Analysis Of Aeromagnetic Data Research Articles

MAGCPD: a MATLAB-based GUI to calculate the Curie point-depth involving the spectral analysis of aeromagnetic data

The Curie point-depth, frequently related to the depth to the bottom of the magnetic source, is widely employed as an estimator of temperature at depth when borehole temperature data are not available. The Curie point-depth is calculated using the spectral analysis of the magnetic data derived from aeromagnetic or satellite surveys. In this paper, MATLAB user-friendly GUI are constructed to calculate the Curie Point Depth using the inversion of aeromagnetic data assuming 2D fractal magnetization and modeling the temperature at depth assuming a 1D steady-state conductive heat transfer model. The program, tested in synthetic and aeromagnetic data, is running under MATLAB 2020a or standalone application with these input parameters: Aeromagnetic data, fractal parameter, Curie temperature, surface temperature, thermal conductivity, surface radiogenic heat production and scaling length of surface radiogenic heat production. The radially averaged amplitude spectrum, scaled spectrum, modeled spectrum, Curie point-depth, and temperature profile at depth are the output parameters of the program. Finally, the program is tested with Texas aeromagnetic data, and the results of the Curie point-depth were compared with borehole data.

Interpretation of Airborne Magnetic and Geo-electric Data: Resource Potential and Basement Morphology of the Ikom–Mamfe Embayment and Environs, Southeastern Nigeria

The Ikom–Mamfe Embayment, which cuts across southeastern Nigeria and southwestern Cameroon, is a bifurcation of the Benue Trough and the NW–SE splay component of the NE–SW trending trough. The Nigerian sector of the embayment, a sedimentary province bounded to the north and south by basement terrains, is considered a relatively frontier basin with little information about its resource potential. Here, airborne magnetic, resistivity and self-potential (SP) data were integrated in studying the Nigerian sector of the embayment and its surrounding localities. This study aimed to delineate (possible) mineral-bearing lineament structures and their corresponding trend orientations, to evaluate their relationship to tectonic fabric, to estimate depth of perturbing causative sources, to map ore bodies, and to identify probable locations for detailed petroleum system analysis. For the first time, 2D electrical resistivity and SP methods were deployed in the sub-surface characterization of the embayment. Results of aero-magnetic data analysis revealed the presence of high magnetic intensities predominantly in the western and northeastern parts of the study area. The high intensities observed at the western part are due to mineral ore bodies present within a sedimentary host. In addition to the presence of mineral ores, the noticeable high magnetic signatures at the northeastern part are associated with the presence of outcropping units of basement complex rocks that comprise mainly of migmatitic metasediments. The large variation in magnetic intensities within the embayment is attributed to the combined effect of igneous intrusives and mineral-bearing lineaments emplaced within the overlying sediments. Analysis of structural lineaments depicts E–W and ENE–WSW as the dominant orientations with minor NW–SE, NE–SW and NNE–SSW trends. The NE–SW and ENE–WSW structures are aligned parallel to the Benue Trough and the Cameroon Volcanic Ranges, and are genetically related. These lineaments occur in the form of faults, fractures and veins, and they are densely distributed within some areas of moderate to high intensities and analytical amplitudes. This suggests a possible relationship between structural lineaments and metalliferous deposits. These lineaments were marked for ground geophysical surveys. The geophysical traces derived from these areas reveal numerous underlying mineral bodies of contrasting resistivity and potential with their host formation. These bodies are shallow magnetic sources exposed in the first and second vertical derivative images. These show remarkable agreement between the geo-electric data and the aero-magnetic data. The results of quantitative assessment show shallow basement depth and, hence, thin sedimentary layer (0.2–2.4 km) within and around the embayment, which is insufficient for the concealment of hydrocarbon resource. In addition, the presence of numerous intrusive rocks implies a high temperature environment favorable for “cooking” of potential source rocks beyond the hydrocarbon generating window. This renders the area disadvantageous for hydrocarbon exploration. However, we discover that the sedimentary thickness (ranging between 3 and 4 km) mapped at the southwestern part of the area could favor the formation and accumulation of hydrocarbon fluids. This area, characterized by moderate igneous intrusion, lies approximately northeast of the prolific Niger Delta oil province and shows fair to good sub-surface structural conditions required for hydrocarbon entrapment. The basement morphology, sedimentary thickness and structural disposition call for a detailed petroleum system analysis within this area.

Study of Curie point depth and heat flow from spectral analysis of aeromagnetic data for geothermal potential of Gubio, Chad Basin, Nigeria

Aeromagnetic data of Gubio area, Chad Basin, northeastern Nigeria, were interpreted quantitatively by employing spectral analysis technique with the aim to estimate the Curie point depth, geothermal gradient and heat flow in order to determine the geothermal nature of the area. Data enhancement (reduction to pole, RTP and band pass filter) was performed on the total magnetic intensity (TMI) map of the area using oasis Montaj software. The enhanced map was divided into four overlapping blocks, and each block was subjected to spectral analysis. The results gave Curie point depth values ranging from 10.63 to 20.07 km, with deepest depth at the northeast, while the shallowest depth was observed to be conspicuous in the southeastern part of the study area. The estimated geothermal gradient ranges from 28.90 to 54.57 °C km−1 with an average value of 40.26 °C km−1, with low values in the northeast direction, and increases towards southeast. The average geothermal gradient of 40.26 °C km−1 indicates the possibility of hydrocarbon generation and accumulation in Chad basin. The estimated heat flow values range from 72.24 to 136.43 mW m−2 with an average value of 100.65 mW m−2, the highest values are found around southeastern part of the study area, and the lowest values are within the northeastern part. The areas of geothermal anomalies with gradient above 50 °C km−1 may be good areas for geothermal reservoir exploration for an alternative source for power generation.

A geophysical study contributing to analysis and characterization of a localized copper occurrence

Characterization of small-scale copper occurrences using traditional prospecting methods is costly and requires the use of different professionals during acquisition, analysis and interpretation phases. Aerogeophysical surveys conducted by governmental institutions even when providing important regional scale results have low-resolution data in locally occurrences. These informations are inefficient in target-scale prospective studies due to the large amount of interpolated data between the measured flight lines. In this study we proposed a geophysical study integrating previous aeromagnetic data analysis to a ground magnetometer survey to characterize a locally copper mineralization in the known Sul-Riograndense Shield ore province, Caçapava do Sul municipality, Rio Grande do Sul State, Brazil. The occurrence is local, observed in a 4 × 2 m outcrop and occurs in metasedimentary rocks. The processed aerial data added to the ground magnetic anomalies, geophysical maps, and subsequent analysis allowed us to enhance the NE-SW direction anomaly (ground survey) and propose a forward 2.5D model defining an enriched copper – sulfides zone geometry and its lateral and depth limits. The model (A – B profile) was defined cross-sectioning the observed ground magnetic anomalies near the surface known occurrence and was generated using susceptibility measurements as input and, additionally, geological information from remote sensing previous data, outcropping rocks, and structures as parameter/comparison. Significant contrasts of anomaly variations (laterally and in-depth) are related to the local ore occurrence and also the presence of sulfides associated with Cu oxides (malachite) with a NE – SW trend coincident with the locally observed and measured structures (faults and joints). Considering the absence of other in-depth investigation methods such as drill core analysis and chemical element quantification (geochemistry), the adopted methodology and forward modeling applied in this study represent an important approach in the lateral and deep recognition and delineation of this occurrence. Therefore, it represents an effective, fast and low-cost tool for preliminary characterization of sulfide-associated Cu mineralized targets in this mineral province.

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.

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.

Estimation of Curie point depth in southwestern Yemen from spectral analysis of aeromagnetic data

Curie point depths in southwestern Yemen were determined from radially averaged power spectra of the reduced to the pole aeromagnetic data by the modified centroid method. The results show that shallow CPD zones occurred in the western and southeastern parts of the area associated mainly with Tertiary and Quaternary volcanic regions, respectively. The distribution of hot springs and hot groundwater wells through the area is correlated well with the mapped shallow zones and thermal gradient regions around them. On the other hand, the deepest CPD zone is attributed to a hot mantle upwelling underplating the crust beneath the volcanic plateau and crystalline basement margins in the middle part of the area. This spot forming the most probable source of magma for the Quaternary volcanic activity in the area. The observed geothermal activity at Al Lisi–Isbil, Damt, and Al Qafr fields is ascribed to the heat derived from shallow magmatic bodies, with temperature less than Curie temperature of magnetite, and also to the heat transferred from the underlain hot mantle spot through a net of deep faults affected this region.

Aeromagnetic data analysis for the identification of volcano-sedimentary complex: case of Permo-Triassic of the Traras Mountains, NW Algeria

In this study, the aeoromagnetic data are analyzed and interpreted to characterize the deep structure of the Traras Mountains (NW Algeria). Thus, the aeromagnetic data processing (reduction to pole, analytic signal, horizontal and vertical gradients and upward continuation) allowed, for the first time, to show an image of the sub-surface topography of the volcano-sedimentary complex, whose age is attributed to the Permo-Triassic. In addition, the application of the 3D Euler Deconvolution to the aeromagnetic data reveals the existence of several structures at different depths with mainly NNE–SSW and NW–SE directions. The structural model obtained from these results, shows a perfect correlation between the dynamics of studied Permo-Triassic complex and the local and regional tectonics.

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.

Delineation of Gold Mineral Potential Zone Using High Resolution Aeromagnetic Data Over Part of Kano State, Nigeria

The study of the geometry and kinematics of deep geological structures, bearing mineralization has advanced greatly by the aggressive progress of geophysical techniques over the last decades. The mineralization zones located in the Shanono local government area of Kano state Nigeria has its genesis controlled by shear zones. This research was aimed at delineating and characterizing subsurface geologic structures around the study area. Both qualitative and quantitative analysis of aeromagnetic data has provided defined distinct pattern of the magnetic signatures. Euler solution of the aeromagnetic data with structural index one, revealed the presence of the major tectonic trends of anomalies in the NE-SW and NW-SE directions. The trends of few of these structures are observed to be similar to fracture orientations in the Nigerian basement complex. These structures control the emplacement of the gold mineralization as these provides the pathways to flow of mineral rich fluid within the host rocks of the study area.

Basement morphology of the middle Benue Trough, Nigeria, revealed from analysis of high-resolution aeromagnetic data using grid-based operator methods

The middle Benue Trough is, the central segment of the Benue Trough, an elongate large intracratonic, Cretaceous to Palaeogene rift basin in Nigeria. This study provides new information about the depth to basement (sediment thickness), basement morphology and tectonics of the middle Benue Trough region through detailed analysis and interpretation of preconditioned high-resolution aeromagnetic data using three grid-based semi-automated depth-estimation methods. Integration of results reveals that the middle Benue Trough region is a moderate to deep, fault bounded rift basin with a maximum sediment thickness (basin fill) of about 6300 m. There are seven deep (>~2500 m) sedimentary sub-basins and several elongated shallow (<~1800 m) basement ridges. These sub-basins and basement ridges exhibit dominant NE-SW tectonic trends. Previously mapped magmatic bodies in the axial region of the Trough occur at depths less than about 1000 m. Most of the imaged subsurface features were previously unknown. Subsurface crustal basement structures show trends predominantly NE-SW, ENE-WSW, NNE-SSW and NW-SE and these generally reflect variations in pre-existing crustal basement structural trends in the area, superimposed by the effects of the regional tectonic stress fields responsible for the Trough's tectonic evolution in the Cretaceous – Palaeogene. The implication of the results in regards to hydrocarbon exploration, particularly when combined with published field geological and organic geochemical studies, is that the middle Benue Trough region is more likely to have moderate to low oil prospects and high gas prospects.

Analyses of high resolution aeromagnetic data for structural and porphyry mineral deposit mapping of the nigerian younger granite ring complexes, North - Central Nigeria

This study report the results of the different geophysical analyses carried out on the aeromagnetic data of north-central Nigeria with the object of delineating the occurrence and evaluate the structural influence on the emplacement of the porphyry mineral deposits of the Ring Complexes. The residual magnetic intensity extracted using Low Cut Guassian filter, from the high resolution aeromagnetic data of north-central Nigeria were filtered to remove high frequency near surface cultural noise and subsequently Reduced to Pole at Low Latitude (RTPLL) to focus anomaly peaks on the corresponding geological sources in order to resolve anomaly complexity associated with mid-latitude potential data. The data were further enhanced using upward continuation filter to extract desired magnetic responses at various continuation distances. Analytic Signal (AS), Centre for Exploration Techniques (CET) Grid and Porphyry Analyses were then carried out on the filtered, transformed and enhanced magnetic data to generate diagnostic magnetic attributes employed to map the boundaries of geologic magnetic sources, extract linear features and delineate the occurrence of porphyry mineral deposits across the study area.The AS responses defined twenty-four (24) arcuate/circular shaped AS anomalies which correspond to Younger Granites Ring Complexes in the northeast, northwest, southeast and central part of the study area from the low AS response Basement Complex rocks that host them. The CET grid analysis delineates several linear structures which generally trend NE – SW, NNE – SSW and ENE – WSW directions and their average length (500 m–17,500 m) and population (212–32) directly and inversely, respectively, correlate with the upward continuation distances. The CET porphyry analysis also delineates fifty (50) porphyry mineral deposits which vary in radial size from 300 m–4300 m. The occurrence of the porphyry mineral deposits within or in close proximity with the Younger Granite Ring Complexes which are either crosscut or flanked by the linear structures, suggests hydrothermal non-orogenic origin of the structurally controlled ring complexes and the associated porphyry mineralisation that result from phase mineralisation that accompanied Jurassic hydrothermal activities.

Curie Point Depth Estimations for Northwest Iran Through Spectral Analysis of Aeromagnetic Data for Geothermal Resources Exploration

The northwest of Iran is considered as a promising geothermal zone owing to its geographical properties, tectonic features, and thermal activities, particularly in Sabalan geothermal field. Several large stratovolcanoes such as Sahand and Sabalan mountains in northwestern Iran, each of which has a vast central dome probably located on a tectonic plate, comprising of intrusive and effusive volcanic rocks. This study mainly aimed at performing the spectral analysis of aeromagnetic data to estimate Curie point depth (CPD), geothermal gradient and heat flow in the northwest of Iran using random magnetization (centroid method and forward modeling of the spectral peak method) and fractal magnetization (de-fractal method). The reduced-to-pole aeromagnetic data were divided into 55 overlapping blocks of 80 × 80 km. The derived range of CPD in the study area using the centroid method, forward modeling spectral peak method and de-fractal method were 9.2–13.9 km, 8.9–13.7 km and 7.2–12.9 km, respectively The derived values of heat flows in the study area using the above-mentioned methods were higher than 104 mW/m2, 105 mW/m2 and 120 mW/m2, respectively. The results of this study were found to have good correlations with wells data and resistivity measurements collected in the Northwest Sabalan geothermal field. Good consistency was also found between the CDPs and earthquake distribution. Moreover, the locations of hot springs and the maximum temperatures of the wells were associated with the variations in the modelled depth of the geothermal resources. Promising regions were in the northeast and southwest parts of the study area.

Determination of Hydro Geological and Petroleum Potential Using High Resolution Aeromagnetic Data, Over Matsina and Environs, Part of Nigerian Sector of Chad Basin, North Eastern Nigeria

Two dimensional spectral analyses of high resolution aeromagnetic data was carried out over matsina and environs North Eastern Nigeria to determine hydrocarbon and groundwater potentials. The analysis was done using Oasis Montaj version 8.2. The result obtained indicates the existence of two source depths. The shallower magnetic sources varies between 0.35 to 0.55 m and deeper magnetic sources also varies between 0.6 to 2000 m. The shallower magnetic sources could be as a result of basic intrusive within the Borno Basin, while the deeper sources correspond to the basement topography underlying the Chad formation. Comparing the result with what was obtained in Gubio, Maiduguri sub basin, it is apparent that the sedimentary thickness over Matsina and and Environs cannot be a potential site for oil exploration rather for ground water exploration.

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.

Structural framework of the Wagad uplift and adjoining regions, Kutch rift basin, India, from aeromagnetic data

The Kutch sedimentary basin formed during the Late Triassic breakup of Gondwanaland is characterised by horst and graben structures consisting of several east–west trending uplifts surrounded by low-lying plains. The eastern part of the basin has a diverse landscape comprising the Wagad uplift, Banni plain, Island Belt uplift and the Rann of Kutch. This area is bounded by major faults like the South Wagad Fault (SWF), Gedi fault and the Island Belt Fault. The lineaments/faults present in the region at different depth levels and the propagation of these features through the different sedimentary layers are studied using the semi-detailed aeromagnetic data collected over the basin. The aeromagnetic anomaly map depicts several major E–W, NE–SW and NW–SE oriented lineaments/faults, which probably represent structural trends associated with different stages of evolution of this rift basin. Power spectral analysis of the differential reduced to pole magnetic data indicates the presence of four magnetic interfaces. The slopes identified from the 1D power spectra were used for designing matched bandpass filters for isolating and enhancing the magnetic signatures present within those interfaces. Different edge detection techniques were used to delineate the magnetic contacts/faults/lineaments present in those interfaces. In addition, we have computed the radially averaged power spectrum of 121 subset grids each with a dimension of 20 km × 20 km from which three magnetic interfaces were delineated and compared with the stratigraphic sequence of the Wagad uplift and adjoining regions. A major NE–SW fault is delineated from this analysis and suggests that this fault has depth persistence as it dislocates the different magnetic interfaces. Integration with stratigraphic data suggests that this fault was formed prior to the deposition of Miocene Kharinadi formation. We have interpreted that this fault, forming the eastern limit of the Banni basin, might have formed during the passage of the Indian plate over the Reunion hotspot. Based on the results of the aeromagnetic data analysis and other published data, we propose a generalised evolutionary model for the study region.

Estimating sedimentary pile thickness, structural lineaments and heat flow in parts of North Central Nigeria from aeromagnetic data

Evaluation, analysis and interpretation of aeromagnetic data acquired over parts of North Central Nigeria were carried out in order to characterise structural features and lineaments, sedimentary pile thickness, geothermal gradient and heat flow in the study area. Fourier domain digital filtering and reduction to pole (RTP) operations were done to enhance the data, while spectral analysis and source parameter imaging (SPI) were used to analyse the data. Results from the 2-D spectral analysis of the enhanced magnetic data suggest that the depth range to the top of magnetic sources Zt is 0.33–0.73 km (average depth of 0.55 km); depth range to magnetic centroid Zo is 2.51–5.83 km (average depth of 3.94 km); Curie point depth range is 4.41–10.96 km (average depth of 7.32 km); and average sedimentary rock cover thickness is 3.94 km. This compares with the results from SPI which gave depth ranges to various magnetic sources as 0.27–3.01 km. Structural lineament analysis indicates the major trend of the structural lineament is in the NE–SW, NW–SE and NNE-SSW. Average geothermal gradient of 82.87°Ckm−1 and heat flow of 207.19 mWm−2 were estimated, with a general increase in heat flow from the southern parts towards the northern parts of the study area. These relatively high geothermal gradient and heat flow may be associated with the mineralogical, thermal and tectonic history of the area, suggesting the study area has the potential of geothermal energy.

Curie point depth, thermal gradient, and heat flow in the Colombian Caribbean (northwestern South America)

Geothermal gradients were estimated at the points of a grid with cell size of 50 km by 50 km in northwestern Colombia. Depths to the bottom of magnetic sources were assumed to represent Curie depths, and were estimated by means of statistical-spectral analysis of aeromagnetic data contained in square windows of 100 km by 100 km, 200 km by 200 km, and 300 km by 300 km. The centroid method and a variation of it that considers the fractal distribution of magnetization were applied. The modified centroid method provided better estimations of Curie depths, which range between 13 km and 47 km. Obtained Curie depths are comparable to those reported in other studies of regional character. The corresponding estimated geothermal gradients correlate quite well with estimations based on the bottom simulating reflector and bottom hole temperatures. Observed differences are small and can be accounted for by local heat flow variations due to shallow ground water flow, or recent sedimentation. Elaborated geothermal gradient and heat flow maps for northwestern Colombia are accurate and consistent with estimates of the thickness of the oceanic crust and continental cortical thicknesses, reported by previous authors. The maps presented in this study represent a contribution to the heat flow studies in northwestern South America.

Assessment of Geothermal Potentials In Some Parts of Upper Benue Trough Northeast Nigeria Using Aeromagnetic Data

The assessment of geothermal potentials over part of the upper Benue trough corresponding to Kaltungo, Guyok, Lau and Dong areas, North Eastern Nigeria using spectral depth analysis of aeromagnetic data has been carried out. The study area is bounded by latitudes 9o00’N and 10o00’N and longitudes 11o00’E and 12o00’E. This research work is necessitated by the need for renewable and alternative sources of energy for use in Nigeria. Regional/residual separation was carried out on the total magnetic field using polynomial fitting method of order one. The residual map was divided into nine overlapping blocks for the spectral analysis. The centroid depths and depth to top of basement were obtained from the plot of log of power spectrum against wavenumber. These two parameters were used to estimate the Curie point depth using , where and are Curie depth, centroid depth and depth to top of basement respectively. The results from the spectral analysis suggested that in the parts of the Upper Benue trough, the basement is deepest at the south western portion towards the Lau area and varies between 0.55 and 3.8 km, while the centroid depth varies from 7.26 to 18.00 km. From the same portion of the trough, the Curie-point depths vary between 12.43 and 33.91 km and the corresponding geothermal gradient and heat flow values varying from 17.10 to 46.66 0C/km with an average of 30.75 0C/km and 42.75 to 116.65 mW/m2 with an average of 75.91 mW/m2 respectively. The maximum heat flow is found around the south western portion of the study area (Lau). The entire study area with high heat flow values might probably be good sources for geothermal and thereby recommended for both geothermal exploration and exploitation.

Depth to Magnetic Sources Using Spectral Analysis of High Resolution Aeromagnetic Data Over Machina and Environs, Northeastern Nigeria

Analysis of high resolution aeromagnetic data over Machina and its environment shows areas of low total magnetic intensity contour values are hosts to thicker overburden sediments and near surface intrusive rock bodies reside over high total magnetic intensity contour regions. Positive and negative residual anomaly values depict the presence of basic and acid rock units; however, the acid rocks dominate over the basic components. Major linear features of the residual anomaly are oriented along the NE – SW direction. Some linear features however, cross cut the major lineaments along the NW – SE, N –S, and E – W directions. A NW – SE cross section of the residual anomaly shows irregularity of the bedrock floor. The negative residual anomalies are underlain by granite rocks, while the positive values are within the domain of basic intrusive. Determination of the magnetic source depth revealed depths to the top of the deeper and the shallower sources ranging from 0.6 – 2.0 km and from 0.4 - 0.9 km respectively. Thicker sedimentary covers are underlain by basement rocks while; shallower magnetic horizons are composed of intrusive igneous bodies. Maximum sedimentary thickness of 2.0 km in the study area might not be adequate enough for hydrocarbon maturation and accumulation. Segment directional histogram data shown on rose diagram exhibits strike directions along the E – W, NE – SW, NW – SE, NNE – SSW and NNE – SSW. Most of the fracture lines dip at angles lower than 10 degrees. The north dipping direction group of lineaments is prevalent. Orientations of the structural elements are in conformity with the dominant regional structural grain of the country. Cross- cutting of the lineaments may be related to the geothermal energy in the area as higher interconnected lineaments are associated with higher geothermal energy. Rugged terrain reliefs might have resulted from the effects of tectonic and structural evolution in the area. Variability of the dip angles is associated with non-uniform framework of the forces of deformation on the rocks and/or differential responses of the rocks to the stress imposed on them.