High-resolution Aeromagnetic Data Research Articles

Estimation of The Structural Pattern and Sedimentary Thickness Over Part Of Anambra Basin, Nigeria Using Aeromagnetic Data

Abstract Aeromagnetic data acquired over part of the Anambra Basin is analyzed to determine the structural pattern and sedimentary thickness of the basin. The study area is covered by high resolution aeromagnetic data on sheets 301 (Udi), 302 (Nkalagu), 312 (Okigwe) and 313 (Afikpo), and lies between latitudes 5o30’0’‘-6o30’0’‘ and longitudes 7o0’0”-8o0’0”. The whole area was divided into 25 overlapping blocks of 37.2km2 each and a 2D energy spectral analysis was carried out. Total magnetic intensity data was subjected to filtering and analytical techniques to determine the structural pattern, mineralization potential, depth to the basement, variation in the sedimentary thickness. The structural map generated using the vertical derivatives shows that the major structural orientation of the area is in the ENE-WSW trend and the minor trend is the NW to SE direction widespread all over the area. These structures are as a result of the various near-surface magnetic intrusion within the study area. The spectral analysis result shows two depth layers, the deep and the shallow depth, the depth to magnetic basement for the deep anomalous source ranges from 3.3km to 4.8 4km with an average depth of 3.99km, while the depth to shallow magnetic sources ranges between 0.46km to 0.67km and an average of 0.56km within the area. The mineralization pattern in this area follows the ENE-WSW direction.

Aeromagnetic interpretation of basement structure and architecture of the Dahomey Basin, Southwestern Nigeria

ABSTRACT Significant yet untapped resources still abound in the Nigerian sector of the Dahomey Basin. Although the presence of an extensive Cretaceous Petroleum System has been confirmed following recent discoveries in Aje and Ogo Fields offshore Lagos, exploration outputs in the Dahomey Basin has so far not been encouraging. Proper understanding of the basement architectural framework and controls on tectonic development remains key to unlock the unrealised potentials in the basin. Hence, a geophysical interpretation of the basement structure and architecture of the Dahomey Basin southwestern Nigeria has been carried out in this study. Various edge enhancement techniques were applied to the high-resolution residual magnetic intensity (HRRMI) grid of the area. This includes first vertical derivative (FVD), total horizontal derivative (THDR), tilt derivative (TDR) and total horizontal derivative of upward continuation (10 km). Determination of the depth to magnetic sources and sedimentary thicknesses in the study area were achieved using standard Euler deconvolution and source parameter imaging (SPI) techniques, with depth range of 4.5–6.3 km attained in the two identified sub-basins located offshore of the study area. Lineament analysis gave insights on the tectonic trends and stress-field orientation in the basin with major trends in the NNE-SSW, NE-SW, NW-SE, and WNW-ESE directions. 2D forward modelling of some selected profiles was employed to characterise the basement pattern and architecture, which depicted a horst-graben architecture. The basement structure and architecture have a major control on the distribution of sub-basins, petroleum systems elements and trap styles in the basin. The study demonstrates the robust application of high-resolution aeromagnetic data in basin-wide mapping of regional subsurface geological features, basement architecture and determination of sedimentary thickness in a frontier basin.

A geophysical investigation of the 2018 Lake Muir earthquake sequence: reactivated Precambrian structures controlling modern seismicity

Seismicity in the intraplate southwest of Western Australia is poorly understood, despite evidence for potentially damaging earthquakes of magnitude > M6. Identifying stress-focusing geological structures near significant earthquake sequences assists in understanding why these earthquakes occur in seemingly random locations across a region of more than 250 000 km2. On 16 September 2018, an ML5.7 earthquake occurred near Lake Muir in the southwest of Western Australia and was followed by an ML5.4 aftershock. The main earthquake formed a mainly north-trending fault scarp ∼5 km in length and with a maximum vertical displacement of ∼40 cm. The main event was followed by a series of aftershocks, one of which had a magnitude of ML5.4. Using high-resolution aeromagnetic data, we analyse bedrock geology in a wide area surrounding the new scarp and map a series of major ∼ east–west-trending faults segmenting eight distinct geological domains, as well as a network of less prominent northwest-trending faults, one of which aligns with the southern segment of the scarp. Surface faulting, surface deformation and earthquake focal mechanism studies suggest movements on north- and northeast-trending structures. The main shock, the aftershocks, surface faulting and changes in InSAR-derived surface elevation all occur in a region bounded to the south by a prominent northwest-trending fault and to the north by a west-northwest-trending domain-bounding structure. Thus, we interpret the north-trending thrust fault associated with the main Lake Muir event as due to local stress concentration of the regional east–west stress field at the intersection of these structures. Further, we propose that a particularly large west-northwest-trending structure may be broadly focusing stress in the Lake Muir area. These findings encourage similar studies to be undertaken in other areas of Australia’s southwest to further the current understanding of seismic release in the region. KEY POINTS A large ML5.7 earthquake occurred in southwest Western Australia in September 2018, damaging infrastructure and forming a 40 cm-high thrust fault scarp. An aeromagnetic interpretation of the Lake Muir region revealed that the new scarp aligned with pre-existing faults that were reactivated. Local and regional structures likely acted as regional stress focusers in the Lake Muir area. Identifying regional stress-focusing structures is important for the purpose of understanding seismic risk in intraplate areas such as Western Australia.

Imaging lateritic bauxite bearing zones in Ekiti, Southwestern Nigeria, using magnetic and electrical resistivity tomography techniques

This research uses geophysical techniques such as magnetic and electrical resistivity tomography to image the lateritic bauxite bearing zones in Orin Ekiti, Southwestern Nigeria. The high-resolution aeromagnetic data were utilized for generating the total magnetic intensity (TMI) map. Different filtering techniques such as Euler deconvolution and total horizontal derivative were also carried out to enhance better understanding of bauxite deposit, with the generation of different maps therein. Low magnetic intensities were observed over charnockitic rock which is a host material for bauxite occurrence. Magnetic low trending NE–SW was observed in the study area. The (EUD and THDR) maps were then superimposed on the geologic map to geo-reference areas that have dominant charnockite. The depth extent and structural signature interpreted from magnetic interpretations show that significant deposit in the study area is at shallow depth which tallies with the geology of bauxite as being a supergene enrichment (surficial deposit). 2D ERT results obtained from five traverses with inter-traverse separation of 45 m and traverse length of 100 m each, established in the NW–SE direction to image the lateritic bauxite deposit based on the prospect shown from the aeromagnetic analysis. The images display the constant resistivity regimes beneath the traverses with different colour bands. The 2D ERT profiles and 3D inversion results show bauxitic zones to be of high resistivity which ranges from 154 to 3814 Ω m, the migmatite gneiss and granitic rocks (unaltered parent rocks) are of considerably lower resistivity than the weathered charnockitic rock and by extension bauxitic zones. These different techniques used in this study have however shown that the area of interest for bauxitic deposit in Orin Ekiti trends in the NE–SW direction with a dominant concentration in the north-eastern (NE) part. By the same token, this research has been able to substantiate the fact that bauxite deposits occur as supergene enrichment.

2D modelling of high resolution aeromagnetic data over northern sector of Bida basin north-central Nigeria

The study was carried out in the northern sector of Bida basin. The study focuses on mapping depths to magnetic basement and basement structural framework that may assist in delineating overlying sedimentary sections that have prospect for hydrocarbon exploration. High resolution aeromagnetic data of the study area was subjected to regional residual separation, analytic signal and 2D modeling using Oasis Montaj geo-software. Results of the analytic signal demarcated the basement/sedimentary contact, interpretation of 2D geologic models revealed a horst and graben structures underlying the sedimentary formations in the northern sector of Bida basin. The graben structures having sedimentary fills to a depth greater than 2 km were viewed as favourable sites for source rock development. In view of the aforementioned areas around Bakoni, northeast of Tshipo, Enagi and southwest of Wuya with thick sedimentary piles were recommended for further application of other geophysical methods of better resolving power to explore the area for hydrocarbon; since the basin has potentials for hydrocarbon generation.

Edge Detection and Depth to Magnetic Source Estimation in Part of Central Nigeria

High-resolution aeromagnetic data covering an area of 24, 200 km2 in north central Nigeria has been acquired and analyzed with the aim of carrying out trend analysis, edge detection (structural delineation) and depth to magnetic source estimation using reduce to the pole (RTP), horizontal gradient magnitude (HGM), center for exploration targeting plug-in (CET), 3D Euler deconvolution and source parameter imaging (SPI) techniques. Trend analysis was applied to the RTP data to delineate structures that have dissected the area. The 3D Euler deconvolution and HGM were correlated by plotting the estimated Euler solutions for a structural index of one (SI=1) on HGM map and the resulting map produced have shown that both methods can contribute in the interpretation of the general structural framework of the study area. The structural delineation based on HGM and CET maps showed that two predominant trends (ENE-WSW) and (WNW-ENE) have affected the area. The trend/depth/contacts of these faults were classified into four groups: Faults <150 m, 150 m - 300 m, 300m - 450 m which are the most predominant fault system based on Euler solutions with a structural index of one (SI=1) and those deeper than 450 m while the result of source parameter imaging (SPI) revealed a depth to source varying from 58 m specifically for areas with shallow depth to the magnetic source to those from deeper source occurring at 588.153m depth especially the south-central portion and the south-eastern portion of the study area.

Dating the Acraman asteroid impact, South Australia: the case for deep drilling the ‘hot shock’ zone of the central uplift

The deeply eroded Acraman structure in the Mesoproterozoic Gawler Range Volcanics, Gawler Craton, South Australia, ranks among the world’s largest known impact structures, with a transient crater ∼40 km in diameter and a ∼90 km-diameter collapse crater. An impact age of ca 590 Ma is suggested by Rb–Sr shale dating of Ediacaran strata hosting a related ejecta band of volcanic fragments in the Adelaide Rift Complex and Officer Basin, and ca 580 Ma by chemostratigraphy. Ascertaining an accurate and precise impact age would greatly benefit Ediacaran biostratigraphic, biogeochemical and magnetostratigraphic global correlations. However, numerous attempts to date the impact, using material from exposures at Acraman and the ejecta band, have been unsuccessful. U–Pb dating of zircons from shattered dacite basement, melt rock and ejecta by three laboratories gave ages related to the 1592 Ma Yardea Dacite. K/Ar and 40Ar/39Ar dating of end-member K-feldspar in melt rock by two laboratories provided early Paleozoic ages, indicating later fluid movement. Although 80% of terrestrial impact structures ≥40 km in diameter have been drilled, Acraman has not. Deep drilling of the ‘hot shock’ zone of the unexposed central uplift is required to obtain zircons with U–Pb ratios that were likely reset by the impact. High-resolution aeromagnetic data for Acraman reveal an elliptical magnetic low measuring 19.5 × 18.3 km, with NNE–SSW-trending major axis and a high-amplitude dipolar anomaly of the central uplift that is offset to the SSW. The magnetic signature suggests oblique impact from the SSW. The source of the dipolar magnetic anomaly, centred ∼1 km below the Lake Acraman salina and with a remanence direction concordant with that of the melt rock, marks the ‘hot shock’ zone and a potential target for drilling. The scientific rewards of such drilling could be substantial. KEY POINTS Acraman in the Mesoproterozoic Gawler Range Volcanics, South Australia, is one of the world’s largest known impact structures, with a related ejecta band of volcanic fragments hosted by Ediacaran (ca 590–580 Ma) strata in the Adelaide Rift Complex and Officer Basin at unfolded distances from 250 km up to 550 km from the impact site. Numerous attempts at U–Pb dating of zircons from shattered volcanic basement and melt rock at Acraman, and zircons from the ejecta, gave un-reset basement ages, and K/Ar and 40Ar/39Ar dating of melt rock gave early Paleozoic ages related to later fluid movement. An accurate and precise age for the impact would provide a reliable age for the ejecta-hosting Ediacaran strata and greatly benefit Ediacaran biostratigraphic, biogeochemical and magnetostratigraphic global correlations. Deep drilling of the ‘hot shock’ zone of Acraman’s central uplift, inferred to be the source of a high-amplitude dipolar aeromagnetic anomaly centred ∼1 km below the Lake Acraman salina, is required to obtain zircons with U–Pb ratios most likely to have been reset by the impact.

Regional groundwater studies using high-resolution aeromagnetic data in Abuja and environs, North-Central Nigeria

Abuja and environs usually experiences water shortage during the dry season as a result of rapid population growth, due to the fact that the water from Lower Usuma Dam used for domestic and industrial purposes are no longer sufficient to cater for its teeming population. The shortage can be minimized through better understanding of lineament configurations of the area. Regional groundwater studies using high-resolution aeromagnetic data in Abuja and environs, North-Central Nigeria were carried out to address water shortages in Abuja and its surroundings. The aim of the study was to identify groundwater targets/potential zones for the purpose of providing sufficient water to the communities in the area. The study area is situated in the North-Central part of Nigeria and lies between latitudes 8° 00’- 9°30’ N and longitudes 6°30’- 8°00’ E. First vertical derivative (1VD) technique was applied to the residual magnetic data of the study area using Oasis Montaj software version 8.3 and thereafter extracted lineaments from 1VD map using ArcGIS software version 10.4.1. Result of 1VD technique indicates that polyphase deformation was pervasive throughout the area as joints, fractures, faults, as well as folds in the map. Major lineament trends identified in the study area are NNE-SSW 27.47%, NE-SW 25.54%, ENE-WSW 18% and N-S 9.57%, the magnitudes and orientations of the lineaments are essential for groundwater movement. The study indicates that Dogon-Kurmi, Gitata, Rafin, Gurku, Karshi, Keffi, Paiko, Farindoki, Takuti, Lambata, Izom, Tudun Wada, Safon Lapai, Mayaki, Gwagwalada, Gidan Ali, Takura, Dafa, Dangara, Abaji, Kwali, Zuba, Madalla, Gauraka, Suleja, Kuje, Abuja, Bwari, Udegi, Zango-Daji, eastern part of Katakwa, Gadabuke, Buga, Koton-Karfe, Bibirako, Kworaki, Toto, Dagoshi and Umaisha have good groundwater prospect. Fieldwork conducted in the area confirmed the existence of lineaments/fractures in the area and as such are targets for groundwater exploration.

Curie depth estimated from high-resolution aeromagnetic data of parts of lower and middle Benue trough (Nigeria)

To quantitatively understand the geodynamic process of a region, study of geothermal parameters underneath the earth surface is very paramount. Curie depth can be an alternative to delineate geothermal parameters. In the present study, we estimated Curie depths from the power spectra of 25 equally window sizes areas/points with 50% overlap extracted from high-resolution aeromagnetic anomalies of parts of lower and middle Benue Trough, Nigeria using modified centroid method based on fractal distribution of magnetic sources. Curie depths with associated uncertainties calculated from the region under study are between 11 ± 2 and 27 ± 2 km. The shallowest depth (11 ± 2) km is calculated around the area of Abakaliki whereas the deepest depth is calculated around Otukpa area of Anambra basin. The shallowest Curie depth as calculated is related with the Abakaliki anticlinorium while the deepest result is in connection with the Anambra basin. These suggest that different geological structures and magnetic anomalies (i.e. high or low magnetic anomaly) influenced the calculated Curie depth results. In the region, it is noted that lower Curie depths (14–18 km) are recorded over the basement rocks and Curie depths between 18 and 22 km within zones of volcanoes. The interpretation hypothesized presence of underplating in the crust and possibly mantle plume as a result of the Mesozoic–Cenozoic volcanic magmatism (magmatic centers) mostly basalts distributed and scattered in the region. It has also been hypothesized that the uncertainties calculated (± 0.2 to ± 5.0) in the region correlate more strongly with the geology, tectonic structures and type of anomalies than estimated Curie depths.

Aeromagnetic mapping of fault architecture along Lagos–Ore axis, southwestern Nigeria

AbstractA seismic wave is released when there is sudden displacement on a fault plane. The passage of this wave along the fault plane or within the lithosphere could result in ground shaking or vibration at the surface of the Earth. To provide a geophysical explanation to this phenomenon, the high-resolution aeromagnetic data of the sedimentary terrain and part of the Basement Complex of Southwestern Nigeria were processed and interpreted to provide fault architecture of the area, which could serve as conduit for the passage of seismic energy in the study area. High-resolution aeromagnetic data along the Lagos–Ore axis are processed for fault mapping in the study area. The reduced-to-equator (RTE) residual aeromagnetic data used were enhanced using the total horizontal derivative (THD) and upward continuation (UC) filtering techniques on Oasis Montaj 6.4.2 (HJ) software. The resultant maps were overlaid and compared with the plotted RTE residual maps for relevant interpretations. Varying signatures of magnetic anomalies are grouped into high (57.9–89.1 nT), intermediate (38.2–57.9 nT), and low (4.0–38.2 nT) magnetic intensities, which are associated with contracting basement rocks features. The obtained lineaments from the THD reveal areas of various deformations such as brittle, which is associated with faults/fractures, and ductile deformation, which is associated with folds of geological features. The faults, as depict by the UC map, reveal different depth ranges of 500–2250 m at the western side and 1,500–1,250 m at the northwestern area of the study. Since it has been on record that September 11, 2009, earth tremor of magnitude 4.4, with the epicenter at Allada, Bennin Republic, 128 km west of Lagos, Nigeria occurred within the study area, it can be inferred that the established geologic fault architecture could be responsible for the hazard and be part or synthetic to the Ifewara-Zungeru fault in Nigeria.

Regional and local controls on Archean rock-hosted cobalt mineralization at the McAra deposit, southern Superior Province, Ontario, Canada

The McAra deposit is in eastern Ontario, Canada, and is hosted in an Archean inlier to the Paleoproterozoic Huronian basin. It is currently estimated to contain ∼2.4 million pounds of cobalt at an average grade of 1.25%. New drill data show the mineralized zone comprises glaucodot–cobaltite veins and breccias that transect a mafic–siliciclastic volcanogenic massive sulfide (VMS) deposit. The high cobalt grade and host stratigraphy at the McAra deposit contrast with five-element (Ag–Co–Ni–Bi–As) deposits at the Cobalt and Gowganda camps in the region that produced high-grade silver and by-product cobalt from veins spatially associated with Nipissing Gabbro intrusions. However, geochemical data from recent core samples alongside fluid inclusion and mineralogical data suggest the cobalt zone at McAra and the five-element veins share a similar metal assemblage and were deposited from similar fluids. The mafic–siliciclastic VMS deposit at McAra contains anomalous amounts of cobalt, suggesting the Archean host stratigraphy was the source for the high-grade cobalt zone. Basin brines in the Paleoproterozoic are interpreted to have leached cobalt from Archean rocks and then redeposited it through oxidation–reduction reactions along synvolcanic faults that controlled earlier VMS deposit formation. High-resolution aeromagnetic data show that McAra is immediately adjacent to a mafic dike that transects the Huronian basin along a northwest-striking, crustal-scale fault system. These data, alongside observations from field mapping, also suggest the deposit is on the margin of a sub-basin that contains an 80 km2 Nipissing sill that may have originally overlain the deposit area and been a hydrologic seal during mineralization. The new deposit- and regional-scale data and interpretations are used to create a model for the McAra deposit and provide evidence for why it is cobalt-rich relative to other five-element veins. The model and data can be used to guide exploration for additional cobalt-rich deposits in the region and similar settings globally.

ANALYSIS OF HIGH-RESOLUTION AEROMAGNETIC DATA OVER PARTS OF SOKOTO BASIN, NORTH-WEST NIGERIA

Sokoto Basin is one of the sedimentary basins suspected to have high hydrocarbon potential. Hence, due to the possible deposit of this economic mineral, it is worthy of being preliminarily investigated. This paper uses high-resolution aeromagnetic data over parts of Sokoto Basin covering longitude 4.00°E-5.00°E and longitude 12.00°N-13.00°N, to assess the sedimentary thickness beneath the subsurface while also establishing the basement topography. The studied area covered four adjacent one-degree sheets, namely, sheet 27 (Lema), sheet 28 (Argungu), sheet 49 (BirninKebbi) and sheet 50 (Tambuwal). Enhancement of the total magnetic intensity map was carried out to improve the anomaly characteristic of source bodies, and two-dimensional Spectral analysis was carried out using GEOSOFT software (Oasis montaj6.24 version) in order to estimate magnetic source depths in the area. The shallower sources occur at a depth range of 0.23 km - 0.79 km with an average depth of 0.47 km, while the deeper sources occur at a depth range of 0.83 km -1.95 km with an average depth of 1.40 km. The maximum depth to the top of the magnetic source body gets deeper around Lema and IllelaKwandu while the minimum depth is around Tambuwal, Danjema and Birnin-kebbi. Thedepth estimated from the spectral analysis compares reasonably well with the results from the Euler deconvolution. The areas with higher sedimentary thickness toward the northern part of the study area are feasible for hydrocarbon generation and are thus recommended for other geophysical surveys.Keywords: Sokoto Basin, sedimentary thickness, hydrocarbon exploration, high-resolution, aeromagnetic data,geophysical surveys

Magnetic Modeling and Potential Hydrocarbon Trap Over Yola and Environs Upper Benue Trough Northeastern Nigeria

With a renewed interest to search for hydrocarbons in the hinter land of Nigeria’s inland basin climaxed after the discovery of a rewarding oil prospects around the Kolmani river II as recently announced by the National Oil Company, the Nigeria National Petroleum Corporation (NNPC). This research was based on analyzing the high-resolution aeromagnetic data over the study area using the Oasis Montaj TM software, in order to get the total magnetic intensity map as well as the residual map, band pass filter map was used to generate magnetic aureoles. GM-SYS module of the Oasis montaj was used for the modeling exercise, the models reveal the horst and graben architecture of the basement with the grabens serving as depocentres, hydrocarbon potentials of the area were highlighted using magnetic aureoles mapping.

Preliminary Investigation of Seismicity in Parts of North Central Nigeria, Using High Resolution Aeromagnetic Data

Qualitative analysis of Aeromagnetic data of parts of north central Nigeria had been carried out with the aim to delineate seismic prone areas. The study area is bounded with latitude 9. 00o to 10. 00oN and longitude 7.00o to 9.00oE with an estimated total area of 24,200 km2. Vertical derivatives and upward continuation filters were used to enhances long wavelength anomalies which could give preliminary information about the magnetic structures present in the study area. The total magnetic intensity map shows both positive and negative anomalies with susceptibility ranging from 33487.7 nT to 33800.9 nT. The high magnetic susceptibilities dominated in the basement region around the north-eastern and north-western parts of the study area which corresponds to Naraguta, Jemma and Kafanchan area. Based on the geology of the area this is attributed to granite, schist and migmatite rocks. The low magnetic values are made of sediment deposition also dominates the south-western part of the study area, corresponding to Abuja and Gitata. The area with magnetic susceptibility values ranging between 33506.6 nT and 33653.8 nT indicates alluvium deposite around Bishini and Kachia area. Lineament from First Vertical Derivative trend in the northeast-southwest and east-west directions, which is an extension from Romanche Fracture Zone. Majority of this lineament trends in the same directions as the Romanche Fault Line which continues at 25 km and 30 km into n inferred closure within the study area which is trending along north-west direction. This, closure occurs probably because of the existence of the paleo fracture zone (Romanche Fracture Zone) within the study area. At 40 km and at 80 km a regional trend in the NE-SW direction in (porphyritic) basement rocks. At the northeast and southeastern part of the area which is made up of basement complex that corresponds to areas around Gitata, Kafanchaan and Jemma are prone to tectonic activities while the southwestern part of the area around Abuja is seismic free. It is suggested that those lineaments identified, most especially at the southeastern part could be the reason for the shaking of the subsurface which result into earth tremors.

Interpretation of high-resolution aeromagnetic data within Dahomey basin, Nigeria; case for hydrocarbon prospectivity

The Ilorin Journal of science (ILJS) is an international and interdisciplinary open–access journal devoted to all aspects of research in Sciences and related fields. It is an official publication of the Faculty of Physical Sciences, University of Ilorin, Ilorin, Nigeria.The Ilorin Journal of science (ILJS) is an international and interdisciplinary open–access journal devoted to all aspects of research in Sciences and related fields. It is an official publication of the Faculty of Physical Sciences, University of Ilorin, Ilorin, Nigeria.

Interpretation of High Resolution Aeromagnetic Data for Hydrocarbon Exploration in Bornu Basin, Northeastern, Nigeria

Hydrocarbon exploration in Bornu basin, Northeastern Nigeria commenced due to the discovery of gigantic hydrocarbon reserves in extended basins in neighboring countries. This study was carried out to map the Mungono and Marte parts of the Bornu basin for geologic structures that could guide in exploring new hydrocarbon fields using aeromagnetic method. Magnetic Intensity grids and their derivatives were used for mapping these structures while depths of magnetic sources (basement) and corresponding sedimentary thickness were estimated using Euler deconvolution and Source Parameter Imaging (SPI) methods. Anomalies show characteristic high positive polarity in the south in contrast to low magnetic signature of northern domain. Features such as faults, folds and intrusive rock bodies were identified as geological structures that could serve as hydrocarbon entrapment. Lineament analysis shows that fractures generally trend NE-SW following the dominant rift system of Bornu basin and Benue Trough. Three basement depressions with thick sediments (more than 3000 m) were also delineated which should be investigated for further petroleum exploration. The outcome of this study would help in delineating promising areas for detail hydrocarbon prospecting in the area.

Analysis of aeromagnetic anomalies of parts of Chad Basin, Nigeria, using high-resolution aeromagnetic data

High-resolution aeromagnetic data over a part of Chad Basin in Nigeria have been analysed with a view to delineate the geological lineaments, estimate sedimentary thicknesses and map the location of structurally controlled sub-basin formation within the studied area. The geological lineaments were mapped using horizontal gradient magnitude method. Spectral analysis and source parameter imaging (SPI) techniques were used to estimate the sedimentary thicknesses. The results revealed the existence of structurally bounded large depression that dominantly spans the south-eastern portion of the study area. The depression is interpreted as a large structurally controlled sub-basin having a width of about 79 km and extending to over 5.7 km in depth from the result on SPI. The depth estimated from spectral analysis shows depth estimate of 1.2–4.8 km. The application of forward modelling revealed the 2D image of the nature of the subsurface (basement morphology and the depths) and the block boundaries coinciding with the geological lineaments. The models also show some areas within the sub-basin extending to a depth of 8.3 km. The maximum depths obtained from the SPI and 2D models (profiles N1–S1 and N3–S3) show a structurally controlled sub-basin sufficient for potential hydrocarbon generation and accumulation.

Qualitative Evaluation of Geophysical Aeromagnetic Data For River Anticline Around The River Niger Area In Koton-Karfi, Southern Bida Basin, Nigeria


 
 
 In this paper a qualitative evaluation of aeromagnetic data maps has been used to preliminarily support the formation of river anticlines beneath major rivers due to isostatic rebound as a result of deep river incision of surface and sub-surface overlying rocks. The regional gradients of digital high resolution aeromagnetic data were removed by polynomial fitting. This involved fitting a plane surface to the reduction to pole map of the aeromagnetic data by using multi-regression least square analysis of the Oasis Montaj 6.4 program. The regional field values from the plane surface are subtracted from the observed data to obtain the residual anomaly values. Power spectrum plots of aeromagnetic data of the study area produced a basement depth contour map. The basement depths of the south-western part of the study area revealed basement uplift with a depth range of 1.8 to 2.5km which lies beneath the Niger River area, SW of the study area, and depicts a river anticline.
 
 

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.

Analysis of high-resolution aeromagnetic (HRAM) data of Lower Benue Trough, Southeastern Nigeria, for hydrocarbon potential evaluation

ABSTRACT The analyses of high-resolution aeromagnetic (HRAM) data of lower Benue Trough in southeastern Nigeria have delineated sections of the basin with requisite sedimentary thickness that could support the generation of oil and gas from right-type organic-matter rich source rock as well as identified intra-sedimentary structural framework that could aid hydrocarbon migration and restrain generated hydrocarbon within available reservoirs. The susceptibility and Analytic Signal (AS) maps derived from processed Gaussian-filtered and Reduced to Pole at Low Latitude (RTPLL) aeromagnetic data discriminate crystalline basement rocks from the sedimentary units. Likewise, many relatively shallow, short (900–1600 m) intra-geologic terrain linear structures and fewer long, deeper (>1.5–43 km) inter-geologic terrains crustal linear structures which reduce in population but increase in lateral extent and depth with increasing continuation distances were delineated from the processed Tilt Derivative (TDR) and the Horizontal components of the Tilt Derivatives grids at different Upward Continuation distances. Euler Deconvolution depth-weighting analyses determined depth to magnetic sources which ranges in value from 120 m above to 5 km below the Minna reference datum. Regions having sedimentary thickness in excess of 3 km with active intra-sedimentary structural elements qualify for further petroleum exploration campaign using other detailed geological and geophysical tools.