Basement Complex Rocks Research Articles

Provenance and tectonic settings of the Eze-Aku Sandstone (Turonian) in Awajir and adjoining areas, Southern Benue Trough, Nigeria: evidence from petrography and geochemistry

Eighteen representative samples for petrographic (6) and geochemical (12) studies were collected from the Turonian (Eze-Aku Formation) sandstones outcropping within Awajir and adjoining areas in the northern section of the Southern Benue Trough. Sandstones of different textural variety underlie the study area: fine-, medium- and coarse-grain sandstones facies. Field study revealed an overall coarsening upward succession, ripple bedding surfaces, cross-stratification and bioturbation, which suggest prevalence of a shallow shelf with relict shoreline environmental settings. Petrographic study show that the sandstones are subarkosic to arkosic and deposited in a humid to semi-humid paleoclimatic condition. Polygenic (mixed) provenance source is inferred for the sandstones and the insignificant presence of sedimentary rock fragments in the framework constituents suggests the Precambrian Basement complex of southern Nigeria as the most likely source area. This result is consistent with trace element ratios such as Cr/Zr (< 0.6) and Cr/Th (0.3–15.7) as well as La/YbN versus CeN diagram which points all the sandstone facies to an intermediate Igneous provenance, unambiguously ruling out the chances of mafic igneous rocks being present in the source terrain. The most probable provenance for the sandstones is the continental Basement complex rocks of Obudu plateau and Oban massifs. The study showed that there was a mild influence of diagenetic alteration on the sandstone facies after deposition in an active continental margin-continental island arc setting.

Radioactivity, radiogenic heat production and environmental radiation risk of the Basement Complex rocks of Akungba-Akoko, southwestern Nigeria: insights from in situ gamma-ray spectrometry

The Basement Complex rocks of Akungba-Akoko, southwestern Nigeria, typically migmatites (M), biotite gneisses (BGN), granite gneisses (GGN), charnockites (Ch), biotite granites (BG) and pegmatites (P), were assessed using ground gamma-ray spectrometry (GRS). This study aimed at determining rocks’ radionuclides concentration, alterations, radionuclides mobilization, radiogenic heat production (RHP) rate (first report for the area) and environmental radiation risk to humans. The results of this study were integrated with previous data on the petrography and geochemistry of these rocks, for detailed interpretation. The results of average elemental and activity concentrations for Akungba-Akoko rocks, were 2.66%, 3.16 ppm and 13.98 ppm, and 831.35, 39.01 and 56.77 $$Bq{kg}^{-1}$$ for 40K, 238U and 232Th, respectively; with increasing rock order of Ch < M < GGN < BGN < P < BG. High radionuclides concentration in the rocks, with exception of charnockites, were determined by high amount of K-feldspar, plagioclase, biotite and accessory minerals—zircon and monazites. On the other hand, the low radionuclides concentration in the rocks, especially in Ch and M, were aided by the variability of the naturally occurring radioactive elements (NORMs) caused by alterations and mobilization during metamorphism and crystallization processes as suggested by radioelements composite, K/eTh ratio and F-parameter of Efimov analyses. RHP average of 2.03 $$\mu W{m}^{-3}$$ above the crustal average range of 0.8–1.2 $$\mu W{m}^{-3}$$ may have significantly contributed to the heat flux in the studied area; however, the RHP of charnockites are lower than the crustal range. The absorbed dose rate average of 87.98 $$nGy{ h}^{-1}$$ was within the permissible range, and other estimated radiological parameters, namely annual effective doses, hazard indices, gamma activity and activity utilization index, were all far below the permissible limit of 1 $$mSv {y}^{-1}$$ for these rocks. However, the annual gonad dose equivalent (618.874 $$\mu Sv{ y}^{-1}$$ ) and excess life cancer risk (1.511 × 10− 3) were above their permissible limits. Due to the high gamma radiations from the pegmatitic and biotite-rich rocks in the studied area, their high usage should be reduced. Hence, periodic monitoring of the study area is advised.

Grain Size and Heavy Minerals Analysis of Maastrichtian Sandstone, Anambra Basin, Nigeria: Implication for Aquifer Properties

The Maastrichtian sediments of Anambra Basin, south western Nigeria was studied for grain characteristics and maturity of the sediments, so that by combining sedimentological characteristics, maturity and its paleoenvironment of deposition of the Ajali sandstone, in order to ascertain the aquifer properties of the groundwater within the study area and by extension the availability of drinking water for both the urban and rural settlers. Grain size analysis (51 samples) and heavy mineral analysis (15 samples each) were analyzed. The textural parameters show that the Sandstone are medium sand, poorly to moderately sorted, coarse to strongly coarse skewed with mesokurtic to leptokurtic grains. The heavy minerals present in lithologic sand and sandstone units of Ajali Formation are mainly zircon, rutile, tourmaline, apatite, staurolite, and opaque minerals (Goethite, hematite, ilmenite), these heavy minerals found in the sandstone are associated with igneous and metamorphic source which indicates that these maastritchian sediments are from basement complex rock The ZTR index of 67.96% and the values of the kurtosis indicates a sub-mature sandstone to mature sandstone, which gives an excellent aquifer properties. Also, the paleoenvironment of deposition of the Maastrichtian sediments is Fluvial. The sand and sandstone bodies deposited in a fluvial system have sheet-like geometries and due to the differences in the extent of aquifer compartmentalization, Sandstone deposited in fluvial environment normally has better hydraulic conductivity which again reveals a good aquifer property. The sedimentological characteristics for the Sandstone exposed at Fugar and environs, is a coarsening upward sequence (increasing grain sizes) with a progressive increase in sorting. since hydraulic conductivity increases with increasing grain sizes and sorting, hence, excellent aquifer characteristics for the groundwater within the study area. The foregoing revealed that the aquifer geometry and properties of the study areas is favourable for the availability of drinking water for both the Urban and rural dwellers within these communities.&#x0D; Keywords: Aquifer geometry, groundwater, hydraulic conductivity, Anambra Basin

Mapping Ground Exposure Rate and External Hazard Index in Part of Basement Complex Rock of North Central Nigeria

In this work, a preprocessed aero radiometric survey data of geologic survey map series of Nigeria basement complex sheet 145 was used to map the spatial distribution of ground level concentration of the three radioelements that contribute significantly to the emission of gamma rays, notably potassium (40K), thorium (232Th) and uranium (238U) and estimating the external hazard associated with human exposure due to the elements. The elemental average concentrations of 40K, 232Th and 238U obtained from the survey data are 1.37485%, 24.5297ppm and 5.5491ppm respectively. The relative concentrations of the three elements are in line with the global trend where Th records the highest mean concentration, followed by U with then K recording the least. Except for K, the values of the other elements were found to be above the global crustal abundance ranges of 2 - 2.5% for 40K, 8 – 12 ppm for 232Th and 2 – 3 ppm for 238U. The mean ground level external dose rate was found to be 213.2 ±21.2 nGyh-1. This is about four times higher than the global average terrestrial dose rate of 55 nGyh-1. The computed external hazard index however gives an average value of 0.329, which is within the acceptable limit (&lt;1). External hazard index above this limit were however recorded at three points, spanning a small area of about 0.096 km2. In situ and ground geophysical measurements are therefore

Interpretation of Airborne Magnetic and Geo-electric Data: Resource Potential and Basement Morphology of the Ikom–Mamfe Embayment and Environs, Southeastern Nigeria

The Ikom–Mamfe Embayment, which cuts across southeastern Nigeria and southwestern Cameroon, is a bifurcation of the Benue Trough and the NW–SE splay component of the NE–SW trending trough. The Nigerian sector of the embayment, a sedimentary province bounded to the north and south by basement terrains, is considered a relatively frontier basin with little information about its resource potential. Here, airborne magnetic, resistivity and self-potential (SP) data were integrated in studying the Nigerian sector of the embayment and its surrounding localities. This study aimed to delineate (possible) mineral-bearing lineament structures and their corresponding trend orientations, to evaluate their relationship to tectonic fabric, to estimate depth of perturbing causative sources, to map ore bodies, and to identify probable locations for detailed petroleum system analysis. For the first time, 2D electrical resistivity and SP methods were deployed in the sub-surface characterization of the embayment. Results of aero-magnetic data analysis revealed the presence of high magnetic intensities predominantly in the western and northeastern parts of the study area. The high intensities observed at the western part are due to mineral ore bodies present within a sedimentary host. In addition to the presence of mineral ores, the noticeable high magnetic signatures at the northeastern part are associated with the presence of outcropping units of basement complex rocks that comprise mainly of migmatitic metasediments. The large variation in magnetic intensities within the embayment is attributed to the combined effect of igneous intrusives and mineral-bearing lineaments emplaced within the overlying sediments. Analysis of structural lineaments depicts E–W and ENE–WSW as the dominant orientations with minor NW–SE, NE–SW and NNE–SSW trends. The NE–SW and ENE–WSW structures are aligned parallel to the Benue Trough and the Cameroon Volcanic Ranges, and are genetically related. These lineaments occur in the form of faults, fractures and veins, and they are densely distributed within some areas of moderate to high intensities and analytical amplitudes. This suggests a possible relationship between structural lineaments and metalliferous deposits. These lineaments were marked for ground geophysical surveys. The geophysical traces derived from these areas reveal numerous underlying mineral bodies of contrasting resistivity and potential with their host formation. These bodies are shallow magnetic sources exposed in the first and second vertical derivative images. These show remarkable agreement between the geo-electric data and the aero-magnetic data. The results of quantitative assessment show shallow basement depth and, hence, thin sedimentary layer (0.2–2.4 km) within and around the embayment, which is insufficient for the concealment of hydrocarbon resource. In addition, the presence of numerous intrusive rocks implies a high temperature environment favorable for “cooking” of potential source rocks beyond the hydrocarbon generating window. This renders the area disadvantageous for hydrocarbon exploration. However, we discover that the sedimentary thickness (ranging between 3 and 4 km) mapped at the southwestern part of the area could favor the formation and accumulation of hydrocarbon fluids. This area, characterized by moderate igneous intrusion, lies approximately northeast of the prolific Niger Delta oil province and shows fair to good sub-surface structural conditions required for hydrocarbon entrapment. The basement morphology, sedimentary thickness and structural disposition call for a detailed petroleum system analysis within this area.

Application of MIKE SHE software for estimation of groundwater recharge in Ogun and Oshun basins, southwestern Nigeria

MIKE SHE software was used to estimate recharge into the aquifers of Ogun and Oshun Basins. Abeokuta within the Ogun Basin and Oshogbo in the Oshun Basin are subdivided vertically into two components: atmosphere, and unsaturated zone. The atmosphere zone comprises of rainfall and potential evapotranspiration, while the unsaturated zones, comprises of the Basement Complex and Sedimentary rock. Daily records from two rainfall stations, Oshogbo station (2008–2011) and Abeokuta station (2010–2014) water years were obtained for simulation of groundwater recharge processes using MIKE SHE model. The simulation results showed that daily groundwater recharge is influenced by rainfall and ranges from 0 mm∙day–1 in January when there was an insufficient rainfall in the two stations to 10.89 mm∙day–1 in Abeokuta and 29.85 mm∙day–1 in Oshogbo in the month of August when the soils had attained field capacity. The study found out that there are more daily groundwater recharge in Oshun basin compared to that of Ogun basin. This was alluded to more rain-fall and less evapotranspiration recorded at Oshun basin as compared to Ogun basin coupled with the sedimentary soil which allows more movement of water into the aquifer of the basin. It is recommended MIKE SHE model should be used to estimate recharge in other basins in Nigeria and Africa for quick and effective daily recharge calculations to permit better and scientific decision making in these areas.

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.

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 &lt; 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.

Interpretation of high resolution aeromagnetic data of Kaoje and its environ, western part of the Zuru Schist belt, Nigeria: implication for Fe–Mn occurrence

This study presents an appraisal of mineralization potential and the geologic record of Kaoje and environs using high-resolution aeromagnetic data. The data were analyzed using the fast Fourier transform technique for reduction-to-equator (RTE), analytic signal (AS), total horizontal derivative (THDR), tilt derivative (TDR), spectral analysis and Euler deconvolution at varying spectral indices. The reduced to equator residual magnetic intensity range from -73.4 to 205.6 nT and are associated with contrasting lithology of the Sedimentary and Basement Complex rocks. The anomalies and analytic signal amplitude unfold and update the extension of Zuru Schist to the southern region of Kaoje, elongated banded gneiss within the schist body, pegmatite intrusion through the migmatite and NNW-SSE trending schist hosted manganite and sandstone-hosted goethite. Estimated depth to shallow and deeper magnetic sources ranged from 0 to 59 m and 225–415 m respectively, and the corresponding Euler solutions revealed perfect clustering along notable geologic features and minerals. The iron mineralization are revealed as sourced from the magmatic bodies that lie beneath the sedimentary rocks and a corresponding sphere geologic model within northwest and southwest of Kaoje at a depth range of 0–225 m. The structural trends suggested the tectonic events in the area and indicate an imprint of Zungeru-Anka transcurrent fault that serves as a conduit for iron mineralizing fluid to Kaoje.

Geology and petrography of precambrian rocks of Katsina urban area, northwestern Nigeria

This present study, the mapped area is located between latitude E07°35'00'' to E07°39'0011" and longitude N13°00'00'' to N12°57'00" of sheet 34NW, Katsina State, Northern Nigeria. The area is underlain by Basement Complex rocks and syeno-granitic rocks which dominate in the area. The two sets of granitic rocks were observed and distinguished by texture. The northwest of the mapped area consists of very coarse to coarse grained syeno-granitic rocks, while in the southeast, the rocks are medium to coarse grained. These outcrops exhibit various systems of joints. The mineralogical compositions determine by thin section results displays: quartz, biotite, muscovite, plagio-clase feldspar, apatite, sericite, hornblende, augite and microcline. There are two generalizations of joints with primary WSW to ENW direction and NE-SW, MMW-SSE and WWW-ESE secondary direction of NE-SW, MME-SSE and WWW-ESE.

The Application of Airborne Geophysical and Satellite Imagery Data in the Delineation of Rock Boundaries and Structural Lineaments in Anka Sheet 52, Northwestern, Nigeria

The understanding of different lithologies and geological structures is a major task of geologists for accurate geological map during geological mapping exercise. In doing so, geologist must be able to cover broad areas of the surface or subsurface of the earth through collection of reliable remote sensing data over a wide region. The Landsat ETM + from Global Land Cover Facility (GLCV), Shuttle Radar Thematic Mapper- Digital Elevation Model (SRTM, DEM) data from Global Mapper version 14, Airborne Magnetic and Radiometric data from Nigeria Geological Survey Agency (NGSA) was acquired and interpreted with the help of computer-image processing technology such as Oasis Montaj and ArcGIS software to process, display and represent results covering the study area (Anka sheet 52). The basis of this technology is the representation of the radiometric data in a digital raster format that contain both amplitude and spatial information. In this format, the data was analyzed, enhanced for visual inspection and combined with other types of data to form colour composite images that clearly subdivide the Basement complex rocks into Pan-African Granites from the Metasediments and the most eye-catching feature is the basement-sedimentary contact. Also, a major NE–SW trending structural lineament referred to as the Anka Fault trends for almost 25km and other subsidiary lineaments trending NW–SE with few E–W trends. Keywords: Landsat ETM + , Magnetic, Radiometric, Structural Lineament, Satellite Imagery. DOI : 10.7176/JEES/10-1-05 Publication date: January 31 st 2020

Utilizing landsat-8 sensor operational land image data for hydrothermal alteration mapping within Anka Schist Belt, northwestern Nigeria

Exploring for mineral deposits within the Anka Schist Belt involves the use of traditional geological techniques such as geochemical and geophysical studies that are very expensive and time consuming. There is therefore need for a better alternative that will provide accurate and reliable information with cost effective and time efficient solution. This effort seeks to explore the potential of remotely sensed digital data in highlighting mineralized zones through hydrothermal alteration studies. Landsat 8 OLI data covering the investigated area was used to detect and map locations of hydrothermal alterations. Image processing methods used were spectral enhancement, false colour composites, band rationing and Principal Component Analysis. Results of false colour composites of band 5: 7: 3 highlighted generally locations of hydrothermal alterations. Band ratios of 4/2, 6/7 and 6/5 revealed the presence of ferric iron minerals, clay rich minerals and ferrous minerals respectively. Principal Components (PCs) of two sets of images (2, 4, 5, 7 H-image and 2,5,6,7 F-image) depicting iron-oxide and hydroxyl mineral deposits as bright pixels were generated. Colour composite of H, F and H+F images enhanced the location of the mineral deposits, by showing areas of mineralization in dark blue (Fe rich), bright yellow (clay rich) and white (Fe and clay rich areas) pixels. Field coordinates of mining locations were superimposed on the remote sensing generated mineral map. The results were found to be in tune. This study recommends the use of remote sensing and geospatial technology in mineral studies through hydrothermal alteration within the basement complex rocks of Nigeria.

Analyses of high resolution aeromagnetic data for structural and porphyry mineral deposit mapping of the nigerian younger granite ring complexes, North - Central Nigeria

This study report the results of the different geophysical analyses carried out on the aeromagnetic data of north-central Nigeria with the object of delineating the occurrence and evaluate the structural influence on the emplacement of the porphyry mineral deposits of the Ring Complexes. The residual magnetic intensity extracted using Low Cut Guassian filter, from the high resolution aeromagnetic data of north-central Nigeria were filtered to remove high frequency near surface cultural noise and subsequently Reduced to Pole at Low Latitude (RTPLL) to focus anomaly peaks on the corresponding geological sources in order to resolve anomaly complexity associated with mid-latitude potential data. The data were further enhanced using upward continuation filter to extract desired magnetic responses at various continuation distances. Analytic Signal (AS), Centre for Exploration Techniques (CET) Grid and Porphyry Analyses were then carried out on the filtered, transformed and enhanced magnetic data to generate diagnostic magnetic attributes employed to map the boundaries of geologic magnetic sources, extract linear features and delineate the occurrence of porphyry mineral deposits across the study area.The AS responses defined twenty-four (24) arcuate/circular shaped AS anomalies which correspond to Younger Granites Ring Complexes in the northeast, northwest, southeast and central part of the study area from the low AS response Basement Complex rocks that host them. The CET grid analysis delineates several linear structures which generally trend NE – SW, NNE – SSW and ENE – WSW directions and their average length (500 m–17,500 m) and population (212–32) directly and inversely, respectively, correlate with the upward continuation distances. The CET porphyry analysis also delineates fifty (50) porphyry mineral deposits which vary in radial size from 300 m–4300 m. The occurrence of the porphyry mineral deposits within or in close proximity with the Younger Granite Ring Complexes which are either crosscut or flanked by the linear structures, suggests hydrothermal non-orogenic origin of the structurally controlled ring complexes and the associated porphyry mineralisation that result from phase mineralisation that accompanied Jurassic hydrothermal activities.

Analysis of principles of equivalence and suppression in resistivity sounding technique

The principles of equivalence and suppression in resistivity sounding technique are phenomena where different resistivity models may produce resistivity curves that are essentially the same. The understanding of these phenomena could be of great importance in using resistivity sounding technique for citing boreholes in places underlain by Basement Complex rocks. In such areas, it would be difficult to identify the fractured/weathered bedrock from the sounding interpretation. This is because the resistivity of the weathered layer is usually intermediate between those of the adjacent layers (i.e. residual overburden) on top and the fresh bedrock below. Therefore, it is important to analyse the problems of suppression and equivalence in resistivity sounding data for estimating thickness and resistivity of the subsurface layers. Several resistivity models were generated ranging from two-layer to five-layer models to investigate these phenomena. The apparent resistivity curves were plotted for these models. The results show that the problems of suppression and equivalence exist in resistivity sounding data. Hence, geophysicists should not make any a priori quantitative inferences using the shape of the resistivity sounding curve.

Delineation of aquifer potential zones using hydraulic parameters in Gombe and environs, North-Eastern, Nigeria

This research is aimed at delineating the groundwater potential zones in Gombe and environs using Dar Zarrouk parameters. The study area is located within longitudes 11°7′0″E to 11°14′0″E, and latitudes 10°15′0″N to 10°21′0″N, it is basically underlain by basement Complex rocks represented by Diorite and Granites, and Cretaceous sedimentary rocks represented by Bima, Yolde, Fika and Gombe Formations. Thirty two (32) vertical electric soundings (VES) using Schlumberger array method with the aid of ABEM Signal Averaging System (SAS) Terrameter was used for the data acquisition. The result of the interpretation shows four to six geo-electric layers. The geo-electric section revealed the major aquifers to be confined and semi confined and consist of Medium grain sandstones, with varying thicknesses. The aquifer hydraulic characteristics indicated that the transverse resistance, ranges from 235.2Ωm2 to 6317.87Ωm2 with an average value of 1789.50Ωm2. The Longitudinal conductance, S, ranges from 0.1415Ωm to 31.933Ωm with an average of 2.002Ωm. The Hydraulic conductivity value range from 2.62m/day to 138.66 m/day with a mean value of 20.662 m/day. The transmissivity values obtained for the various layers range from 78.34 m2/day to 13284.02m2/day, with the average value been 893.57 m2/day. Four groundwater potential zones were delineated including medium grain sandstones, Sandstones, clayey sand and shaly sand.

English

A ground radioactivity survey report and it geological analyses are presented in this work. The survey was aimed at delineating possible zones of concentration of pegmatite intrusions, a rock whose components are useful in the in the electrical and ceramic industries among others. The survey covers longitude 12°54’-13°00’E and latitude 10°7’-10°15’N, with a total surface area of 155.52 km2. Dominant plutonic rocks in the area are coarse grained/pegmatitic granites which occur as intrusion in the metamorphic rocks (gneiss and migmatite). The survey was undertaken with a Geiger counter at station spacing of 1 min (1ežŒ) following mostly a system of grid lines. A total of 48 stations were occupied and measurements of the radiometric field variations were made. Thirteen radio-lineaments have been mapped, majority (7) align with pan African deformational direction (N-S, NE-SW). Others align in the NW and E-W directions. Some radio-lineaments correlate or align with geomorphologic features of hills and straight channel streams. Based on high radiometry and ground truthing results the northern sector of the study area is designated as a pegmatite zone. Other high radiometric zones are suggested as targets for investigation for possible pegmatite occurrences because of the economic importance of this rock. Key words: Radiometric anomalies, basement complex rocks, pegmatites, lineaments and geomorphic features.

English

This work presents a reconnaissance study to delineate potential mineral zones in the schist belt areas of Kano State. These parts of the state have received little or no attention for a long time and activities of artisanal miners suggest that the area is of economic mineral value. Airborne magnetic data acquired from Nigerian Geological Survey Agency (NGSA) were first reduced to the equator before subjecting them to first and second vertical derivatives. The short wavelength anomalies recorded in the study area, ranging from -99.182 to 88.338 nT indicate that the area is characterized by crystalline basement complex rocks. The results of the vertical derivatives show that lineaments (depicting faults, fractures and contacts) which represent veins of possible mineralization exist in the study area. The trend of these lineaments is in the NE-SW and E-W directions with the NE-SW trend dominating. Location with high mineral favorability is bounded within longitudes 7°51’ E to 8° 12’ E and latitudes 11° 46‘ N to 12° 30’ N in the NE – SW directions. The trend cuts through Gwarzo, Shanono, Bagwai, Tsanyawa, Bichi and Kunchi. Key words: Airborne magnetic data, Lineament, Mineralization, Schist Belt and Vertical derivatives.

Field Geology and Structures of Migmatitic Gneisses Around Ibillo-Okene Area, Southwest Nigeria

Ibillo-Okene migmatites are a typical example of the Basement Complex rocks of southwest Nigerian, which is part of the larger West African shield. They lie directly north and constitute the northern closure of the Igarra Schist Belt. They are interbanded with relics of metasedimentary units called older metasediments as well as overlain by younger metasediments. These units are affected by co-genetic or similar episodes of deformation that has both petrogenetic and economic significance as observed in Igarra Belt south of this area. Though this area is interesting in terms of geology and tectonic setting, detailed geological and structural interpretation of features in the area is lacking due to limited accessibility. Land Sat 8 and shuttle radar topographic mission (SRTM), data constitute useful tools for preliminary reconnaissance survey as well as structural interpretation. Based image interpretation, a minimum of three deformation events were identified: The first event (D1) which is essentially a ductile deformation produced foliations and isoclinal folds which are axial planar such that both the eastern and western limbs of the folds are parallel with regional metamorphic foliation trend S1 (NNW-SSE) and dominant lineament trends (ENE-WSW). The second event (D2) is believed to have produced a progressive reactivation of the D1 event with accentuation of the E-W compression leading to folding of the axes of F1 folds. The third event (D3) has two deformational stages: a ductile deformation at the onset at a higher temperature and pressure and a brittle deformation at the later stages with lower temperature and pressure. Geologic fieldwork which was further conducted to validate structures and units identified from image processing revealed that the migmatites are essentially metatexites which to the northwest is dialational, dialational net-structured in the northeast and straumatic in the southeast. The southwest of the area constitute the basinal closure of the Igarra area overlain by relics of the metasedimentary units. This research underscore the relevance of remotely sensed data in geological investigation whose results have important implications in terms of regional tectonics and geological mapping as well as in land-use planning and other areas such as hydrogeology or geotechnics. Keywords: Migmatite, Ibillo, Okene, metasediments, Remote sensing. DOI : 10.7176/JEES/9-2-08

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.

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.