High Magnetic Anomalies Research Articles

Contribution of Magnetotelluric inversion and potential field modeling to map the Gour Oumelalen deep geological Structure, Central Hoggar, Algeria

The Gour Oumelalen area is situated in the northern part of the Egere-Aleksod terrane (Central Hoggar, South of Algeria). This area is one of the best preserved Palaeoproterozoic and Archaean zones in Central Hoggar. The aim of this study based on a survey of 33 Magnetotelluric (MT) soundings, aeromagnetics and gravity data, is to investigate the crustal structure and its architecture beneath this area.As the first stage, we have determined dimensionality of the regional electric conductivity structure. For this purpose, we have used the impedance and phase tensor approaches. Our results suggest that the underling regional conductivity structure is complex. In the central part it presents a 3D geometry, and beyond, it is mainly 2D; with a strike direction oriented in the North-South direction. Thus, the MT data were inverted using the Occam's inversion algorithm (v.3); which is a powerful tool to modeling and inverting the 2-D MT data. The obtained geo-eletric models, show clearly a high resistive upper crust with a resistivity up to 1000 Ω m; overlies a conductive lower crust with a resistivity approximately less then 100 Ω m. Although, our resulting cross-sections confirm the major Precambrian faults, especially the Ounan shear zone, which is characterized by a high conductivity anomaly.At the second stage, using the joint modeling of gravity and magnetic data, we have characterized the different geological units. Although, our modeling reveals that the thicknesse of the upper crust is deeping toward the East, from 16 to 25 km. The Moho depth reaches an average value of 40 Km. Moreover, in the centre of the survey area, the Moho depth decreases and becomes equal to 20 Km. This uplifting of the upper mantle may corresponds to the high magnetic anomaly of the Tisseliline pluton. It seems also related to the magmatic intrusion along the Ounan Shear Zone.

Drone-based Magnetics over Mechanized Diamond Mine in Panna District, Madhya Pradesh, India

A drone-based magnetic survey was conducted with a magnetic sensor for the first time in India over a mechanised diamond mine. The paper briefly describes the findings of the drone-based Magnetic surveys over the Majhgawan Diamond Mine in Panna District, Madhya Pradesh, India. The data was interpreted using the Geometrics interpretation software. The experiment showed a promising result in deciphering the lamproite pipe depicted by a magnetic high intruded into the Baghain sandstone of the Kaimur Group. From the total magnetic anomaly map, it can be observed that a high magnetic anomaly of about 27 nT in the central part of the pipe which forms a part of the near-circular anomalous zone, is associated with the diamond-bearing pipe and demarcates its boundary.

Unearthing Egypt’s Golden Legacy: Geophysical Insights and New Opportunities in the Central Eastern Desert

Gold mining in Egypt’s Central Eastern Desert (ECED) has a rich history dating back to the Old Kingdom period. In recent years, there has been renewed interest from international mining companies, and several potential areas for gold mining have been identified. Extensive studies have been conducted on the deposition and occurrence of gold in the region, identifying over 100 areas of deposition. Aeromagnetic and radioactive surveys have played a crucial role in locating gold occurrences in ECED by utilizing data from these techniques to identify potential gold deposits. This study utilized geophysical data, including total aeromagnetic intensity (TM) and radiometric data, to identify hydrothermal zones and locate potential areas of gold occurrence. The radiometric ternary map was used to refine the search for gold deposits. Magnetic data were analyzed using edge detection tools to determine the structural framework of the area, facilitating the identification of regions with a high potential for gold occurrence. By integrating these geophysical datasets, this study provided a comprehensive understanding of the geological features and potential for gold mineralization in the study area. The area is divided into four sections by three shear zones, with high magnetic anomalies observed in the southeastern part. The radiometric data revealed that gold occurrence is associated with hydrothermal alteration zones, identified using the K/Th ratio and radiometric ternary map. However, not all these zones contain gold, and the area’s structure and magnetic suitability must be considered when selecting suitable locations for gold extraction. The study area presents a promising opportunity for gold exploration, with the integration of edge detection and radiometric analysis being crucial in identifying suitable locations for exploration.

The structurally‐controlled polyphase Au mineralization in the southern Youjiang Basin: Insights from magnetotelluric imaging

The Youjiang Basin, located on the southwestern margin of the Yangtze Craton, hosts significant Upper Triassic and Lower Cretaceous gold (Au) deposits. Isotope studies suggest that the polyphase Au mineralization in the Youjiang Basin is derived from Indosinian and Yanshanian magmatic events, but the structural plumbing system beneath the basin remains poorly understood. We collected 32 magnetotelluric (MT) stations extending from the southern margin of the Youjiang Basin which hosts the Zhesang, Badu, and Jinya Au deposits at the western margin of the Jiangnan Orogenic (JNO) belt. The full impedance tensor of MT data is utilized to generate a high-precision lithospheric resistivity model by three-dimensional (3-D) inversion. Importantly, our MT data reveals several crustal conductors (<30 Ω·m) underlying major structures in the northwestern part of the study area. These crustal conductive anomalies spatially overlap with high-magnetic anomalies and polymetallic Au-Sn deposits. We interpret these anomalies as solid conductive materials such as graphite and/or sulfides related to the structurally controlled Mesozoic Au mineralization. Additionally, we interpret these conductive anomalies beneath the known Au deposits as the conduits of magmas and solidified paleo-magma chambers that were emplaced along deep-seated northwestern faults and likely documenting the genetic relationship between Au mineralization and Mesozoic magmatism. The synthesis of the electrical resistivity structure and metallogenic considerations is presented in a schematic sketch model illustrating that the deep-seated northwest-trending structures likely acted as a plumbing system controlling both the migration and emplacement of magmas and related oxidizing fluids that subsequently precipitated the polyphase Au deposits.

Magnetic response contrast of Oligo-Miocene basaltic magmatism and structural control during its ascent at the northern tip of the Red Sea Rift

Oligo-Miocene volcanic activity has occurred along the northern Egyptian margin of the Red Sea Rift system, leading to the creation of small-volume monogenetic volcanoes. This research delves into the morphology and setting of these rift-related volcanics by combining aeromagnetic data, remote sensing, and field verification. Basaltic exposures in the study area were mapped using False Color Composite (FCC) and band ratios in Landsat 8 OLI data. In a map view, these mappable volcanic rocks appear as discrete semi-circular basaltic bodies and as discontinuous dikes. The basaltic bodies are aligned along ENE and NW-oriented zones, with most dikes orientated NW-SE. Multiple isolated high magnetic zones with NE and NW orientations were identified. Most basaltic outcrops coincide with high magnetic zones except for Gabal Abu Treifiya along the Cairo-Suez Road. The integration and combination of three layers of surface and subsurface structure patterns reveal an array of variance. The dominant trend of surface and deeper structural lineaments is NW-SE and NE-SW respectively. In contrast, shallow structural lineaments have NW-SE, NE-SW, E-W, and N–S trends. Long linear grabens result from the pairing of NW-SE normal faults. The basaltic occurrences such as Qattamiya and Abu Treifiya are located at the intersection of the NW-SE and E-W normal faults along the NW-SE linear grabens. The field investigation at both locations reveals a polyphase magmatic feeding system manifesting in the surface today as coherent and volcaniclastic rock units. This suggests a diverse range of eruptive styles through a complex feeder system that involves more than one volcanic cone. Though the two areas have good basaltic exposures, yet they have different magnetic responses. The severe alteration of Abu Treifiya's volcanic rocks into nonmagnetic minerals assemblage of zeolite, smectite, calcite, and hydrolysis of basaltic glass diminishes the expected high magnetic anomaly. This study contributes to our knowledge of Rift-related volcanism and the factors influencing the distribution of these volcanic materials.

Imaging Pleistocene volcanic edifices along the Egyptian Red Sea margin: Insights from reflection seismics and 3D constrained inversion of gravity and magnetic data

Several volcanic buildups have been documented using gravity and magnetic data at specific locations in the Northern Red Sea (NRS). Most of these volcanoes were never sampled, and only a few were imaged by seismic or bathymetry data. Furthermore, the confidentiality of commercial datasets does not allow adequate knowledge of these structures and their morphology and physical properties. In this study, 2D and 3D seismic reflection data and 3D constrained inversion of magnetic and gravity data have been used to infer densities and magnetic susceptibilities of volcanic features in the central part of the NRS and to evaluate the distribution and geometry. This study indicates that the results of the 3D inverted models show a good fit with the volcanic structures inferred from seismic data and, thus, that the inversion technique adopted can be a reliable tool for detecting other edifices where seismic data are missing. The 3D inverted density and magnetic susceptibility models suggest that at least eight isolated structures with similar gravity and magnetic properties exist in the study area. They are associated with high densities and magnetic susceptibility anomalies with average values of 2700 kg/m3 and 0.025 SI, respectively. These magmatic structures are deeply rooted in the sedimentary cover and emerge at elevations of 100 to >650 m relative to the seabed. They developed in a sector interpreted as containing thinned continental crust, accompanied by the ascension of magma through prominent rift-related normal faults. Magmatic activity likely started in the Pleistocene and continues to the present day.

Exploration of suspected magnetite ore minerals in Emure – Ekiti, Southwestern Nigeria using integrated geophysical methods of very low frequency electromagnetic (VLF-EM) and magnetics

Investigation on the occurrence of magnetite ore minerals in Emure – Ekiti, Southwestern Nigeria was carried out by integrating magnetic and very low frequency electromagnetic (VLF-EM) methods on the suspicion that the major part of the magnetite ore being sought lies in the subsurface. Eight traverses in total were established with five traverses occupied in the northeast–southwest direction and the other three in the northwest–southeast direction. Six traverses were established across the exposed part of the pegmatite (magnetite) veins to serve as a control. Inter-station spacing of 1 m was chosen, so as not to miss any significant ore occurrence. The VLF-EM profile is a plot of the real and filtered real components. The KH-filter geophysical software was used to invert real data into a two-dimensional subsurface map that revealed variations in conductivity. The results of the geophysical interpretation for both methods indicate anomalous signatures observed on the exposed section of the pegmatitic veins, which are indicative of magnetite ore. These anomalous signatures align with certain zones along the Tr4 and Tr8 transects. Some of the high magnetic anomalies observed on traverse 5, 6, and 7 coincide with low conductivity suggesting the concentration of minerals such as quartz, microcline, plagioclase, and biotite, which are commonly associated with magnetite. The study has not only enhanced the mapping of the subsurface characterisation of the deposit but also confirms the reliability and suitability of using magnetics and VLF-EM geophysical methods for mapping magnetite deposits.

Deep Structure of Siletzia in the Puget Lowland: Imaging an Obducted Plateau and Accretionary Thrust Belt With Potential Fields

AbstractDetailed understanding of crustal components and tectonic history of forearcs is important due to their geological complexity and high seismic hazard. The principal component of the Cascadia forearc is Siletzia, a composite basaltic terrane of oceanic origin. Much is known about the lithology and age of the province. However, glacial sediments blanketing the Puget Lowland obscure its lateral extent and internal structure, hindering our ability to fully understand its tectonic history and its influence on modern deformation. In this study, we apply map‐view interpretation and two‐dimensional modeling of aeromagnetic and gravity data to the magnetically stratified Siletzia terrane revealing its internal structure and characterizing its eastern boundary. These analyses suggest the contact between Siletzia (Crescent Formation) and the Eocene accretionary prism trends northward under Lake Washington. North of Seattle, this boundary dips east where it crosses the Kingston arch, whereas south of Seattle the contact dips west where it crosses the Seattle uplift (SU). This westward dip is opposite the dip of the Eocene subduction interface, implying obduction of Siletzia upper crust at this southern location. Elongate pairs of high and low magnetic anomalies over the SU suggest imbrication of steeply‐dipping, deeply rooted slices of Crescent Formation within Siletzia. We hypothesize these features result from duplication of Crescent Formation in an accretionary fold‐thrust belt during the Eocene. The active Seattle fault divides this Eocene fold‐thrust belt into two zones with different structural trends and opposite frontal ramp dips, suggesting the Seattle fault may have originated as a tear fault during accretion.

Subsurface Qualitative Investigation for Mineral Exploration using Aeromagnetic Data

This research investigated the subsurface qualitative investigation for mineral exploration of Ibadan Southwest Nigeria, using high resolution aeromagnetic data. The data acquired from Nigeria Geological Survey Agency (NGSA) were subjected to different filtering processing techniques to produce magnetic anomaly maps which were analyzed to detect the subsurface geologic features that are indicative of the potential mineral deposits in the study area. The processing techniques applied in this study to delineate the magnetically active regions were Total Horizontal Derivative (THD), Analytic Signal Amplitude (ASA) and Upward Continuation (UP) method at 150 m and 250m. The results obtained show THD values ranged between 0.002 nT and 0.039 nT connoting regions between non-magnetic body region and high magnetic anomaly regions. The ASA technique revealed susceptibility contrast region between 0.0022 and 0.1472 nT/m; these depict region of geologic body housing the mineralized zones. Thus, there is potential for mineral exploration in the study area.

The crustal structure of the Longmenshan fault zone and its implications for seismogenesis: new insight from aeromagnetic and gravity data

Abstract. Although many geophysical models have been proposed in the Longmenshan fault zone (LFZ) and its surrounding areas, the deep structure of the seismic gap and its constraint of the Wenchuan and Lushan earthquakes remain uncertain. Based on the compiled aeromagnetic data and Bouguer gravity data, we have tried to create a more detailed and reasonable magnetic and density model using 2D forward modeling and 3D inversion and made the deep structure of the LFZ visible. The research shows that structure is heterogenous across the LFZ. The earthquake epicenters are located in regions with high-magnetic anomalies and gravity gradients that are associated with rigid blocks that were likely to accumulate stress. However, the seismic gap shows low-magnetic anomalies and transition of gravity anomalies related to a weak zone. The Sichuan Basin has two NE-trending banded high-magnetic blocks extending beneath the LFZ that firmly support the idea that the crust of the Sichuan Basin has subducted downward the LFZ. More importantly, the basement subducts to approximately 33 km west of the Wenchuan–Maoxian fault, with a low dip angle beneath the middle segment of the LFZ, whereas the distance decreases to approximately 17 and 19 km under the southern segment. Thus, the crust of the Sichuan Basin beneath the middle segment extends farther than that beneath the southern segment, with the seismic gap as the transition zone. Therefore, we propose that the structural heterogeneity of the basement on the western margin of the Sichuan Basin may be the main reason for the different focal mechanisms and geodynamics of the Wenchuan and Lushan earthquakes.

Structural Characteristics of the Yushuwan Fault in the Northeastern Ordos Basin: Implications for Basin Tectonics and Hydrocarbon Exploration

The Yushuwan fault is located in the transition zone among the Yimeng uplift, Jinxi fold belt and Shanbei slope in the northeastern Ordos basin and marks the boundary between Palaeozoic and Mesozoic strata. According to the field geological survey and geophysical data, this study shows that the Yushuwan fault is a deep-cut northwest-southeast-oriented strike-slip basement fault. A total of 17 apatite and zircon fission track points show that the basin experienced several stages of uplift at 190 Ma, 150–170 Ma, 110–130 Ma, 60–80 Ma, and 20–40 Ma. The characteristics of the Yushuwan fault indicate that the northeastern part of the basin is not a simple slope but rather a step with a large drop. Therefore, in the area to the southwest of the Yushuwan fault, there should be high natural gas resource potential and good exploration prospects. The contour values of the magnetic anomaly on the southwestern side of the fault are high, and the contours are dense; in contrast, the contour values of the northwest magnetic anomaly are low, and the gradient is gentle. Therefore, the fault represents the eastern boundary of the Yimeng uplift, and restricts the eastward extent of the high magnetic anomaly zone in the Yimeng uplift area.

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.

High resolution magnetic anomalies, volcanism and tectonics of the active “La Fossa” vulcanic system (Vulcano island) and Lipari island (South Italy)

In this paper we present the new high-resolution magnetic anomaly map of the La Fossa Caldera system and Lipari island (Southern Italy), obtained by merging two low-altitude aeromagnetic surveys. In these islands a variegated ensemble of magnetic anomalies develops in the north-south direction. The La Fossa Caldera is characterized by very high-intensity and short-wavelength magnetic anomalies, related to mafic intrusive/effusive sources, mainly aligned along the NNW-SSE and NS faults. Instead, the Lipari island is characterized by lower intensity anomalies related to sources with more evolved chemistry, elongated in the NE-SW, NNE-SSW and EW of the subordinate faults. Both the two sets of structures belong to the Tindari-Letojanni strike slip fault-system, a regional lineament along which the southern side of the Aeolian Archipelago is emplaced. The study identifies three distinctive magnetic zones on the Lipari island: the southern, the central, and the north-western ones. The southern zone is characterized by negative magnetic monopoles in correspondence with the younger rhyolitic domes and a Curie Isotherm upwelling. The central part of the island has an average lower intensity of positive anomalies, corresponding to the less evolved products of the intermediate Lipari volcanic epochs. The north-western side is characterized by higher intensity anomalies related to older volcanic epochs. The interplay among strike-slip tectonics, chemistry of the uprising magmas, and the thermal setting has contributed to the overall anomaly pattern in this sector of the Aeolian Archipelago. This interpretation is supported by the application of digital enhancement to the total intensity magnetic anomaly field and by the spatial correlation analysis of the magnetic and volcano-tectonic features. The obtained insights are useful to better understand the relationship between arc volcanism and tectonics. Moreover, they can also outline new inferences to forecast future eruptions of the active La Fossa volcanic system. In fact, recent unrest signals were registered at La Fossa Cone, which is one of the present-day active volcanoes of the Aeolian Archipelago, along with Stromboli island. Key pointsLa Fossa volcanic system of Vulcano and Lipari islands high resolution aeromagnetic surveys; Strike slip tectonics magnetic anomaly signature; Spatial correlation analysis of volcano-tectonic and magnetic features.

Distribution of magmatic rocks in eastern Yin'e Basin revealed by 3D gravity and magnetic inversion

Magmatic activity has important influence on sedimentary cap structure, hydrocarbon generation and reservoir formation. There are multiple periods of volcanic activities in Yin'e Basin and it is of great significance to study the distribution of magmatic rocks in the basin for the prospective investigation of oil and gas resources. The residual gravity and magnetic anomalies are extracted from the original gravity and magnetic data in the eastern area of Yin'e Basin and used for 3D inversion. The spatial distribution of magmatic rocks in the study area is explained based on the inverted 3D density and magnetic susceptibility. The physical properties of the magmatic rocks in Yin'e Basin are distinctly different from their surrounding rocks in physical properties. The acidic igneous rocks are mainly low-density and medium-high magnetic (a few are weakly magnetic), and the intermediate-basic igneous rocks are mainly high-density and high-magnetic. The local low gravity anomaly with high magnetic anomaly area may be caused by the acidic igneous rocks intruding into the Carboniferous and Permian basement, while the local high gravity anomaly with high magnetic anomaly area may be caused by the intrusion of intermediate-basic igneous rocks. 14 weakly magnetic acidic igneous rocks, 16 medium-strong magnetic acidic igneous rocks and 25 intermediate-basic igneous rocks are inferred from the 3D inverted density and magnetic susceptibility. Acidic igneous rocks, which are distributed in the whole region, have large scale and mainly banded along the NEE direction. The intermediate-basic igneous rocks, which are generally small and most of them are equiaxed, are mainly distributed along the boundary of Zongnaishan-Chulu Uplift and Shangdan Depression, as well as the southern basin periphery of Shangdan Depression. The well-developed acidic magmatic rocks in Suhongtu and Shangdan Depressions, whose scale is relatively large, may be of great significance to the formation and distribution of oil and gas in Yin'e Basin.

Towards better delineation of hydrothermal alterations via multi-sensor remote sensing and airborne geophysical data

Integrating various tools in targeting mineral deposits increases the chance of adequate detection and characterization of mineralization zones. Selecting a convenient dataset is a key for a precise geological and hydrothermal alteration mapping. Remote sensing and airborne geophysical data have proven their efficiency as tools for reliable mineral exploration. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Advanced land imager (ALI), Landsat 8 (L8), and Sentinel 2 data are widely-used data among various types of remote sensing images in resolving lithological and hydrothermal alteration mapping over the last two decades. ASTER is a well-established satellite in geological remote sensing with detailed Short-wave infrared (SWIR) range compared to visible and near-infrared region (VNIR) that controls iron-associated alteration detection. On contrary, ALI has excellent coverage of the VNIR area (6 bands), but does not possess the potentiality of ASTER for the SWIR and thermal regions. Landsat 8 is widely used and highly recommended for lithological and hydrothermal alteration mapping. The higher spatial (up to 10 m) resolution of Sentinel 2 MSI has preserved its role in producing accurate geological mapping. Notwithstanding the foregoing, implementing the four datasets in a single study is time-consuming. Thus, an important question when commencing an exploration project for hydrothermal alterations-related mineralization (orogenic mineral deposits in the current research) is: which dataset should be adopted to fulfill proper and adequate outputs? Here the four widely recommended datasets (ASTER, ALI, L8, and sentinel 2) have been tested by applying the widely-accepted techniques (false color combinations, band ratios, directed principal component analysis, and constrained energy minimization) for geological and hydrothermal alteration mapping of Gabal El Rukham-Gabal Mueilha district, Egypt. The study area is covered mainly by Neoproterozoic heterogeneous collection of ophiolitic components, island arc assemblage, intruded by enormous granitic rocks. Additionally, airborne magnetic and radiometric data were applied and compared with the remote sensing investigations for deciphering the structural and hydrothermal alteration patterns within the study area. The results demonstrated a different extent from one sensor to another, highlighting their varied efficacy in detecting hydrothermal alterations (mainly hydroxyl-bearing alterations and iron oxides). Moreover, the analysis of airborne magnetic and radiometric data showed hydrothermal alteration zones that are consistent with the detected alteration pattern. The coincidence between high magnetic anomalies, high values of the K/eTh ratio, and the resultant alterations confirm the real alteration anomalies. Over and above that, the remote sensing results and airborne geophysical indications were verified with fieldwork and petrographic investigations, and strongly recommend combining ASTER and Sentinel 2 results in further investigations. Based on the outputs of the current research, we expect better hydrothermal alteration delineation by adopting the current findings as they sharply narrow the zones to be further investigated via costly geophysical and geochemical methods in mineral exploration projects.

Integrated Identification of Lithology Using Seismic and Magnetic Anomaly Data for Granite and Gneiss Basement: A Case Study of the LiShui Depression in the East China Sea Basin

Granite and gneiss buried hill reservoirs are controlled by their lithology and dark mineral content. Therefore, lithological identification and dark mineral content analysis are important research tools in the early stage of buried hill exploration. In this paper, the relationships between the seismic facies and lithology, magnetic susceptibility, and magnetic anomalies of granite and gneiss are analyzed based on the lithological characteristics of the LiShui depression (LS depression) in the East China Sea Basin (ECSB). The waveform classification method is used to identify granite and gneiss, and the waveform classification results reveal that areas with continuous distribution of a single seismic trace model or two seismic trace models represent good continuity, and can be interpreted as gneiss. Areas with a mixed distribution of multiple seismic trace models represent chaotic and poor continuity, which can be interpreted as granite. The mixed linear zone with multi-seismic trace models is a fault zone, and the rock is cataclasite. In addition, reduction to the pole (RTP) and downward continuation technique for magnetic data processing were used to determine the dark mineral content. Overall, the granite and gneiss can be divided into three types based on magnetic anomaly data: high, moderate, and low magnetic anomaly areas. The areas in which granite with moderate and low magnetic anomalies is distributed are the favorable exploration target areas. The above method provides a technical means of lithological identification in the early stage of buried hill exploration.

New insights on the origin of Barra volcanic ridge system, offshore Ireland: A long-distance influence of the Iceland mantle plume

The Iceland Plume has significantly impacted the North Atlantic region. Igneous edifices and large seamounts in the Rockall region were linked to Iceland plume pulsations during the Late Cretaceous to Mid-Eocene. In the south of the Rockall Basin a chain of northwest-southeast trending volcanic ridges known as the Barra Volcanic Ridge System (BVRS) have been identified on seismic and magnetic datasets. However, the timing, morphology, extent, and emplacement mechanism of the BVRS are not well understood. To investigate the volcanic ridge system, we analyze a 360-km-long pre-stack time migrated seismic section along the margin, which covers the southern extent of BVRS. The high velocity (4.5–4.8 km/s) obtained by using first arrival travel time tomography of downward continued data set, high magnetic anomaly and the typical morphology of the ridges suggest that they could be volcanoes of basaltic compositions. The integration of gravity and seismic data constrain the crustal structure and thickness, which indicates that the crust could be as thin as 4 km beneath the BVRS, requiring a maximum stretching factor >6. Folded compressional structures and lava flows within the Early Paleocene to Mid-Eocene sediments draping the volcanic ridges, suggest that these volcanic intrusions possibly have occurred post Early Paleocene age, which is approximately the same time-period when Iceland mantle plume arrived in the Rockall region. These results suggest that the BVRS developed because of pre-existing lithospheric configuration in the Rockall Basin and could be one of the southernmost volcanic provinces of the North Atlantic Igneous Province (NAIP).

An integrated geophysical and geological 3D model to characterize the feeder system of La Joya Honda and La Joyuela maars complex in central Mexico

La Joya Honda maar is recognized as one of the largest maar craters of the world (∼1200 m x 930 m), and La Joyuela maar, with axes of ∼1160 m x ∼790 m, is located in San Luis Potosí, México. Geophysical characterization using terrestrial magnetometry, aeromagnetic data, satellital gravimetry, and petrographic analysis of rock samples were interpreted jointly to improve the knowledge of both maars, their structural root geometry, and dimension maar-diatreme volcanoes. Magnetic and gravimetric analysis of both maars exhibit high magnetic anomaly values (≥400 nT) related to low gravimetric signatures (-5.2 to 1.5 mGal) and show characteristic geophysical maar behavior, complemented by positive anomalies (0.137 nT/m and 0.019 mGal/m, respectively) in the Analytic Signal result. Additionally, associated with the diverse tectonic and faulting events that the area has been subjected to, lineaments analysis and rose diagrams were used to determine structural tendencies, indicating the regional stress field (NNW trending) related to local fault orientations (E-W, NE-SW), which might be expected for the formation of maars with a comparable fracturing disposition at a depth between La Joya Honda and La Joyuela maars. This investigation shows the first magnetic inversion model in the zone, identified two vertical conduits susceptibility isosurface (2.53x10-4 SI) with an exceeded depth of -12 km below both volcanic structures, where regional analysis of lineaments and Werner solutions determine weak cortical structures. Furthermore, the petrological evidence (xenoliths) supports the geophysical model, which helps to understand regional factors that make the ideal environmental conditions for maar formation. Our new results contribute to the knowledge of the feeder system of the maars complex found in La Joya Honda and La Joyuela maars, demonstrate that the combination of different regional structural and local trends controls the magmatic evolution producing preferential paths for magma ascent.

The Western Segment of the Precambrian Suture Between the Yangtze and Cathaysia Blocks: Constraints From Magnetotelluric Data in Southwest China

AbstractThe western segment of the suture zone between the Yangtze and Cathaysia blocks, which is the most important tectonic boundary related to the formation and rifting of south China, is enigmatic and not fully understood due to the sporadic exposure of Precambrian strata and ophiolites. Three‐dimensional electrical resistivity models derived from inversion of magnetotelluric data identified a lithospheric‐scale conductive zone extending northeastwards beneath the Youjiang basin, which was interpreted as the western segment of the suture zone. The high conductivity and coincident high magnetic anomalies closely match the location of Carlin‐type gold deposits, which can be explained by fluids and gold‐bearing sulfide minerals in a fossil suture zone. Inconsistent with the southeast‐dip resolved at the eastern segment of the suture zone (the Jiangshan‐Shaoxing fault) in the earlier study, the slightly north‐dipping geometry at the western suture zone implies the reactivation by northward subduction and closure of the Paleo‐Tethys Ocean.

Magnetic Signature of Gold Deposits: Example from Um Garayat Region, South Eastern Desert, Egypt

Magnetic methods of exploration have proved to be efficient and have potential in the gold mineralization industry. New magnetic processing technologies aid in improving the process of interpretation and gold opportunity identification. In this work, we show the possible application of combined digital magnetic filters to explore new gold mineralization localities with application to a well-known Au mineralization zone. Um Garayat (UG) region, southeastern desert, Egypt, is an ancient example of a potential area for gold mining. Modern analysis showed that other types of mineral concentrations are present. So, exploiting the magnetic signature of the area for future investment is of great interest. The old UG gold mine is characterized by volcanic and tectonic features such as faulting and folding that affect the arc sedimentary rock sequence of repeated deformation stages. A thorough geophysical effort has been carried out around the old gold mine in the UG area to explore the extension of mineralized ore deposits. A detailed geophysical survey using magnetics was carried out in this study together with the available aeromagnetic data. Field data sets on appropriate sites were measured, processed, and evaluated by suitable software. High magnetic anomalies were detected based on grid filter analysis and contact occurrence maps as marked as possible ore deposits after satisfying the geologic conditions for gold formation. An integrated understanding of attained results revealed that the new possible ore deposits are related directly to fault and fracture zones in the shape of lenses of variable thickness in this zone. Results show that newly detected mineral occurrences in the UG area are also controlled by major faults and hydrothermal solution enrichment along fault zones at a depth ranging from 20 to 70 m. Favorable fault/joint mineralized places were located. The relationship between the Au-quartz vein's strike direction compared with magnetic anomaly lineament analysis was studied. Search for new sources of Au and other mineral deposits in addition to quartz veins is needed as pockets of accumulated mineral-rich rock fragments are deposited in drainage wadis and fault/joint zones because of hydrothermal solution enrichment.