Horizontal Gradient Magnitude Research Articles

Salinity Fronts in the South Atlantic

Monthly climatology data for salinity fronts in the South Atlantic have been created from satellite SMOS sea surface salinity (SSS) measurements taken from 2011–2019, processed at the Barcelona Expert Center of Remote Sensing (BEC), and provided as high-resolution (1/20°) daily SSS data. The SSS fronts have been identified with narrow zones of enhanced horizontal gradient magnitude (GM) of SSS, computed using the Belkin–O’Reilly algorithm (BOA). The SSS gradient fields generated by the BOA have been log-transformed to facilitate feature recognition. The log-transformation of SSS gradients markedly improved the visual contrast of gradient maps, which in turn allowed new features to be revealed and previously known features to be documented with a monthly temporal resolution and a mesoscale (~100 km) spatial resolution. Monthly climatologies were generated and analyzed for large-scale open-ocean SSS fronts and for low-salinity regions maintained by the Rio de la Plata discharge, Magellan Strait outflow, Congo River discharge, and Benguela Upwelling. A 2000 km-long triangular area between Africa and Brazil was found to be filled with regular quasi-meridional mesoscale striations that form a giant ripple field with a 100 km wave length. South of the Tropical Front, within the subtropical high-salinity pool, a trans-ocean quasi-zonal narrow linear belt of meridional SSS maximum (Smax) was documented. The meridional Smax belt shifts north–south seasonally while retaining its well-defined linear morphology, which is suggestive of a yet unidentified mechanism that maintains this feature. The Subtropical Frontal Zone (STFZ) consists of two tenuously connected fronts, western and eastern. The Brazil Current Front (BCF) extends SE between 40 and 45°S to join the subantarctic front (SAF). The STFZ trends NW–SE across the South Atlantic, seemingly merging with the SAF/BCF south of Africa to form a single front between 40 and 45°S. In the SW Atlantic, the Rio de la Plata plume migrates seasonally, expanding northward in winter (June–July) from 39°S into the South Brazilian Bight, up to Cabo Frio (23°S) and beyond. The inner Plata front moves in and out seasonally. Farther south, the Magellan Strait outflow expands northward in winter (June–July) from 53°S up to 39–40°S to nearly join the Plata outflow. In the SE Atlantic, the Congo River plume spreads radially from the river mouth, with the spreading direction varying seasonally. The plume is often bordered from the south by a quasi-zonal front along 6°S. The diluted Congo River water spreads southward seasonally down to the Angola–Benguela Front at 16°S. The Benguela Upwelling is delineated by a meridional front, which extends north alongshore up to 20°S, where the low-salinity Benguela Upwelling water forms a salinity front, which is separate from the thermal Angola–Benguela Front at 16°S. The high-salinity tropical water (“Angola water”) forms a wedge between the low-salinity waters of the Congo River outflow and Benguela Upwelling. This high-salinity wedge is bordered by salinity fronts that migrate north–south seasonally.

Application of Airborne Magnetic Data to Assess the Structures that Favour Gold Mineralization within Southern Parts of Katsina State, Nigeria

The Nigerian schist belts are endowed with gold mineralisation and to delineate the geological structures that favour gold mineralisation, the airborne magnetic data that cover the study area was employed. Also, the residual magnetic anomaly data of the research area was reduced to the Equator (RTE) followed by the application of the centre for exploration targeting (CET) plug-in and three source edge mapping techniques; analytic signal (AS), first vertical derivative (FVD) and the horizontal gradient magnitude (HGM), for structural delineation and subsequently the structural density map of the area was produced. Structural density varies from 0.186 km/km2 low to 0.93 km/km2 high. Portions within the study area with high structural densities are Bakori in the southwest, Shanono in the northeast, Gwarzo situated directly south of Shanono, north and south of Karaye, the border between Kafur and Rogo in the south, all within the schist. Since structures are conduits for the migration of mineralisation fluids, areas with high structural densities will be viable for gold mineralisation. Also, comparing the structural density map of the area to the analytic signal map of the area has revealed the high structural density portions to coincide with the high analytic signal zones. This implies that structures within these portions are responsible for the migration of mineralization fluid into these environments.

Estimation of ground depth of radioelements sources in Ogun State, Southwestern Nigeria using gradient techniques

Radioelement exploration has gained economic interest recently due to its usefulness in the detection and delineation of mineral deposits. In this study, the airborne radiometric data were analysed for depth estimation of the radioelement deposit in Ogun state, Nigeria. Three enhancement gradient techniques, namely; Analytical Signal Amplitude (ASA), Horizontal Gradient Magnitude (HGM) and Local Wave Number (LWN) were employed to estimate the possible depth of radioelements for mineralization. Geosoft's (Oasis Montaj) software and Potential Field's (PF) software were used to conduct the estimations. The result obtained revealed shallow sources of 0.584 km (LWN) and 0.387 km (ASA), and deep-seated sources of 5.950 km (ASA) and 5.880 km (ASA) for uranium and thorium, respectively. The shallow source and deep source for potassium are 0.259 km (ASA) and 2.540 km (ASA), respectively. In this study, the position and depth of the source were automatically estimated using linear equations based on derivatives without the use of any a priori knowledge. The three gradient methods are therefore found suitable in estimating the depth to radioelement anomalous source.

Integration of magnetic and geological field data into geological mapping and rutile mineralization targets in the Minta locality (Haute-Sanaga, Cameroon)

This study combines the processing and interpretation of magnetic data with geological fieldwork. The purpose is to establish the geological map and rutile mineralization targets map of Minta area (Haute-Sanaga, Cameroon). To this, a strategic geological field survey was first conducted. It highlighted some geological structures, especially magnetite quartzites, which is considered as the potential sources of primary rutile mineralization. Several methods were applied to the magnetic data, including upward continuation (UC), vertical derivative (DZ), analytical signal (AS) and horizontal gradient magnitude (HGM). The regional-residual separation method based on the UC was used to develop the residual map which was very helpful to understand the distribution of magnetic anomalies related to rutile mineralization in this area. The structural model of the study area was established by combining the analysis of the AS and HGM maxima with the analysis of the topographic model. Since magnetic relief variation characterizes the lithological information changes according to the filtered map considered, a set of categorization processes based on the anomaly signals was applied to each of filtered maps according to the geological information sought. It is based on the interpretation of structural models, combined with previous works and the spatial distribution of geological data collected. This process produced a set of partial lithological models, which were then combined with the interpreted structural model to produce the geological map of the study area. This map also shows the spatial distribution of the various targets of potential rutile mineralization interpreted on the DZ model as rectilinear anomalies, with a signal range of 0.78–0.88 nT/m.

Earth observation approach for targeting stratiform deposit of manganese in central India

The stratiform manganese deposits, hosted within the Sausar Group of rocks, in Madhya Pradesh state of India, has undergone polyphase deformation and metamorphism. The region is an enterprising geosite to understand the lithological and tectonic control on manganese mineralization. We have carried out a conjugate remote sensing based analysis using Visible, Near Infrared and Short Wave Infrared bands (VIS-NIR-SWIR) of optical imagery from multiple sensors supplemented with analysis of L-band microwave data over the Balaghat district of Madhya Pradesh to delineate prospective areas for manganese exploration, supported by the lab and field-based evidence.The enhanced image products (i.e.band ratios, principal components) and spectral anomaly map derived from Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) and Sentinel-2B multispectral bands are used to delineate the lithological contrast of the host rock and indicate key locales of mineralization. The geological structures interpreted using the merged product of Advanced Land Observation Satellite Phased Array L-band SAR (ALOS PALSAR −1), Landsat 8 PC bands (2 & 3) and the processed Horizontal Gradient Magnitude (HGM) from advanced satellite gravity model (EIGEN-6C4), illustrates the structural control on the mineralization. The petrological details derived from the host rock samples shows microstructures like micro-folding, foliations, quartz grain elongation etc., thus representing the microscale deformations within the rock units occurring in the area.The lab-based spectral signatures of manganese-bearing host rock was resampled to image spectra and spectral anomaly map using ConstrainedEnergyMinimization(CEM), which shows good correlation with the existing mine locations.The information from remote sensing and lab analysis has been integrated thematically using the knowledge-based Weighted Sum Method (WSM) with existing mine locations as the training dataset. The derived mineral prospect map indicates several new areas of manganese prospectivity which can serve as a guide for detailed future explorations in the region .

Use of Land Gravity Data in Small Areas to Support Structural Geology, a Case Study in Eskişehir Basin, Turkey

Various researchers have contributed to the literature on the locations and lengths of existing faults in the Eskişehir Basin, Turkey. However, the majority of the literature on the subject bases its results on fault indications observed on the surface, for example, surface ruptures. In addition, studies using geophysical methods in order to reveal buried faults have also fallen short regarding depth compared to gravity. In order to have a better understanding, the gravity method was applied with a total of 448 gravity measurements on five parallel lines in the north–south direction of the study area, which also includes the urban area of the Eskişehir Basin. Considering the neotectonics of the Eskişehir basin, the measurement lines were chosen to perpendicularly cut the east–west extending faults of the Eskişehir fault zone. For the first time in the literature, a detailed Bouguer gravity anomaly map has been obtained for the Eskişehir Basin using land gravity measurements. The edge detection Horizontal Gradient Magnitude (HGM) and Euler Deconvolution (ED) methods were applied to obtained Bouguer anomaly data. Both of these use spatial analysis of Bouguer gravity anomalies. An HGM map shows the presence of maximum amplitude areas in the south and north of the study, and these areas were found to be compatible with the known faults in the literature. ED solutions also support HGM maximums. The relationship between the lineaments obtained from the edge detections and the seismicity of the region were examined. It can be seen that the results obtained from both the HGM and ED edge detection methods are highly compatible with each other, and highly related to the structural geology of the region. Although great agreement with the faults in the literature was determined by both methods, only the ED method showed a number of newly found faults in the area. In addition, the locations of the known faults in the region were supported by the geo-physical gravity method for the first time.

Mapping transpressional and transtensional relay zones by coupling geological and geophysical field data: The case of the central Cameroon shear zone in the Mbere administrative division of the Adamawa region in Cameroon

The aim of this study was to map the transpressional and transtensional relay zones of the Central Cameroon Shear Zone in the Mbere Administrative Division of the Adamawa Region of Cameroon using, geological and geophysical data analysis. The central Cameroon Shear Zone (CCSZ) is characterised by several large strike-slip faults oriented between N030E and N070E. The geological and structural field data analysis revealed two deformation regimes (strike-slip and tensile) that exhibit characteristic deformation markers identified in the field. The dextral movements on the strike-slip faults of the CCSZ were associated with these markers, the two regimes were found to be associated with the D3 deformation along the CCSZ. The tensile regime generated transtensional structures and led to the formation of the Cretaceous Mbere and Djerem basins, whereas the transcurrent regime caused the transpressional tectonics. Structural analysis of the joints and veins of the D4 deformation shows that their directions describe those of the major axes of the CCSZ. As the D4 deformation is controlled by transcurrent tectonics, to show that the vein intrusions constitute transpressional relay zones and to derive different models, processing, and interpretation methods (spectral analysis, shaded relief analysis, magnetic signal filtering, upward continuation, horizontal gradient magnitude, analytical signal, and 2.5D inversion) have been applied to the geophysical data. Magnetic residual analysis shows that the transpressional relay zones are characterised by high-frequency rectilinear magnetic anomalies (207.12–305.809 nT) and interference along the strike-slip faults. Through the superimposition of the geophysical interpretations, a structural model integrating the two deformation regimes with relay and Cretaceous basin models was developed.

Delineation of the subsurface boundary between the Central and Southern Eastern Desert, Egypt

The shear zone characterization is a substantial task for understanding the influencing tectonic movements. In this study, an integrated approach of remote sensing and aeromagnetic data is introduced to imagine and trace the subsurface shear zone between the Central (CED) and Southern (SED) domains of the Egyptian Eastern Desert in comparison with the previously proposed approaches mainly using only surface criteria. To produce an enhanced geological map reflecting the different lithological units along both sides of the surficial shear zone, Landsat-8 images are processed and interpreted using False Color Composite (FCC), Color Ratio Composites (CRC). Moreover, the associated lineaments and their trends are extracted from Digital Elevation Model (DEM) data using the lineaments extraction approaches. For delineating the subsurface structures pattern and tracking the probable subsurface CED/SED boundary, aeromagnetic datasets are reduced to magnetic pole (RTP) and, then, interpreted by applying significant techniques comprising upward continuation, Gaussian separation filter, horizontal gradient magnitude (HGM), and tilt derivative angle (TDR). The best path of the shear zone line at depths was imagined; this path agrees with some geologists' opinion regarding the superficial description of the CED/SED separating shear zone. On the other hand, trend analysis was applied on the subsurface and surface data, reflecting a positive matching between the resulting trends from the magnetic and remote sensing data. The NW direction represents both data's major trend and less common NNW NS, NNE, and ENE trends. This relation reflects the extension and effect of the subsurface structures on the surface in the study area.

Integration of remote sensing and geophysical data for the extraction of hydrothermal alteration zones and lineaments; Gabal Shilman basement area, Southeastern Desert, Egypt

In the Gabal Shulman area of the southeastern desert of Egypt, ASTER and geophysical aeromagnetic data provide useful information for detecting hydrothermal alteration zones and structural features at the surface and subsurface. The band ratio of the data from ASTER, constrained energy minimization (CEM) and Crósta algorithms help to identify new potential alteration zones in the study region. The aeromagnetic data were used to enhance the exploration study in the study area. The Horizontal Gradient Magnitude (HGM) filter was used to map the lineaments in the area. The statistical analysis of the lineaments shows that the main directions controlling the study area are northwest, north, north-northeast, and northeast. Finally, the results of ASTER and the geophysical aeromagnetic data show the presence of new hydrothermal alteration zones in the study region. These alteration zones are mostly associated with two main structures trending NNW-SSE and N-S, mainly along tectonic shear zones (thrust faults) and contacts between serpentinites and basic metavolcanics.

Structural analysis and basement topography of Gabal Shilman area, South Eastern Desert of Egypt, using aeromagnetic data

The existing work deals with the structural analysis and detecting basement depth of G. Shilman area, South Eastern Desert (SED), Egypt. This work includes interpreting aeromagnetic data to map out structures within the study area and determine the depth of the magnetic basement which can be an aide to advance exploratory study. The first vertical derivative (1st VD) enhanced the short-wavelength and high-frequency features of the data. The analytic signal (AS) and horizontal gradient magnitude (HGM) maps well the structures of G. Shilman area. Statistical analysis of the delineated structures indicated that the NW, N_S, NNE and NE are the main structural trends controlling the study area. This suggests that the area was dominated by various stress regimes. The source parameter imaging (SPI) method which acts strongly at all magnetic latitudes was applied to the data to map the basement topography of G. Shilman area. The basement depths vary from about 0.1 km to about 1.5 km at the deepest part of the study area. The depth examination indicates that the recent deposits are not thick and reflect the shallow nature of the basement in G. Shilman area. The results of our study gives more accurate interpretation for the structural regime of the study area and can be applied for alike areas.

Influence of Pan-African tectonics on older Precambrian basement structural fabrics as revealed from the interpretation of aeromagnetic and remote sensing data of Ikole/Kabba region, southwestern Nigeria

Reliance on structural data from geological mapping will be grossly inadequate to establish an informative regional tectonogenic interpretation in southwestern Nigeria mainly because of poor exposure of outcrops due to severe weathering in the tropical region. Therefore high resolution aeromagnetic anomaly and Landsat-8 OLI/TIRS data were adopted for tectonic analysis of Ikole/Kabba area where qualitative analysis of Landsat-8 imagery provides surface lineaments with major E − W and N–S trends. Processing of the aeromagnetic anomaly data utilizing the horizontal gradient magnitude and total gradient methods indicated various E − W, NW - SE, N–S and NE - SW structural features in agreement with the surface lineaments; lending credence to the existing geologic structural interpretation. The resulting synoptic structural interpretation suggests the preservation of two major successive events; an earlier prominent E-W trending lineaments resulting from a N–S compressional deformation, succeeded by a brittle deformational event characterized by NW-SE and NE-SW trending lineaments. Additionally, the magnetic basement depth map deduced from the source parameter imaging technique shows depth values between 50 m and 650 m, which represent depths to the top of structural features within the basement rocks of the region. The collective interpretation of high resolution aeromagnetic anomaly and Landsat-8 data provides significant information about regional tectonics and structures that are good conduits for mineral deposits within the study area.

Prospectivity modelling of Canadian magmatic Ni (±Cu ± Co ± PGE) sulphide mineral systems

New mineral deposit discoveries are required to meet the forecasted demand for some critical raw materials. Governments are responding to that challenge by investing in mineral systems research and by by making government geoscience datasets freely available to the public and explorers. However, translating conceptual mineral system models to mappable geological, geochemical, and geophysical proxies is difficult with incomplete data of variable quality from modern and legacy surveys. Herein we address those knowledge gaps and propose a new open source workflow in R for prospectivity modelling using public geoscience datasets. We focus on the largest footprints of magmatic Ni (±Cu) sulphide mineral systems and their critical raw materials (±Co ± PGE). Multiple prospectivity models are presented, including data-driven methods (e.g., weights of evidence, gradient boosting machines) that use the features of known mineral occurrences as a training set and a hybrid method that also incorporates conceptual mineral system criteria. All models are validated using data from northern Canada (i.e., north of 60° latitude) as a test set. Statistical analysis of the prospectivity results suggests that rock types and geological ages are two of the most important predictive datasets, which correspond to the sources and drivers within the mineral system framework, respectively. Variable importance plots further suggest that geological boundaries (e.g., horizontal gradient magnitude of the gravity data and multi–scale edges) and the close spatial association between areas of high mineral potential and the edges of thick continental crust represent prospective ore-forming pathways. Model performance and the best combination of predictors and hyperparameters for each model are based on the receiver operating characteristics (ROC) plots, which yield a range of area under the curve (AUC) from 0.846 to 0.923 for the spatially independent test set. Most Canadian geological provinces, possibly with the exception of the Grenville orogen for the hybrid and weights of evidence methods (AUC = 0.716–0.726), yield comparable model performance, suggesting that the heterogeneous spatial distribution of different mineral system sub-types (e.g., komatiite-associated, rift-related, Alaskan-type, and hydrothermal awaruite) have a relatively minor impact on the prospectivity results. Monte Carlo-type simulations further suggest that the expert weightings used in the hybrid method (AUC = 0.843) are only slightly better than an average model constructed from random combinations of weightings (AUC = 0.809). The general agreement between different methods and multiple iterations of the same model demonstrate that public geoscience datasets can effectively reduce the search space to support mineral exploration targeting (i.e., less than 8% of map pixels contain more than 80% of the known Ni mineralization). However, vast segments of the Canadian landmass have not undergone systematic geological surveying or data acquisition. Prospectivity modelling can thus also be used by governments and academia to prioritize areas for future targeted geoscience research.

Integrating of Remote Sensing and Airborne Magnetic Data to Outline the Geologic Structural Lineaments That Controlled Mineralization Deposits for the Area around Gabal El-Niteishat, Central Eastern Desert, Egypt

The Gabal (G.) El-Niteishat area lies in the Central Eastern Desert of Egypt which is known for various mineral resources and geological structures. Umm Gheig, Umm Naggat, Umm Shaddad, Wadi (W.) Zeidun and Sigdit represent some important regions that contain mineral deposits in the study area. Various filters such as first vertical derivative (FVD), horizontal gradient magnitude (HGM), tilt derivative (TDR) and near-surface were applied to the airborne magnetic data for the study area to deduce the structural lineaments and magnetic source edges which were controlled by the presence of mineral deposits. Processed Landsat ETM+ images are used for delineating the rock unit boundaries that are exposed in the study area such as serpentinite, metagabbro, metavolcanics and metasediments. Also, band ratios, principal component analysis (PCA) and false-color composite image (Crosta alteration image) were applied to get specific results about the alteration zones. The structural lineaments analysis illustrated that the common trends that affected the study area were NW-SE, NE-SW, E-W and N-S. Integration of remote sensing and airborne magnetic data exhibited the relation between mineralization and structural lineaments.

Structural interpretation of magnetic and satellite remotely sensed data of Osun State, Southwestern, Nigeria

ABSTRACT This study delineates surface and subsurface structural features in the hard rock terrain of Osun State using magnetic data and satellite remote sensing imageries. To achieve this aim, several image enhancement methods were applied to the magnetic data and satellite remotely sensed imageries to improve visualization and interpretation. The subsurface lineaments were detected and traced out from the maxima of Horizontal Gradient Magnitude, peaks of Analytical Signal Magnitude, and an Euler solution of Osun state. The magnetic lineament map reveals that the structural trend in the area is dominant by NE-SW and NNE-SSW. These structural trends were found to be consistent with the regional tectonics of the Southwest Basement of Nigeria. The NE-SW is the most conspicuous structural trend in the study area. The satellite imageries depict a characteristics feature of the occurrence of underlying structures in the basement complex of Osun State. The major lineament trends delineated in the composite surface lineament map are the NE-SW, NNE-SSW, and ENE-WSW directions. The 2.5 D model across the unmapped lineaments confirmed the existence of a thin dyke’s characteristic of fracture/fault in a typical basement complex terrain. The derived lineaments may serve as a reference for future geological and structural mapping.

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.

Source edge detection (SED) of aeromagnetic data: synthetic examples and a case study from Haimur area, south Eastern Desert, Egypt

Delineating the horizontal boundaries of magnetic sources presents a significant tool for understanding geologic structures. Many of enhancements for recognizing the boundaries of magnetic sources have been introduced. These enhancements are generally proposed based on the gradients of the magnetic field (horizontal and vertical). In this paper, the horizontal gradient magnitude (HGM), tilt derivative (TD), and horizontal tilt angle derivative (HTAD) filters were utilized to synthetic magnetic data. These filters are further applied to real aeromagnetic data of Haimur area, south Eastern Desert (ED) of Egypt data for source edge detection (SED) of the residual and regional geologic features. The adequacy of the HTAD filter is indicated using synthetic models and real data. Compared with the conventional HGM and TD methods, the SED-HTAD filter provided more detailed imaging for buried models and represented the residual and regional sources of Haimur area more clearly than HGM and TD filters.

Analysis of aeromagnetic data: Application to Early-Late Cretaceous events in parts of Lower Benue trough, Southern Nigeria

The study of the sedimentary sequence in parts of the Nigerian lower Benue trough has been carried out to understand the sedimentary thickness and its structural framework using high resolution aeromagnetic gridded data. It represents background investigation for targeting new mineralization zones and probable locations for detailed petroleum system analysis in the study area. The first order vertical derivative and the horizontal gradient magnitude of the reduced to the magnetic equator anomaly map were derived while edge detection techniques such as analytic signal, tilt derivative and horizontal derivative of tilt were implemented. Quantitative interpretations such as three dimensional Euler deconvolution, spectral analysis, and Source Parameter Imaging were applied to the residual magnetic intensity anomaly map. The results obtained show the Abakaliki Albian Asu River Group, the Caniacian Awgu shale and the Agala / Amasiri sandstones of Agubala and Ngbo to be severely intruded by rocks suspected to be basic or ultrabasic plutonic rocks. The basement topography, the sedimentary thickness of about 3800 m characterized by moderate volcanic intrusions, and the presence of a prominent anticlinorium for hydrocarbons preservation in Okpoto and environs call for a detailed petroleum system analysis. Structures hosting Lead-Zinc-Copper mineralization were identified in Ishieke, Ekeriegwe, Ugbuloke, and Abakaliki during an onsite mapping of notable structures. The mineralized structures in the areas are generally of dual origins − hydrothermal and volcanic. The hydrothermal minerals are connected to lineament intersections and occur as veins and veinlets in sedimentary rocks and feldspars while volcanic related ones occur as grains and with gangues in volcanic rocks.

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.

Analysis of Aeromagnetic Data of Ikwo and Environs, Southeastern Nigeria: A Mineral and Hydrocarbon Exploration Guide

In the face of impending global energy crises, with demand for minerals and energy surpassing availability, the need to explore relatively frontier areas becomes imperative. In this study, high-resolution airborne magnetic data covering Ikwo and its adjacent areas were utilized to delineate possible mineral-bearing lineaments, determine depth to magnetic causative structures, and assess the sedimentary pile thicknesses with their implication for hydrocarbon and mineral exploration. The total magnetic intensity grid shows an acute change in magnetic intensity values, which reflect the subsurface geological environment. The second vertical derivative image indicates that the western, northwestern and southeastern-most parts of the area are most likely to possess abundant shallow magnetic bodies, which are most probably mineral deposits or igneous intrusive rocks. Ground-based electrical resistivity profiling and induced polarization methods were used to confirm the presence of these shallow bodies. Lineament analysis depicts NE–SW as the principal lineament orientation with minor E–W and N–S trends. The horizontal gradient magnitude revealed two depth models. Deeper bodies, attributed to intra-basement structures were marked as lying between 1.2 km to 4 km whereas shallow intrusive rocks occur within a depth range of 0.2 km to 1 km. The presence of numerous intrusive rocks and a relatively thin sedimentary thickness means that the area is unlikely to favor hydrocarbon accumulation. However, it appears viable and promising for solid mineral exploration.

Seismotectonic lineament mapping over parts of Togo-Benin-Nigeria shield

ABSTRACT This study carried out a seismotectonic analysis of parts of Togo-Benin-Nigeria shield by delineating and characterising crustal discontinuities using gravity bouguer anomaly data. This was with a view to understand the significance of the discontinuities to the seismicity of the area. Three dimensional (3-D) Euler deconvolution and horizontal gradient magnitude (HGM) at varied upward continued layer were applied on the filtered bouguer gravity data to highlight crustal discontinuities and determine their dip directions. The result showed that 89 lineaments were mapped as faults/fractures from the gravity data. The lengths of the lineaments range from about 6.2 to 94.3 km. The prominent fault/fracture trends were in the N-S and NNE-SSW directions with less dominant trends in the NE-SW and NW-SE directions. The prominent N-S trend pattern aligns with the general N-S foliation strike emplacement across the shield. The Lagos-Ibadan-Ijebu-Ode fault line was identified in this map as having close proximity to locations of previous earth tremors and therefore might be associated to those events.