Evaluation of Aeromagnetic Anomalies Over Okigwe Area, Southeastern Nigeria (original) (raw)
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Total field aeromagnetic anomalies over Kogi-Auchi area have been evaluated in order to map the magnetic lineaments and estimate the depth to basement (sedimentary thicknesses). Aeromagnetic and radiometric data of the area (sheet 246, 247, 266 and 267) were acquired, digitized and analyzed. The slope methods were applied in the analysis of the residual contour map. The result obtained using the slope methods reveals two depth sources in the study area; on the average the deeper magnetic sources range from 2.3 to 4.9 km, while the shallower magnetic sources range from 1.1 to 1.6 km. These shallower sources are probably due to the presence of igneous intrusives and/or magnetized bodies within the sedimentary cover. Visual study of the residual anomaly map shows the presence of igneous intrusive in the entire North and Southwestern part of the study area. The One Vertical Derivative (1VD) lineament map shows the Fault trending in Northwest-Southwest (NW-SW) and Northeast-Southwest (NE-SW) direction and this conforms to the Niger-Benue basin itself. Hydrocarbon exploration is not recommended since the area has low thickness of sediment on the average. All this deduction were reached after due consideration of qualitative and quantitative interpretations supported by geological information of the area.
Aeromagnetic study of Okitipupa region, Southwestern Nigeria. .pdf
Aeromagnetic technique is used for mapping of inland extension of Chain Fault zones into the south part of Nigeria using aeromagnetic data study area was processed to produce various maps mineral accumulation as well as to understand mapping. Analyses involved the application of Upward Continuation, Vertical Derivative pole, total magnetic intensity, analytical investigation revealed the nature of m magnetic intensities. Qualitative and quantitative inte knowledge of the survey area yielded information on the depth of geological features (e.g. rock contact, faults or fractures), structures and magnetic properties of rock units. size mineralized bodies and shallow features in the study area were mapped. On the upward continuation filtered map, a west -east linear feature with a trend similar to the major orientation of the regional faults in shown area was estimated. The rift valleys in the area are long, deep valleys bounded by parallel faults, or fractures. In addition, the predominant SW/NE, SE/NW and E fracture/faults cut the basement and penetrated the overlyin area.
Geological interpretation of aeromagnetic data in some parts of northcentral Nigeria
Journal of African Earth Sciences (and the Middle East), 1992
Airborne magnetic data and field observations were used to define structural trends in some parts of North Central Nigeria. The aeromagnetic anomalies of the Jurassic Younger Granite complexes are distinctive with relatively high amplitudes and short wavelengths and are directly associated with the outcrop patterns of the intrusions. The mosaic pattern of magnetic anomalies may be used to identify the Younger Granite ring complexes. The aeromagnetic data also contain evidence of linear structural discontinuities. Some of these linear features are long and extend through the survey area. They are idemified by a pattern of contour offsets and probably reflect deep crustal features cutting some of the Younger Granite known to be mineralised. In particular, a major fault is mapped which cuts the Ririwai complex to the East. This fault [rending NW-SE, appears to extend southwards through the area. The lineaments probably acted as conduit through which mineralized fluid flowed. The regional trends of structures are revealed on the aeromagnetic map, these being mainly northeast-southwest and northwest-southeast. The Northwestsoutheast trends are superimposed on the northeast-southwest trends. This overprinting of one magnetic anomaly trend over the other suggests that the Northeast-southwest lineaments are older than the northwestsoutheast lineament patterns. Three known tin-bearing ring complexes show strong magnetic anomalies which make them more prominent than the other complexes on the coloured magnetic anomaly map. This characteristic should assist in locating new provinces for primary tin deposits.
Aeromagnetic Data Interpretation for Geostructural Analysis of Ibadan, Southwestern Nigeria
International journal of engineering research and technology, 2013
The digitized aeromagnetic data of Ibadan obtained from the Nigeria Geological Survey Agency NGSA has been analysed for the purpose of delineating the geostructural settings of the area. Ibadan is located in present Oyo State, South Western Nigeria underlain by basement complex rocks of the Precambrian age and bounded within longitude 3 0 30'E to 4 0 00'E and latitude 7 0 00' to 7 0 30' N. The aeromagnetic anomaly map, its analytic signal amplitude, its vertical gradient magnitude, the Euler solutions and residual magnetic intensity map helped in identifying the nature and depth of the magnetic sources in the study region. The residual magnetic intensity map shows areas of magnetic highs and magnetic lows. The NorthWestern part shows prominent magnetic clusters trend, relatively prominent along the South East and the North central trending North, which signify areas of magnetic conductive materials which could be higher magnetite (a common magnetic rock) intrusion, buried metallic materials or areas of thin overburden. The depth estimate from analytic signal amplitude revealed magnetic depth range from 0.26-4.28 km while the results from the vertical gradient revealed minimum and maximum limit on source depth to be 0.16 km and 2.87 km respectively. The Euler Deconvolution overestimated the shallow depth to top of the magnetic source and the magnetic basement depth ranging from 0.02 km to 6.78 km respectively. The result obtained from the enhancement techniques used shows the shallow magnetic source depth values in the range 0.263 km to 0.881 km while the magnetic basement depth values are in the range 0.02 km to 6.78 km.
Egyptian Journal of Petroleum, 2017
This study, which spans latitude 5°N-5.30 I N and Longitude 13°E-13.5°E with an approximate area of about 3400 km 2 within the Northwestern Sokoto basin of Nigeria, aims to delineate possible source of stress regime, determining the structural features and their corresponding trend directions, delineating lithologic boundaries as evidenced by magnetic disturbances caused by different rock types and estimating the hydrocarbon viability within the study area by interpreting the behavior of the geophysical data obtained from the Nigeria Geological Survey Agency, NGSA in half degree sheet. The aeromagnetic data was subjected to both qualitative and quantitative analytical techniques using Oasis Montaj software, version 8.1. The result of the qualitative analysis generated some magnetic gradient maps showing dominant and minor magnetic structures trending E-W, NE-SW and NW-SE. These trends are possible fault indicators within the region. Similarly, the qualitative analysis revealed lithologic boundaries trending in the E-W and NW-SE direction. The dominant E-W trend possibly highlights the stress regime and also represents the Pre-Pan African Orogeny that was characterized by small brittle deformation which resulted in the development of conjugate strike-slip fault systems while the truncated NE-SW, NW-SE trends indicate Pan-African Orogeny. On the other hand, quantitative analysis performed on the aeromagnetic data by means of Source Parameter Imaging (SPI) quantitative method reveals depth to deep seated magnetic sources to range from 54.1 m to 3384.4 m but with an average of about 739 m. The dominant E-W tectonic magnetic trending structures and a thickness average of 739 m limit the possibility of oil and gas exploration. Thus the possibility of hydrocarbon exploration even when seismic sections are run within the study area will be very minimal.
Interpretations of aeromagnetic data over lokoja and environs, Nigeria
International Journal of Advanced Geosciences, 2014
Total field aeromagnetic anomalies over Kogi-Auchi area have been evaluated in order to map the magnetic lineaments and estimate the depth to basement (sedimentary thicknesses). Aeromagnetic and radiometric data of the area (sheet 246, 247, 266 and 267) were acquired, digitized and analyzed. The slope methods were applied in the analysis of the residual contour map. The result obtained using the slope methods reveals two depth sources in the study area; on the average the deeper magnetic sources range from 2.3 to 4.9 km, while the shallower magnetic sources range from 1.1 to 1.6 km. These shallower sources are probably due to the presence of igneous intrusives and/or magnetized bodies within the sedimentary cover. Visual study of the residual anomaly map shows the presence of igneous intrusive in the entire North and Southwestern part of the study area. The One Vertical Derivative (1VD) lineament map shows the Fault trending in Northwest-Southwest (NW-SW) and Northeast-Southwest (NE-SW) direction and this conforms to the Niger-Benue basin itself. Hydrocarbon exploration is not recommended since the area has low thickness of sediment on the average. All this deduction were reached after due consideration of qualitative and quantitative interpretations supported by geological information of the area.
Journal of African Earth Sciences, 2018
The purpose of this study is to analyze the aeromagnetic data of Ikom and its environs in Cross-River State, Nigeria in order to delineate the structural lineaments according to their spatial and directional attributes as well as define the depth to magnetic causative bodies. This was achieved with the aid of an acquired, digitized and processed aeromagnetic intensity contour map covering Ikom and its adjacent areas. The aeromagnetic data was subjected to diverse data enhancement and transformation routines. Regional-residual analysis was implemented on the total magnetic intensity map (contour interval = 20 nT) to generate a residual magnetic intensity contour map. Results show that the area is characterized by a very complex pattern of magnetic intensities of both long and short wavelengths. Sequel to the regional-residual anomaly separation, azimuth orientation of the lineament structures delimited on the maps portray N-S and NE-SW as the principal trends with E-W and NW-SE as the minor trends. Two depth sources were obtained by employing the commonly known Peter's half-slope method. Depth range for the deeper causative sources is 0.83 km to 3.5 km with a magnetic intensity range of-30 nT to-220 nT while the superficial sources had a range of 0.2 km to 0.75 km and a magnetic intensity that vary from-10 nT to 20 nT. The deeper magnetic sources are attributed to the underlying pre-Cambrian basement complex rocks and intra basement structures such as fractures and faults whereas the superficial sources are due to basement intrusives as well as ore-bearing veins present in the overlying Cretaceous rocks. The shallow basement depth and prevalence of intrusives and linear structures are indications of an area of good mineral prospects but unfavorable for hydrocarbon formation.
Modeling Earth Systems and Environment, 2017
Aeromagnetic data of Idah and Angba environs, north central Nigeria, has been interpreted by applying spectral analysis and forward and inverse modeling methods. Quantitatively, spectral analysis and forward and inverse modeling techniques were employed in interpretation with the aim of determining depth/thickness of the sedimentary Basin and magnetic susceptibilities that give clue on the type of mineralization prevalent in the area. The result from spectral analysis revealed two main magnetic anomaly source depths; deep magnetic anomaly source and the shallow magnetic anomaly source. The deep magnetic anomaly source varies between 2.194 and 6.764 km with an average depth value of 5.014 km which represents the depth to sedimentary thickness. The shallow anomaly source varies from 0.597 to 1.592 km with an average depth value of 1.093 km and these were observed within the basement region. Forward and inverse modeling estimated depths for profiles 1-5 were 526, 461, 4347, 1751, and 6847 m, respectively, with respective susceptibility values of 0.0003, 0.0879, 0.0800, 0.0004 and 0.0700 which indicate intermediate and basic igneous rocks (diorite, andesite and gabbro or basalts) and basic sedimentary rocks (sandstone and limestone). The maximum depths obtained from these two applied methods show sufficiently thick sediments suitable for hydrocarbon generation and accumulation. Keywords Aeromagnetic data • Idah and Angba area • Spectral analysis • Forward and inverse modeling • Magnetic anomalous sources
Ijebu-Ode and its environs in southwestern Nigeria is located on a geological transition zone from the Precambrian migmatite gneiss rocks and Cretaceous sedimentary rock units of Abeokuta Group. Unique geological structures, complex coexistence of different rock types and poorly defined basal/lateral contacts between the basement and sedimentary rocks typify tectonic events that accompany crustal thinning and downwarping at the basement/sedimentary-basin edge. This posed serious geological decision challenges especially since it is difficult to characterize the area either as sedimentary or crystalline. Aeromagnetic data were collected, the data were filtered, inverted and enhanced using appropriate software packages and subsequently employed to generate model of the subsurface basement topography. The magnetic intensity distribution in the field ranged from −120 to +80 nT and was found to depend on the size, depth of burial and the thickness of low susceptibility superficial material overlying the magnetite rich crystalline rocks. High magnetic intensity characterized the basement rocks while lower values distinguished the metasediments rocks and sedimentary terrain. The average radial power analysis delineated shallow and relatively deep sources as the two distinct types of magnetic anomalies. Euler deconvolution results referenced to the Minna, Nigeria datum indicate depth range from −80 to +30 m for sources located below and above the mean ground level, respectively. Euler result also revealed that the depth to magnetic sources is heterogeneous and highly erratic around the transition zone, ranging between −25 and +12 m. This study identified rugged and undulating basement topography around the contact zone; it also delineated the lateral and basal contacts between the two coexisting rock types. Aeromagnetic mapping of basement sedimentary transition zone around Ijebu-Ode has proved very efficient in providing relevant information about the nature of the basement topography which provided vital information requisite for drilling and some engineering constructions decisions.
2017
The analysis of aeromagnetic data over Middle Benue Trough and its adjourning basement terrain using Source Parameter Imaging (SPI) in Oasis montaj version 8.2 indicates that, the depth to magnetic sources in adjourning basement varies between 0.2 km to1.7 km. The depth to magnetic source at the middle of the study area which made up of the Cretaceous sediments of middle Benue varies between 4 km to 6 km. The shallow depth at the adjourningbasement could be as a result of basic intrusive rocks of the basement terrain, while the deeper sources at the middle of the study area that made upof cretaceous sediments of middle Benue, could be due to rifting of the Benue Trough. From the results obtained the adjourning basement terrain could be a potential site for mineral exploration while, the sedimentary section belonging to the middle Benue Trough could be a potential site for petroleum exploration.