Nigerian Geological Survey Agency Research Articles

Integrated Geophysical Investigation for Gold Mineralization Potential over Southern Parts of Kebbi State and its Environs, Northwestern Nigeria

The potential zones of gold mineralization were identified in this study using aeromagnetic and aero-radiometric methods. The Nigerian Geological Survey Agency (NGSA) provided half-degree airborne magnetic and radiometric datasets covering the southern part of Kebbi State. Magnetic data were subjected to first vertical derivative (1VD), total gradient amplitude (TGA), total horizontal derivative (THD), source edge detection (SED), center for exploration targeting (CET), Euler deconvolution (ED) and source parameter imaging (SPI) to identify favourable structures to gold mineralization. Aero-radiometric data delineation of the region of hydrothermal alteration zones through the K/eTh ratio, K_deviation, F_parameters, and Ternary image analyses were successful. The results of the magnetic data techniques revealed the regions of major structures/or lineaments with gold mineralization attributes, trending in the NE to SW directions and the SE to NE parts of the study area. The depth to the structures of the magnetic source hosting gold mineralization was less than 5 m using algorithm ED and SPI techniques. Normalized radiometric data showed the area of anomalously high and moderate hydrothermal altered zones. The region's designation as a gold field is supported by major fault lines observed on the 1VD, a sequence of bristle fractures from the CET analysis, and high values of K_deviation and F_parameter, all of which are were visible on the Ternary images. The integrated results revealed zones of major structures and hydrothermal regions of gold fields at Agwara, Western Magama, Rijau, Fakai, Bukkuyum, and Borgu in the SE of the study area.

CRUSTAL THICKNESS BENEATH UTAKO ABUJA USING RECEIVER FUNCTION ANALYSIS

Understanding the Mohorovicc discontinuity (Moho depth) is crucial in unraveling the Earth’s subsurface structure. In this research, we present the report of the crustal thickness and the ratio of the primary wave to the shear wave velocities (p-to-s) beneath the seismic station located at the Nigerian Geological Survey Agency (NGSA) Abuja using Receiver Function Analysis (RFA). The primary objective of this study is to determine the depth of the Moho boundary and gain insights into the geological properties of the Earth’s crust and upper mantle beneath the receiver station. This analysis focused on teleseismic earthquakes that were recorded at the station between 2020 and 2021, with epicentere distances between 30o and 90o and magnitudes 5.5 or greater. The P wave Receiver Function (PRF) was modeled from iterative time domain deconvolution using the converted phases (Ps) at the Moho interface.

2-Dimensional joint inversion modelling of the Niger – Delta basement using potential field data

Sub-surficial models predict the occurrence and geometry of strata, geological structures, inclusions, tectonic settings and so on. Robust data including geologic information, airborne gravity, and magnetic data, with constraining drill–depth data are here integrated to model the topography of the basement that underlies the Niger Delta sedimentary sequence. The aim was to elucidate the existence of a petroleum system from the unexplored depths of the delta near the basement, hypothetically controlled by the basement structures. Airborne total magnetic intensity (TMI) and Bouguer gravity anomaly (BGA) of the Niger Delta, obtained from the Nigerian Geological Survey Agency that were noise–filtered and corrected are used. The gradient of the geomagnetic field was removed from the magnetic data and the data was reduced to the equator (RTE). As precursory operations, sub-surficial lineament structures were delineated from these grids using the Tilt Derivative filters, and the depths were determined using the Source Parameter Imaging (SPI) technique. Subsequently, basement topography models were generated across four (4) profiles in a gravity-magnetic joint inversion scheme. Consequently, the strata that constitute the Niger – Delta ‘cake’ from the Cretaceous to Recent were modeled. The results showed that the Late Cretaceous Synrift Clastics (LCSC) formation presumed to directly overlie the basement may vary in thickness from 2.15 to 2.74 km. The lineament structures were found to dominantly trend in NE – SW direction. The depth to the basement, from the 2-dimensional models, ranges approximately from 13.18 to 19.35 km. It is postulated that while the Tertiary Niger Delta is characterized by lineaments engendered by diapiric instability of the over–pressured Paleocene – Pliocene marine shales, there exist other lineament structures beneath with NE – SW as the dominant trends, offshoots of Mid – Atlantic fracture zones including Chain and Charcot. Basement undulations, which are relicts of the vast subsidence Passive margins undergo during their formation are observed. These resultant synclinal structures create accommodation for the extensive deposition of the LCSC. The juxtaposition of this reservoir facie, the lineament-laden undulating Passive basement escarpment, and, the Paleocene – Pliocene Marine Shale formation could make for another petroleum system.

Seismic Background Noise Analysis from the Seismic Station Located at the University of Abuja, Northcentral Nigeria

Abstract: In October 2018, the Federal Government of Nigeria established several seismic stations in different places in the country. Three of these stations are located in the Abuja region (the Federal Capital Territory, or FCT) and are managed by the Nigerian Geological Survey Agency. Over the past few years, several low to intermediate earthquakes have been recorded within and around the Abuja region. These occurrences have provided valuable opportunities to study seismic earth noise using the dataset collected from the VolksMeter II seismometer installed at the University of Abuja. The data was processed using the Win QUAKE software to analyze the seismic background noise by identifying its sources. This analysis aimed to examine the seasonal and/or daily noise levels and check the seismometer’s stability through spectral display. The physical examination and/or quantitative observation of the spectrum revealed that there was a distinct area with densely high ranges between 0.08 and 10 s, corresponding to a frequency range of 0.1Hz–12.53Hz. This assessment involved a full Fast Fourier Transform (FFT) calculation. The spectral analysis indicated the presence of noise burbles, primarily attributable to instrumental noise. These noise burbles were prominent in the east-west direction during the months of March, April, May, and June 2019, with frequencies of 0.03Hz, 0.04Hz, 0.03Hz, and 0.03Hz, respectively. A similar pattern was observed in the north-south direction, with noise peaks of 0.07Hz in the months of January, April, and July 2019. The findings from this study of seismic noise amplitude demonstrate a clear correlation with the global seismic noise models. The sources contributing to the station’s noise levels encompass factors such as wind, geological influences, instrumental noise, and human activities including machinery and airport operations as well as vehicular traffic. These observations highlight the potential of using background seismic noise to quantify tremors and monitor their spatial variations, a task that remains difficult with traditional approaches. Keywords: VolksMeter II, Seismic station, Background noise, Spectrum, University of Abuja.

The Correlation of Geothermal Energy Potential Deduced from Aeromagnetic and Aeroradiometric Data of Akiri and Environs, North-Central Nigeria

The aeromagnetic and aeroradiometric data were combined to investigate the geothermal energy potential of Akiri and Environs, North-Central Nigeria. The aeromagnetic and aeroradiometric data were obtained from the Nigerian Geological Survey Agency (NGSA), Abuja. The data consists of nine square map sheets of Wamba, Kwolla, Shendam, Lafia, Akiri, Ibi, Makurdi, Akwana and Wukari. The LANDSAT imagery data of the study area was obtained from the National Centre for Remote Sensing, Jos. The spectral analysis method was applied to aeromagnetic data to obtain the geothermal parameters of the magnetic sources. The results show that the depth-to-top of magnetic sources in the study area ranges between 0.76 and 4.46 km; while the depth-to-centroid ranges between 7.29 and 19.6 km. The depth-to-bottom of magnetic sources corresponds to the Curie point depth (CPD) in the study area which is the depth at which magnetic rocks lose their magnetism. The results show that the CPD varies between 12.70 and 37.22 km, the geothermal gradient varies between 15.58 and 45.67 ◦C/km, and the geothermal heat flow varies between 38.9 and 114.17 mW/m2. Two dimensional structural models were constructed to show the estimated depths at each profile taken. The models show uplifted crust and mantle in some areas due to magmatic intrusions which gave rise to low CPDs (12 to 28 km) which resulted to high geothermal heat flow values (60 to 115 mW/m2). The results show that there are low values of CPD in some areas which indicates that the study area has geothermal energy potential. The study shows that the geothermal energy potential deduced from aeromagnetic data correlates well with the geothermal energy potential deduced from aeroradiometric data.

Qualitative interpretation of high resolution aeromagnetic data of abeokuta metropolis for geological characterisation

Qualitative interpretation of aeromagnetic maps involves the visual inspection and pattern analyses of produced maps to identify potential geological structures in the magnetic field by processing the dataset to characterize the Earth's magnetic variations and map subsurface geological structure which is important to tackle the challenges of resource management, environmental assessment and infrastructure design in the study area. This technique has been employed to a part of Abeokuta metropolis of Ogun state, Southwestern Nigeria, using high resolution aeromagnetic dataset acquired from the Nigerian Geological Survey Agency (NGSA). Pre-processing analyses such as data transformation, map re-projection and power spectrum plot were performed on the dataset to minimize noises and remove unwanted variations. The application of Reduction to Magnetic Equator (RTE) filter was to remove asymmetries in the data and position the peaks of magnetic anomalies over their sources while the Gaussian (low pass) filter was aimed at improving the signal-to-noise ratio. Low magnetic zones indicated by blue colours from the total magnetic fields possibly reveal the sedimentary intrusions into the area, intermediate magnetic regions having green, yellow and red colourations suggest transition zones and the Northeastern portion of the maps indicated with pink colours correlate to the core basement regions. Derivative filters are applied as enhancement techniques to accentuate the inferred linear subsurface structures interpreted as cracks, fractures, lineaments, etc. These structures are predicted mineral entrapments or fault lines whose NE-SW orientation conforms to the Pan African Orogeny and they can aid environmental assessments generally.

Radiogenic heat production estimation towards sustainable energy drive in northeastern Nigeria

An estimate of the radiogenic heat production (RHP) across the different petrologic units of northeastern, Nigeria was previously not performed. Hence, their geothermal potentials are not widely known. However, an airborne radiometric data of equivalent uranium, (eU), equivalent thorium (eTh,) and percentage potassium (% K) acquired by Nigerian geological survey agency (NGSA) in the year 2009 was deployed in the evaluation of the RHP across the major petrologic outcrops of northeastern, Nigeria. The objective of this study is to estimate the quantity of RHP across the 13 petrologic units of the northeastern Nigerian terrain via the use of an empirical equation (RHP=ρ(0.0952Cu+0.0256CTh+0.0348Ck)). The petrologic units studied are; medium-coarse grained biotite-hornblende granites (OGe), porphyritic biotite-hornblende granites (OGp), banded gneiss (bG), charnokytes (Ch), ignimbrites (JYG), migmatites-gneiss (MG), basalts (bb), Gombe sandstones (GS), Pindiga Formation (PS), Yolde Formation (YL), Bima sandstones (BS), Keri-Keri Formation (KK), and alluvium (AL). Basic/preliminary processing such as; signal integration, signal validation, and examination of spurious data were applied prior to the RHP computation. The results of the heat production analysis performed show the range of RHP to be from 1.11μW/m3 to 3.35μW/m3 Hence, the maximum heat production value of 3.35μW/m3 was recorded along porphyritic biotite-hornblende granites (OGp) rock block, while the least value of 1.11μW/m3 was recorded over alluvium (AL) rock outcrops. Furthermore, the spatial distribution of the RHP values over the study location shows a gradual increase from the middle, low heat production (sedimentary zones) to the high heat producing areas (granitic and metamorphic zones) around eastern and western parts. The petrologic units arranged in order of decreasing magnitude of radiogenic heat generation are; OGp > MG > OGe/bG > bb > GS > Ch > JYG > BS > PS/YL > KK > AL. On a general note, the petrologic units studied were classified as low in terms of geothermal character based on comparison with other previous global RHP studies.

Subsurface Structural Characterization as Deduced from High-Resolution Aeromagnetic Data over The Confluence Zones in Central, Nigeria

This study aimed to delineate the intrusion body that controls the structural setting and formation around the river Niger-Benue confluence zone with particular attention to its solid mineral potentials, this is achieved in mapping subsurface structural features through the analysis of recent high-resolution aeromagnetic (HRAM) data-sets with the purpose of examining their effects on geological structures that characterize the confluence zones from the study area. To obtain the necessary reduction in geomagnetic variation, measurements of regional gradients and time variation were used. After applying the reduction to the magnetic equator (RTE) to the corrected magnetic data that was obtained from the Nigerian Geological Survey Agency, NGSA, it was possible to determine the regional expansions of subsurface structural units for both qualitative and quantitative interpretations. In addition, the edge detection method is used to depict the structures and buried subsurface anomalies. Different handling processes were applied to the (HRAM) data, such as local wavenumber (SPI), power spectrum analysis, and Euler and Werner deconvolution analysis. The RTE magnetic anomaly caused by local structures and anomalous body delineated six sub-basins with low amplitude response, which agrees with the total gradient anomaly (analytic signal) and tilt of angle derivative that clearly outlined and characterize edges of lithostratigraphic of Niger-Benue river confluence zones. The sub-basin delineated are the southern Bida basin and northern Anambra basin. The source parameter imagings as well as the Euler and Werner deconvolution were used to delineate major subsurface structures and determine their source depth. Results showed that the area was affected by different lineament trending NE-SW, E-W, and S-E trends. Directional analysis indicates that the dominant trend agrees with the regional fault orientations. The estimated depth to the top of the lineaments on average varies from 0.3 km to 4.6 km and it is relatively deeper in the basins compared to the surrounding areas giving clues to the amount of sediment infill. A 2D forward model showed a sedimentary thickness ranging from 1 to 7 km, and this estimated depth is consistent with the average of 3.5 km proposed by previous researchers.

Sedimentary thickness and basement depths of eastern Niger delta, Nigeria, from aeromagnetic data and implications for hydrocarbon prospects

A knowledge of sedimentary thickness and basement depths of a basin is necessary in understanding the structural set up of formations and evaluation of the hydrocarbon potentials of a region. In this work aeromagnetic data, obtained from the Nigerian Geological Survey Agency (NGSA) Abuja, has been interpreted to obtain sedimentary thickness, structural faults and intrusions including the basement depths of the eastern Niger Delta, Nigeria with the implications for hydrocarbon prospecting. Results from magnetic attribute analysis, total horizontal derivative operations, spectral analysis and source parameter imaging reveal the following: the study area is magnetically heterogeneous; the magnetic intensities range for the region is from – 46.2 nT to 160.3 nT, with residual magnetic intensity values of -15 nT to 13 nT revealing sediments with low magnetic rocks in the southwestern and southeastern parts of the study area and magnetic rocks and basement intrusions in the northwestern, northeastern and central parts of the study area; sedimentary thickness range from 96.5 m to 6601.5 m hosting faulted anticline and syncline structural bodies good enough for hydrocarbon formation and trapping and a maximum depth to basement of 6601.5 m. The sedimentary thickness and structural types, influenced by the basement intrusions, make the region a hydrocarbon potential area and it is recommended that prospecting in the southern and northern parts of the study area should be intensified.

Investigation of relative abundance of radioelement concentration over a portion along Birnin Yauri, Northwestern Nigeria

The radiometric method involves the measurement of naturally occurring radioactive materials emitting the ionization radiation (α, β, from rocks). In the field, the gamma rays and their adequate energies are detected by a spectrometer coupled with the scintillation detector. Three (3) high resolution airborne radiometric data obtained from the Nigerian geological survey agency (NGSA) were used to obtain the concentration of Potassium (K), Uranium (U) and Thorium (Th) respectively in the study area. The gridded data were fed into Oasis montaj software for appropriate filtering, in other to produce solutions for radioelement concentration across the area under study, thereafter producing shaded count maps as well as ternary maps. The result of the analysis revealed that potassium concentration is between 0.090 to 2.455% with an average of 2.365%. The thorium concentration values ranged from -0.539 to 15.221 ppm with an average of 7.341 ppm. The uranium concentration revealed values from -0.402ppm to 3.902ppm with an average of 1.75ppm. The ternary map of the radiometric data showed a red/cyan colour grid depicting potassium which is more pronounced across the area, followed by the uranium content(blue) covering an appreciable portion across with only but a few (green) coloured shaded regions depicting thorium. The results obtained have shown that the area has substantial amount of radioelement concentration, with potassium being the most abundant covering the central and western half of the area while the uranium content is more abundant towards the mid-western half and eastern parts of the area. The thorium content is minimal across the region.

Curie-Point Depths, Geothermal Gradients and Sub-Surface Heat Flow Estimation from Spectral Analysis of High-Resolution Aeromagnetic Data over Gongola Basin and Its Environs, Northeastern Nigeria

Geothermal energy resources have been established globally to be among the sustainable and environmentally harmless means of energy generation. Curie-point depths (CPD), temperature gradients, and heat flow data over the study area were computed using a spectral analysis method in order to have a preliminary view of the geothermal implications (prospect) of the current area. Aeromagnetic data acquired by the Nigerian Geological Survey Agency (NGSA) in the year 2009 was used for the research. The results showed the minimum, maximum, and the average CPD values as 8.18 km, 31.48 km, and 13.0 km, respectively. The minimum, maximum and average thermal gradients obtained were 18.42 °C/km, 70.91 °C/km, and 50.2 °C/km, respectively. The heat flow data obtained ranged from 33.15 mW/m2 to 177.28 mW/m2, with an average value of 110.65 mW/m2. Locations depicting shallow CPDs anomalies (Alkaleri, Darazo, Dukku, Misau, Wuyo, Deba, and Tula), also showed conformity with high heat flow areas. As such, they are regarded as areas of promising geothermal prospects and are recommended for further detailed investigation. Locations depicting a high magnetic susceptibility contrast from a generated analytic signal map, as well as high temperature gradients, high heat flow, and shallow CPDs are attributed to crustal thinning along the sedimentary basin and magmatic intrusions along basement areas, respectively. The magnetic depth to the basement calculated for the study area using the source parameter imaging (SPI) method ranges from 0.610 km to 3.055 km. The present study has provided an insight on preliminary information, regarding new areas of possible geothermal prospects for further detailed investigation.

Geophysical Evaluation of Central Nigeria Earth Tremor Activities using High Resolution Airborne Magnetic Data

The aim of this study is to investigate the actual causes of earth tremors in Central Nigeria using geophysical technique. Since 1933 till date (over 88 years), small to moderate magnitude earthquakes have either been observed or instrumentally recorded in Nigeria. However, the specific causes of the intra plate earthquakes in Nigeria is still not well known. In this study therefore, a high-resolution aeromagnetic data analysis was performed to evaluate the various theories proposed as the causes of tremor activity in central Nigeria with a view to ascertaining the actual causes of earthquakes in the West African country that lies on a stable crust. The total magnetic intensity data acquired from the Nigerian Geological Survey Agency (NGSA) in the Central Basement complex of Nigeria, was processed and filtered using the tilt derivative, lineament analysis, and advanced Analytic Signal- Hilbert Solution filter. To define the trends of both major and minor structure, a lineament plot was extracted and plotted. The analysis revealed a dominant NE-SW and NW-SE trending structure that is distributed throughout the study area. The regional North Atlantic Romanche fault system, which extends from the offshore (Niger Delta) into the continental crust, was mapped and is thought to extend from Gwagwalada in the study area's south, through Gwarinpa and Mpape, to Kwoi, and beyond Kafanchan.Findings from our study have indicated that, areas prone to Earth tremors are linked to the Romanche fault by numerous NE-SW and NW-SE faults that act as conduits for seismic energy that causes tremor. Using lineament density analysis, tremor active areas have been interpreted to be highly deformed; thus, seismic energy induced into the environment would result in tremors. This study demonstrates that the regional North Atlantic Romanche fault system is the primary source of seismic energy that causes the earth tremors in central Nigeria.

Curie Point Depth, Heat Flow and Geothermal Gradient Determined from Analysis of Aeromagnetic Data over parts of the Lower Benue Trough and Anambra Basin, Nigeria

This paper evaluates the aeromagnetic data over parts of the Lower Benue Trough and Anambra Basin of North central and Southeastern Nigeria obtained from the Nigerian geological Survey Agency, Abuja to quantitatively determine the Curie Point Depth, Geothermal gradient, and Heat flow using Oasis montaj software, Fourpot software, and Surfer software. The results revealed that the average Curie point Depth of the Study area is 8.07594 km, the Geothermal gradient obtained has an average value of 73 oC/km, areas with low and intermediate geothermal gradient are, Southeast of Obubra, Northeast of Obi, North West of Odolu, and Awgu. The study area has an average heat flow of 170 mW/m2 , it is observed from the map that the areas around Igunmale, Abakaliki, Udi, Ejekwe and some area around Nkanu East have high heat flow rate attributed to presence of intrusive rock. Consequently, the study area is characterized by low, intermediate and high magnetic anomalies, the most prominent trend observed is in the ENE -WSW and NE – SW minor trend direction and has high heat reservoir potential which can be harnessed as geothermal energy, there is also a possibility of high temperature and pressure hydrocarbon reservoir potential.

Structural Analysis of High Resolution Aeromagnetic Data. A Case Study of Akko and Environs, Gongola Basin upper Benue Trough Northeastern Nigeria: Implication for Mineralization and Groundwater Potentials

Magnetic method had proved very effective in the area of subsurface anomaly studies and structural delineation worldwide. Sheet number 151(Akko sheet) of the high resolution digital airborne magnetic data was obtained from the Nigerian Geological Survey Agency (NGSA). Analysis of the data was done using first horizontal and first vertical filters while the residual field was obtained using the polynomial fitting method. Lineaments of the study area were generated from SRTM (shuttle radar thematic mapper) and DEM (digital elevation model) by producing four shaded relief images at solar altitude of 45˚, 50˚, 60˚ and 90˚. The first horizontal and first vertical derivative filters exhibited magnetic trend consistent with the lineament trend of the study area, which showed major trends in NE-SW and NNW-SSE direction and minor trends along NW-SE.

Interpretation of Aeromagnetic Data of Part of Gwagwalada Abuja Nigeria for Potential Mineral Targets

This study analyzes aeromagnetic data over a section of Gwagwalada in Abuja. The data were obtained from the Nigerian Geological Survey Agency acquired at 100 m terrain clearance. The study area spans longitudes 7.0875 E to 7.1458 E and latitude 8.9625 N to 9.0 N (about 27 km2). The dataset was reduced to the equator (RTE) and downward continued by 50 m. Analytic signal filter was applied on TMI-RTE grid to detect the edges of the magnetic bodies present. The structure was observed to trend NE-SW. The CET lineament map reveals intersections such as junctions and corners on the map. This revealed structure liable for potential mineralization zone. Euler deconvolution technique applied over the transformed dataset ascertain the location and depth of the structure,having a maximum depth of about 421 m and a minimum of about 59 m.Variation in magnetic depth and susceptibility contrast is specified by the gridded SPI depth map.

Structural Exploration of Aeromagnetic Data over Part of Gwagwalada, Abuja for Potential Mineral Targets Using Derivatives Filters

Aeromagnetic data are consistently used for economic interest targeting and geological mapping. Besides solving problems that are concerned with the basement, the method has become a useful tool in exploring minerals,hydrocarbons occurrence,groundwater investigations, and geothermal potentials. This study analyses aeromagnetic data from the Nigerian Geological Survey Agency acquired at 100 m terrain clearance over a section of Gwagwalada in Abuja. The study area spans longitudes 7.0875° E to 7.1458° E and latitude 8.9625° N to 9.0° N (about 27 km2 ). After a reduction to the equator (RTE) transformation, the data is downward continued by 50 m. Different filters are applied to outline area of alteration associated to mineral deposit. Regional geologic structures trend NE - SW.The application of vertical derivatives (FVD and SVD) to the RTE grid enhanced shallow structures which trend NE - SW. Horizontal gradients along the X- and Y- directions enhance geological contacts attributable to blind faults. The Tilt derivative (TD) accentuated fault lines which trend NE - SW.

Detection of Sulphide Deposit Using Uranium/Potassium Ratio Map

Potassium (K) response is associated with minerals that can be easily weathered, whereas uranium (U) is usually related to residual clay, oxides and accessory minerals. With a view to interpret for the detection of sulphide deposit based on similar responses exhibited by the various rock units, radiometric data set was interpreted. The study area is located within Latitude +8000’00’’to +8030’00’’ and Longitude +5030’00’’E to +6000’00’’E. The data was collected in most parts of the Nigeria by Fugro Airborne Services Ltd. Johannesburg in collaboration with the Nigerian Geological Survey agency using a light aircraft that was flown in NW-SE direction with a nominal terrain clearance of 80 m and at a speed of 70-80 m/s, with a flight line spacing of 500 m apart. The acquired data was subjected to elemental concentration enhancement using Geosoft Oasis Montaj Software. From the interpreted data, the red coloured portions indicate high uranium and low potassium formations (H-U/K), while the blue coloured portions indicate low uranium and high potassium formations (L-U/K). The regions L-U/K have recorded low U/K ratios, meaning that L-U/K have very low uranium count rates as compared to the count rates of potassium in these regions; this signifies potassium abundance. This also suggests igneous activities that usually culminate to the emplacement of the meta-volcanic lithologies. H-U/K and M-U/K (Moderate U/K formations) are seen to have patches of high U/K ratios within the central portions. This high U/K ratio was therefore, as a result of sulphide deposition.

ANALYSIS OF HIGH RESOLUTION AEROMAGNETIC DATA OF SOME PARTS OF BENUE TROUGH, NIGERIA

This work is aimed to determine the depth to basement of some magnetic sources in the study area. Four aeromagnetic sheets were acquired from the Nigerian Geological Survey Agency which includes (Bajoga, 131, Gulani, 132, Gombe, 152 and Wuyo, 153). The study area covers an estimated area of about 12100km2 between latitude 90N-110N and longitude 110E-130E. The total magnetic field of the study area have been evaluated. In order to determine the basement depth, spectral analysis technique was applied. Detailed analysis of the aeromagnetic data for the study area was performed. The procedure involved in the analysis include reduction to equator to remove the effect of inclination, contouring of the total magnetic intensity, separation of the regional and residual anomalies using polynomial fitting of first order, qualitative interpretation and quantitative interpretation. The residual field of the study area composes of low magnetic anomalies reaching a minimum value of -158.6nT as observed in the northern and southern parts and high magnetic anomalies reaching a maximum value of 178.1nT as observed in the western part of the study area. The result from the spectral analysis for each block shows that the depths to the magnetic source are 5.20Km for block 1, 5.74Km for block 2, 7.59Km for block 3 and 3.56Km for block 4. The average depth to magnetic source in the study area was found to be 5.52Km. Based on the computed average sedimentary thickness obtained in this study area, hydrocarbon accumulation in the study area is feasible.

Determining the occurrence of potential groundwater zones using integrated hydro-geomorphic parameters, GIS and remote sensing in Enugu State, Southeastern, Nigeria

In many parts of Nigeria, water resource is scarce, and where available, determining their abundance is difficult. In the present paper, various groundwater potential zones for the evaluation of groundwater availability in Enugu State have been delineated using remote sensing and GIS techniques. The satellite images and conventional data obtained from US Geological Survey, World Soil Resources Office in Cooperation with Land and Water Development Division/FAO and Nigerian Geological Survey Agency are used to prepare the thematic layers viz. drainage density, geomorphology, slope, landcover/land use, soil, geology, rainfall and lineament density were converted to raster data adopting feature to raster converter device in ArcGIS. The raster maps of abovementioned factors are assigned a definite score and weight computed from multi-influencing factor approach. Additionally, each weighted thematic layer is statistically computed to generate groundwater potential zones map of the study area. The groundwater potential zones thus obtained were divided into four categories, viz., super-abundant, moderately abundant, abundant and scarce zones. The groundwater resources map demonstrates that the study area is dominated by abundant and scarce groundwater potential zones which covers surface area of about 6073.44 km2 (73.27%) of the study area while the remaining 2294.98 km2 (26.73%) are dominated by super-abundant and moderately abundant groundwater potentials. However, the result validation with boreholes/wells yield data collected from the study area showed good correlations with respect to groundwater potential zones map. It is concluded that the use of hydro-geomorphic approach is very efficient for the determination of groundwater potential zones.

Characterization of structural failures founded on soils in Panyam and some parts of Mangu, Central Nigeria

Structural failure of buildings, roads, and other infrastructures has led to the loss of lives and monumental damage to the economy. In developing countries such as Nigeria, the failures are always attributed to the nature/type of soils in the area without considering other factors. With the increase in civil engineering constructions and the scramble for a limited portion of competent soils for such constructions, land, therefore, is becoming man’s most priced commodity for agriculture, residential and industrial purposes. No works of such have been done in the area, it is, therefore, imperative to study the cause(s) to prevent further loss of lives and the negative effects of such on the economy. The study was carried out at Panyam and some surrounding localities on latitudes N9021′ and N9026′ and longitudes 9011′E and 9016′E an area of 72 km2. A total of forty samples were collected out of which twenty were selected for swelling potentials determination due to their cohesive nature within the 1.5 m depth. To characterize the swelling of the soils, inferential testing methods; direct method comprising Liquid Limit and Plasticity Index with values ranging from 30% – 70% and 10% – 27% respectively, and the indirect method (Free Swell Index, FSI) whose values range from 9.1% – 90% were used. Most of the soils analyzed based on the geotechnical standards were categorized relatively safe for civil infrastructure. Structural studies employed the direct measurements of surface structures to get the orientations of structures measured. Landsat image and Total Magnetic Intensity (TMI) map of the area was acquired from the Nigerian Geological Survey Agency (NGSA) for subsurface structural analysis. The RTP-TMI (reduce to pole) grid data of the area were processed to improve magnetic anomalies associated with edges of surface/near-surface geological structures using the MAGMAP two-dimensional fast fourier transform (2D-FFT) filters package in Oasis Montaj v7.2 software. Geophysical studies using aeromagnetic data at a near-surface depth of 40 m and fractures measured on the surface both revealed a major trend in the NNE – SSW. It was observed that structures constructed across the major trend suffered little to moderate damage while those constructed along the major fractures trend suffered severe damage. It was concluded that both soils and fractures played individual roles in the collapse of infrastructure in the area.