0.24 - 1.02 25 IV

Ar-139 539.49 Araromi BH

Araromi FM

0.08 0.18 0.26 411 0.31 0.51 1.01 17 IV

Ar-145 557.78 Araromi BH

Araromi FM

0.21 3.10 3.31 423 0.06 0.66 2.05 151 II-III

Ar-148 566.93 Araromi BH

Araromi FM

0.28 5.18 5.46 424 0.05 - 2.75 188 II-III

Ar-151 572.72 Araromi BH

Araromi FM

0.52 3.70 4.22 426 0.12 - 1.83 202 II-III

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010 Table 2. Bulk geochemical and selected biomarker parameters for the analysed Araromi shale from Gbekebo well in Dahomey Basin Sample Number Depth (ft)

TOC (wt%) S1 S2

Tmax

(oC) HI PI Pr/Ph %C27 %C28 %C29 %C30 OL C29S/S+R GB 304 2735.7 0.50 0.00 0.01 430.00 2.00 0.00 GB 305 2739 0.63 0.12 0.36 425.00 57.14 0.25 GB 306 2758.8 1.02 0.14 0.51 425.00 50.00 0.22 GB 307 2772 1.01 0.13 0.48 432.00 47.52 0.21 1.06 36.94 25.55 37.06 0.45 0.00 0.23 GB 309 2788.5 0.69 0.05 0.24 425.00 34.78 0.17 GB 310 2798.4 0.91 0.04 0.34 430.00 37.36 0.11 1.28 45.28 26.62 28.09 0.00 0.00 0.18 GB 311 2801.7 0.99 0.06 0.55 430.00 55.56 0.10 GB 312 2818.2 0.95 0.08 0.41 425.00 43.16 0.16 GB 313 2824.8 1.00 0.28 0.42 432.00 42.00 0.40 GB 314 2828.1 0.68 0.12 0.44 435.00 64.71 0.21 0.78 24.10 41.81 32.77 1.32 0.00 0.25 GB 315 2831.4 0.91 0.07 0.36 435.00 39.56 0.16 0.93 23.62 35.50 38.88 2.00 0.06 0.31 GB 316 2834.7 0.76 0.06 0.21 437.00 27.63 0.22 GB 318 2838 0.82 0.06 0.30 431.00 36.59 0.17 1.18 22.16 39.74 36.59 1.51 0.00 0.26 GB 320 2867.7 1.24 0.06 0.15 422.00 12.10 0.29 GB 323 2897.4 1.67 0.12 1.29 435.00 77.25 0.09 GB 324 2904 1.70 0.06 0.83 432.00 48.82 0.07 1.25 31.95 41.15 24.29 2.61 0.00 0.31 GB 325 2910.6 1.87 0.27 3.01 427.00 160.96 0.08 GB 326 2917.2 2.13 0.18 5.25 430.00 246.48 0.03 38.20 38.47 20.83 2.50 0.00 0.26 GB 327 2920.5 2.12 0.17 3.01 427.00 141.98 0.05 GB 402 2963.4 1.97 0.21 1.39 432.00 70.56 0.13 31.39 31.00 33.51 4.11 0.23 GB 421 3144.9 1.66 0.28 0.42 415.00 25.30 0.40 GB 450 3319.8 2.24 0.31 5.01 433.00 223.66 0.06 1.13 33.68 38.20 25.09 3.02 0.20 0.29 GB 451 3323.1 2.52 0.32 6.44 432.00 255.56 0.05 GB 454 3333 4.78 0.81 13.75 434.00 287.66 0.06 GB 455 3336.3 3.33 0.73 10.30 431.00 309.31 0.07 2.02 30.15 30.74 33.89 5.23 0.21 0.16 GB 456 3342.9 3.94 1.29 12.88 426.00 327.07 0.09 1.39 37.91 33.23 26.73 2.13 0.12 0.47 GB 460 3372.6 1.54 0.31 1.09 434.00 70.78 0.22 0.96 34.20 33.56 29.00 3.24 0.09 0.19

HI = Hydrogen index (100*S2/TOC). PI = production Index S1/(S1+S2). Pr/Ph = pristane/phytane. % C27-C30 = % individual C27-C30 ααα sterane to sum of C27-29 ααα regular steranes. OL = 18α(H) + 18β(H) oleanane/C30 17α(H),21β(H)- Hopane. C29 S/S+R = ratio of 5α(H),14α(H),21α(H) - steranes (20S/S+R) thermal maturity parameter.

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Olabisi A. Adekeye and Samuel O. Akande; Continental J. Earth Sciences 5 (1): 42 - 55, 2010

Received for Publication: 30/01/10 Accepted for Publication: 02/04/10 Corresponding Author Olabisi A. ADEKEYE Department of Geology and Mineral Sciences, University of Ilorin, P. M. B. 1515, Ilorin, Nigeria. Email: geologistolabisi@yahoo.com

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Continental J. Earth Sciences 5 (1): 56 - 63, 2010 ISSN: 2141 - 4076 ©Wilolud Journals, 2010 http://www.wiloludjournal.com

GROUNDWATER EXPLORATION IN A BASEMENT COMPLEX TERRAIN USING ELECTRICAL RESISTIVITY SOUNDING (VES): A CASE STUDY OF RIMIN GADO TOWN AND ENVIRONS, KANO

STATE NORTH CENTRAL NIGERIA.

1E.Y. Mbiimbe, 2 N.K. Samaila and 2D. K. Akanni 1Department of Geology, Gombe State University, PMB 127 Gombe, Nigeria, 2Geology Programme Abubakar

Tafewa Balewa University, Bauchi, Nigeria.

ABSTRACT Groundwater occurrence and distribution in Basement Complex is localized and confined to weathered /fractured zones. Hence exploration for groundwater in such terrains posses a great challenge to groundwater development agencies as in most cases the risk of failure of such projects is very high. This study was carried out with the aim of demonstrating the application of vertical electrical sounding method of investigation in the exploration for groundwater in Rimin Gado town and environs. A total of 16 VES points were probed located in 4 settlements spread at a distance of 200-300m apart. ABEM SAS 300C terameter was used to generate field data applying the Schlumberger Array with an AB/2 of 1.5-100m. The field data were simulated using Zhody and OFFIX software. The results show that there are 2-4 Geo-electric layers: topsoil (sandy/lateritic), highly weathered Basement (clay and sandy clay), slightly weathered/ fractured Basement (Clay,sand/clayey sand) and Fresh bed rock. Three basic resistivity zones were identified: low resistivity zone (49-95 ohm-m) corresponding to highly weathered Basement material, the high resistivity zone (294-1543 ohm-m) representing fresh bed rock and intermediate resistivity zone (114-219 ohm-m) corresponding to slightly weathered/ fractured Basement. ButuButu and Dan Isa with a weathered Basement thickness of 25-34m and resistivity of 66-140 ohm-m therefore have high potentials for good Borehole yields. It is suggested that groundwater exploration in Basement Complex terrain should include geophysical investigation especially VES along with geological methods as an integral part of the program. KEYWORDS: Groundwater Exploration, VES, Rimin Gado, Kano State, Nigeria.

INTRODUCTION Groundwater is one essential but necessary substitute to surface water in every society. It’s no doubt a hidden, replenish able resource whose occurrence and distribution greatly varies according to the local as well as regional geology, hydrogeologic setting and to an extent the nature of human activities on the land. Groundwater occurrence in a Precambrian Basement terrain is hosted within zones of weathering and fracturing which often are not continuous in vertical and lateral extent (Jeff, 2006). There is a steady rise in the demand for groundwater in most hard rock areas most of which can not boast of any constant surface source of water supply (Adanu, 1994). The failure rate in most groundwater project recorded in Basement Complex aquifers has informed the general acceptance of a geophysical survey as a compulsory prerequisite to any successful water well drilling project (Dan Hassan, 1999). The electrical resistivity method involving the vertical electrical sounding (VES) technique is extensively gaining application in environmental, groundwater and engineering geophysical investigations ( Zohdy et al 1980, Aina et al 1996, Olorufemi et al 1993 and 2004 and Afolabi and Olorufemi 2004). This paper is a report of the findings of an investigation carried out to establish the role and significance of vertical electrical resistivity method in groundwater exploration in Rimin Gado town and environs. The main objectives of the investigation were: To establish that groundwater development in Basement complex is facilitated by proper geophysical investigation prior to drilling. To show the role of Vertical Electrical Sounding in groundwater exploration in hard rock areas.

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E.Y. Mbiimbe et al.,: Continental J. Earth Sciences 5 (1): 56 - 63, 2010 To define the nature and distribution of groundwater in typical Basement Complex aquifers. Study Area Rimin Gado town is located within latitudes N 11056’ and N 12000’ and longitudes E 08012’ and E 080 18’. The town is situated along the Kano- Sokoto high way and is the head quarter of the Rimin Gado local Government area of Kano state. It has a growing population of about 76,855 inhabitants (1999 Estimate) mostly involved in agricultural activities as a means of livelihood. The area is part of the tropical climate zone of North central Nigeria with a mean annual rainfall of about 635mm (Wardrop Engineering, 1990). There are two seasons the raining season which begins in May and ends in October and the dry season which runs from November to April. The Sudan savannah vegetation characterized by sparse shrubs generally less than 6m high defines the vegetation pattern of the area. The area is gently low lying with Dutsen Dan Isa as the only prominent outcrop. River Gata which runs in the NW-SE direction constitutes the main drainage system with other seasonal streams as its tributaries giving a dendritic pattern of drainage. Geology The geology of the area is part of the Precambrian Basement Complex of North Central Nigeria. The mineralogy of the rocks are described in the works of Falconer 1911, Raeburn and Jones ,1934, , Barber and Jones 1960, McCurry 1973, Schroeter, 1974,Van Breemen etal 1977,Wright et al 1985,Macdonald and Partners, 1986 and Kogbe 1989. The major rock types in the area include older granites, gneiss, migmatites and metasediments mainly to the North and North West of the study area. These metasediments are mostly undifferentiated schist and quartzite. In some parts the older granites have been intruded by felsic dykes and are also associated with anatectic migmatites and a host of syn-tectonic and post tectonic granites with a common genetic origin. The unweathered bedrock is characterized by rapid grain size variations from micro to pegmatitic regions but normal sizes are dominant (Uma and Kehinde, 1994). The Basement is generally fractured with North-South and Northeast- Southwest lineaments very prominent and easily picked from aerial photographs. The summary of the geology of the study area and location of probe points is presented in figure 1.

FIG 1. GEOLOGIC MAP/LOCATION OF VES POINTS OF THE STUDY AREA

Groundwater occurrence The hydrogeologic setting of the study area is typical of any Basement Complex terrain and groundwater in such terrains is usually found in three situations (Bannerman and Ayibotele1984):

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E.Y. Mbiimbe et al.,: Continental J. Earth Sciences 5 (1): 56 - 63, 2010 Fractured poorly decomposed or fresh rock overlain by a relatively deep zone of well decomposed rock. The fractured rock Fractured veins (quartz and Aplite) occurring in an otherwise non water bearing weathered mantle. Groundwater is known to be more promising within granular alterite and the transition zone immediately overlying the fresh bedrock (Chilton and Smith-Carrington 1984).In the study area groundwater was identified to occur within the weathered mantle developed on the crystalline rocks mainly pinkish granite and granite gneiss and within fractured pegmatite and quartz veins in the moderate – highly decomposed granite –gneiss. The zone of weathering is extremely irregular as confirmed by the variations in the depth to bedrock which varies from 6.78m at ButuButu to 85.66m at Atawa. The granitic suite mainly the older granites have experienced prolonged weathering and tectonism which has given rise to thick weathered mantle of 30-40m and a sequence of fractures whose borehole yields have been consistently good (50lpm). Data source and method of study Introduction This research was carried out with the primary goal of generating data from field measurement which is required to identify potentials of groundwater occurrence in the study area. Using ABEM SAS 300 terameter a total of 16 points were investigated spreading across four different settlements. The probe points were selected at a lateral distance of 200-300 m apart and the depth of investigation falls between 1.5- 100m (electrode separation). The settlements used for the study are Juji,Atawa,ButuButu and Dan Isa. Basic principle of the Method Groundwater through the various dissolved salts it contains is ionically conductive and enables electric current to flow into the ground. Consequently measuring the ground resistivity gives the possibility of identifying locations with high potentials of water bearing based on the following properties: A hard rock without pores or fractures and a dry sand without water or clay are very resistive (several tens of thousands ohm-m) A porous or fractured rock bearing fresh water has a resistivity which depends on the resistivity of the water and the porosity (several tens to several thousands ohm-m) An impermeable clay layer which has bound water has low resistivity (several units to several tens ohm-m) Mineral ore bodies (iron, sulphide etc) have very low resistivity due to their electronic conduction usually lower or much lower than 10 ohm-m The value of any geophysical method of survey is measured by the amount of geological information that can be deduced from the interpretation of the data obtained (Ariyo and Adeyemi 2009) Method of study In the study, the electrical resistivity method with schlumberger array using ABEM SAS 300 C terameter was employed for the acquisition of VES data in the field. A total of sixteen (16) VES points at a lateral distance of 200-300m apart were investigated four from each of the four settlements that make up the study area. The depth range of investigation falls within 1.5-100m. The acquired field data was first plotted on a log log paper to produce a field curve which was subsequently correlated with a standard curve using the curve matching method. The data generated was interpreted using Zhody and OFFIX computer soft wares to give information on the geo-electric layers, the thickness of the layers, the resistivity of the layers and depth to bed rock.

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E.Y. Mbiimbe et al.,: Continental J. Earth Sciences 5 (1): 56 - 63, 2010 RESULTS AND DISCUSSIONS The results of the 16 VES points are presented in table 1. The simulated results of the 16 VES points reveal the presence of 2-4 geoelectric layers. These layers are grouped as: topsoil (clayey, sandy or lateritic), weathered Basement (clays/sandy clays), slightly weathered/ fractured Basement (clayey sand) and fresh bedrock. The resistivity of the topsoil varies from 49-885 ohm-m while the thickness varies from 0.9- 4.9 m. the resistivity and the thickness of the weathered Basement range between 55 and 1543 ohm-m and 1.2- 34.2m respectively. The resistivivity of the fresh bed rock is in the range of 294 ohm-m and above. The results further differentiate three basic resistivity zones: very low resistivity zone (49-95 ohm-m), very high resistivity zone (294-1543 ohm-m) and the zone of intermediate resistivity (114-219 ohm-m). The three zones correspond to; highly weathered Basement, fresh bed rock and slightly weathered Basement/fractured Basement respectively. The aquifer in the study area is therefore defined by the highly weathered zone and the slightly weathered/fractured zones which are in agreement with Ariyo, 2007 and Olayinka, 1999 observation that common aquifers in typical Nigerian Basement Complex are composed of weathered and fractured Basement. The variation recorded in the resistivity and thickness of the aquiferous materials is due to the different rates at which different rocks respond to weathering from one location to another.

Table 1: Simulated results of resistivity data from the study Area.

Location VES POINTS

Layers Thickness (m)

Resistivity (Ohm-m)

Inferred Litho-strata Remarks

JUJI 01 1 4.9 885 Lateritic Topsoil 2 28.3 66 Weathered Basement

(sands/ sandy Clays) Possibly Aquiferous

02 1 4.9 885 Lateritic Topsoil 2 28.3 66 Weathered Basement

(sands/ sandy Clays) Possibly Aquiferous

03 1 1.1 49 Clayey Topsoil 2 32.1 77 Weathered/Fractured

Basement Possibly Aquiferous

04 1 1.1 393 Sandy Topsoil 2 32.1 109 Weathered Basement

(sands/ sandy Clays) Possibly Aquiferous

Atawa 05 1 0.94 79 Sandy Topsoil 2 3.5 291 Laterite 3 15.9 80 Weathered Basement

(sands/ sandy Clays) Possibly Aquiferous

4 9.5 123 Slightly Weathered Basement

Possibly Aquiferous

06 1 3.4 175 Lateritic Topsoil 2 19.8 96 Weathered Basement

(sands/ sandy Clays) Possibly Aquiferous

07 1 2.3 197 Lateritic Topsoil 2 20.3 98 Weathered Basement

(sands/ sandy Clays) Possibly Aquiferous

3 10.6 105 Slightly Weathered Basement

Possibly Aquiferous

08 1 3.3 150 Lateritic Topsoil 2 12.1 95 Weathered Basement

(sands/ sandy Clays) Possibly Aquiferous

3 17.7 132 Slightly Weathered Basement

Possibly Aquiferous

ButuButu 09 1 10.5 68 Weathered Basement (sands/ sandy Clays)

Possibly Aquiferous

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2 22.6 1543 Slightly Weathered to Fresh Basement

10 1 1.1 124 Sandy Topsoil 2 1.2 79 Weathered Basement

(sands/ sandy Clays)

3 30.9 262 Slightly Weathered to Fractured Basement

Possibly Aquiferous

11 1 2.5 70 Weathered Basement (sands/ sandy Clays)

2 34.3 151 Slightly Weathered to Fractured Basement

Possibly Aquiferous

12 1 13.8 91 Weathered Basement (sands/ sandy Clays)

Possibly Aquiferous

2 16 193 Slightly Weathered to Fresh Basement

Dan Isa 13 1 3.3 99 Sandy Topsoil 2 29.8 78 Weathered &fractured

Basement Possibly Aquiferous

14 1 2.9 280 Lateritic Topsoil 2 17.4 113 Weathered Basement

(sands/ sandy Clays) Possibly Aquiferous

3 9.5 140 Slightly Weathered Basement

15 1 0.9 216 Lateritic Topsoil 2 3.5 55 Weathered Basement

(sands/ sandy Clays) Possibly Aquiferous

3 25.4 144 Slightly Weathered Basement with minor Fractures

Possibly Aquiferous

16 1 0.9 527 Lateritic Topsoil 2 28.9 225 Slightly Weathered to

Fresh Basement Possibly Aquiferous

CONCLUSION The method of investigation adopted by this study has helped in the identification of the aquiferous units and has provided an understanding of aquifer dimensions especially the thickness of the weathered mantle, the depth to bed rock and fractured zones which are required for locating points with high potentials for groundwater occurrence. The study has also revealed that ButuButu and Dan Isa have very high potentials for good borehole yields while Atawa and Juji can provide moderate yields. It is therefore suggested that groundwater development through borehole construction in the study area as well as other Basement Complex should be preceded by geophysical investigation (VES). This will minimize the problems associated with the occurrence and distribution of groundwater in Basement Complex terrains. ACKNOWLEDGEMENT The authors are grateful to some members of Staff of ATBU Bauchi and the Computer analyst in Jos whose contributions made this research a success. REFERENCES Adanu E.A. (1994) “Groundwater Development and Management in the Basement Complex Terrain in Zaria, Kaduna Area “Water Resources 4(1&2): 64-68. Afolabi,O. and Olorunfemi M.O. (2004), “ Laboratory Modelling of Geoelectric Response of a leakin Underground Petroleum Storage tank in Sand Formation” Global Journal of Geological Sciences. 2 (2): 207-220. Aina A. Olorunfemi M.O. and Ojo J .S. (1996), “An integration of Aeromagnetic and Electrical Resistivity Methods

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E.Y. Mbiimbe et al.,: Continental J. Earth Sciences 5 (1): 56 - 63, 2010 in Dam Site Investigation “Geophysics 61 (2): 349-356. Ariyo S.O., (2007) “Hydro-Geophysical Investigation for Groundwater at Atan/Odosenbora Area, Southwestern Nigeria” Ife journal of Science. 9 (1): 87-92 Ariyo S.O. and Adeyemi G.O. (2009) “Role of Electrical Resistivity Method for Groundwater Exploration in Hard Rock Areas: A case study from Fidiwo/Ajebo Areas of Southwestern Nigeria” Pacific Journal of Science and Technology 10 (1): 483-486 Bannerman R.R. and Ayibotele N.B. (1984) “Some Critical Issues with Monitoring Crystalline Rock Aquifers for Groundwater Management in Rural Areas.” Challenges in African Hydrology and Water Resources, IAHS publ. (144): 47-56. Barber W. and Jones D.G. (1960) “The Geology and Hydrogeology of Maiduguri, Borno Province” Rec. Geol. Surv. Nig. Chilton J.P. and Smithcarrigton A.K. (1984) “Characteristics of Weathered Basement Aquifer in Malawi in Relation to Rural Water Supplies, “Challenges in African Hydrology and Water Resources, IAHS publ. (144) 57-72. Dan Hassan M.A. and Adekile (1991)” Geophysical Exploration for Groundwater in Crystalline Basement Terrain: A case study of Zabenawan Dansudu, Kano State, Nigeria” Journal of mining and Geology 27 (2): 71-75. Dan Hassan M.A. and Olurunfemi, M.O.(1999) “Hydrogeophysical investigation of a Basement Terrain in the North Central part of Kaduna State Nigeria” journal of mining and Geology 35 (2) pp 189-206 Falconer J.D. (1911), “The Geology and Geography of Northern Nigeria.” McMillan, London pp295. Jeff D. (2006) “Forum for groundwater” htt://www.waternet.co.za/groundwater/(3) December 2006. Kogbe C.A. (1989) “Geology of Nigeria Edited “2nd revised edition Paris , Rock View International pp538 Macdonald and Partners (1986) “Final Report on Rural Water Supplies for Kano State” vol. 2 Unpublished Report. McCurry P., (1973) “Geology of Degree Sheet 21 (Zaria)” Overseas Geol.Min Res. 45 London. Oluronfemi M.O. and Fasuyi s.A . (1993) “Aquifer types and Geoelectrical/ hydrogeologic Characteristics of Central Basement Terrain of Nigeria “Journal of African Earth Science (16): 309-317. Olorunfemi M.O., Afolayan J. F. and Afolabi, O. (2004)“Geoelectric/Electromagnetic VLF Survey for groundwater in a Basement Terrain: A case Study,” Ife journal of Science 6 (1): 74-78. Olayinka A.I (1999) “ Electromagnetic Profiling and Resistivity soundings in Groundwater Investigations near Egbeda- Kabba Kwara State, Nigeria “ Journal of mining and Geology, 27 (2): 243-250. Raeburn C. and Jones B.( 1934), “The Chad Basin Geology and Water Supply” Bull. Geol. Surv. Nig. (15). Schroeter P.Y. (1974) “The Hydrogeology of Bauchi Town Northern Nigeria” Rec. Geol. Surv. Nig. (8): 17-23. Uma K.O. and Kehinde M.O. (1994)“Potentials of regolith Aquifers in relation to Water Supplies to rural Communities: A case study from parts of Northern Nigeria” journal of Mining and Geology 30 (1): 97-109

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E.Y. Mbiimbe et al.,: Continental J. Earth Sciences 5 (1): 56 - 63, 2010 Van Breeman O. R.T., Pidgeon and Bowden P. (1977) “ Age and Isotope Studies of Some Pan African Granites from North Central Nigeria “ Precambrian Res., (4): 307-309. Wardrop Engineering Inc (1990) “Final Report on Rural Water Supply Project for Kano “ Wright E.P and Herbert R. (1985) “Collector Wells in Basement Aquifer” Waterlines (2): 8-11. Zohdy A.A.R., Eaton G.P. and Mabey D.R. (1980) “Application of surface Geophysics to Groundwater Investigations:” Techniques of Water Resources Investigations of the United States Geological Survey 1-3

FIG.2a. A TYPICAL 3- LAYERED VES CURVE. FIG.2b. A TYPICAL 3- LAYERED VES CURVE. (FIELD CURVE) (SIMULATED

CURVE)

FIG.3a. A TYPICAL 2 - LAYERED VES CURVE. FIG.3b. A TYPICAL 2 - LAYERED VES CURVE.

(FIELD CURVE) (SIMULATED)

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E.Y. Mbiimbe et al.,: Continental J. Earth Sciences 5 (1): 56 - 63, 2010

FIG.4a. A TYPICAL 4 - LAYERED VES CURVE. FIG.4b. A TYPICAL 4- LAYERED VES CURVE.

(FIELD CURVE) (SIMULATED)

Received for Publication: 05/06/10 Accepted for Publication: 20/07/10 Corresponding Author E. Y. Mbiimbe, Department of Geology , Gombe State university, PMB 127, Gombe , Nigeria.