Benue Trough Research Articles

Exploratory mapping of structures controlling mineralization in Southeast Nigeria using high resolution airborne magnetic data

High resolution airborne magnetic data of some regions of Southeast Nigeria were analyzed to map structures controlling mineralization. Such data can be used for mineral assessment programs, surficial geologic boundaries, hydrocarbon exploration at reconnaissance stage, mapping of hydrothermally altered rock zones and geologic structures. First and second vertical derivatives, upward continuation, source edge detection, analytical signal, Centre for Exploration Targeting (CET) and standard Euler deconvolution operations were done to delineate the spatial distributions and depths to the different magnetic sources. The enhanced maps showed major and minor magnetic anomaly centres in the Lower Benue Trough (LBT) and Ikom-Mamfe Rift (IMR) characterized by thin (151–745 m) sedimentation. Also, within these areas there exist some isolated pockets of intermediate depths (745–1634 m) occurring in the neighborhood of these magnetic anomalies. The Calabar Flank (CF) characterized by minor remnants of post-Cretaceous intrusions has sedimentation of over 6126 m in some locations. The 2000 m upward continued TMI map revealed the existence of major deep-seated weak zones believed to have originated during the rifting episode connected with the formation of the Benue Trough. The abundance of intrusive bodies in the LBT and IMR render these parts of the study area unattractive for hydrocarbon exploration. Nevertheless, they possess high base metal mineralization potential while CF is a favorable site for hydrocarbon search.

English

3D Moho interface has been computed from the airborne Bouguer anomaly beneath the southern part of the Benue Trough (BT), using the MATLAB program 3DINVER.M. From the study, the maximum Moho depth of 27.5 km and the minimum Moho depth of 18.1 km were computed. Interpretation of the gravity data of the southern part of the BT suggests that igneous input contributed greatly to the understanding of its concomitant deep crustal processes. The Moho depth elevation from the area is calculated to be around 9.4 km. This is in agreement with the Moho uplift within the study region as suggested by earlier researchers. Key words: Lower Benue trough, crust, mantle, bouguer gravity data, 3DINVER.M.

AMBIENT SEISMIC NOISE FOOTPRINTS AND SPECTRA IN THE MIDDLE BENUE TROUGH, NIGERIA

Ambient noise was analysed from a two-dimensional (2D) seismic data acquired in the Middle Benue Trough, Nigeria for the purpose of characterizing the ambient seismic noise. Sercel 428XL recording instrument was deployed on 3 traverse lines where dynamite explosive sources and geophone detectors were used. The acquired data was processed using frequency wavenumber (FK) and wild amplitude attenuation (WAA) algorithms. The dominant amplitude of the primary reflection ranges between -20dB and -10dB, while those of the ambient seismic noise varies between -42dB and -3dB. The primary reflections have dominant frequency varying from 6Hz to 75Hz while that of ambient seismic noise varies between 4Hz and 70Hz. Analysis of the noise shows two distinct ground roll modes with velocities between 400 ms-1 and 810 ms-1 both of which are dispersive with wavelength (λ) of 61.5m and peak frequency at 6.5Hz. Analysis of passive noise records acquired showed that ambient seismic (background) noise level excluding source-generated noise average of 91.56% are below 25µV, which is the tolerance noise level limit. The combination of frequency wavenumber FK and WAA filters effectively attenuated the surface waves especially ground rolls and other high amplitude noise making the primary reflection very visible and better enhanced. The filtered amplitude values estimated from signal-to-noise (SNR) analysis using cross correlation (XC) method are much higher than the values of the unfiltered amplitudes indicating that SNR are highest when noises are attenuated from the data than when noise algorithm is not applied to the data. The attributes of these seismic noises will provide further information and solution for their suppression during seismic data acquisition and processing.

Effects of Trace Elements Compositions of Igneous Intrusions on Public Health in Ishiagu Area of the Southern Benue trough, Southern Nigeria

Some health implications of structurally-controlled igneous intrusions in Ishiagu area of southern Benue Trough were studied using the field investigations, trace element geochemistry and geostatistical studies of some of the igneous rocks, the surrounding water and edible vegetables. Results of the study revealed that the average concentrations of these trace metals in the igneous rocks decreased from Mn to Mg as follows: Mn (1431 ppm), Sr (419.5 ppm), Ba (58.11 ppm), Cu (45.63 ppm), Pb (5.48 ppm), As (1.20 ppm), Mo (3.270 ppm), Cd (0.960 ppm) and Mg (0.940 ppm); in water decreased from Mg to Cd as follows: Mg (5.840 mg/l), Sr (1.270 mg/l), Fe (0.3 mg/l), Mo (.013 mg/l), Mn (0.002 mg/l), Ni (0.001 mg/l), As (0.0004 mg/l), Ni (0.001 mg/l), Co (0.0001 mg/l), and Cd (0.0001 mg/l), while in the edible vegetables trace elements decreased from Fe-Ni as follows: Fe (8540 mg/kg), Mg (4085 mg/kg), Al (2352.1 mg/kg), Pb (360.76 mg/kg), Sr (182 mg/kg), Zn (53.38 mg/kg), Ba (46.3 mg/kg) Cu (21.75 mg/kg), Mo (8.97 mg/kg) and Ni (4.92 mg/kg). Geostatistical analysis of the edible vegetables indicates that the bioaccumulation factor of the vegetation with respect to the rock decreased from Pb to Ni as follows: Pb> Mo >Cd >As> Fe > Cr > Cu > Zn>Sr>Mg>Ni. The concentrations of Fe, Ni, Cu, Cr, Mn, Cd, Pb and Zn in water and edible vegetables are higher than the permissible levels recommended by World Health Organization. Thus, the inhabitants of the study area are at risk of myocardial infarction, insulin alteration, anemia, neurodegenerative conditions in humans, renal dysfunction, metal fumes fever, hair and skin discoloration, respiratory tract diseases, carcinogenic diseases, kidney disease, fanconi syndrome, lipid peroxidation of the heart, liver and spleen, hypertension, anemia, colic, headache, brain damage and central nervous system disorder, kidney disease, neurotoxin, lipid peroxidation in the heart, liver and spleen, fanconi syndrome, oesteomalacia, renal dysfunction, learning disabilities and hyperactivity, loss of vision, heart and liver failures, skin irritation, hazardous effects on lungs and brains. The outcome of this study has provided a data base for intervention endeavors for health practitioners to comprehensively monitor and control health issues arising from geologic and mining processes in Ishiagu area of Ebonyi State. The area is in dire need of standard medical facilities, which will, among other things, offer medical aids, document such health matters and keep surveillance so as to detect impact of the trace metals on the health of the inhabitants of the study area.

Paleo-environmental Conditions, Paleoclimatic Significance and Effects of Weathering on Clay Deposits in the Lower Benue Trough, Nigeria. Mineralogical Approach

Combined methods for mineralogical identifications were used to characterise the clay deposits within the Lower Benue Trough of Nigeria to interpret paleo-environmental conditions, the paleoclimatic significance of the trough, and effects of weathering on the minerals as factors that favour its deposition/accumulation within the trough which host other important industrial minerals like coal, barite, limestone etc. Bulk-sample random-powder XRD data and data for clay fractions deposited onto zero-background quartz plates were measured. The samples contained kaolinite, vermiculite, and traces of smectite, and the non-clay phases included quartz, microcline, and muscovite. All samples were unaffected after glycolation, confirming the absence of significant smectite. Muscovite was characterized by the nature of its 10 Å basal peak with a width of <0.10° 2θ, which was very sharp. DTA/TGA results support the presence of kaolinite, and the characteristic kaolinite O-H, Al-OH, Si-OH and SiO-Al FTIR bands also confirmed its presence. Vermicular and book-like morphologies were observed under the SEM, typical of kaolinitic clay from in situ alteration. High kaolinite abundance in these sediments is consistent with intense weathering of parent rocks rich in Al under wet/ tropical paleo-climatic conditions with fresh and/or brackish water conditions in a continental setting. The variety of observed morphologies suggests that the deposits suffered more of chemical weathering. The clay deposits in Lower Benue Trough are quartz-rich, kaolinitic and derived from the chemical weathering of Al-rich source rocks.

Modeling of porosity and permeability for hydrocarbon Exploration: A case study of Gongola arm of the Upper Benue Trough

Irreducible water saturation is one of the fundamental parameters in characterizing hydrocarbon formations, playing key role in volumetric and recovery calculations and permeability definition within a reservoir. The determination of the reservoir permeability using the irreducible water saturation in a shaly sand transition zone has been problematic due to the presence of the bound water saturation. In this research, a model was developed based on the Coates and Dagan permeability model formulation using the dual water model parameters. In this model formulation using the three models, a sensitivity coefficient for conditioning the permeability field at the transition zone was introduced. The sensitivity factor is a quotient function of bound water saturation and the total water saturation. The localized nature of the well data in the determination of the depositional architecture (porosity and permeability) were extrapolated away from or interpolated between acquisition locations using the areal coverage provided by seismic data. The analysis of the well information from the Kolmani River showed that the hydrocarbon lies at depth between 2071m and 2194m (Cenomenian-Turonian Yolde formation). The acoustic map within the reservoir shows the occurrence of dense uniform marine shales and sandstones. It also shows the depositional process has been uniform and sequential. High density clastic materials were also discovered within the reservoir. The permeability results obtained by equating the bound water and total water saturations to the irreducible water saturation gave the 26mD and 16mD as the upper (clean sand) and lower (pure shale) limits of the effective permeability values for the reservoir. The result obtained using the new model showed that the effective permeability is 21mD within the transition zone. Other petrophysical results showed that the reservoir has an effective porosity of 20% and effective water saturation of 12%. Based on these reservoir results, it is understood that the well is highly compact and will not flow during production.

Petrographic Assessment of Some Industrial Minerals in Selected Part of Southern Benue Trough, Nigeria

Some part of the Southern Benue Trough (Afikpo and Anambra Basins) has been mapped to determine the areas of occurrence of industrial minerals and to determine their lateral extent. The result shows that Southern Benue Trough is enriched with mostly industrial minerals of sedimentary and magmatic origin. The magmatism that occurred in the study area and its evolutionary processes led to mineralization of the study area. Interaction of the magma with host rocks gave rise to mineral genesis. The contamination and assimilation processes that occurred in the magmatic stage resulted to enrichment of minerals in the study area. The contact relationship of the magma with the host rock created a contact aureole though the resultant minerals (metamorphic minerals) of the contact aureole are not significant and exposed. The repetitive transgressive-regressive sedimentary cycle that occurred in the Southern Benue Trough probably resulted to the massive deposition of industrial minerals of sedimentary origin. The dominant and significant industrial minerals in Afikpo and Anambra Basins are sandstones (ferruginized sandstone, calcareous sandstones and carbonaceous sandstones), clay mineral (kaolinite), pebbles, igneous rocks of diverse levels of emplacement (intrusive/ extrusive), olivine , hematite, Feldspar, mica and quartz.

Geochemical and palaeocurrent analysis of the Tertiary Kerri–Kerri Formation in the Gongola Sub-Basin of the Northern Benue Trough North-eastern Nigeria: implications for provenance, tectonic setting and palaeoweathering

Geochemical and palaeocurrent analysis was carried out on the sediments of the Kerri–Kerri Formation in the Gongola Sub-Basin of the Northern Benue Trough, North-eastern Nigeria in order to infer their provenance, tectonic setting and palaeoweathering conditions in the source area. The sediments of the Kerri–Kerri Formation were geochemically classified as litharenite and greywackes. Provenance studies suggested derivation from pre-existing sedimentary rocks with little influence from felsic igneous rocks, while the tectonic discrimination parameters suggest continental rift of passive margin setting. The weathering indices such as chemical index of alteration, plagioclase index of alteration and chemical index of weathering indicate low to moderate intensity of chemical weathering in the source area. Index of compositional variation and SiO2/Al2O3 indicate that the studied sediments are compositionally mature to immature. The palaeocurrent analysis of the Kerri–Kerri Formation suggested south western direction, which indicate that the sediment were source from the north eastern direction. From the provenance studies, source area weathering, and palaeocurrent direction of the Kerri–Kerri Formation, it can be inferred that most of the sediments are from pre-existing Cretaceous sedimentary rocks of the Gongola Sub-Basin and have not undergone long transportation.

Mechanism of the Mesozoic African rift system: Paleostress field modeling

The Mesozoic African rift system is an important continental rift system related to the Central African Shear Zone. While several geological models have been discussed, the mechanism of the Mesozoic African rift system is still unclear. One model proposed that the mechanism of the Mesozoic African rift system was inherited from the Benue Trough, which is a failed arm of the Guinea triple junction. Other models suggested that the mechanism of the Mesozoic African rift system could be clarified by the spreading of the Atlantic and weak lithospheric zones, such as the Pan-African suture zone. In this research paper, we create a shell model that considers spherical curvature, the heterogeneous structure of the African basement framework, and a combination of the upwelling St. Helena plume and seafloor spreading. The calculation of the model is solved through the finite element software ANSYS, and the modeling results match the actual geological evidence. In this study, nine other models are created with altered rock parameters or boundary constraints and compared to the original model to examine the influence of these factors. Compared to the nine comparative models, the original model best reflects the calculated results, which indicates that the coupling of the St. Helena mantle plume and ocean-ridge spreading caused the initial lithospheric rifting at ∼130 Ma and that the heterogeneities within Africa did not affect the extension direction of the rift basin but did influence the location of the rift basin.

Correction to: An evaluation of potential toxic metals in sediments of a tropical watershed in southern Benue Trough, Nigeria

Correction to: An evaluation of potential toxic metals in sediments of a tropical watershed in southern Benue Trough, Nigeria

Depositional variability of an ancient distributive fluvial system: The upper member of the lower cretaceous Bima Formation, Northern Benue Trough, Nigeria

The upper Bima Formation in the Northern Benue Trough has been interpreted as a distributive fluvial system. Previous stratigraphic studies on the Bima Formation were focussed on localized, qualitative, sedimentary facies analysis without regional context or quantitative information about sand-body scale and architecture. This study quantitatively analysed sand-body thickness variations in the upper member of the Bima Formation across the Northern Benue Trough, documented the spatial variations in channel dimensions. Photo-realistic virtual outcrops were generated for four study sites using data acquired with an unmanned aerial vehicle and processed photogrammetrically. Analysis of the virtual outcrops illustrated spatial variation in the thickness of channel infill components, a downstream decrease in proportion of multi-storey channel belt facies association (from 98% to 5%), an increase in floodplain facies association (from 0% to 13%), an increase in the proportion of isolated channel fill facies association (from 2% to 80%) and a slight decrease in average grainsizes of channel fill sandstone. These observations are interpreted to represent evidence of a distributive fluvial system (DFS) or mega-fan with the proximal part of system at Tula, Ture and Tashan Alaji to the medial part at Hinna having an increase in frequency and thickness of the flood plain facies association and abundance of isolated channel fill facies associations. This study demonstrates the regional facies variability of the upper Bima Formation and has provided a basis for comparison with other ancient distributive fluvial system.

Basement configuration and lineaments mapping from aeromagnetic data of Gongola arm of Upper Benue Trough, northeastern Nigeria

The petroleum prospect evaluation of the Gongola arm of the Upper Benue Trough in the northeastern part of Nigeria has been undertaken through the analyses of High Resolution Aeromagnetic data (HRAM) acquired over the basin, with a view to determining sections of the basin having basement geometry, sedimentary thickness and structural framework among others that could support generation and preservation of the hydrocarbon resource. Processed, transformed and enhanced Total Magnetic Intensity (TMI) data were subjected to various analyses to define terrain geology, extract lineaments and delineate basement geometry, which were subsequently employed to generate basement model and structural framework of the basin. Most of the extracted lineaments trend ENE – WSW direction while Analytic Signal - Euler Deconvolution depth-weighting generate solutions which range in sediment thickness from 50 m above to over 5 km below the Minna reference datum, thus presenting undulating basement topography. Three sub-basins having depths in excess of 3 km, separated from each other by intra-basin subsurface basement highs, were delineated. The coexistence of considerably thick (3–5.7 km) sedimentary rock units and underlying structurally active basement rocks, assured geothermal gradient for organic matter maturation and guaranteed trapping of generated oil and gas within reservoirs’ structural traps.

An evaluation of potential toxic metals in sediments of a tropical watershed in southern Benue Trough, Nigeria

This study assessed heavy metal contamination in sediments within the Anambra drainage basin in Southern Benue Trough, Nigeria. Twelve river sediments were collected from the basin upstream and downstream in two seasons—rainy and dry seasons. The control was collected from the basin source. Samples were analyzed using X-ray fluorescence (XRF) spectroscopy for common major Potential Toxic Metals (PTMs). Concentration of zinc (Zn), nickel (Ni), manganese (Mn), iron (Fe), chromium (Cr), lead (Pb), vanadium (V), molybdenum (Mo), scandium (Sc) and europium (Eu) were detected in trend: Fe > Mn > Zn > Pb >>> Cr > Ni > Mo > Eu > Sc. Contamination trend in rivers shows Adada > Oji > Ezu > Obele > Mamu > Ankpa. The rainy season and the upstream sediments had lower concentrations than the dry season and downstream, respectively. Sediments had higher PTMs concentrations than the background sediments, though most PTMs concentrations were within the recommended standards- USEPA, WHO and Consensus-Based Sediment Quality Guidelines (CBSQGs). Contamination factor (Cf), enrichment factor (Ef), and geo-accumulation index (Igeo) recorded range from 0 to 15, 0 to 6.69 and − 8.43 to 3.32 respectively, signifying significant accumulation and enrichment of PTMs. Pollution load index (PLI) of the heavy metals ranges between 0.24 and 1.34, which suggest that at the different seasons, the basin was enriched with PTMs to a pollution level through anthropogenic activities. In the Anambra drainage basin, concentration and distribution of heavy metals may have been influenced by both non-anthropogenic and anthropogenic processes such as geology of the area, weathering and erosion as well as mining and agricultural activities.

Petrographic and Sediment Logical Studies of Bima Sandstone Formation out Croped at Lokoro area, Yola Arm of the Benue Trough, Northeastern Nigeria

Petrographic and Sedimentological Studies of the Bima Formation which outcroped at Lokoro area of Guyuk was conducted. This was achieved after mapping the area on a scale of 1:25,000. Analyses on the textures, lithologies and the environment of deposition of the Bima sandstone is presented.The Bima Sandstone of Lokoro area of Guyuk are mostly medium to coarse grained, texturally and mineralogically matured quartz arenites. The formation shows lateral variation in thickness and consists of arkosic, clayed, medium to very coarse cross bedded sandstone. In the thin section the grains are prodominantly quartz with many of the quartz floating in the cement while other grains exhibits point contacts. Some dark colour mineral grains, greyish and little brownish mineral grains were visible under the petrographic microscope. The petrographic studies also shows that sample is mainly silica in the form of quartz and iron oxides are predominantly the cementiing materials for the Bima sandstone as seen in Figure #2, #3, #4 and #5.The grain sizes range from 1.36 – 1.83mm indicating a medium – coarse grained sandstone that is poorly sorted.This poorly sorted attribute noted is a disqualification of the Sandstone from being an ideal potential reservoir in the basin. The quartz present is sub-angular to subrounded with iron oxide induced reddish brown colouration.

Regional 1D hydrocarbon maturation modelling of the Cenomanian–Turonian Lokpanta Shale, southern Benue Trough, Nigeria: Implications for the origin of Niger Delta deep sea oils

Basin modelling, constrained by geochemical data from eight wells, was carried out, across the late Cretaceous and Early Palaeogene sediment packages of south-eastern Nigeria sedimentary basins. The study was aimed at establishing the sediment burial history, thermal maturation of the source rock and timing of hydrocarbon generation. The Late Cenomanian to Early Turonian Lokpanta Shale, which is the basal unit of the Eze-Aku Formation in the Eze-Aku Group, consists of alternating dark grey to black shales, marl and siltstones. The upper sections are mainly alternating sandstones, shales and limestones. This unit is the key petroleum source rock for the basin. Numerical 1D basin model of the study area revealed that the Cenomanian to Turonian times was the main phase of rifting in the Benue Trough evidenced by rapid subsidence. Subsidence rates varied widely in all the wells studied, ranging from 29–61 m/Mya (million years ago) and averaging 44 m/Mya. Subsidence rates also varied widely through geological time from the Cretaceous to the Palaeogene. The Cenomanian–Turonian and the Maastrichtian ages recorded the highest subsidence rates (169.75 and 168.28 m/Mya, respectively). These phases of rapid subsidence correspond to the main phase of rifting (Cenomanian–Turonian) and periods of increased sediment supply (Campanian and Maastrichtian), due to rapid erosion and unroofing of the structurally inverted Benue Trough, post-Santonian. Vitrinite reflectance values (1.87–4.78% Ro) indicated that the Lokpanta source rock (Late Cenomanian–Early Turonian) is mature to overmature. The vitrinite maturation profiles and the geochemical data suggested the generation of hydrocarbon before the Santonian compressional uplift of the Abakaliki–Benue Trough with its resultant sediment folding, which displaced the depo-centre from the Abakaliki Basin to the Anambra and Afikpo platforms. The subsequent erosion and non-deposition in the Abakaliki Basin raised the Lokpanta Shale above the oil generative window. The renewed sedimentation in the Campanian resulted in sagging due to sediment load creating the Anambra Basin. The lack of an effective trapping mechanism in the pre-Santonian may imply that hydrocarbon generated before the uplift migrated away, probably to upper and/or lower horizons (observed as oil shows in the region); some of which may be contributing to the Niger Delta crude. This is evidenced by the correlation of the Niger Delta deep sea samples to the Cretaceous (Lokpanta Shale) source rock and occurrence of biomarkers of Cretaceous origin (ab-hopanes and oleananes in the Opuama Channel complex, northern depobelt, Niger Delta).

Evaluation and characterization of groundwater of the Maastrichtian Lafia formation, Central Benue trough, Nigeria

Hydrochemical assessment of groundwater in the Lafia formation, Central Benue trough, Nigeria was carried out with the aim of determining its quality for domestic and irrigation purposes. Thirty groundwater samples from boreholes and hand-dug wells were analyzed using atomic spectrometry and titrimetric methods. The water quality index (WQI) was evaluated from physicochemical parameters and used in assessing the groundwater quality for drinking, while the electrical conductivity (EC), percentage sodium (%Na), sodium absorption ratio (SAR) and magnesium hardness (MH) were evaluated to assess its suitability for irrigation. The physico-chemical parameters in order of dominance are \(\hbox {HCO}_{3}^{-} >\hbox {NO}_{3}^{-}>\) Cl- > \(\hbox {PO}_{3}^{-} >\hbox {SO}_{4}^{2-}\) for the anions and \(\hbox {Fe}^{3+}>\hbox {Na}^{+}>\hbox {Ca}^{2+}>\hbox {Mg}^{2+}>\hbox {Pb}^{2+} >\hbox {K}^{+}\) for the cations. The pH indicates acidic to weakly alkaline water (5.1–7.3); EC ranges from 110 to 1396 \(\upmu \)S/cm, while the total dissolved solids range between 136.9 and 3.4 mg/l, based on which it is classified as freshwater. WQI showed that only 40% of the groundwater samples are suitable while 60% are unsuitable for drinking and will therefore require treatment. Three water facies: \(\hbox {Ca}^{2+} + \hbox {Mg}^{2+}, \hbox {Ca}^{2+} + \hbox {Na}^{+} + \hbox {K}^{+}\) and \(\hbox {HCO}_{3}^{-}\) characterized the area indicating the groundwater-quality situation. Based on EC classification, 33.33% of the water samples are considered excellent, 60% as good, 6.67% as permissible while on the basis of %Na, only 13.34% are unsuitable for irrigation. SAR of 96.67 and 3.33% of the groundwater samples indicate excellent and doubtful waters, respectively. 93.4% of groundwater samples has MH < 50 and are considered suitable for irrigation.

Gravity Modeling of the Au–U Mineralized Crust at the North-Central Cameroon Illustrating Crustal Permeability

The north-central Cameroon is located at the northern edge of Archean Congo–Sao Francisco craton and at the east of the West African craton. This area includes various Neoproterozoic to Holocene geological litho-structural units. It corresponds to a juvenile crust resulting from the collision of the above cratons. Geological features associated with the Poli–Ounianga–Kebir heavy gravity line trending NE–SW crosscuts the study area and hosts several deposits, chiefly auriferous and uraniferous ore deposits. Uraniferous bodies are described at the SW and NE sides of the Benue Trough and are related to hydrothermal processes and structural events in Neoproterozoic granitoids of Poli (Cameroon) and Zabili (Chad). Gold ore deposits are found around faulted zones mostly in the Tchollire shear zone. Gravity data derived from the Earth Gravitational Model EGM2008, combining terrestrial, maritime and satellite-derived data, were used to model the crust of the north-central Cameroon. The geophysical filtering enabled to highlight that the most fractured areas with the deepest faults are situated on the positive anomalies of the mineralized volcano-sedimentary belts of Poli and Bibemi. The Benue Trough that crosscuts the volcano-sedimentary belts exposes few structural features due to the weak gravity signal of Cretaceous sedimentary cover. The radially averaged power spectrum analysis brought out the density contrast depths of some geological belts and revealed the Moho discontinuity of the study area at about 24 km depth. This Moho depth is in accordance with the assumption of a thin crust and a mantle upwelling in the study area proposed by previous works. Thus, the presence of geological formations of mantle, crustal and mixed crustal-mantle origin such as mafic rocks as well as calc-alkaline to alkaline granitoid outcropping in the study area may be the consequence of the proximity of the upper mantle to the surface. Moreover, fractures highlighted in this work brought out the crustal permeability in the study area illustrating migratory passages for mantle formations found at the surface. Based on the gravity field analysis, the proposed models of basement in this study provide geological architecture highlighting the presence of more or less dense rocks and hydrothermal fluids migration along faults as key elements for ore deposits formation.

Use of Modelling Approach in evaluation of Fractured Shale Aquifers for irrigation purpose; a case study of Oju, Lower Benue Trough Nigeria

Abstract Groundwater samples were evaluated for irrigation purpose, within selected part of Oju area of Benue State, Nigeria. The study area lies within Asu River Group of the Lower Benue Trough, southern part of Nigeria. Physicochemical parameters were analyzed using APHA, 2012 method. Results from the study showed that pH falls within slightly basic to acidic, with Ec value ranging from 127 to 760 μS/cm, SSP ranges from 1.53 to 43.78, Sodium Percentage ranges from 1.55 to 77.8 %, Kelly Ratio ranges from 0.01 to 0.77, Magnesium Absorption Ratio ranges from 0.00 to 61.98 and total hardness Total Hardness ranges from 72.00 to 425.5 within the study area. The above listed parameters were below various permissible standard value for irrigation except for MAR at LBT/04, Na % at LBT/09, 13 and 14, SAR at 01 and 04 and TH at LBT/04 that were slightly above various permissible standard values. From Gibbs plot it was observed that rock dominance is the major factor that influences groundwater except for few sampling point were precipitation dominance was observed to have influence on groundwater within the study area.

Heavy metals and rare earth elements distribution in the brine fields of awe, keana and giza, central benue trough, Nigeria

Groundwater in the brine fields of Awe, Keana and Giza, Central Benue Trough, Nigeria were investigated with the aim of determining the degree of its contamination which is vital for the proper planning and management of groundwater resource. Thirty (30) groundwater samples (10 from each location) from boreholes and dug wells were analyzed for physiochemical parameters (rare earth elements, heavy metals, major cations and anions) using enhanced ICP-OES/ICP-MS method. Results showed rare earth elements (RREs) such as Ce, Dy, Eu, Er, Gd, Hp, Nd, Sm, Tb and Yb are concentrated in the groundwater. Hydrochemical analysis revealed five (5) hydrochemical facies namely; Ca-HCO3, NaCl, NaHCO3, Ca-Na-HCO3 and Ca-Mg-Cl facies characterized the area indicating the groundwater quality situation. The weathering and leaching of mafic minerals from sandstone, shale, clay and barite mineralization control the concentration of calcium, sodium and magnesium ions. Total variance of 74.93% in the data set from principal component analysis (PCA) of the hydrochemicals revealed that the mineralization of the host rocks, weathering of galena, uranite, feldspathic minerals, dissolution of limestone and dolomite control the hydrogeochemistry of the area. The spatial distribution of the RREs in the study area showed that a strong positive correlation exists between brine and the RREs except Uranium which showed variation and is an indication of a distinct source from the RREs.

English

The aeromagnetic data of Otukpo (sheet 270) and Ejekwe (sheet 289) areas of the lower Benue Trough of Nigeria were interpreted quantitatively. The quantitative interpretation employed spectral analysis technique with the aim of locating specific basement depths to buried magnetic source rocks in the study area. First order polynomial fitting was adopted for regional-residual separation of the total magnetic intensity (TMI) map. The result of the spectral analysis indicates two depth source models; with depths to the deep sources varying from 2546.5 to 4177.3 m, having an average depth of 3058 m; while the depths to the shallow magnetic sources vary from 309.4 to 762.5 m, with an average depth of 527 m. The Otukpo area has greater sediment thickness capable of hydrocarbon accumulation than the Ejekwe area. This is supported by the presence of many intrusions at the Ejekwe area, with large lateral extents, indicative of over mature source rocks. Keywords: Aeromagnetic data, spectral analysis, basement depths, hydrocarbon potential.