Precambrian Basement Complex Research Articles

Evaluation of groundwater potential zones using integrated geophysical approach in Obun-Ewi, Ondo East local government, Southwestern Nigeria

Obun-Ewi area is underlain by the Precambrian Basement Complex rocks of Southwestern Nigeria. The area suffers from a shortage of freshwater and the main source of water is rainwater. Groundwater provides an alternative solution to face the gap between water demand and available water in this area. Groundwater study involving the application of a very low frequency electromagnetic (VLF-EM) survey and vertical electrical sounding (VES) was carried out in parts of Obun-Ewi area Ondo State, Nigeria to evaluate the groundwater potential of the study area. ABEM WADI equipment was used to establish six (6) VLF-EM traverses with a station interval of 10 m. The inversion of the real component data of VLF-EM into 2D pseudo-sections was generated using Karous-Hjelt software. Linear features assumed to be minor fractures/conductors inferred from the filtered real pseudo-sections helped in choosing twenty-three (23) vertical electrical sounding points that were further probed using DDR-3 resistivity equipment. The Schlumberger electrode configuration was employed with half-current electrode separation (AB/2) ranging from 1 to 100 m. The partial curve matching technique was used to interpret the VES data quantitatively. The geoelectric parameters (depths and resistivities) were used to produce the geoelectric sections, isoresistivity map, isopach maps of the weathered layer and overburden, longitudinal unit conductance map and bedrock relief map of Obun-Ewi, Ondo town. The results obtained from the geoelectric sections revealed three subsurface geologic layers, namely: the topsoil, weathered layer (comprises of clay/sandy clay and laterite), and fractured basement/fresh bedrock. The topsoil resistivity varied from 56 to 1222 Ωm, and depth ranged from 0.5 to 1.8 m. The weathered layer resistivity values ranged from 16 to 1168 Ωm; while the thickness varied from 0.7 to 6.2 m. The overburden thickness varied between 1.6 and 7.2 m. The delineated weathered and fractured basement columns constituted the aquifer units. The composite groundwater potential map generated demarcated the study area into good, moderate and poor groundwater potential zones. The groundwater potential map revealed that about 69.6% of the study area fell within the poor groundwater potential rating, about 21.7% constituted the moderate groundwater potential rating while the remaining 8.7% constituted high groundwater potential rating. The study concluded that the groundwater potential of Obun-Ewi, Ondo town is generally poor, with areas around central South (around VES 9) and far Northern part of the study area (around VES 21) has good groundwater potential, suitable for siting boreholes.

GEOLOGY AND MINERAL RESOURCES OF EBONYI STATE, SOUTHEASTERN NIGERIA

Ebonyi State is underlain at depth by the Precambrian Basement Complex and by Cretaceous sedimentary units which include the Abakaliki Formation, Nkalagu Limestone, Amasiri Sandstone and Afikpo Sandstone and spans through Southern Benue Trough and Anambra Basin. Shales, sandstones, siltstones and limestones which range from shallow to deep marine depositional environments have intermediate to basic intrusive dolerites, extrusives and pyroclastics rocks emplaced in them. The sediments are dominated by physical structures such as faults, folds, fractures, joints, cross beds, mud cracks and an unconformity; chemical structures such as concretions and solution cavity; and biogenic structures such as burrows and bioturbation. The presence of benthic foraminifera such as Bolivina anambra and Haplopragmoides sp. suggest an upper bethyal deep to shallow marine environment for the sediments. Natural resources and mineral deposits such as lead, zinc, granite, limestone, dolerite, pyroclastics, salt-lake/brine, sand, laterites, clay, kaolin, iron ores, chalcopyrite, illmenite, fluorite, marble stone, quartz and copper ore which spread across the area, contribute largely to the gross domestic products of the state. Data gathered shows that 26% of the mineral deposits are partially exploited, 30 % are locally exploited, 4 % are highly exploited, while 39 % are dormant. Unfortunately, the reserve estimate of these mineral deposits are yet to be documented. Keywords: Anambra Basin, Ebonyi State, Mineral deposits, Southern Benue Trough, Structure; Uncomformity

Petrography of Allanite-bearing Tonalite from Iwo Region, Osun State, Nigeria

Abstract Primary, secondary and accessory minerals in tonalitic rocks from Iwo region of the Precambrian Basement Complex of Southwestern Nigeria were identified and analysed with the aim of determining the various processes involved during the crystallisation of magma. Thin sections of tonalite were prepared and studied with the aid of a petrographic microscope. The mineral assemblages observed are biotite, plagioclase, alkali-feldspar, amphiboles, pyroxene, quartz, muscovite and chlorite. Allanite, titanite, apatite and zircon occur as accessory minerals. Muscovite and chlorite are found to be secondary minerals. The mineral allanite has a characteristic form of zoning and shows evidence of metamictisation, and is surrounded by dark-coloured biotite having radioactive haloes. Titanite is anhedral to subhedral crystals and forms reaction rim round opaque minerals. Plagioclase shows evidence of compositional zoning as well as plastic deformation of the twin lamellae. The allanite observed is primary in nature and has undergone radioactive disintegration; chlorite and muscovite are formed by secondary processes of chloritization and sericitisation, respectively. The tonalite is formed as a result of rapid cooling of magma close to the Earth's surface.

Petrochemistry and petrogenesis of the Precambrian Basement Complex rocks around Akungba-Akoko, southwestern Nigeria

Abstract Field, mineralogical and petrochemical studies of the Precambrian Basement Complex rocks around Akungba-Akoko were carried out with the aim of determining their petrology, petrochemical characteristics and petrogenesis. The petrology of Akungba-Akoko area comprises migmatite, granite gneiss and biotite gneiss intruded by biotite granite, charnockite and minor felsic and basic rocks. Seventeen representative samples of the granite gneiss, biotite gneiss, biotite granite and charnockite were collected during field geological mapping of the area for petrographic and geochemical analyses. Modal mineralogy revealed that the granite gneiss, biotite gneiss and granite have assemblages of quartz + feldspar + mica + hornblende + opaques and are granitic in composition. The charnockite is characterized by anhydrous mineral assemblage of quartz + feldspar + biotite + hornblende + pyroxene + opaques. Petrochemical data of the rocks revealed that they are moderately to highly enrich in SiO2, sub-alkaline, peraluminous, magnesian to ferroan and calcic and have K/Rb < 283. The geochemical characteristics and discrimination of the rocks indicated that the granite gneiss and biotite gneiss are orthogneisses formed by metamorphism of igneous protoliths of granitic composition and the biotite granite and charnockite are of igneous/magmatic origin. The biotite granite, charnockite and the igneous protoliths of the biotite gneiss are I-type granitoids formed from crustal igneous-sourced melt(s), while the igneous protoliths of the granite gneiss is a S-type granitoid probably derived from shallow crustal or sedimentary-sourced melt(s). Tectonic discrimination of the rocks indicated that they were formed during a phase of magmatic activity related to collision and subduction.

Industrial rocks and minerals of Jordan: a review

Mineral resources of Jordan were utilized by different civilizations since prehistoric time. The following review highlights important and strategic commodities that are found in a small country with a potential promising future. Jordan is rich in its diverse industrial rocks and mineral resources that are part of the whole stratigraphic sequence from the Precambrian basement complex to the Recent sediments. Such diversity of resources enables Jordan to be not only a host of some unlimited resources but also a natural geology museum. The known commodities include, among others, phosphates, bituminous marl (oil shale), tar sand, varicolored marbles, travertine, radioactive minerals, building and construction materials, clays and clay minerals, diatomaceous earth, porcelanite, Dead Sea brines, rock salt, chalk, limestone, gypsum, glass sand, basalt, pyroclastics, zeolites, granite, copper, manganese, gold, etc. Some of these commodities are unique and unusual in its mineralogy, chemistry, and origin. A novel geopolymerization process was developed in Jordan to produce green building materials (geopolymers) by using Jordanian kaolinite. Volkonskoites (Cr-rich smectite) of Jordan act as a sink for hazardous elements. Varicolored marbles of Jordan are considered a natural cement factory and are analogs of cementitious repositories with the highest alkaline circulating waters in the World. New minerals were reported for the first time, some of which are only known in meteorites. The unusual enrichment of the reduced sensitive elements (RSE) in the oil shale (similar to the source of Mississippi Valley-type deposits) makes it unique as a potential source of these strategic elements.

Magnetic Susceptibility Mapping of Rocks and Depth Estimation of Anomalies: A Case Study of Igarra and Its Environs

Magnetic Susceptibility Mapping and Depth Estimation of Anomalies were carried out on Igarra and its environs, Southwest Nigeria. This was to assist in mineral exploration in the area. The study area is located within the Igarra schist belt which is underlain by rocks of Precambrian basement complex. The Total Magnetic Field over the study area was obtained by digitizing the aeromagnetic map of Auchi (Sheet 226) acquired from the Nigerian Geologic Survey Agency (NGSA). A total of 19 (nineteen) magnetic anomalies were identified on the map; 5 magnetic highs and 14 lows. 8 anomalies have a NW-SE strike direction, 4 in the NE-SW and 7 in the E-W direction. The amplitude of the anomalies and strength of the total field were used to determine the susceptibility values for each of the anomalies. The Susceptibility values were used to generate a Magnetic Susceptibility map of the study area on SURFER 13 software. TMI plots on the anomalies were carried out on MICROSOFT EXCEL 2010. Depth estimates of the anomalies were got using three methods: The Half Width rule, Hannel rule and Tirburg rule. The Susceptibility map shows a noticeable pattern of increase in magnetic minerals from the Southwestern to the Northeastern part of the map. The Depth of the basement anomalies were relatively shallow ranging from 0.8 km to 2.6 km. The results of this work provide a preliminary guide to those that engage in mineral exploration / exploitation in the area.

Combine electrical resistivity method and multi-criteria GIS-based modeling for landfill site selection in the Southwestern Nigeria

An integration of remote sensing and geophysical data was carried out in Odode-Idanre using Geographic Information System (GIS) approach with the aim of developing a landfill site selection map of the area. The area falls within the Precambrian Basement complex of southwestern Nigeria. The remote sensing involved the processing and interpretation of Landsat-7 EMT + image covering the study area and the data were used to produce the lineament, slope, drainage and land use maps of the area. The geophysical investigation involved the vertical electrical sounding (VES) technique using Schlumberger configuration with half electrode spacing (AB/2) varying from 1 to 65 m, One hundred and one (101) soundings stations were occupied within the study area. The interpretation of the VES data was used to generate the geoelectric section and determine Dar Zarrouk parameters. The results were used to generate thematic overburden and the coefficient of anisotropy maps. The geoelectric sections generally identified four geologic/geoelectric sequences that comprise topsoil, weathered layer, fractured Basement and fresh Basement. The depth to the Basement is generally less than 10 m. The multi-criteria evaluation (MCE) analysis were used to assign weights to slope, land use, drainage density, lineament density, coefficient of anisotropy and overburden thickness using the analytical hierarchy process (AHP) and this was used to produce the landfill suitability map. The area was classified into unsuitable, moderately suitable and suitable zones. The unsuitable areas cover about 21.9%, moderately suitable areas cover about 55% and the suitable areas cover about 23.1%. The suitable areas are scattered and discontinuous but predominant within the southern part of the area. For the development of waste dump site within the study area, it should be located within the southern part which was found to be suitable.

Geochemical characterization of Granitoids in Katchuan Irruan area: further evidence for peraluminous and shoshonitic compositions and post-collisional setting of granitic rocks in the Precambrian Basement Complex of Nigeria

Petrographic studies on Granitoids from Katchuan Irruan and adjoining areas, southeastern Nigeria, has shown that they are garnetiferous biotite granite, aplitic granite, porphyritic hornblende biotite granite, porphyritic muscovite biotite granite, weakly foliated leucogranodiorite and simple pegmatite. They are closely associated with the Precambrian Basement Complex rocks which they intruded. Modal analysis shows that the rocks consist of quartz (10%–25%), oligoclase (10%–30%), K-feldspar (15%–35%), biotite (3%–25%), with occasional garnet, hornblende, muscovite, and accessory chlorite, haematite and magnetite. Geochemical data indicates that the rocks are generally shoshonitic, alkali-calcic to calcic, ferroan and peraluminous. They are enriched in large ion lithophile elements as well as high field strength elements (Hf, Ta, Yb, Sm, Zr and Y). Their trace elements and REE patterns are similar, indicating that they are co-genetic. They are characterized by high fractionation factor (La/Yb)N (3.04–228.44) and pronounced negative Eu anomalies (Eu/Eu*) (0.23–0.71). Their overall geochemical features indicate that they were most likely derived from partial melting of crustal materials in an orogenic (post-collisional) tectonic setting. They are therefore related to the Pan-African granites, otherwise known as the Older Granites which were emplaced during the Pan African orogenic event.

GEOLOGICAL AND LITHOLOGICAL MAPPING OF PART OF IGARRA SCHIST BELT USING INTEGRATED GEOPHYSICAL METHODS

Integrated geophysical techniques involving magnetic and radiometric data were used to investigate the subsurface geometry of Igarra schist belt in Precambrian basement complex of southwestern Nigeria which falls within the latitude range of 7° 1635.6” to 7° 1736.0’ North and longitude range of 6° 0534.1” to 6°05’44”East, with a view to interpret the geology of part of Igarra schist belt and estimate the depth to basement of magnetic source in the area. Six profiles were established with the objective of delineating the metasediments and its structural attributes, and geophysical measurements were made at 5m intervals along these profiles. The results of magnetic datasets were presented as maps and profiles of varying magnetic intensities and the causative rock types. Qualitative interpretation of the magnetic data using Reduction to pole, Analytical signal, first vertical, horizontal and tilt derivatives, upward continuation filters shows what has been interpreted as the signature of a near-vertical fault, trending along a NE-SW and NW-SE direction while radiometric datasets gave geochemical rates of U, Th and K as well as the effect of water contents on the rocks present within the study area. Qualitative and quantitative interpretation of individual magnetic anomalies and geological knowledge of the survey area yielded information on the depth of the geological features (e.g. rock contact, faults or fractures), structure and magnetic properties of rock units. 3D Euler deconvolution and Average radial spectrum were adopted to estimate the depth of the magnetic sources which ranges from – 92.895m to 73.95m; -115.45m to 57.44m and 63m to 44.1m; 88.2m to 81.9 m respectively. The Igarra schist belt has evolved different episodes of orogenies and the metasediments were formed from low grade regional metamorphism of argillaceous sediments such as shales or sediments of varying composition.

Integrating magnetic and stratigraphic data to delineate the subsurface features in and around new Galala City, Northern Galala Plateau, Egypt

ABSTRACTThe Egyptian Government is developing a new city, Galala, above the Northern Galala Plateau, western side of Gulf of Suez between Ain Sukhna and Zafarana. The aim of the study is integrating magnetic and stratigraphic data to delineate the subsurface features beneath the New Galala City, in order to avoid the possible geological hazards. The stratigraphic succession in the study area consists of Precambrian basement complex overlain unconformably by Phanerozoic sequence. The Phanerozoic sequence composed mainly of siliciclastic-dominated rocks superimposed by carbonate-dominated rocks. The carbonate-dominated rocks cover most surface area, whilst the siliciclastic-dominated rocks exposed along eastern and southern foot slope of the Northern Galala Plateau. The observed palaeo-karst surfaces, fissures, caves, sink-holes and fault zones within carbonate rocks may cause some geological hazards in the study area. The total intensity aeromagnetic map was subjected to un-prescribed structural index 3D-Euler Deconvolution (ED), the tilt angle derivative (TDR) and the power spectrum in order to estimate both trends and source depths. The source depths range from 500 m to 4000 m, which result from the Precambrian basement complex. However, the trends of encountered structural elements are mainly NE–SW, NW–SE, NNW–SSE and E–W directions.

DEFORMATION MECHANISMS, TIMING AND SHEAR SENSE ANALYSIS OF PART OF THE PRECAMBRIAN TERRAIN OF SOUTHWESTERN NIGERIA.

The study area is part of the polycyclic Precambrian Basement Complex of southwestern Nigeria, which comprises meta-sediments and granitoids of varying compositions. The area was primarily deformed into a large-scale sheeted structure, which was sequentially followed by developments of first and second phases of folding that interfered with each other. Brittle to semi-ductile shear deformations, initiated by an ESE-directed transport of the hanging wall of a major NE-SW trending low-angle normal fault culminated in the third phase of fold and development of widespread shear zones. Latter phases of deformation resulted in rotation of finite strain axis relative to the instantaneous strain during a non-coaxial progressive simple shear deformation. We posit that the dominant terminal mechanism of deformation in the area is the late-kinematic progressive heterogeneous simple shear during the late- to post-Pan African orogenesis.

Analysis of aeromagnetic anomalies and structural lineaments for mineral and hydrocarbon exploration in Ikom and its environs southeastern Nigeria

The purpose of this study is to analyze the aeromagnetic data of Ikom and its environs in Cross-River State, Nigeria in order to delineate the structural lineaments according to their spatial and directional attributes as well as define the depth to magnetic causative bodies. This was achieved with the aid of an acquired, digitized and processed aeromagnetic intensity contour map covering Ikom and its adjacent areas. The aeromagnetic data was subjected to diverse data enhancement and transformation routines. Regional-residual analysis was implemented on the total magnetic intensity map (contour interval = 20 nT) to generate a residual magnetic intensity contour map. Results show that the area is characterized by a very complex pattern of magnetic intensities of both long and short wave-lengths. Sequel to the regional-residual anomaly separation, azimuth orientation of the lineament structures delimited on the maps portray NS and NE-SW as the principal trends with E-W and NW-SE as the minor trends. Two depth sources were obtained by employing the commonly known Peter's half-slope method. Depth range for the deeper causative sources is 0.83 km–3.5 km with a magnetic intensity range of −30 nT to −220 nT while the superficial sources had a range of 0.2 km–0.75 km and a magnetic intensity that vary from −10 nT to 20 nT. The deeper magnetic sources are attributed to the underlying pre-Cambrian basement complex rocks and intra basement structures such as fractures and faults whereas the superficial sources are due to basement intrusives as well as ore-bearing veins present in the overlying Cretaceous rocks. The shallow basement depth and prevalence of intrusives and linear structures are indications of an area of good mineral prospects but unfavorable for hydrocarbon formation.

Application of geophysical approach to highway pavement failure: a case study from basement complex terrain southwestern Nigeria

Geophysical survey involving Schlumberger Vertical Electrical Sounding, 2-D imaging dipole–dipole technique and ground magnetic method were carried out along Ibadan-Ife Highway located in the Precambrian Basement Complex of Southwestern, Nigeria to examine the geological factors responsible for Highway pavement failure. This was with the view to detailing the subsurface geoelectric sequence, mapping the subsurface structural features within the sub-grade soil and delineating the bedrock relief as a means of establishing the cause(s) of the road pavement failure. The geoelectric sections, 2-D resistivity structures and modeled magnetic profiles revealed that the stable segments were founded on a shallow/outcropping basement near homogeneous substratum devoid of major geological features while linear features suspected to be fault/fractured zones, buried stream channels, bedrock depressions and lithological contacts were identified beneath the failed segments of the highway pavement. The geoelectric sections generally identified four geologic layers comprising the topsoil, weathered layer, partly weathered/fractured basement and fresh bedrock. Thus, the failed portions of the road are probably precipitated by very thick and low resistive substratum (clay) beneath the highway pavement and the identified suspected linear features are the major geological factors responsible for the highway pavement failure.

Review of the occurrence and structural controls of Baryte resources of Nigeria

Baryte occurrences in Nigeria are spread across the Cretaceous Benue Trough which comprises of carbonaceous shales, limestone, siltstones, sandstones as well as in the northeastern, northwestern and southeastern parts of the Precambrian Basement Complex comprising of metasediments and granitoids. The mineralization is structurally controlled by NW-SE, N-S and NE-SW fractures. The common mode of occurrence for these barytes is the vein and cavity deposits type usually associated with galena, sphalerite, copper sulphide, fluorite, quartz, iron oxide as gangue minerals. Principal areas of baryte occurrences in Nigeria include Nassarawa, Plateau, Taraba, Benue, Adamawa, Cross River, Gombe, Ebonyi, and Zamfara. A large part of the vast baryte resources in Nigeria is still underexploited and further exploration work is needed to boost its exploitation. The inferred resource and proven reserve of baryte is put at over 21,000,000 and about 11,000,000 metric tons respectively. The economic evaluation of these barytes is viable having low (SG = < 3.5) to high (SG = 5.3) grades. The presence of associated minerals produces low quality barytes and as such blending and beneficiation is required to improve its quality.

Exploration for iron ore in Agbado-Okudu, Kogi State, Nigeria

This report details the result of geophysical exploration for iron ore; which involved vertical magnetic intensity (∆Z) and gravity measurements, to delineate the geometry and depth extent of the deposit and acquiring quantitative and qualitative information for pre-drilling purposes in Agbado-Okudu. It is located about 3 km from Jakura along Lokoja-Jakura marble quarry and within low latitude precambrian basement complex district of Kogi State, Nigeria. A total of 517 magnetic measurement points along 16 traverses and 330 gravity reading along 11 profiles on the deposit in northeast–southwest azimuth were undertaken. The magnetic and gravity data enhancement involved linear regression curve fitting and fast Fourier transform, which were used to construct residual magnetic (RM) and gravity (RG) anomalies, analytic signal amplitude, Euler deconvolution at varying spectral indices (SI), power spectrum, and source parameter image (SPI), using the submenu of Geosoft Oasis Montaj software. Interpretation of the RM and RG anomalies revealed a primary causative body which perfectly correlates the positive anomalies and iron ore deposit, in form of a horizontal or gently dipping dyke with strike length of 600 m and average width of 110–130 m, within the gneiss complex in the north and trending south of the area. A secondary causative body associated with the negative anomalies and inferred as a vertical/near vertical thin sheet striking northeast–southwest coincided with the granitic and quartzitic intrusion. The NW–SE and E–W lineament trend conformed Kibarian and Liberian orogeny cycles of generally known structural trends in Nigeria, which shows that the iron ore deposit is structurally controlled. Depths to sources were estimated within range ≤ 2–24 m and 37.5–60 m, regarded as shallow and relatively deep depths, respectively. Ten vertical boreholes ranging in depth between 50 and 100 m are recommended, five of which require a priority attention to ascertain the thickness of the primary causative body.

EVALUATION OF GROUNDWATER POTENTIAL OF ODEDA LOCAL GOVERNMENT AREA, OGUN STATE, SOUTHWEST NIGERIA

Evaluation of groundwater potential in Odeda Local Government Area, Ogun State, Southwestern Nigeria, has been carried out in this study using Vertical Electrical Sounding method. The study area is underlain by Precambrian Basement Complex rocks of Southwestern Nigeria. These rocks are inher-ently characterized by low porosity and permeability. The interpretation of thirty (30) vertical electrical sounding (VES) conducted using the Schlumberger electrode array shows four geo-electric layers in the subsurface within the study area. The overburden thickness varies from 5.9 to 39 m across the study area. This was used to prepare the groundwater potential map which assisted in the zoning of the area into low, medium and high groundwater potential zones. The study showed that about 60% of the study area falls within the low/medium rated groundwater potential zone while the remaining 40% constituted the high groundwater potential zone. Hence, the groundwater potential rating of the area is generally low.

Evaluation of Groundwater Potentials for Borehole Drilling by Integrated Geophysical Mapping of Auchi-South Western Nigeria Using Very Low Frequency Electromagnetic Profiling (VLF-EM) and Vertical Electrical Sounding (VES)

An integrated geophysical survey involving Very Low Frequency Electromagnetic (VLF-EM) and electrical resistivity sounding was conducted at Auchi- Southwestern Nigeria, in order to delineate the fissured zones and associated groundwaterbearing media for borehole drilling in the study area. The area is underlain by the Precambrian Basement Complex rocks and in some places sedimentary rocks. The VLF-EM traverses were established along two traverses using ABEM-WADI equipment, with a station interval of 10 m and with lengths ranging from 200 to 240 m. Linear fissures presumed to be geologic fissures inferred from the filtered real and filtered imaginary assisted in selecting seven VES points that were further probed using ABEM SAS 1000 Resistivity meter. The spreading were conducted using the convectional Schlumberger electrode configuration with half-current electrode separation (AB/2) that ranged from 1 to 225 m,was used for the sounding. The VES data were presented as depth sounding curves and were suitably iterated using Schlumberger O’Neil software. The VLF filtered real profile showed a high peak trend signifying a fracture signature. The delineated weathered and basement column constituted the aquifer units for borehole drilling. Six lithologic formations were delineated which included the top soil, clay/shale, fine grained sand, coarse grained sand, fractured bedrock and fresh bedrock. Four Model field curves were delineated which included HAKQ, HKQQ, KHAA and KHKH. There are two main targets for groundwater exploration in the study area. These included the weathered zone (fine and medium grained sand) and the fractured zone. The thickness of these zones varied between 15.2 to 50.1 m. Based on the geophysical parameters such as thin overburden thickness, clayey weathered layer and low fractured basement characterized by the study area, it is therefore inferred that the groundwater potential of the area is low. Nevertheless, the study has justified the use of integrated geophysical mapping as a better tool in evaluating the groundwater potential in crystalline terrains. Keywords : Integrated geophysical survey, electromagnetic profiling, vertical electrical sounding, groundwater resources, Auchi

The use of index tests to determine the mechanical properties of crushed aggregates from Precambrian basement complex rocks, Ado-Ekiti, SW Nigeria

This study assessed the possibility of using index tests to determine the mechanical properties of crushed aggregates. The aggregates used in this study were derived from major Precambrian basement rocks in Ado-Ekiti, Nigeria. Regression analyses were performed to determine the empirical relations that mechanical properties of the aggregates may have with the point load strength (IS(50)), Schmidt rebound hammer value (SHR) and unconfined compressive strength (UCS) of the rocks. For all the data, strong correlation coefficients were found between IS(50), SHR, UCS, and mechanical properties of the aggregates. The regression analysis conducted on the different rocks separately showed that correlations coefficients obtained between the IS(50), SHR, UCS and mechanical properties of the aggregates were stronger than those of the grouped rocks. The T-test and F-test showed that the derived models were valid. This study has shown that the mechanical properties of the aggregates can be estimated from IS(50), SHR and USC but the influence of rock type on the relationships should be taken into consideration.

Groundwater Potential and Vulnerability Assessment from Integrated Geophysical Methods, Borehole Logging, and Hydrogeological Measurement

Geophysical investigations and hydrogeological measurements were carried out in Akoko area of Ondo State, Nigeria which are characterized by rugged hills of Precambrian Basement Complex of Southwestern Nigeria comprising mainly of the Migmatite-Gneiss-Quartzite Complex of Archean-Proterozoic age. The study was aimed at evaluating the groundwater potential of the area and assess the vulnerability of the aquifers/water bearing units within the phreatic zone to contamination especially from surface activities/anthropogenetic sources. Seventy soundings were carried out along fifteen traverses where the VLF-EM measurement was also conducted. The hydrogeological measurement involved determination of static water level/vadose zone thickness from 138 wells. Also four borehole were drilled after thorough geophysical investigations in order to constrain the interpretation of the geophysical investigation. Findings show that the major water bearing units/aquifer in the area are the weathered layer (clayey in nature) and fractured basement as delinated on the geoelectric sections, borehole sections, and very low frequency electromagnetic. The combination of these aquifer units are common in Ikare and Akungba parts of the study area. The visible depth of groundwater exploitation in the area is between 10 – 40 m. The static water level is generally less than 5 m. The map of the overburden shows that Akoko area is generally made up of thin overburden thickness except at Irun, Ogbagi, Arigidi, and Oke Agbe that showed moderate overburden thickness (10 m – 20 m). The static water level measured in the study area ranged from0.75 m – 16 m, with a modal range of 1.1 – 3.0 m as they constituted for about 78 % of the area. This generally showed that the static water level was shallow across the study area, thus suggesting that the surficial aquifers/water bearing units would be highly vulnerable to anthropogenetic/surface activities which are the major sources of groundwater contamination. Clay or silt, characterized by low resistivity (1 – 100 Ω-m) and very low permeability, and impervious or semi-impervious topsoil materials (laterite and lateritic sand), characterized by high resistivity values (&gt;400 Ω-m) constitutedthe protective layers that cappedthe vadose zones in the area. The topsoil can provide protection to a reasonable extent, but limited due to its thin thickness across the 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.