Southwestern Basement Complex Research Articles

Size Distribution And Heavy Mineral Pattern In Some E Gbe Streams, Southwestern Nigeria

The Egbe-Isanlu schist belt has received scholarly attention from several researchers but there is no documented report on types and the distribution of heavy minerals in streams of the area. This study is intended to reveal the types of heavy minerals, the distribution and possible source rocks to guide prospectors in gems. The study area lies within latitude 08o 03' and 08o 16 ' and longitude 05o 31' and 05o 43’ of the Southwestern Basement Complex terrain in Nigeria. Fifteen stream sediment samples were collected at appropriate points along river channels, air dried at room temperature, sieved and subjected to heavy mineral separation process using bromoform. Graphic mean, sorting, skewness and kurtosis were determined and heavy minerals identified under microscope. The graphic mean ranges between 0.67 (coarse sand) to 2.49 (fine sand), skewness between 0.75 and -0.10 and Kurtosis between 0.87 and 1.88. The calculated ZTR index ranges between 6.86% and 3.35.0%. The identified heavy minerals in the study area included tourmaline, epidote, rutile, zircon, kyanite, staurolite, garnet and zeolite. These minerals are modernly distributed across the sampled area and in some locations, they are relatively high in abundance. Some of the heavy minerals are angular to sub-angular in shape suggesting a short distance of travel from source. The graphic mean gives values that suggests a moderately to poorly sorted sediment and skewness indicated a platykurtic and leptokurtic nature for the sediments. Calculated ZTR index classified the sediments as immature to sub-mature indicating a short distance of travel suggesting that the sediments could have been derived within the catchment area. The presence of zircon, tourmaline and rutile suggests that the sediments might probably have its source from acid intrusive rocks and pegmatites.
 
 

English

The Osogbo central solid waste dumpsite in Osun State, Nigeria falls within the Ilesha Schist Belt, southwestern basement complex of Nigeria. Thirty-three (33) Vertical Electric Sounding (VES), and 2-D Electric Resistivity Tomography (ERT) data were acquired across various locations in the study area using ABEM Terrameter SAS 300, respectively. Schlumberger configuration with a maximum spread length of 100 m, for the VES was used, while four traverses of ERT were conducted, using Dipole-Dipole Array with average traverse length of 112.50 m. A smoothness-constrained least-squares inversion was then applied to the ERT data using a 2-D inversion algorithm [that is, DIPRO for Windows, version 4.01. Generally, the results defined the contaminated leachate plumes as electrically conductive, with anomalous resistivity values. Both the VES and the 2-D tomography identified zones of low resistivity values, between 24 and 67 ?m, from 10 to 20 m deep, as leachate contaminant plumes. Some of the weathered and fractured basement rocks indicated that the subsurface soil and groundwater have been contaminated by the leachates, which appears to have migrated outside landfill site. Zones within the sub-surface, with resistivity values relatively high (> 300 Ωm) and depth above 30 m might be pollutant free. Solid wastes management calls for the adoption of the best practicable environmental management approach through the governments’ enforcement of circular economic policies, using extended producer responsibility (EPR) model and construction of engineered landfills to replace unsanitary landfills. The conduct of environmental impact assessment (EIA), prior to commencement of operations and phytoremediation of closed sites is also crucial. Key words: Tomography, leachate, pollution, contaminant plume.

Frequency-Domain Electromagnetic and VLF Data with An Application to Modeling of Basement Structures: A Case Study Within, Ibadan Area, Southwestern Nigeria

The study area, the church camp is within Ibadan which fall within southwestern basement complex of Nigeria and it is mainly by migmatite-gneiss. The hard rocks are usually characterized by basement fracture which may serve as a conduit for groundwater passage. This has necessitated detail geological and geophysical investigation to accurately and precisely delineate this structure. Geological mapping alongside very low frequency Electromagnetic (VLF-EM) techniques were adopted in which conductivity data were acquired along Fifteen (15) VLF profiles using ABEM WADI. Thirteen (13) of these profiles were in the East-West (E-W) direction which is the dip direction of the structural elements, while the remaining two profiles were in North-South (N-S) direction. The data obtained from the field were processed, filtered and presented inform of profiles and Karous-Hjelt (K-H) filtered pseudo-section to visualise conductivity in (2-D). Pockets of conductive structures were delineated and were interpreted as fractures of various dimension and orientation. Some are single fracture and others are closely-spaced double fractures which some of them joined or fused together at depth with some suspected to contain water while some are dry base on their conductivity/resistivity signature exhibited. In conclusion, VLF-EM has proven to possess the capability to characterize and model the basement fractures and define their dimension, axial orientation and indicates their parallelism which also signifies their origin as regard stress regime that produces the fracture.

Radiogeochemistry, uranium migration, and radiogenic heat of the granite gneisses in parts of the southwestern Basement Complex of Nigeria

The radiogeochemistry of granite gneisses in Akunu-Akoko (AK) and Ayere (AY) areas of the southwestern Basement Complex of Nigeria was studied using gamma-ray spectrometry, and geostatistical analysis and modeling. This study was aimed at determining the concentrations of radionuclides (K, U, and Th) in these rocks, as well as alteration scenarios, nature and rates of uranium migration (UM), levels of radiological hazards, and rate of radiogenic heat production (RHP). The interquartile (lowest Q1 < highest Q2 < highest Q3) elemental concentrations for 40K, 238U, and 232Th were 0.23 < 3.75<4.06%; 1.00 < 4.20<5.40 ppm; and 4.10 < 16.10<30.20 ppm, respectively, within the minimum and maximum limits of BDL (below detection limit) to 5.23%, BDL–9.70 ppm, and 0.40–60.20 ppm. The average activity concentrations of 40K, 238U, and 232Th with values of 629.28, 38.58, and 49.96 Bqkg−1, respectively, were above their crustal averages in the order of AK3<AK2<AK3<AY3<AY1<AY2. Variability in K-eU-eTh content and alteration in the rocks were affirmed by radioelement ratios and F-parameter. The high radionuclide concentrations may be attributed to high levels of radioactive materials, as well as trace and rare earth elements. Low radionuclide concentration in rocks is due to weathering, metamorphism, and 12–86% outward UM. The absorbed dose rate (ADR) average of 75.09 nGyh−1 was within the allowable range, with regression R-squared (R2) prediction values of 25–92% from the radionuclides. The average radium activity was below the permissible limit of 370 Bqkg−1, and the annual effective doses, hazard indices, gamma activity, and activity utilization index were all far below the safe limit of 1 mSvy−1. However, gonad equivalent and excess lifetime cancer risk were above their permissible limits. RHP average of 1.89 μWm−3 above the crustal range of 0.8–1.2 μWm−3 will considerably contribute to the heat flux in the areas. Based on the prediction accuracy of the R2 results, 36–86% of RHP rates in the rocks are achievable from the radionuclides.

Geological and Geochemical Prospecting for Gold Mineralization in Bode-Saadu Axis, Southwestern Nigeria

Geological and geochemical studies of gold mineralization in Bode-Saadu axis, Southwestern Basement Complex, Nigeria have been conducted in order to study their mode of occurrence, structural settings, pattern of distribution and potential. Geological studies reveal that granite and gneiss granite are the prominent rocks in the area and exist in the north-eastern, north-western and southwestern part of the area whereas mica and amphibole schist occur as low-lying exposure. Petrographic studies reveal spatial association between gold mineralization and the fractured zones. Geochemical studies show that the gold concentration in rocks and stream sediments from the region is low with the exception of a few areas with high values ​​and is related to the occurrence of fissure in the northeast-west direction. The distribution pattern of gold in the region is skewed NE-SW, indicating that gold mineralization is structurally controlled. Keywords: Geochemical prospecting; Geological studies; Gold mineralization; Structurally controlled.

English

In this study, effort has been made to achieve a comprehensive geophysical investigation on immediate and remote causes of structural/foundation failures, specifically highway(s) within the southwestern basement complex region of Nigeria. Geophysical survey involves the use of Very Low Frequency Electromagnetic method (VLF-EM) which was complemented with electrical resistivity method using two techniques; 2D Electrical Resistivity Tomography (ERT) and Vertical Electrical Sounding (VES) along Akure/Oba-Ile Airport Road, which covers a pilot test of 600 m. The VLF-EM survey produced EM anomalies and identified possible linear features along the study area. The results obtained from the VES were used to determine the second order parameters for determination of subsurface integrity/competence. The geoelectric sections identified three to five geoelectric/geologic subsurface layers along the traverse. The ERT gave information on the subsurface characteristics whose section delineated five major geologic layers comprising of the topsoil, weathered basement, fractured zone, partly fractured basement and the fresh basement. This shows that fracture and weathering are responsible for the structural failures along the study area which are products of probability functions of geodynamics. The methodology can be adopted as a model to proficiently and quickly detect changes in subsurface resistivity, integrity and identify anomalous zones which can serve as useful tool in the understanding of the probability functions of geodynamics that can bring structural and foundation failures within the basement complex region. Key words: Road, longitudinal conductance, subsurface integrity, dipole-dipole, geoelectric section, very low frequency.

Integrated geophysical investigation of aquifer and its groundwater potential in phases 1 and 2, Federal University Oye-Ekiti, south-western basement complex of Nigeria

Electrical resistivity method is frequently used in groundwater studies. It is one of the many geophysical methods used in finding, locating, and defining subsurface water. The geoelectrical survey was done in Federal University Oye-Ekiti, phases 1 and 2, south-western Nigeria, to assess the groundwater potential. Fifteen very low frequency electromagnetic traverses, three dipole–dipole profiles and three Wenner profiles and 25 vertical electrical soundings were occupied and investigated with maximum current electrode, were arranged with an equal potential spacing (AB/2) of 1–100 m with the aid of ABEM SAS 300C resistivity meter and presented as VES curves. Twenty-five VES location were evenly distributed within the study area. The VES interpretation results are of different VES curves types, namely QA, HA, KH, AH, H, KHK, KQ and AK types. The geoelectric sections delineated three to four geoelectric layers, which are the topsoil with resistivities and thickness values ranging between 113.4 Ωm and 753.1 Ωm and 0.4 and 4.4 m, respectively. The weathered layer has resistivity and thickness values ranging between 37.4 Ωm and 278.1 Ωm and 1.3 and 9.8 m, respectively. The partially weathered layer resistivity and thickness values ranging 495.1–651.1 Ωm and 10.2–22.2 m; for lateritic zones, it shows the resistivity and thickness values ranging 280.6–730 Ωm and 0.1–6.3 m. The geosections show a relatively thin overburden of less than 2.1 m. The third layer is the fractured basement. The fresh basement has a resistivity ranging between 930.5 and 4660 Ωm with depth starting from about 10 m to infinity (∞). Based on relatively thin overburden and the moderate to high fracture density of the basement bedrock, it was concluded that the groundwater potential of the study area is generally low to moderate. However, the aquifer in the north-eastern and south-eastern parts of the study area was determined to be of good quality. It can yield reasonable quantities of water that can serve the university community.

In situ natural radioactivity and radiological hazard assessments of granite gneiss outcrops in parts of the Southwestern Basement Complex of Nigeria

Radioactive emission (gamma ray) emanating from rock materials constitutes threats to humans and their environment. Hence, the natural radioactivity and radiological hazard indices of some granite gneiss outcrops with their residual soils from two different localities within the Southwestern Basement Complex of Nigeria were assessed using Gamma-ray spectrometry. The study aimed at determining the natural radiation levels of granite gneissic rocks and associated radiological threats to people living in the study area from gamma ray exposure. Data were collected along six geophysical traverses of 200 m each with station spacing of 5 m using the portable hand-held Gamma-ray Spectrometer. The results of weighted mean values of the elemental and activity concentrations for 40K, 238U, and 232Th are 2.00 ± 1.43%, 3.13 ± 0.90 ppm, 12.32 ± 4.99 ppm and 629.28 ± 447.29, 38.58 ± 11.02, 49.96 ± 20.23 respectively. The obtained mean concentration ratios of 1.32 for U/Th and 2.14 for Th/U were higher than 0.26 and lower than 3.5 global standard ratios respectively. The increase in activity concentrations and concentration ratio may have suggested the enrichment of radioactive minerals in the granite gneissic rocks. The annual outdoor and indoor effective doses of gamma ray exposure for people living in the study area were below the world permissible standard of 1 , thus, the area is radiologically safe. However, increase in estimated mean of AGDE and ELCR; 525.620 and 1.273 above the world permissible standards of 300 and respectively does not translate to significant radiological threats. Therefore, control measure by constant monitoring of the radioactivity levels of the area and rocks should be practiced.

Tectonic and structural analysis of the Migmatite–Gneiss–Quartzite complex of Ilorin area from aeromagnetic data

ABSTRACTIn an effort to have better understanding of the geologic settings and structural disposition of the Nigerian basement rocks, Ilorin area, a notably complex region within the South-western Basement Complex of Nigeria was studied using aeromagnetic data so that existing knowledge on the geology of the area can be appraised and updated. The aeromagnetic data was enhanced using various techniques which include the Total Horizontal Derivative (THD), Standard Euler Deconvolution, Tilt Derivative and Spectral Analysis. Striking features observed over the Residual Magnetic Field map were NE-SW trending anomalies aligned diagonally and running from the SW to the NE, forming a band having a width of between 16,000 and 20,000 m that coincided with the Banded Gneiss region on the geologic map; conspicuous E-W trending magnetic low whose location lies very close to the boundary between Migmatite and Banded Gneiss; and a ring-like magnetic low occurring in the south-eastern part of the residual map with no surface expression on the geologic map. Residual Magnetic Field values ranged from +157 to −202 nT. The THD map showed that the Banded Gneiss was the most deformed unit within the Migmatite–Gneiss–Quartzite complex. Major fractures coincident with Banded Gneiss boundaries appeared to be possible channels from which heat was leached in the regional system during metamorphism such that the Banded Gneiss region attained a relatively lower grade metamorphism than the Migmatite sharing boundary with it. Result from the spectral analysis showed that the magnetic basement in the eastern region was downthrown abruptly relative to that in the western portion. The abruptness was interpreted to mean that such subsidence was fault controlled. The study concluded that the presence of major fractures interfering with metamorphic processes in a regional settings may influence the grades of metamorphism that may result; that the schist region in the study area could be overlying a region of downthrown bedrock; and that the stress pattern that defined the crustal deformation pattern at the near crust in the past had changed compared to the currently dominant pattern.

Geophysical evaluation of groundwater potential in part of southwestern Basement Complex terrain of Nigeria

The geophysical assessment of groundwater in Awa-Ilaporu, near Ago Iwoye southwestern Nigeria was carried out with the aim of delineating probable areas of high groundwater potential. The area falls within the Crystalline Basement Complex of southwestern Nigeria which is predominantly underlain by banded gneiss, granite gneiss and pegmatite. The geophysical investigation involves the very low frequency electromagnetic (VLF-EM) and Vertical Electrical Sounding (VES) methods. The VLF-EM survey was at 10 m interval along eight traverses ranging between 290 and 700 m in length using ABEM WADI VLF-EM unit. The VLF-EM survey was used to delineate areas with conductive/fractured zones. Twenty-three VES surveys were carried out with the use of Campus Ohmega resistivity meter at different location and at locations areas delineated as high conductive areas by VLF-EM survey. The result of VLF-EM survey along its traverse was used in delineating high conductive/fractured zones, it is, however, in agreement with the delineation of the VES survey. The VES results showed 3–4 geoelectric layers inferred as sandy topsoil, sandy clay, clayey and fractured/fresh basement. The combination of these two methods, therefore, helped in resolving the prospecting location for the groundwater yield in the study area.

Integrating aeromagnetic and Landsat™ 8 data into subsurface structural mapping of Precambrian basement complex

The integration of Aeromagnetic data and remotely sensed imagery with the intents of mapping the subsurface geological structures in part of the South-western basement complex of Nigeria was developed using the PCI Geomatica Software. 2013. The data obtained from the Nigerian Geological Survey Agency; was corrected using Regional Residual Separation of the Total Magnetic field anomalies enhanced, and International Geomagnetic Reference Field removed. The principal objective of this study is, therefore, to introduce a rapid and efficient method of subsurface structural depth estimate and structural index evaluation through the incorporation of the Euler Deconvolution technique into PCI Geomatica 2013 to prospect for subsurface geological structures. The shape and depth of burial helped to define these structures from the regional aeromagnetic map. The method enabled various structural indices to be automatically delineated for an index of between 0.5 SI and 3.0 SI at a maximum depth of 1.1 km that clearly showed the best depths estimate for all the structural indices. The results delineate two major magnetic belts in the area; the first belt shows an elongated ridge-like structure trending mostly along the NorthNortheast-SouthSouthwest and the other anomalies trends primarily in the Northeast, Northwest, Northeast-Southwest parts of the study area that could be attributed to basement complex granitic intrusions from the tectonic history of the area. The majority of the second structures showed various linear structures different from the first structure. Basically, a significant offset was delineated at the core segment of the study area, suggesting a major subsurface geological feature that controls mineralisation in this area.

Geophysical mapping of the inland extension of Deep Ocean Fault zones, south-western Nigeria

Research activities close to the south western edge of the coastal line has shown inland extension of deep oceanic features identified as regional fault zones. This research work focused on mapping of inland extension of Chain Fault zones into the south-western part of Nigeria using both satellite images and aeromagnetic intensity map over a 55 km by 55 km Ifon Basement-Sedimentary area. The area is a transition zone between the south-western basement complex and sedimentary basin of the south-western Nigeria. Interpretations of magnetic field over the area revealed intra-sedimentary features identified as fault zone which form an alignment and inland extension pattern with the offshore Chain fault zone. On the account of the qualitative and quantitative interpretation of the acquired aeromagnetic data, the Landsat-ETM+ multi-spectral bands and Digital Elevation Model (DEM) of the topography of the area, the evidence of inter-sedimentary tectonic events are recorded in the geomorphic characteristics of the study area’s terrain in relation to the underlying influence of geology and structural trends revealed by extracted lineaments. From geophysical and geomorphologic interpretations, the observed geomorphic characteristics show three physiographical areas: the northern uplifted block (connection of a series of hills cut by deep-sided valleys), the central SW-NE trending subsided block (or graben) and the southern uplifted block. This geomorphic pattern of a series of flat and highly undulating terrain broken by a series of deep valleys and hills is believed to be related to rifting arising from the influence of the transform fault zones, which subdivide the area into smaller units. The rift valleys in the area are long, deep valleys bounded by parallel faults, or fractures. In addition, the predominant SW/NE, SE/NW and E-W trending linear structures mapped as fracture/faults cut the basement and penetrated the overlying Cretaceous and Tertiary sediments in the study area. Key word: Chain Fault zones, transform faults, rifting, inter-sedimentary tectonics, south-western Nigeria Embayment.

Evaluation of Resistivity Anisotropy of Parts of Ijebu Igbo, Southwestern, Nigeria Using Azimuthal Resistivity Survey (ARS) Method

This study was carried out to determine the anisotropic properties of parts of the Southwestern Basement Complex of Nigeria in Ijebu Igbo, which is underlain by migmatite gneiss and older granites.The surface water level (SWL) of 107 hand-dug wells were measured to determine the groundwater flow direction of the area. Thirty Azimuthal Resistivity Survey (ARS) were investigated along four azimuths; 0°, 45°, 90°, and 135° to determine the electrical anisotropy, the trend of fractures and their behavioural pattern with depth. The quantitative interpretation of the Radial Vertical Electrical Sounding (RVES) curves involved the use of partial curve matching, and computer iteration using WINRESIST program ...

Geochemical and Mineralogical Studies of Kaolinitic Clays in Parts of Ilorin, Southwestern Basement Rock Area, Nigeria

This study is focused on the clay deposits at Akerebiata area in Ilorin (north-central Nigeria), southwestern basement complex, Nigeria. The chemical and mineralogical compositions of the clays were investigated with the aim of determining their provenance, weathering history and most suitable use. X-Ray Diffraction (XRD) method was employed for the mineralogical analysis while X-Ray Fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectrophotometer (ICPMS) methods were used to for the determination of the bulk elemental composition. XRD analysis revealed kaolinite as the predominant clay mineral (54.2 to 90.9 wt. %) indicating intensive chemical weathering of aluminium-rich source rocks and exhaustive leaching under a warm, humid condition. Other non-clay minerals in the assemblages are quartz, rutile, anatase, microcline and plagioclase. Results of geochemical analysis show predominance of SiO₂ (47.14 to 64. 92 wt. %) and Al₂O₃ (19.47 to 29.39 wt. %) which support the kaolinitic nature of the clay and classify the clay as aluminosilicates. The relatively high mean values of the Chemical Index of Alteration (CIA) and Chemical Index of Weathering (CIW) (87.15 and 90.09) also suggest an intensive chemical weathering in the source area. Other relevant geochemical indices; plot of TiO₂, ratios of Th/Co, Th/Cr, Cr/Th and relative proportion of Ni and Cr reveal felsic igneous parent rock. The clays are characterized by light colour, fineness, low-moderate LOI, mineral assemblage and chemical composition that make them favorably compared with standards for refactory, ceramics, pottery and paints.

Preliminary investigation on industrial properties of the Olode-Falansa pegmatite, Southwestern Nigeria

In Olode-Falansa area, which is part of the southwestern basement complex of Nigeria near Ibadan, the major rock types are granite gneiss, quartzite, medium-grained granite and pegmatite. In particular, the pegmatites which occur as low-lying bodies, with a mineralogy dominated by pinkish-white microcline perthite, quartz, muscovite and plagioclase plus accessory constituents of garnet, beryl and tourmaline have been investigated for their distribution, physical, chemical and mineralogical characteristics in order to evaluate their industrial qualities. Chemical analysis shows variations in the major elements contents of the main minerals. In particular, quartz samples have 94.02 to 97.30% SiO 2 ; 0.86 to 2.60% Al 2 O 3 ; 0.05 to 1.02% K 2 O; and 0.13 to 1.29% Fe 2 O 3 , while the feldspar samples are 61.37 to 67.83% SiO 2 ; 16.85 to 18.40% Al 2 O 3 ; 11.35 to 14.32% K 2 O and 0.04 to 0.11% Fe 2 O 3 respectively. The total alkalis (Na 2 O+K 2 O) indicate K-feldspar composition. The specific gravity for quartz ranges from 2.60 – 2.63, while that of feldspar is from 2.55 –2.58. Water absorption capacity is higher for quartz (25.10 – 27.10%) than feldspar (4.61 – 5.80%). Compressive strength of selected pegmatite minerals indicates values from 133.24 to 223.84MN/m 2 . This investigation shows that the pegmatites have good potential for industrial uses. They can be used directly as raw materials or after beneficiation. In particular, the quartz and feldspars can find application in the refractory, glass, ceramic and abrasive industries. They can also be found useful in minor construction works especially in homes and offices. Muscovite can be used as thermal and electrical insulators, while the beryl can be useful as ornaments. The associated rocks such as gneisses, quartzites and granites can be useful in interior and exterior decorations as well as in tiles manufacturing. KEY WORDS: Olode Pegmatite; K-feldspar; Quartz; Raw Materials Global Journal of Geological Sciences Vol.2(2) 2004: 255-264