Total Magnetic Intensity Data Research Articles

Revealing the Hidden Paleomagnetic Information from the Airborne Total Magnetic Intensity (TMI) Data

Revealing the Hidden Paleomagnetic Information from the Airborne Total Magnetic Intensity (TMI) Data

Mapping of geological structures and sediment thickness from analysis of aeromagnetic data over the Obudu Basement Complex of Nigeria

Abstract In this study, geologic structures, as well as attendant orientations and sediment thickness, in the Nigerian Obudu Complex were delineated using the Centre for Exploration Targeting (CET), and depth determination methods such as source parameter imaging (SPI) and standard Euler deconvolution (SED). The CET, SPI, and SED procedures were applied on the total magnetic intensity data. Also, the enhanced TMI data using analytic signal, first-vertical derivative, total-horizontal derivative, and tilt-angle derivative filters were further subjected to CET operation, with the aim of mapping both subtle and prominent lineaments. In general, mapped geologic structures trends in the NE–SW, NNE–SSW, E–W, and N–S directions. Overall, the dominant geologic structural orientations of NE–SW and NNE–SSW reflect the regional strike orientation. The regional striking of the lineation, which is caused by the Pan-African orogeny and subsequent post-orogenic processes, has an impact on these orientations. The N–S and E–W structural deviations from the main NE–SW and NNE–SSW trends are initiated by the YGS of the post-orogenic events. Overall, these complex geologic structures are probable sites for metallogenic minerals.

Unveiling the mineral resources and structural patterns in the Middle Benue Trough: a comprehensive exploration using airborne magnetic and radiometric data

The Middle Benue Trough (MBT) in Northcentral Nigeria is a geologically significant area with vast mineral resource potential. Employing airborne magnetic and radiometric data, this study utilized the Centre for Exploration Targeting on enhanced total magnetic intensity data to reveal geologic structures, lithological units and mineralization zones. Lineaments predominantly trended in NE-SW direction, with noteworthy orientations in NNE-SSW and E-W. Radiometric anomalies correlated with distinct lithological units, pinpointing granitic gneiss, alluvium, shale, siltstone and sandstone. A magnetically concentrated and potassium-rich area indicated potential polymetallic-magnetic mineralization. The 2D model illustrated igneous intrusions influencing prevalent geologic structures, such as sediment baking and doming. Thorough analysis, including source parameter imaging, standard Euler deconvolution and 2D forward modelling, revealed sediment thicknesses below 1500 m. This research enhances understanding of the MBT’s geological features, offering valuable insights for mineral exploration and resource assessment in the region.

EVALUATION OF UPWARD CONTINUATION AND REDUCTION TOEVALUATION OF UPWARD CONTINUATION AND REDUCTION TO MAGNETIC EQUATOR ON AIRBORNE MAGNETIC DATA MAGNETIC EQUATOR ON AIRBORNE MAGNETIC DATA

This research work is aimed at interpreting the airborne magnetic data of the study area for mapping the basement geologic structures using magnetic image enhancement filters. It focus on performing filtering techniques to expose and identify the magnetic properties of the basement structures at various continuation distances. The procedure applied to Total Magnetic Intensity (TMI) data of the study area using Oasis MontanjTM software were Reduction to Magnetic Equator (RTME) to remove the inclination effect as well as positioning the peak of the anomalies over their sources so as to improve the orientation of the magnetic sources, separation of regional and residual magnetic anomalies. These was followed by application of upward continuation at 500 m, 1000 m, 2000 m and 3000 m height. The results of the RTME shows the amplitude of the magnetic anomalies ranging from -37.577 nT to 27.398 nT. High magnetic anomaly is dominated in the northwest, southeast through southern part of the study location. Furthermore the results of the Upward Continuation (UC) revealed a wider wavenumber anomalies as well as height above the near surface. Hence the results of this research has displayed an enhanced geological magnetic structures located in the study area and also shows an improved quality of magnetic anomalies as the continuation distances increases.

Upward continuation of total magnetic field intensity data over Sokoto basin, north-western Nigeria

High-resolution aeromagnetic data covering the Sokoto basin, north-western Nigeria were acquired and analyzed using regional enhancement techniques, upward continuation and second order regional. The objective was to delineate major geological structures. The data, which are in form of a grid, were knitted using Oasis Montaj software to obtain the magnetic total field intensity map. The composite grid was reduced to a magnetic equator to align the peaks of magnetic anomalies over the center of their causative bodies. The reduced grid was continued at various planes of observation to understate anomalies due to shallow features. The planes were at 10 km, 20 km, 30 km, 40 km, 50 km, 70 km, and 100 km above the surface. Upward continuation maps produced greatly enhanced the long-wavelength (low wavenumber) anomalies associated with deeper subsurface regional structures. The continuation revealed a high magnetic intensity anomaly in western parts of the area and low magnetic intensity anomalies in the eastern parts. The low magnetic intensity in the eastern part is interpreted as a sedimentary deposit. The residual field was removed from the total magnetic field data using the second-order least square method to get the second-order regional field. The regional field analysis agrees with the upward continuation result.

3D Focusing Inversion of Full Tensor Magnetic Gradiometry Data with Gramian Regularization

Full tensor magnetic gradiometry (FTMG) is becoming a practical method for exploration due to recent advancements in superconducting quantum interference device (SQUID) technology. This paper introduces an efficient method of 3D modeling and inversion of FTMG data. The forward modeling uses single-point Gaussian integration with pulse basis functions to compute the volume integrals representing the second spatial derivatives of the magnetic potential. The inversion is aimed at recovering both the magnetic susceptibility and magnetization vectors. We have introduced a 3D regularized focusing inversion technique that utilizes Gramian regularization and a moving sensitivity domain approach. We have also developed a new method of magnetization vector decomposition into induced and remanent parts. The case study includes applying the developed inversion method and computer code to interpret a helicopter-borne FTMG survey carried out over the Thompson Nickel Belt. We have analyzed and separately inverted the observed FTMG and total magnetic intensity (TMI) data using the developed 3D inversion methods to obtain the subsurface susceptibility and magnetization vector models. Furthermore, we present a comparison of the inversions utilizing the FTMG data and the TMI data.

Application of Aeromagnetic Data Analysis and Interpretations to Investigate Solid Mineral Potential in Part of Bauchi, Northeast Nigeria

Abstract: The distribution of surface and subsurface magnetic materials within the study area, the delineation of geologic lineaments, and an estimate of the depth to magnetic sources were all determined by interpreting high resolution aeromagnetic data that covered a portion of Bauchi, northeastern Nigeria, lying between Latitudes 9040'00"N to 10010'0"N and Longitudes 900'0"E to 9040'0'E. The Aeromagnetic map, analytical signal, and horizontal derivative filters used on total magnetic intensity data after reduction to the magnetic equator (RTE) show that the Toro and its environs contain highly magnetic minerals thought to be potential deposits of iron ore. The lithological map and the lineament maps have a good connection. Further examination of the findings reveals that the research area has varying degrees of Ferro-, para-, and diamagnetic mineralization (of the iron and non-iron varieties). The geological source bodies are thought to be located between 177.389 and 991.626 meters deep, according to the Euler depth solution. This shows that during the orogenic process, a sequence of strong deformations were present alongside the Toro.

Magnetic constraints and susceptible inversions of Balapur Fault at central Kashmir Basin, NW Himalaya

Research subject. Subsurface investigations of the Balapur Fault at central Kashmir Basin, NW Himalaya through groundmagnetic surveys and data interpretations. Materials and methods. The total magnetic intensity data was obtained using ground magnetic surveys carried out by proton precession magnetometers at 15 m spacing. The magnetic constraints and inversions of the Balapur fault in the central Kashmir basin of NW Himalaya were analyzed. Results. The total magnetic intensity was found averaging at 97.7 with 45.8 nT as magnetic minima and 140.9 nT as magnetic maxima. The minima’s ranging from 45.8 and 55.8 nT in the gridded profile are inferred at the Balapur fault. Further, the fault-related susceptibility index was recorded from 0.0035 SI to 0.0015 SI, and the observed and predicted response values were found ranging between 67.1 to 87.7 and 67.4 to 86.6 nT respectively. Conclusion. The study suggests that the Balapur fault in the central Kashmir has produced high subsurface hydraulic activities and, therefore, evident low magnetic anomalies. The analysis reveals a thick minima region related to the fault and also indicated the presence of associated structures with the main Balapur fault segment.

Determining the Tectonic Implication Derived from Geophysical Data of Bahr An-Najaf Basin, SW Iraq

Free-air gravity, magnetic and topographic data derived from satellite imagery are used to study the main geological structures and features in the Bahr An-Najaf Area SW Iraq. A comparison between this map and gravitational and magnetic maps along with two profiles, each one on a map for the same location and direction. Both profiles show a decrease in values in the eastward direction of the two maps. The total magnetic intensity data of the study area are converted to reduction to pole data and drawn as a magnetic map. It is clear from the reduction to pole map that the rates of uplift and subsidence that occurred in the basement rocks are due to the faults in the Bahr An-Najaf region. The location of the Bahr An-Najaf Depression coincided with the negative anomalies on both the free-air gravity map and the reduction to pole magnetic map. Both maps are also used to define the important faults in the area, especially the Abu Jir Fault.

Comparative study of estimating the Curie point depth and heat flow using potential magnetic data

Abstract The estimation of the Curie point depth (CPD) and heat flow (HF) from magnetic data is useful for geothermal and tectonic studies. However, the methodology of estimating these values is still controversial as numerous studies have used different types of transformed magnetic data. Most studies utilize the total magnetic intensity (TMI) or the reduced to the pole (RTP) data, and since shallow magnetic bodies may affect the final CPD values, low-pass (LP) wavelength filtering has also been used to estimate the CPD. In this study, the two-dimensional radially averaged spectral analysis was applied to the land-based magnetic data from the Sinai Peninsula. TMI and RTP data were both analyzed, using different LP filtered wavelengths, and the final CPD and HF values were compared. The cut-off wavelength parameter was selected in terms of the geologic complexity. The results show that the estimated CPD values are well correlated regardless of whether the magnetic data were either TMI or RTP. The RTP data produced a spatial shift in the CPD smaller than the window size being used. Additionally, the centroid method is primarily dependent on the wavenumber, which varied slightly on applying the RTP. There were slight differences in the estimated CPDs when a short LP filter (e.g., 20 km) was applied, whereas increasing the wavelength (e.g., 40 km) caused the CPD values to increase exceeding the plausible depth limits, and the associated spatial trends varied when compared to the other methods. In areas where the basement rocks were shallow or exposed, a LP filter can be applied with short cut-off wavelength. The estimated CPDs were discussed in the context of seismicity data, gravity-based Moho depths, and HF measurements.

Structural Setting of the Sixtymile Gold District, Yukon, Canada: Insights into Regional Deformation and Mineralization from Field Mapping and 3D Magnetic Inversion

The Sixtymile gold district, Yukon, Canada has been mined for placer gold since the late 19th century. However, increasing demand for gold has prompted exploration of new lode deposits. Previous studies in the nearby Klondike gold district have shown correlation between placer deposits and bedrock occurrences. Poor bedrock exposure and a complex deformation history, however, make it difficult to determine structural controls on gold mineralization. Through structural analysis involving mesoscopic-scale field observations of fractures, faults, foliation, and folds, and 3D geophysical inversion, the goal of this study was to determine the structural setting of the Sixtymile district to enhance discovery success. Structural measurements in the Glacier Creek, Miller Creek, Bedrock Creek, and Sixtymile River areas show the relationships among the orientations of foliation, fractures, and veins. In most localities, veins are found both parallel and at high angles to foliation, and there is generally a weaker correlation between fractures and veins compared to between foliation and veins. This correlation between foliation and veins is corroborated by inferred gold-bearing horizons from gold assay data. Outcrops of oblique reverse and strike-slip faults, possibly related to a larger-scale thrust-zone, and to the left-lateral Sixtymile-Pika Fault, respectively, were documented for the first time in this study. The results of the 3D probabilistic inversion of total magnetic intensity data for magnetic susceptibility show that magnetic susceptibility highs are preferentially associated with volcanics, but also point to possible intrusive bodies or hydrothermal alteration zones associated with mineralization. A geologic cross-section through the lithologies demonstrates highly variable deformation styles, including extensive folding, possibly indicative of a multiphase deformational history necessitating further, more detailed investigations of the area.

Geophysical Evaluation of Central Nigeria Earth Tremor Activities using High Resolution Airborne Magnetic Data

The aim of this study is to investigate the actual causes of earth tremors in Central Nigeria using geophysical technique. Since 1933 till date (over 88 years), small to moderate magnitude earthquakes have either been observed or instrumentally recorded in Nigeria. However, the specific causes of the intra plate earthquakes in Nigeria is still not well known. In this study therefore, a high-resolution aeromagnetic data analysis was performed to evaluate the various theories proposed as the causes of tremor activity in central Nigeria with a view to ascertaining the actual causes of earthquakes in the West African country that lies on a stable crust. The total magnetic intensity data acquired from the Nigerian Geological Survey Agency (NGSA) in the Central Basement complex of Nigeria, was processed and filtered using the tilt derivative, lineament analysis, and advanced Analytic Signal- Hilbert Solution filter. To define the trends of both major and minor structure, a lineament plot was extracted and plotted. The analysis revealed a dominant NE-SW and NW-SE trending structure that is distributed throughout the study area. The regional North Atlantic Romanche fault system, which extends from the offshore (Niger Delta) into the continental crust, was mapped and is thought to extend from Gwagwalada in the study area's south, through Gwarinpa and Mpape, to Kwoi, and beyond Kafanchan.Findings from our study have indicated that, areas prone to Earth tremors are linked to the Romanche fault by numerous NE-SW and NW-SE faults that act as conduits for seismic energy that causes tremor. Using lineament density analysis, tremor active areas have been interpreted to be highly deformed; thus, seismic energy induced into the environment would result in tremors. This study demonstrates that the regional North Atlantic Romanche fault system is the primary source of seismic energy that causes the earth tremors in central Nigeria.

Interpretation of the subsurface tectonic setting of the Natrun Basin, north Western Desert, Egypt using Satellite Bouguer gravity and magnetic data

The Natrun Basin, north Western Desert of Egypt, represents a significant oil and gas province as it contains numerous oil and gas production fields. The basin has huge hydrocarbons recovery, mainly from the Jurassic rocks and minor amounts from Cretaceous rocks. The satellite Bouguer gravity, magnetic data, geologic, and available deep-drilled wells represent the primary data for the current research. The study's main goals are to interpret the subsurface tectonic setting, investigate the tectonic evolution of the Natrun Basin, and estimate the depth to the basement surface. Several geophysical techniques were applied to the satellite Bouguer gravity and magnetic data using Geosoft Oasis Montaj (Version. 8.3.3, 2015) to achieve the study's goals. The total magnetic intensity data was transformed into the reduced to pole map to prepare the magnetic data for further separations. The power spectrum was applied to detect the cut-off wavenumbers used in high and low-pass filters to separate the regional and residual anomalies. The first vertical derivative was applied to enhance the residual anomalies. The total horizontal and tilt derivatives were calculated to delineate the edges of the subsurface causative bodies. The 2D modeling was applied to estimate the depth to the basement surface and reveal the configuration of the subsurface rock units. A basement structure map was constructed to reveal the subsurface tectonic setting and evaluation of the Natrun Basin. The depth to the basement surface ranges between 1880 m and 6200 m. The subsurface tectonic setting of the basin was controlled by the N–S East Africa, NE-SW Hercynian, E-W Mediterranean, ENE-WSW Syrian Arc, NW-SE Gulf of Suez, and NNE-SSW Aqaba tectonics from the oldest to the youngest, respectively.

Recovering Magnetization of Rock Formations by Jointly Inverting Airborne Gravity Gradiometry and Total Magnetic Intensity Data

Conventional 3D magnetic inversion methods are based on the assumption that there is no remanent magnetization, and the inversion is run for magnetic susceptibility only. This approach is well-suited to targeting mineralization; however, it ignores the situation where the direction of magnetization of the rock formations is different from the direction of the induced magnetic field. We present a novel method of recovering a spatial distribution of magnetization vector within the rock formation based on joint inversion of airborne gravity gradiometry (AGG) and total magnetic intensity (TMI) data for a shared earth model. Increasing the number of inversion parameters (the scalar components of magnetization vector) results in a higher degree of non-uniqueness of the inverse problem. This increase of non-uniqueness rate can be remedied by joint inversion based on (1) Gramian constraints or (2) joint focusing stabilizers. The Gramian constraints enforce shared earth structure through a correlation of the model gradients. The joint focusing stabilizers also enforce the structural similarity and are implemented using minimum support or minimum gradient support approaches. Both novel approaches are applied to the interpretation of the airborne data collected over the Thunderbird V-Ti-Fe deposit in Ontario, Canada. By combining the complementary AGG and TMI data, we generate jointly inverted shared earth models that provide a congruent image of the rock formations hosting the mineral deposit.

Interpretation of ship-track magnetic data near Narcondam and Barren Island volcanoes revisited

We interpret the legacy ship-track magnetic and bathymetric profile data to investigate the role of the lithospheric scale West Andaman Fault (WAF) in the dormant Narcondam and active Barren Island volcanoes. We use data-based automated interpretation of total magnetic intensity (TMI) profiles using a contact model in order to delineate geometrical and physical parameters of several faults including the WAF and then investigate its implications in recent volcanism at the Barren Island. Our data-based interpretation of TMI data requires transformation of it into the first order analytical signal and tilt angle, which in turn, requires estimation of the first order horizontal and vertical derivatives of TMI data. We ensure robust estimation of the first order horizontal and vertical derivatives using Savitzky–Golay derivative filter and Hilbert–Noda transformation, respectively. We have identified several anomaly segments of the TMI anomaly profiles and used data-based quantitative interpretation in each segments with a contact model. We then make a comprehensive interpretation using bathymetry, geological setup and the results from quantitative data-based interpretation of magnetic data, and ascertain possible role of the WAF in Barren Island volcanism.

Inversion of Magnetic Data Acquired with a Rotary-Wing Unmanned Aircraft System for Gold Exploration

A hexacopter unmanned aircraft system instrumented with a caesium vapour magnetometer recorded total magnetic intensity over a 5.0 km2 prospective gold area in the Abitibi Subprovince of the Canadian Precambrian Shield. The survey also included a N–S repeatability line which showed that the unmanned aircraft system was very stable in flight with average standard deviations from nominal altitude and easting being 1.8 m and 0.7 m, respectively. The total magnetic intensity map revealed the structural framework of the banded iron formations present in the survey area and showed that the gold ore zones are not directly associated with magnetic highs but rather with steeply dipping faults. The total magnetic intensity data was inverted in 3-D using unconstrained and constrained approaches with 12.5 m (northing) × 12.5 m (easting) × 5 m (depth) cells and a maximum of 20 iterations. The processed (after diurnal corrections, heading correction, and tie-line levelling) total magnetic intensity data was input directly in the unconstrained inversion algorithm. Initial model building for the constrained inversion was a much more laborious process involving the inclusion of 15 synthetic structures based on borehole magnetic susceptibility measurements and knowledge of the local geology. The results of both inversion approaches were very similar. They revealed the presence of near-vertical thin sheets, individually resolvable down to approximately 400 m. In this particular case, the straightforward unconstrained inversion yielded a realistic and detailed model of the subsurface in approximately 1 h of runtime. Unmanned aircraft system total magnetic intensity data could therefore be processed and inverted almost immediately after acquisition and have an impact on decisions made in the field while a survey is still in progress.

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.

Application of Ground Magnetic Geophysical Method in the Delineation of Subsurface Structures of Dala Hill in Kano Ancient City, Northwest Nigeria

Ground Magnetic measurement was carried out with the aim of delineating the subsurface structures on Dala hill, Kano State. Total magnetic intensity data were acquired using the SCINTREX proton precession magnetometer along closely spaced traverses. The acquired total magnetic intensity data were reduced and plotted using Golden Surfer software to produce the 2D and 3D surface maps for visual inspection. Five profiles AB, CD, EF, GH and IJ were selected for forward modelling using Mag2dc software to give detail information about the causative body parameters. The depths of these bodies from the surface fall in the interval 0.0 m to 8.5 m. The high magnetic anomaly field ranges from -21,752 to 47,205 nT which suggested area of iron occurrences. The study categorized the identified major anomalous features into two: the shallower bodies which penetrated down to a maximum depth of 67.3 m were inferred to be disturbed sediments, fire pits and kilns; whereas the rest, the deep-rooted features with greater depth of penetration reaching up to 193.2m, have high susceptibility range of up to 7.3 SI units, were interpreted to be intrusive ferromagnetic bodies. The findings of the study were in close agreement with recent archaeological findings about the hill.

Characteristics of magnetic anomalies and subsurface structure constraints of Balapur fault in Kashmir basin, NW Himalaya

The study used total magnetic intensity (TMI) data to evaluate the incidence and characteristics of the Balapur fault in the Kashmir basin, NW Himalaya. The ground magnetic surveys were carried out at ~25 m station spacing in various linear profiles and grids across the fault. The magnetic measurements external to the Earth were recorded after every minute to remove the diurnal variations. The convenient filtering and derivative techniques were applied to the TMI database to assess the strike and subsurface constraints of the Balapur Fault. The study shows a clear relationship between the magnetic minima's and the inferred Balapur fault. The strike of the fault is found ~100 km from SE-NW of the Kashmir basin and is associated with several fractures throughout its course. The analysis also recorded TMI susceptibilities at the northwest Balapur fault in the Baramulla region where fault branching has also taken place. The study suggests that the fault is tectonically active and may host a significant magnitude earthquake in the region. The study also indicates that the fault may have further extensions and needs more subsurface geophysical studies. Further, our study signifies the role of ground magnetic surveys in subsurface fault evaluations.

Application of aeromagnetic data to map subsurface structural features in Ewekoro, Southwestern Nigeria

In this study, aeromagnetic data were interpreted and analyzed in order to map the subsurface geological structures at Ewekoro, southwestern, Nigeria. To accomplish this goal, some image enhancement techniques were applied to the magnetic data by which concealed subsurface structures were revealed. The total magnetic intensity data were reduced to the magnetic pole using Fourier transformation technique. The results of these filtering techniques were displayed with a number of maps. From the interpreted maps, a number of lineaments majorly trending in NE–SW direction were identified. These lineaments were indications of faults or fractures due to the displacements that might have arisen from tectonic events in the area. The estimated depths from the power spectrum technique suggest the presence of two magnetic sources the shallow and deep sources at depth of 0.02–0.75 km, respectively. The deep source indicates the basement rocks underlying the sedimentary cover in the area.