Ground Magnetic Survey Research Articles

Impact Craters in South America, by Acevedo R. D., Rocca M. C. L., Ponce J. F., and Stinco S. G. Heidelberg: Springer, 2015. 104 p. SpringerBriefs in Earth Sciences: South America and the Southern Hemisphere. ISBN 978-3-319-13092-7.

Impact Craters in South America, by Acevedo R. D., Rocca M. C. L., Ponce J. F., and Stinco S. G. Heidelberg: Springer, 2015. 104 p. SpringerBriefs in Earth Sciences: South America and the Southern Hemisphere. ISBN 978-3-319-13092-7.

Integration of Ground Magnetics and Energy Dispersive X-Ray Fluorescence Spectroscopy in Ilmenite Prospection in Magaoni, Kenya

The geology of Magaoni area is associated with the presence of heavy minerals [1]. Magaoni’s neighbours Maumba and Nguluku where ilmenite was discovered by Tiomin Resource Inc. in 1996, using drilling and chemical analysis [2]. Ilmenite mineral is known to be magnetically weak, but provides observable magnetic response [3]. In this study, ground magnetic survey method was carried out to map magnetic anomalies of established stations, associated with ilmenite bearing formations. The magnetic contour map plotted showed weak and shallow magnetic signatures spread throughout the study area. 2D Euler deconvolution solutions revealed presence of magnetised formations from near surface to a maximum depth of about 450 m at some points. The weak magnetic formations of near surface indicated presence of ilmenite. Energy dispersive X-ray spectroscopy was done on soil samples collected randomly from the study area to determine the percentage of iron and titanium oxides. The results showed elevated values of titanium dioxide, ranging from 1.5% to 13% which is way above the global average of about 0.7% [4]. The percentage of iron oxide was low, ranging from 1.5% to 4%, this being the reason for weak magnetisation of the study area.

Ground Magnetic, GPR, and Dipole-Dipole Resistivity for Landfill Investigation

Ground magnetic, ground penetrating radar (GPR), and dipole-dipole resistivity were carried out to environmentally investigate a landfill. In this context, these geophysical techniques were conducted to identify the subsurface contents of the landfill, furthermore, specify any possible leakage and/or contamination in the study area. The ground-magnetic survey carried out in the study area comprised 31 profiles each 120 m in length. Different wavelength filters were applied to the measured data. Vertical derivative, downward continuation, apparent susceptibility, band-pass, and analytical signal filters separated successfully the shallow sources. Whereas, upward continuation and low-pass Gaussian filters isolated significantly the deep magnetic sources. 3D Euler deconvolution (SI = 3) remarkably estimated the depths of the shallow sources (0 - 10 m) of the landfill contents. The conducted GPR and dipole-dipole resistivity allocated tangibly the locations and depths of the near surface anomalies. Both techniques didn’t reveal any possible leakage and/or contamination. Noteworthy, integration among magnetic, GPR, and dipole-dipole resistivity confirmed positively the results of each method. Nevertheless, some anomalies were recognized successfully by one technique and not by the others.

Integrated interpretation of the magnetotelluric and magnetic data from Mahallat geothermal field, Iran

Magnetotelluric (MT) and ground magnetic surveys were conducted on the Mahallat geothermal field situated in Markazi province, central Iran, as a primary part of the explorations and developments of a geothermal energy investigation program in the region. Mahallat region has the greatest geothermal fields in Iran. MT survey was performed in November 2011 on an 8 km profile crossing the hot springs with a total of 17 stations. The 2D inversion of the determinant MT data was performed using a 2D inversion routine based on the Occam approach. The 2D resistivity model obtained from the determinant data shows a low resistivity zone at 800-2000 m depth and a higher resistivity zone above the low resistivity zone, interpreted as geothermal reservoir and cap rock, respectively. It also revealed two major concealed faults which are acting as preferential paths for the circulation of hydrothermal fluids. To obtain more geophysical evidence, a ground magnetic survey with 5000 stations was also performed over an area of 200 km2 around the MT profile. Magnetic measurements show a main positive anomaly of about +1000 nT over the study area, which could be interpreted as an intrusive body with the high magnetic susceptibility (i.e. mafic and ultramafic rocks) into the sedimentary host rocks. We interpret the body as the heat source of the geothermal system. Structural index and depth estimation of the anomaly indicate that the intrusive body is similar to a cylinder extending from about one kilometer depth down to greater depths. The results of MT and magnetic investigations indicate a geothermal reservoir which proves the preliminary geological observations to a great extent.

The nature of geomagnetic anomalies in metamorphosed chromite-bearing dunites: a case study of the southern Klyuchevskoy complex, Central Urals

Chromite mineralization in metamorphosed dunites from the southern Klyuchevskoy dunite-harzburgite ultramafic complex (Central Urals) has been investigated using geomagnetic surveys along with laboratory studies of ore-forming and accessory spinels of the same genetic type. Magnetization in the study area is carried mainly by accessory Fe-Cr-spinel of a variable Fe2+(Cr2-xFex3+)O4 composition. Metamorphism caused changes in element contents and in both crystal and magnetic structure of the primary nonmagnetic accessory spinel, unlike the almost fresh ore-forming spinel. Thus, ore bodies stand against their host rocks, which is a prerequisite for the use of geomagnetic surveys for exploration of podiform chromite deposits in dunite-harzburgite complexes. Ground magnetic surveys at a test site composed of faulted rocks bearing disseminated chromite mineralization in metamorphosed dunites resolved a chromite ore zone and a fault block boundary showing up as geomagnetic anomalies. Laboratory studies using high technologies (thermomagnetic analysis at 4 to 1000 K, as well as magnetic resonance and magnetic force spectroscopy) revealed, for the first time, magnetic clusters (superparamagnetic phases) in primary nonmagnetic accessory spinel, which are responsible for the magnetic properties of the host rocks. Microscale variations in Cr-spinel correlate with the geomagnetic anomalies recorded by field surveys at the test site.© 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Application of Magnetic Survey in the Investigation of Iron Ore Deposits and Shear Zone Delineation: Case Study of Mutomo-Ikutha Area, SE Kenya

The main objective of this research was to use ground magnetic survey to delineate shear zone and iron ore deposit within the Neoproterozoic rocks of Mutomo-Ikutha area of south eastern Kenya. Total field magnetic data was recorded by using high resolution proton precision geometric magnetometer which recorded total components of the ground magnetic anomaly data running through sixteen traverses. The field data was qualitatively and quantitatively interpreted and the results gave values for the total component measurements of ground magnetic anomaly that varied between a minimum negative peak value of about 250 nanoTesla and a maximum of about 1000 nanoTesla. 550 nanoTesla was considered to be threshold of the iron mineralization within the area. The results indicated that the western part of Mutomo-Ikutha was sheared, faulted and contained iron ore mineralization trending in the north-south direction. Areas with high anomalous values were geochemically proven to contain magnetite.

Groundmagnetic Method for Subsurface Structural Analysis around Ogbagba,Southwestern Nigeria

The results of Groundmagnetic survey around Ogbagba near Iwo part of southwestern Nigeria were presented for evaluation of the subsurface structural analysis in the area, with a view to determine the promising area for hydrological purposes and also competent area for engineering activities. Total field magnetic data was recorded using proton precession magnetometer. A total of ten traverses were established and presented as ground magnetic profiles of varying magnetic intensity which were subjected to both qualitative and quantitative interpretation. The result of the investigation revealed information on the subsurface geological features which were interpreted as the competent and the weak zones within the study area.

Active fault mapping in Karonga-Malawi after the December 19, 2009 Ms 6.2 seismic event

The East African Rift System (EARS) has natural hazards – earthquakes, volcanic eruptions, and landslides along the faulted margins, and in response to ground shaking. Strong damaging earthquakes have been occurring in the region along the EARS throughout historical time, example being the 7.4 (Ms) of December 1910. The most recent damaging earthquake is the Karonga earthquake in Malawi, which occurred on 19th December, 2009 with a magnitude of 6.2 (Ms). The earthquake claimed four lives and destroyed over 5000 houses. In its effort to improve seismic hazard assessment in the region, Eastern and Southern Africa Seismological Working Group (ESARSWG) under the sponsorship of the International Program on Physical Sciences (IPPS) carried out a study on active fault mapping in the region.The fieldwork employed geological and geophysical techniques. The geophysical techniques employed are ground magnetic, seismic refraction and resistivity surveys but are reported elsewhere. This article gives findings from geological techniques. The geological techniques aimed primarily at mapping of active faults in the area in order to delineate presence or absence of fault segments. Results show that the Karonga fault (the Karonga fault here referred to as the fault that ruptured to the surface following the 6th–19th December 2009 earthquake events in the Karonga area) is about 9km long and dominated by dip slip faulting with dextral and insignificant sinistral components and it is made up of 3–4 segments of length 2–3km. The segments are characterized by both left and right steps.Although field mapping show only 9km of surface rupture, maximum vertical offset of about 43cm imply that the surface rupture was in little excess of 14km that corresponds with Mw=6.4. We recommend the use or integration of multidisciplinary techniques in order to better understand the fault history, mechanism and other behavior of the fault/s for better urban planning in the area.

Coupling ground and airborne geophysical data with upscaling techniques for regional groundwater modeling of heterogeneous aquifers: Case study of a sedimentary aquifer intruded by volcanic dykes in Northern Ireland

AbstractIn highly heterogeneous aquifer systems, conceptualization of regional groundwater flow models frequently results in the generalization or negligence of aquifer heterogeneities, both of which may result in erroneous model outputs. The calculation of equivalence related to hydrogeological parameters and applied to upscaling provides a means of accounting for measurement scale information but at regional scale. In this study, the Permo‐Triassic Lagan Valley strategic aquifer in Northern Ireland is observed to be heterogeneous, if not discontinuous, due to subvertical trending low‐permeability Tertiary dolerite dykes. Interpretation of ground and aerial magnetic surveys produces a deterministic solution to dyke locations. By measuring relative permeabilities of both the dykes and the sedimentary host rock, equivalent directional permeabilities, that determine anisotropy calculated as a function of dyke density, are obtained. This provides parameters for larger scale equivalent blocks, which can be directly imported to numerical groundwater flow models. Different conceptual models with different degrees of upscaling are numerically tested and results compared to regional flow observations. Simulation results show that the upscaled permeabilities from geophysical data allow one to properly account for the observed spatial variations of groundwater flow, without requiring artificial distribution of aquifer properties. It is also found that an intermediate degree of upscaling, between accounting for mapped field‐scale dykes and accounting for one regional anisotropy value (maximum upscaling) provides results the closest to the observations at the regional scale.

Geophysical Exploration of Fractured-Media Aquifers at the Mexican Mesa Central: Satellite City, San Luis Potosí, Mexico

Groundwater is scarce in arid and semi-arid zones in the Mexican Mesa Central. It is found at depths over 200 m, and its movement is primarily through fractures. This work aims to present a geophysical methodology, which shows the potential of combining natural and induced methods to locate confined aquifers in fault zones. The studies begin by interpreting the aeromagnetic survey, mainly by seeking lineaments associated with low magnetic anomalies, which are correlated with fault zones, and/or fractures and/or geological contacts where ferromagnetic minerals have undergone oxidation due to their association with recharge zones. These aeromagnetic lineaments are confirmed on land by a ground magnetic survey. After locating these areas, interpreted as permeability zones, their possible association with moist zones is confirmed by applying the vertical electrical sounding (VES) technique. H-type curve is associated with the presence of saturated zones. This study used the proposed methodology to interpret four main aeromagnetic lineaments and 12 main ground magnetic lineaments in a 36 km2 (6 km × 6 km) area. Twenty-six SEV were performed over these magnetic lineaments, of which about 50 % were associated with H-type resistivity curves, interpreted as being associated with moisture. Of the 12 VES with inferred groundwater potential, two wells have been drilled to date, one having an extraction flow of 70 lps.

Combining multi-scale geophysical techniques for robust hydro-structural characterisation in catchments underlain by hard rock in post-glacial regions

• Aquifer characterisation should be incorporated in integrated catchment studies. • Interpretation of monitoring data requires accurate sub-surface conceptual models. • Spatial heterogeneity in post-glacial hard rock environments makes this a challenge. • An integrated geophysical methodology at the scale of interest is effective. • Cross-comparison of techniques strengthens accuracy and 3D resolution. Accurate conceptual models of groundwater systems are essential for correct interpretation of monitoring data in catchment studies. In surface-water dominated hard rock regions, modern ground and surface water monitoring programmes often have very high resolution chemical, meteorological and hydrological observations but lack an equivalent emphasis on the subsurface environment, the properties of which exert a strong control on flow pathways and interactions with surface waters. The reasons for this disparity are the complexity of the system and the difficulty in accurately characterising the subsurface, except locally at outcrops or in boreholes. This is particularly the case in maritime north-western Europe, where a legacy of glacial activity, combined with large areas underlain by heterogeneous igneous and metamorphic bedrock, make the structure and weathering of bedrock difficult to map or model. Traditional approaches which seek to extrapolate information from borehole to field-scale are of limited application in these environments due to the high degree of spatial heterogeneity. Here we apply an integrative and multi-scale approach, optimising and combining standard geophysical techniques to generate a three-dimensional geological conceptual model of the subsurface in a catchment in NE Ireland. Available airborne LiDAR, electromagnetic and magnetic data sets were analysed for the region. At field-scale surface geophysical methods, including electrical resistivity tomography, seismic refraction, ground penetrating radar and magnetic surveys, were used and combined with field mapping of outcrops and borehole testing. The study demonstrates how combined interpretation of multiple methods at a range of scales produces robust three-dimensional conceptual models and a stronger basis for interpreting groundwater and surface water monitoring data.

Distribution of buried hydrothermal alteration deduced from high‐resolution magnetic surveys in Yellowstone National Park

AbstractYellowstone National Park (YNP) displays numerous and extensive hydrothermal features. Although hydrothermal alteration in YNP has been extensively studied, the volume, geometry, and type of rock alteration at depth remain poorly constrained. In this study, we use high‐resolution airborne and ground magnetic surveys and measurements of remanent and induced magnetization of field and drill core samples to provide constraints on the geometry of hydrothermal alteration within the subsurface of three thermal areas in YNP (Firehole River, Smoke Jumper Hot Springs, and Norris Geyser Basin). We observe that hydrothermal zones from both liquid‐ and vapor‐dominated systems coincide with magnetic lows observed in aeromagnetic surveys and with a decrease of the amplitude of short‐wavelength anomalies seen in ground magnetic surveys. This suggests a strong demagnetization of both the shallow and deep substratum within these areas associated with the removal of magnetic minerals by hydrothermal alteration processes. Such demagnetization is confirmed by measurements of rock samples from hydrothermal areas which display significantly decreased total magnetization. A pronounced negative anomaly is observed over the Lone Star Geyser and suggests a significant demagnetization of the substratum associated with areas displaying large‐scale fluid flow. The ground and airborne magnetic surveys are used to evaluate the distribution of magnetization in the subsurface. This study shows that significant demagnetization occurs over a thickness of at least a few hundred meters in hydrothermal areas at YNP and that the maximum degree or maximum thickness of demagnetization correlates closely with the location of hydrothermal activity and mapped alteration.

Magnetic and seismic refraction survey for site investigation of an urban expansion site in Abha District, Southwest Saudi Arabia

Ground magnetic and seismic refraction survey is carried out on an urban extension site in the southwest of Ahud Rufeidah town, southwest Saudi Arabia. The purpose of the survey was to map the surface topography of the bedrock and thickness of the alluvium overburden. The ground magnetic survey based on an assumption that the alluvial sediments is less or non-magnetic relative to the underlying gneiss basement rock. In this context, a total of 3,750 survey stations were measured along 40 east–west survey profiles, striking roughly perpendicular to the extension of the expected structures. In addition, 13 seismic refraction spreads were conducted along four seismic survey profiles across the expected pathways of buried alluvial channels in order to provide additional details about the depth and boundaries of the buried channels. The ground magnetic survey results show the presence of a basin combining two sub-basins filled with alluvium sediments that occupy the middle area of the investigated site. This basin is a closed basin that has no outlet, and there are four small and narrow channels that convey water and sediments from the eastern and southern hills into sub-basins. These channels are represented by narrow and elongated low magnetic anomalies extending towards the basinal area. The thickness of the alluvial sediments is verified using seismic refraction survey that indicates a greater thickness, exceeds 20 m, of low velocity sedimentary overburden inside the interpreted sub-basins and surrounding buried alluvial channels. These soft alluvial sediments can be deceptive and dangerous for urban foundations.

Magmatic occurrences in the Central Arava (southern Israel) based on Geology and Magnetometry

The Eshet Ridge is located in the Central Arava near Wadi Paran. Geological data were collected using ground magnetic surveys and petrophysical measurements (magnetic susceptibility and density). The goal was to reveal the structure and nature of a concealed magmatic body under the ridge. Integrated gravity and magnetic interpretation together with seismic reflection data (including 2¾ modeling) indicated the presence of a deep-seated basic magmatic intrusion. Occurrence of Fe-mineralized rocks along the ridge supports subsurface data. The magmatic body was intruded in the hard Turonian rocks of the Eshet Ridge. Basic magmatic exposures dating from the Early Miocene were evident along Wadi Ashosh (in the eastern Negev) and its margins 18km. to the north of the ridge. A new outcrop of basic magmatic intrusion was found southwest of the Tzukim settlement. Magnetic measurements indicated a similarity between their magnetic pattern and the Ashosh basic magmatics, which were dated to 20.4±0.7Ma. Volcanoclastic tuff pebbles (magnetic susceptibility of around 2–7*10−3SI) surrounded by conglomerate were discovered at two sites in Wadi Demma and Wadi Menuha (streams that drain near the Eshet Ridge and 2km south of it, respectively). The conglomerates contained mostly limestone, chalk and chert fragments; not more than 5% of which were volcanic pebbles. Two pebbles were dated to 24.4±0.7and 21.5±0.5Ma. The magmatic outcrops in Wadi Ashosh, the magmatic dyke near Tzukim and the volcanic purple and black pebbles near Wadi Menuha were all dated to the very Late Oligocene–Early Miocene. The magmatic body identified in this study under the Eshet Ridge was termed the Eshet Intrusion and is connected to, and even the source of, all these phenomena.

The Stardalur magnetic anomaly, SW-Iceland: a review of research in 1968--2012

Prominent geophysical anomalies of several km extent were noted in the vicinity of the farm Stardalur in southwestern Iceland in a gravity survey published in 1954, as well as in a 1968 total-field aeromagnetic survey published in 1970, and a seismic refraction study of the crust published in 1971. Further low-altitude and ground magnetic surveys were conducted around Stardalur in 1969–1973, and an exploratory hole was drilled to 200 m depth in 1969–1970 at the site of a very distinct peak in the ground anomaly. Various studies were carried out on a core (to 143 m depth) and on cuttings recovered by the drilling. From 41 m depth down, this material consisted of altered olivine tholeiite lava flows, with a mean remanent magnetization intensity of the order of 15 times the average for Icelandic Tertiary lavas. Modelling of the anomaly peak, which was found to reach at least 27μT above the main geomagnetic field intensity of 52μT, indicated that the lava flows formed a body of dimensions about 200 by 600 m striking NE to NNE, inside a caldera structure. This structure probably dates from a normal-polarity subchron around 2 m.y. ago during the Matuyama geomagnetic chron. Further studies on samples from the Stardalur drill core revealed the presence of quite pure and slightly cation-deficient magnetite, whose percentage in the lavas is more than twice the average for Tertiary basalts in Iceland. The magnetite has largely been formed by exsolution from titanomagnetite, but it is also present in small grains which have separated from olivine. A very minor proportion of the magnetite may be of single-domain size, and it appears not to be a decisive factor in the bulk magnetic properties of the lavas. For instance, the natural remanence is much less resistant to alternating-field demagnetization than could be expected for single-domain grains. It is not certain whether it is a primary thermal remanence or of secondary origin, although the former seems more plausible. In agreement with the conclusions of previous researchers, it appears likely that the strong magnetization is due to a chance combination of circumstances (such as high magnetite content, high oxidation state, and strong ambient field) rather than to some unique phenomenon. In this paper, a new ground magnetic survey at Stardalur is presented, along with a simple model of the source of the main anomaly peak. The geological reasons for the creation of that source remain unknown, but comparisons are made with a magnetic anomaly at Hvanneyri in western Iceland which has similarities with the Stardalur anomaly.

Magnetic responses from an iron-rich gossan in a volcanic terrain and a limestone-hosted strata-bound manganese deposit, Central Province, Papua New Guinea

Author: Mosusu, N1*., Saroa, D1., Abiari, I1., Verave, R1., Irarue, P1., and Kolotein, P2. To interpret magnetic responses ('magnetic signature') of different mineral settings in Papua New Guinea (PNG), field campaigns were conducted by the Geological Survey Division in mineral fields in the Rigo District, Central Province of Papua New Guinea. Geological mapping accompanied by a ground magnetic survey was conducted over iron-rich gossans within a volcanic sequence at Kore. A similar program was undertaken in a sedimentary-hosted manganese field near Kemaea village. The gossans are within the Middle Miocene Kore Volcanics which are bounded to the south by the Middle Miocene Gidobada Limestone. In contrast, the manganese nodules at Kemaea, are within the Late-Middle Eocene Port Moresby beds and are bounded to the north-east by the Early Eocene-Middle Oligocene Sadowa Gabro. The results of the magnetic survey show significantly different responses that are apparently related to the style of mineralisation. The total magnetic response of a gossan within the volcanic rock unit is characterised by high frequency signals that require extensive filtering to outline the trend of distinct magnetic source. In contrast, the limestone-hosted strata-bound manganese deposit has a well-defined north-westerly structural trend that is easily distinguished within the response of the total magnetic field. Applying a reduced to magnetic equator algorithm and generating an upward continuation of the magnetic field enhances these structural trends. The analytical signal of the magnetic field also enhances the interpretation of the signal from the two different sources. The results of the survey demonstrate that background knowledge of mineral systems, including major mineral composition and style of deposit is essential to interpret imagery from ground magnetic surveys of mineral deposits and that different styles of mineralisation generate unique magnetic responses.

Ground Magnetic Survey for The Investigation of Mineral Deposit at Itesi Village in Orile Ilugun, Odeda , South West Nigeria

Advances in technique development and data interpretation have greatly improved our ability to visualize the subsurface. A Magnetic survey was carried out at a site in Itesi village, Ilugun, Odeda Local Government Area of Ogun State, Nigeria using a portable proton precession magnetometer (G-856 AX). A total of ten profiles were established in an E-W direction in the study area. The acquired magnetic field data were corrected for drift. Qualitative and quantitative interpretations were adopted to obtain negative peak value and the maximum positive peak value. The depth to top of basement rock was estimated using Peter’s Half slope. Likewise the depth to centre of basement rock was estimated using the Half width rule. The contour maps, 3-D surface map and the 1-grid vector map present the subsurface image.
 The whole survey area has a total length of 100 m at a line spacing of 10 m and a breadth of 45 m at 5 m spacing. The whole area was characterized by complete varying negative amplitudes from a very low peak value of about -9.9 nT and a maximum positive peak value of about 17.4 nT respectively. The closely spaced, linear sub-parallel orientations of contours from the South western part of the map suggest the possibility of faults or local fractured zones.

English

  In this study, ground magnetic survey of Sumaje Village, Ogo Oluwa  area of Oyo State, Nigeria  using high resolution proton-precession geometric magnetometer model G-856AX measures total components of the ground magnetic. The field data was qualitatively and quantitatively interpreted. Profile 1 has the highest amplitude of 18.2 nT and profile 2 has the highest width of 32 m. The depth to the basement rocks ranges between 6.25 to 13.75 m. The highly mineralized region of the study area is between traverse 1 to 5. Magnetic anomaly obtained varied between a minimum negative peak value of about -14.3 nT and a maximum positive value of about +3.8 nT. The maximum depth to basement rock is about 13.75 m. Ground magnetic contour map, 3-D map, and vector map showed that magnetic anomalies are as a result of rocks present in the region. The major rocks and minerals suspected to be found in this studied area and its environs are slate, gneiss, serpentenite, rhyolite, pegmatite, gabbro, basalts, oceanic basalts and hematite.   Key words: Magnetic field, magnetic anomaly, magnetometer and Sumaje village.

Detection of Magnetically Susceptible Dyke Swarms in a Fresh Coastal Aquifer

Groundwater constitutes the main source of freshwater in Shalatein, on the western coast of the Red Sea, in Egypt. The fresh aquifer of Shalatein is intensively dissected by shallow and deep faults associated with the occurrence of dykes and/or dyke swarms. In this context, synthesis of electrical resistivity, ground magnetics, and borehole data was implemented to investigate the freshwater aquifer condition, locate the intrusive dykes and/or dyke swarms, and demarcate the potential freshwater zones. Nine Schlumberger VES’s with maximum current electrode half-spacing (AB/2) of 682 m were conducted. The subsurface was successfully delineated by general four layers. The fresh aquifer of the Quaternary and Pre-Quaternary alluvium sediments was effectively demarcated with true resistivities ranged from 30 to 105 Ωm and thickness ranged between 20 and 60 m. A ground magnetic survey comprised 35 magnetic profiles, each 7 km in length. Magnetic data interpretation of the vertical derivatives (first and second order), downward continuation (100 m), apparent susceptibility (depth of 100 m), and wavelength filters (Butterworth high-pass of wavelengths 300 m) clearly reflected the deep-seated structure. The computed depth by the 3D Euler deconvolution for geological contacts and faults (SI = 0) ranged from 14 to 545 m, whereas for dyke and sill (SI = 1), it ranged from 10 to 1,095 m. The western part of the study area is recommended as a potential freshwater zone as it is characterized by depths >100 m to the top of the dykes, higher thickness of the fresh aquifer (45–60 m), depths to the top of the fresh aquifer ranging from 25 to 40 m, and higher resistivities reflecting better freshwater quality (70–105 Ωm).

Delineation of the subsurface structures and basement surface of the Abu-Rodaym area, Southwestern Sinai, using ground magnetic data

The present study deals with the analysis of data from a ground magnetic survey that was conducted in the Abu-Rodaym area of the Southwestern Sinai Peninsula, Egypt. This survey was carried out to delineate the subsurface structural framework, and to identify the thickness of the sedimentary basin of the study area. Locating these structures, and determining the localities of maximum sedimentary thicknesses that consist mainly of sandstone, serves as a preliminary process in exploring the confined aquifer beneath the surface of the Abu-Rodaym area. This will greatly benefit Bedouins who suffer greatly from a lack of water in the driest region in the country. The processing, analysis, and interpretation, of the total intensity magnetic data shows that there are three sets of faults striking mainly in the N-S, NW-SE, and NE-SW, directions. The depth to the basement surface was found to fluctuate from about 45 m, to more than 100 m, beneath the ground surface. It was also found that the variations in magnetic observations were produced by the striking structures that are mainly responsible for the variations in thicknesses of the sedimentary rocks in the area.