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Copyright of Geology & Resources is the property of Geology & Resources Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Dongzhongla deposit is a skarn-type lead–zinc ore deposit located in the eastern segment of the Gangdese metallogenic belt, situated in the Xizang province, China. The high-altitude mountainous terrain of the region poses significant challenges to ground-based exploration. To facilitate more accurate mineral exploration in the deposit and its surrounding area, a high-resolution airborne magnetic survey was conducted over the mining area and its periphery. The airborne magnetic data were processed using derivative and Euler deconvolution methods, yielding results that reflect the geological structural features of the study area. By integrating the geological characteristics of the ore deposit, we inferred that the areas of magnetic anomaly extensions and the peripheries of other magnetic anomalies are favorable zones for mineralization, providing positive leads for further mineral exploration. [ABSTRACT FROM AUTHOR]

Copyright of Geology & Exploration is the property of Geology & Exploration Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Dongzhongla deposit is a skarn-type lead–zinc ore deposit located in the eastern segment of the Gangdese metallogenic belt, situated in the Xizang province, China. The high-altitude mountainous terrain of the region poses significant challenges to ground-based exploration. To facilitate more accurate mineral exploration in the deposit and its surrounding area, a high-resolution airborne magnetic survey was conducted over the mining area and its periphery. The airborne magnetic data were processed using derivative and Euler deconvolution methods, yielding results that reflect the geological structural features of the study area. By integrating the geological characteristics of the ore deposit, we inferred that the areas of magnetic anomaly extensions and the peripheries of other magnetic anomalies are favorable zones for mineralization, providing positive leads for further mineral exploration.

Unmanned aerial vehicle (UAV) aeromagnetic measurement, as an efficient, convenient and low-cost geophysical exploration method, has been widely used in geological survey, mineral resources exploration, and engineering prospecting. First, we outline the historical process of UAV aeromagnetic measurement systems in the past two decades. The domestic and international progress of research and development, and the application of UAV aeromagnetic measurement are summarized. We compare the advantages and disadvantages of three main types of UAV flight platforms and their application scenarios in the field of aeromagnetic measurement. The types and characteristics of UAV aerial magnetometers are analyzed. Second, we carefully discuss the interference problem of aeromagnetic measurement. The principle of aeromagnetic compensation is mathematically described. The applications of various aeromagnetic measurement compensation methods are discussed. The characteristics of UAV electromagnetic interference and related suppression methods are summarized. The relevant ways to further improve the accuracy of UAV aeromagnetic measurement on the basis of traditional magnetic compensation are pointed out. Finally, the typical application cases of UAV aeromagnetic measurement technology are shown and the challenges and developments of UAV aeromagnetic measurement technology are foreseen. [ABSTRACT FROM AUTHOR]

The long-term development of the geophysical industry, in which the methods of magnetometry are in maximum demand, as the simplest in instrumental and methodological execution, has determined the development of remote measurement methods implemented both from space and airborne carriers. The necessity to use the latter as an obligatory component of field surveys, providing coverage of significant areas, determines the need for using the unmanned low-tonnage carriers. Their use is implemented to search for predictive elements of structural (spatial, genetic) control of endogenous gold ore occurrences that allow predictive constructions, i.e., solving the problem of increasing gold reserves, which is being performed within the framework of federal programs. The purpose of the survey is to develop a system of instrumental and subsequent interpretation approaches in the organization of unmanned magnetometer survey, implemented for structural and geological mapping by the example of the Neryungrinsky district of Yakutia. Within the framework of the digital model formation of the relief and the anomalous magnetic field, a survey method using an unmanned aircraft, its technical characteristics are considered; the analysis and the author's modification of the office analysis of magnetometry data are performed. Based on the obtained materials, a physical and geological model of the investigated area was created, which is presented in the form of a geological and structural cut, accompanied by the physical characteristics of the structural and material complexes. The refinement of the physical and geological model was implemented by a joint morphostructural analysis of the remote base and the anomalous magnetic field using the results of quantative interpretation of the anomalous magnetic field. The result of the study is presented by an updated geological basis with the allocation of promising ore sites for their detailing as part of the planned large-scale geological and geophysical surveys. The scientific novelty of the work consists in the synthesis of the tried and tested methods of unmanned aeromagnetometric measurements and geostructural reconstructions, which allow the processing of both potential and non-potential geofields.

As underwater disturbances (natural or artificial) occur in the ocean, moving seawater crossing the geomagnetic fields will produce weak circular currents. These currents can induce measurable magnetic fields, which might be useful for monitoring ocean internal waves using aeromagnetic survey. In this research, a spectral-element method (SEM) based on Gauss–Lobatto–Legendre (GLL) polynomials is presented to characterize the magnetic field induced by the underwater pressure waves. A concise mathematical model is established through combining the acoustic wave equations and Maxwell's equations. Specifically, the acoustic–magnetic coupling simulation adopts the nodal-based SEM for acoustic analysis and edge-based SEM for electromagnetic analysis. The proposed SEM has spectral accuracy, as the error exponentially decreases with the order of the basis functions. Additionally, by adopting an independent modeling and mesh scheme in two solvers, respectively, the waste of computing resources is avoided. The experimental analysis demonstrates that the induced magnetic fields mechanically propagate with the acoustic wave, producing the pseudo-radiation phenomenon. The signals of these magnetic fields may extend for tens of kilometers and exist for hours under certain circumstances, which provide a theoretical basis for underwater target identification via high-sensitivity atomic magnetometer. [ABSTRACT FROM AUTHOR]

Numerical analysis of geophysical data to uncover Precambrian belts and probably to enclose mineral deposits is becoming once more communal in mining activity. The method is founded on typifying zones branded to comprehend deposits and looking for analogous areas. The proposed work outlines a semi-automatic image processing system for the structural and mining investigation of the Bou Azzer inlier, which varies from preceding approaches as it is centered only on aeromagnetic data. The aeromagnetic signature of what seem to be geologically expressive features are pursued within the aeromagnetic items. Cobalt and associated mineralizations in the Bou Azzer inlier are recognized to arise nearby main crustal discontinuities revealing as significant shear zones, which turn act as drains for mineralizing fluids. Mineralization occurs in sectors of structural complexity beside the shear zones. Developing towards the semi-automatic uncovering of such regions, the furthermost prospective extents are those everywhere inferred structural complexity occurs next to the regions of magnetic discontinuity. The proposed method is mainly based on the approach developed by the center for exploration targeting. The study was led by means of aeromagnetic data from the Bou Azzer inlier, which is considered one of the most productive and prospective regions for minerals and base metal mineralization in Morocco. The combined results obtained from geological and geophysical data prove that prospective areas have a dominant trend of NNE-SSW, NW-SE, NNW-SSE, E-W, and NE-SW directions. The CET Grid and Porphyry Analyses show that the probable porphyry mineral deposit locations mainly concentrated in the center of inlier, the Foum Zguid dyke, and northern and eastern part, which correspond to the Bou Azzer ophiolitic complex and platform deposits of the Lower Neoproterozoic Tachdamt-Bleïda. [ABSTRACT FROM AUTHOR]

Aeromagnetic compensation is a technology used to reduce aircraft magnetic interference, which plays an important role in aeromagnetic surveys. In addition to maneuvering interferences, the onboard electronic (OBE) interference has been proven to be a significant part of aircraft interference, which must be reduced before further interpretation of aeromagnetic data. In the past, most researchers have focused on establishing linear models to compensate for OBE magnetic interference. However, such methods can only work using accurate reference sensors. In this paper, we propose a data-driven OBE interference compensation method, which can reduce OBE interference without relying on any other reference sensor. This network-based method can integrally detect and repair the OBE magnetic interference. The proposed method builds a prediction model by combining wavelet decomposition with a long short-term memory (LSTM) network to detect and predict OBE interference, and then estimates the local variation of the magnetic field to remove the drift of the interference. In our tests, we construct 10 semi-real datasets to quantitatively evaluate the performance of the proposed method. The F1 score of the proposed method for OBE interference detection is over 0.79 , and the RMSE of the compensated signal is less than 0.009 nT. Moreover, we also test our method on real signals, and the results show that our method can detect all interference and significantly reduce the standard deviation of the magnetic field. [ABSTRACT FROM AUTHOR]

The results of studies aimed at optimizing the stochastic method of taking into account the terrain when interpreting aeromagnetic survey data are presented. The method is based on the consistent application of the method of empirical mode decomposition and the method of group accounting of arguments The results of a medium-scale aeromagnetic survey conducted in Eastern Siberia were used as actual data. It is shown that the preliminary classification of the studied territory by the nature of the relief and the magnetic field strength allows us to determine the components of the magnetic field that correlate with the relief within the selected classes. To assess the quality of correlation dependencies, the ratio of the standard deviation of the models to the variance of the magnetic field amplitudes of the analyzed frequency component were used. This allows us to compare models with different statistical characteristics of the anomalous magnetic field and divide the components into correlated and uncorrelated with the terrain. The results obtained confirm the possibility of the existence of strong correlational relationships between the magnetic field and the relief in a certain range of spatial frequencies and offer specific methodological methods for applying this stochastic approach to reducing the magnetic field in the areas of the development of platobasalts.

Abstract Kusatsu-Shirane volcano is one of the active volcanoes in Japan. Phreatic explosions occurred in Mt. Shirane in 1983 and most recently, in 2018, in Mt. Motoshirane. Information on the subsurface structure is crucial for understanding the activity of volcanoes with well-developed hydrothermal systems where phreatic eruptions occur. Here, we report aeromagnetic surveys conducted at low altitudes using an unmanned helicopter. The survey aimed to obtain magnetic data at a high spatial resolution to map the magnetic anomaly and infer the magnetization intensity distribution in the region immediately after the 2018 Mt. Motoshirane eruption. The helicopter used in the survey was YAMAHA FAZER R G2, an autonomously driven model which can fly along a precisely programmed course. The flight height above the ground and a measurement line spacing were set to ~ 150 m and ~ 100 m, respectively, and the total flight distance was 191 km. The measured geomagnetic total intensity was found to vary by ~ 1000 nT peak-to-peak. The estimated magnetization intensity derived from measured data showed a 100 m thick magnetized surface layer with normal polarity, composed of volcanic deposits of recent activities. Underneath, a reverse-polarity magnetization was found, probably corresponding to the Takai lava flow in the Early Quaternary period (~ 1 Ma) mapped in the region. Our results demonstrate the cost-effectiveness and accuracy of using drone magnetometers for mapping the rugged terrain of volcanoes.

• NSAS and HADR combined are among the largest water bodies in North Africa. • Their interconnectivity remains speculative due to the lack of in-situ investigations. • Using an EM geophysical survey, we identified this connectivity over 330 km2. • Faults orientations and basement depth control flows between HADR and NSAS. • Under extended drought, reductions in the HADR level can alter NSAS sustainability. Egypt, relying heavily on the Nile as its primary water resource, is facing a rising water budget deficit due to increasing consumption, hydroclimatic changes, and upstream river damming. To address the above, innovative management of High Aswan Dam Reservoir (HADR), the third largest artificial reservoir on Earth, and its exchange with the surrounding groundwater system is suggested to develop new agricultural areas. However, the interconnectivity mechanism between the HADR and the fossil Nubian aquifer, the largest transboundary aquifer in Africa, remains speculative due to the lack of in-situ investigations. To address this deficiency, we perform a geophysical survey using aeromagnetic, time-domain electromagnetic, and vertical electrical resistivity sounding in a 330 km2 pilot area to the northwest of the HADR that is hypothesized to have a dense fracture system that could act as a conduit between these two large water bodies. Our survey results show the presence of normal faults cross the reservoir to the tangential basement and the sedimentary cover that are water-saturated and act as recharges to the Nubian fossil aquifer. These in-situ investigations confirm previous orbital gravity observations by GRACE-FO hypothesizing the interconnectivity between the reservoir and the Nubian aquifer, which was subject to debate. We suggest that such connecting areas between these two water bodies can be optimal sites for future agricultural development using improved management of surface water-groundwater exchanges for irrigation. Finally, our findings highlight upcoming challenges for this linkage if the level of HADR reaches below ∼160 m above mean sea level (amsl) due to upstream dam operation during the Nile's extended drought periods. Under these conditions, the Nubian aquifer could discharge back into the HADR at the investigated site, changing the water budget of the aquifer and compromising the planned agriculture developments in the adjacent areas, which account for ∼ 10 % of the total arable land in Egypt. [ABSTRACT FROM AUTHOR]

With the majority of coal mines in uncovered and semi-covered coal strata now explored and developed, most of the undiscovered coal-bearing strata are concealed. Compared with expensive drilling, deep targets such as concealed coal-bearing strata can be more efficiently and cost-effectively discovered through geophysical methods. We designed an integrated geophysical exploration approach to detect coal-bearing strata in the Yangjiazhangzi (YJZZ) area. Large-scale magnetotellurics (MT) is used to describe the geological structure along with its profile through the YJZZ area. An aeromagnetic survey was used to delineate the spatial distribution characteristics of the YJZZ syncline, a coal-bearing prospect tectonic unit. Localized exploration with controlled-source audio magnetotellurics (CSAMT) and MT reveals coal-bearing targets for drilling. Drilling results verified the targets identified through the integrated geophysical approach. Coal-bearing strata in the Benxi formation, the Taiyuan formation, and the Shanxi formation of the Permo-Carboniferous age are found between 630 and 770 m. This case study demonstrates that the multidisciplinary geophysical strategy can provide reliable results and credible data interpretation for deep coal seam resources exploration. The findings of this study can provide reference for explorers to carry out their specific exploration cases. [ABSTRACT FROM AUTHOR]

Miyakejima volcano experienced its latest eruption in 2000 with the summit subsidence, and the next event is expected in the near future. An aeromagnetic survey in Miyakejima was conducted in March 2021 in order to investigate the current state of its magnetization structure to identify the potential for another eruption and, thus, mitigate volcanic disaster. The survey flight was conducted using an uncrewed aerial vehicle (UAV), a multirotor drone, to deploy a scalar magnetometer. After processing geomagnetic field data from this survey, in combination with data from previous surveys conducted by using another UAV, an uncrewed helicopter, the average magnetization intensity was determined to be 12.4 A/m. Further, the surrounding area of the crater was relatively highly magnetized; however, the crater rim had a low magnetization intensity. Temporal variation was detected between 2014 and 2021 and dominated the central part of the observation area. Decreased magnetization intensity was identified beneath the caldera, which may become recently demagnetized due to heat supply traveling through fractures in the impermeable layer from the deep heat reservoir. [ABSTRACT FROM AUTHOR]

ABSTRACT: The Qinghai-Tibet Plateau (also referred to as the Plateau) has long received much attention from the community of geoscience due to its unique geographical location and rich mineral resources. This paper reviews the aeromagnetic surveys in the Plateau in the past 60 years and summarizes relevant research achievements, which mainly include the followings. (1) The boundaries between the Plateau and its surrounding regions have been clarified. In detail, its western boundary is restricted by West Kunlun-Altyn Tagh arc-shaped magnetic anomaly zone forming due to the arc-shaped connection of the Altyn Tagh and Kangxiwa faults and its eastern boundary consists of the boundaries among different magnetic fields along the Longnan (Wudu)-Kangding Fault. Meanwhile, the fault on the northern margin of the Northern Qilian Mountains serves as its northern boundary. (2) The Plateau is mainly composed of four orogens that were stitched together, namely East Kunlun-Qilian, Hoh-Xil-Songpan, Chamdo-Southwestern Sanjiang (Nujiang, Lancang, and Jinsha rivers in southeastern China), and Gangdese-Himalaya orogens. (3) The basement of the Plateau is dominated by weakly magnetic Proterozoic metamorphic rocks and lacks strongly magnetic Archean crystalline basement of stable continents such as the Tarim and Sichuan blocks. Therefore, it exhibits the characteristics of unstable orogenic basement. (4) The Yarlung-Zangbo suture zone forming due to continent-continent collisions since the Cenozoic shows double aeromagnetic anomaly zones. Therefore, it can be inferred that the Yarlung-Zangbo suture zone formed from the Indian Plate subducting towards and colliding with the Eurasian Plate twice. (5) A huge negative aeromagnetic anomaly in nearly SN trending has been discovered in the middle part of the Plateau, indicating a giant deep thermal-tectonic zone. (6) A dual-layer magnetic structure has been revealed in the Plateau. It consists of shallow magnetic anomaly zones in nearly EW and NW trending and deep magnetic anomaly zones in nearly SN trending. They overlap vertically and cross horizontally, showing the flyover-type geological structure of the Plateau. (7) A group of NW-trending faults occur in eastern Tibet, which is intersected rather than connected by the nearly EW trending that develop in middle-west Tibet. (8) As for the central uplift zone that occurs through the Qiangtang Basin, its metamorphic basement tends to gradually descend from west to east, showing the form of steps. The Qiangtang Basin is divided into the northern and southern part by the central uplift zone in it. The basement in the Qiangtang Basin is deep in the north and west and shallow in the south and west. The basement in the northern Qiangtang Basin is deep and relatively stable and thus is more favorable for the generation and preservation of oil and gas. Up to now, 19 favorable tectonic regions of oil and gas have been determined in the Qiangtang Basin. (9) A total of 21 prospecting areas of mineral resources have been delineated and thousands of ore-bearing (or mineralization) anomalies have been discovered. Additionally, the formation and uplift mechanism of the Plateau are briefly discussed in this paper.©2021 China Geology Editorial Office.

Surtsey, a young basaltic island off the south coast of Iceland, was built by volcanic activity in 1963–1967 from a pre-eruption oceanic seafloor depth of 130 m. An aeromagnetic survey was carried out in October 2021 over a 60 km2 area covering Surtsey and its surroundings. It aimed to explore the internal structure and the possible existence of basaltic intrusions associated with the five vents active at different times over the 3.5 years of eruptive activity. The survey line spacing was 200 m and the flying altitude was generally 90 m a.s.l. The strongest anomalies (amplitude ∼700 nT) are caused by the 30–100 m thick subaerially erupted lava field on the southern part of Surtsey, formed in two episodes of effusive activity:1964–1965 and 1966–1967. 2D spectral analysis and Euler deconvolution indicate that the causative bodies of anomalies outside the island of Surtsey are located within the uppermost 300 m of the seafloor and their horizontal dimensions are similar to or smaller than their depth. 3D forward modeling of the island and its surroundings, constrained by observations during the formation of the island and drill cores extracted in 1979 and 2017, is consistent with an absence, at all vents, of pillow lava and therefore effusive activity in their opening phases. However, the data support the existence of a 10–20 m thick pillow lava field on the seafloor, 2.5–3 km2 in area, extending about ∼1 km to the south of Surtsey. The field is considered to have been fed by magma reaching the seafloor via channelized intrusive flow through the foreset breccia constituting the submarine part of an emerging lava delta during the early stage of effusive eruption in May–July 1964. The general scarcity of significant magnetic bodies within the edifices is consistent with magma fragmentation dominating the submarine eruptions from the onset of activity. A small magnetic anomaly is observed over the submarine edifice of Surtla, built during short-lived activity over ∼10 days in 1963–1964. This anomaly is consistent with observed subaqueous weak or moderate explosive activity that may have allowed a dyke to be preserved within the submarine tephra mound. More violent Surtseyan activity was observed at other vents, however, and may have destroyed any initial dykes that, if preserved, might have been resolved magnetically. Indications of magnetized volcanic rocks of unknown age predating the Surtsey eruption are found beneath the flank of the ephemeral island of Jólnir, the southernmost of the Surtsey vents. [ABSTRACT FROM AUTHOR]

The research relevance is caused by the expediency of using model concepts adequate to real physical and geological conditions, while reducing the results of magnetic prospecting in the areas of development of platobasalts. The aim of the research is to evaluate the influence of the Earth’s sphericity on the anomalous magnetic field under conditions of a sharply dissected relief of the day surface which is composed of magmatic mountain rocks that have an increased magnetization (on practical materials). Methods: calculation of corrections for the influence of magnetic terrain by solving the direct problem of magnetic exploration for a region with a radius of 20 km in two versions: for flat and spherical models of the Earth. Comparison of the results and spatial-statistical analysis of the identified differences were carried out. It was assumed that the magnetization vector of the rocks forming the relief is directed along the modern geomagnetic field of the region. Variable laterally effective magnetization of the upper part of the section was determined by solving the linear inverse problem of magnetic exploration. Results. The paper describes briefly the problem of taking into account the influence of the terrain relief in measuring the magnetic field over volcanogenic formations. On the example of materials of a large-scale high-precision aeromagnetic survey, performed in the central part of the Norilsk ore region, the nonlinear signal distortions associated with the curvilinearity of the earth's surface were shown. The amplitude of these distortions (absolute value) reaches 100–200 nT and more, with relatively small differences in elevations for different models. This is due to the high values of the vertical gradient of the magnetic field. Findings. In order to suppress the intense noise anomalies caused by magnetic rocks composing the upper part of the geological section, the author proposed the calculation of topographic corrections using the spherical model of the Earth. It also seems promising to use a statistical approach, implicitly taking into account the shape of the earth's surface, to isolate anomalies of «relief» nature. A comparison of the results obtained and a spatial-statistical analysis of the revealed differences are performed.

Numerical analysis of geophysical data to uncover Precambrian belts and probably to enclose mineral deposits is becoming once more communal in mining activity. The method is founded on typifying zones branded to comprehend deposits and looking for analogous areas. The proposed work outlines a semi-automatic image processing system for the structural and mining investigation of the Bou Azzer inlier, which varies from preceding approaches as it is centered only on aeromagnetic data. The aeromagnetic signature of what seem to be geologically expressive features are pursued within the aeromagnetic items. Cobalt and associated mineralizations in the Bou Azzer inlier are recognized to arise nearby main crustal discontinuities revealing as significant shear zones, which turn act as drains for mineralizing fluids. Mineralization occurs in sectors of structural complexity beside the shear zones. Developing towards the semi-automatic uncovering of such regions, the furthermost prospective extents are those everywhere inferred structural complexity occurs next to the regions of magnetic discontinuity. The proposed method is mainly based on the approach developed by the center for exploration targeting. The study was led by means of aeromagnetic data from the Bou Azzer inlier, which is considered one of the most productive and prospective regions for minerals and base metal mineralization in Morocco. The combined results obtained from geological and geophysical data prove that prospective areas have a dominant trend of NNE-SSW, NW-SE, NNW-SSE, E-W, and NE-SW directions. The CET Grid and Porphyry Analyses show that the probable porphyry mineral deposit locations mainly concentrated in the center of inlier, the Foum Zguid dyke, and northern and eastern part, which correspond to the Bou Azzer ophiolitic complex and platform deposits of the Lower Neoproterozoic Tachdamt-Bleïda.

Kusatsu-Shirane volcano is one of the active volcanoes in Japan. Phreatic explosions occurred in Mt. Shirane in 1983 and most recently, in 2018, in Mt. Motoshirane. Information on the subsurface structure is crucial for understanding the activity of volcanoes with well-developed hydrothermal systems where phreatic eruptions occur. Here, we report aeromagnetic surveys conducted at low altitudes using an unmanned helicopter. The survey aimed to obtain magnetic data at a high spatial resolution to map the magnetic anomaly and infer the magnetization intensity distribution in the region immediately after the 2018 Mt. Motoshirane eruption. The helicopter used in the survey was YAMAHA FAZER R G2, an autonomously driven model which can fly along a precisely programmed course. The flight height above the ground and a measurement line spacing were set to ~ 150 m and ~ 100 m, respectively, and the total flight distance was 191 km. The measured geomagnetic total intensity was found to vary by ~ 1000 nT peak-to-peak. The estimated magnetization intensity derived from measured data showed a 100 m thick magnetized surface layer with normal polarity, composed of volcanic deposits of recent activities. Underneath, a reverse-polarity magnetization was found, probably corresponding to the Takai lava flow in the Early Quaternary period (~ 1 Ma) mapped in the region. Our results demonstrate the cost-effectiveness and accuracy of using drone magnetometers for mapping the rugged terrain of volcanoes. [ABSTRACT FROM AUTHOR]

Magnetic surveys have been widely used in archaeological field investigations. However, conventional survey methods are often restricted by complicated field conditions and ambiguities in data interpretation. In this study, a novel magnetic survey system was designed for pre-archaeological investigation (preliminary survey prior to the archaeological excavation) based on a modified quadrotor unmanned aerial vehicle (UAV) and was successfully applied to an archaeological area with a complex landform in Huizhou, China. Results show that the target anomaly identified by UAV aeromagnetic survey corresponds well to the location of a potential archaeological site. Subsequent soil analyses further confirm the archaeological value of UAV aeromagnetic results and provide strong constraints on the interpretation of target anomalies. This study demonstrates that the newly proposed UAV aeromagnetic system can adapt to the various field conditions with the advantages of flexibility and efficiency, which has great potential for future archaeological investigations.

In addition to the physical parameters such as magnetization intensity distribution, the volume and the shape of the magnetized material, directions of the magnetization and the ambient field, the distance between the observation surface and the causative sources significantly affects the shape and the amplitudes of the magnetic anomalies. Aeromagnetic surveys are performed using either a draped surface or a constant elevation plane above sea level. These surveys can easily reconnoiter large territories in a short time. However, the magnetic anomalies may be attenuated resulting in some losses in the data resolution based on the flight height of the survey. In this paper, these effects were investigated in a detailed manner through some synthetic anomalies generated from 2D and 3D hypothetical subsurface models. Besides, magnetic terrain effects were also examined in the synthetic simulations which were produced for different scenarios. Real aeromagnetic anomalies obtained using a drape flying survey mode over the rugged high topographic relief of the Mount Nemrut stratovolcano (Bitlis, eastern Turkey) and its close vicinity were also investigated. Numerical simulations show that although both data acquisition modes have some weak sides, the level flying mode is more advantageous than the drape flying mode in general. Better anomaly interpretation can be achieved by reducing the draped data set into the one observed over a horizontal plane or vice versa and comparing these two data sets. Lastly, a simple computational process which can be performed in the Fourier wavenumber domain is proposed for data reduction procedure. [ABSTRACT FROM AUTHOR]

Copyright of BHM Berg- und Hüttenmännische Monatshefte is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Recent advancements in geophysical exploration have been realized through reliably integrating unmanned aerial vehicle platforms with lightweight, high‐resolution magnetometer payloads. Unmanned aerial vehicle aeromagnetic surveys can provide a contemporary data product between the two end‐members of coverage and resolution attained using manned airborne and terrestrial magnetic surveys. This new data product is achievable because unmanned aerial vehicle platforms can safely traverse with magnetometer payloads at flight elevations closer to ground targets than manned airborne surveys, while also delivering an increased coverage rate compared to walking conventional terrestrial surveys. This is a promising new development for geophysical and mineral exploration applications, especially in variable terrains. A three‐dimensional unmanned aerial vehicle aeromagnetic survey was conducted within the Shebandowan Greenstone Belt, northwest of Thunder Bay, Ontario, Canada, in July 2017. A series of two‐dimensional grids (∼500 m × 700 m) were flown at approximate elevations of 35, 45 and 70 m above ground level using a Dà‐Jiāng Innovations multi‐rotor unmanned aerial vehicle (S900) and a GEM Systems, Inc., Potassium Vapour Magnetometer (GSMP‐35U). In total, over 48 line‐km of unmanned aerial vehicle aeromagnetic data were flown with a line spacing of 25 m. The collected aeromagnetic data were compared to a regional heliborne aeromagnetic survey flown at an elevation of approximately 85 m above the terrain, with a line spacing of 100 m, as well as a follow‐up terrestrial magnetic survey. The first vertical derivative of the gathered unmanned aerial vehicle total magnetic field data was calculated both directly between each of the different flight elevations, and indirectly by calculating the values predicted using upward continuation. This case study demonstrates that low flight elevation unmanned aerial vehicle aeromagnetic surveys can reliably collect industry standard total magnetic field measurements at an increased resolution when compared to manned airborne magnetic surveys. The enhanced interpretation potential provided by this approach also aided in delineating structural controls and hydrothermal fluid migration pathways (a pair of adjacent shear zones) related to gold mineralization on site. These structural features were not clearly resolved in the regional manned airborne magnetic data alone, further demonstrating the utility of applying high‐resolution unmanned aerial vehicle aeromagnetic surveys to mineral exploration applications. The conclusions and interpretations drawn from the unmanned aerial vehicle aeromagnetic data, coupled with historical data, were applied to make a new gold mineralization discovery on the site, assayed at 15.7 g/t. [ABSTRACT FROM AUTHOR]

In the Qihe area, the magnetic anomalies caused by deep and concealed magnetite are weak and compared with ground surveys, airborne surveys further weaken the signals. Moreover, the magnetite in the Qihe area belongs to a contact-metasomatic deposit, and the magnetic anomalies caused by the magnetite and its mother rock overlap and interweave. Therefore, it is difficult to directly delineate the target areas of magnetite according to the measured aeromagnetic maps in Qihe or similar areas, let alone estimate prospective magnetite resources. This study tried to extract magnetite-caused anomalies from aeromagnetic data by using high-pass filtering. Then, a preliminary estimation of magnetite prospective resources was realized by the 3D inversion of the extracted anomalies. In order to improve the resolution and accuracy of the inversion results, a combined model-weighting function was proposed for the inversion. Meanwhile, the upper and lower bounds and positive and negative constraints were imposed on the model parameters to further improve the rationality of the inversion results. A theoretical model with deep and concealed magnetite was established. It demonstrated the feasibility of magnetite-caused anomaly extraction and magnetite prospective resource estimation. Finally, the magnetite-caused anomalies were extracted from the measured aeromagnetic data and were consistent with known drilling information. The distribution of underground magnetic bodies was obtained by the 3D inversion of extracted anomalies, and the existing drilling data were used to delineate the volume of magnetite. In this way, the prospective resources of magnetite in Qihe area were estimated.

Abstract Gravity and aeromagnetic potential methods are proven to be adequate geophysical techniques for studying the subsurface structure of continental basement areas hidden beneath sedimentary basin. In this study, we present the study of that large part of the Moroccan Western Meseta which is hidden beneath the Phosphates Plateau and Tadla Basin, based on gravity and aeromagnetic data analysis and interpretation. A subsurface structural map of the study area has been established. This reference map shows how the subsurface structural lineaments deduced from the gravity and aeromagnetic data can be continued into the regional crustal-scale faults outcropping around the study area in the Rehamna, Jebilet and Central Massifs. The analysis of this map reveals that: i) the area is predominantly controlled by faults having NE and NW major trends, with E-W and N-S minor trends; ii) these trends are associated with the main phases of deformation that the area underwent during the Variscan Orogeny, the Triassic-Jurassic rifting, and the Atlas tectonic inversion, respectively; iii) many faults already highlighted by previous geophysical investigations are confirmed, and some new crustal-scale structures are revealed; iv) the subsurface continuity of the major, Variscan crustal-scale faults such as the West Meseta Shear Zone, the Smaala-Oulmes Fault Zone and the Fkih Ben Salah Fault is evidenced, and v) the Khouribga-Oulmes Anticlinorium appears to be bounded to the south by a newly described, NW-striking Phosphate Plateau Fault. Highlights • Use various edges detection filters to detect the main subsurface gravity lineaments and magnetic trend. • Subsurface structural map of the Tadla Basin and Phosphates Plateau. • Continuity of the major Variscan faults under the sedimentary cover of Tadla Basin and Phosphates Plateau. • Truncation of the NE-SW Variscan faults by the E-W Alpine faults. • Southward extension of the main Central Meseta structures except the Khouribga-Oulmes anticlinorium limited by a NW-SE fault. [ABSTRACT FROM AUTHOR]

Aeromagnetic surveys are important in geophysical prospecting and magnetic anomaly detection. Magnetic fields are typically measured by optically pumped magnetometers (OPMs) mounted on an aircraft. Platform-generated magnetic interference severely compromises the sensitivity of the OPMs. Therefore, aeromagnetic compensation is necessary. However, measurement uncertainties of three-axis magnetometers influence the qualities of aeromagnetic compensation and there is no method that can directly predict the qualities of aeromagnetic compensation before calibration flights. To address this issue, we propose a method to calculate the systematic errors of aeromagnetic compensation caused by measurement uncertainties of three-axis magnetometers and analyze the performance of aeromagnetic compensation in advance of calibration flights. It can be used to estimate the residual errors of aeromagnetic compensation theoretically. Using this method, researchers can assess whether aircraft platforms are appropriate to implement aeromagnetic surveys or not before carrying out experiments in practice. Field experiments are carried out to exhibit how to use the method to calculate the measurement uncertainties of aeromagnetic compensation in different conditions. The results of the experiments demonstrate the validity of the method. [ABSTRACT FROM AUTHOR]

The application of a newly developed physics-based earthquake simulator to the active faults inferred by aeromagnetism in southern Calabria has produced a synthetic catalog lasting 100 ky including more than 18,000 earthquakes of magnitude ≥ 4.0. This catalog exhibits temporal, spatial and magnitude features, which resemble those of the observed seismicity. As an example of the potential use of synthetic catalogs, a map of the peak ground acceleration (PGA) for a given exceedance probability on the territory under investigation has been produced by means of a simple attenuation law applied to all the events reported in the synthetic catalog. This map was compared with the existing hazard map that is presently used in the national seismic building regulations. The comparison supports a strong similarity of our results with the values given in the present Italian seismic building code, despite the latter being based on a different methodology. The same similarity cannot be recognized for the comparison of our present study with the results obtained from a previous study based on our same methodology but with a different geological model. [ABSTRACT FROM AUTHOR]

The Alpine Fault is very well delineated by recent high-resolution aeromagnetic data sets over much of its length in New Zealand’s South Island. Aeromagnetic data acquired over parts of the West Coast, Tasman and Marlborough regions for the New Zealand Government reveal different types of total magnetic intensity anomalies associated with the fault that can be characterised as truncated, step, ridge, trough and broad anomalies. Fault-terminated Permian ultramafic rocks, Late Cretaceous basalt and some Early Cretaceous intrusions are attributed to the more prominent truncated anomalies. The pre-eminent step anomaly is associated with relatively magnetic Alpine Schist juxtaposed against variable but generally less magnetic Western Province rocks. Strongly positive ridge anomalies occurring in the Alpine Fault zone are associated with Mesozoic mafic metavolcanic and ultramafic rocks. A trough anomaly associated with the Alpine Fault occurs in the southernmost survey and may reflect some hydrothermal demagnetisation. Broad, low-amplitude anomalies underlying the hanging wall are attributed in one instance to the extension of the magnetic Hohonu Range granitoids and dikes extending southeast in the footwall and in other places as magnetic schist rocks in the hanging wall. The apparent great-circle displacement of the Alpine Fault based on offset of magnetic anomalies associated with the Dun Mountain Ultramafics Group rocks is c. 461 km, in close agreement with the more precise 459 km inferred from geological map offset. [ABSTRACT FROM AUTHOR]

Abstract: We report on a high‐resolution, low‐altitude aeromagnetic investigation of the central Apennine extensional seismogenic zone, hit by destructive historical earthquakes including the 2009 L'Aquila seismic sequence. Central Apennines are predominantly made by thick (>4 and possibly up to 12 km) packages of shelf and deep marine limestones and dolomites of Mesozoic age, unconformably covered by upper Pliocene‐Holocene continental sediments lying on (often active) normal fault hanging walls. Seismogenic faults cut the carbonates down to 10‐ to 12‐km depth, where the brittle‐ductile transition occurs. Aeromagnetic data were collected during June 2014 with a cesium magnetometer, along 200‐m‐spaced flight lines. Apart from a regional 80‐nT anomaly that we modeled at 30‐ to 40‐km depths in the lower crust of the Adria plate, weak magnetic residuals are observed. As expected, normal faults cutting the diamagnetic carbonates lack any magnetic fingerprint. However, shallow continental basins yield clear anomalies of 2‐ to 8‐nT intensity, as they contain both residual soils and tephra erupted after 0.7 Ma by volcanoes from the Tyrrhenian margin of Italy. Basin margins imaged by aeromagnetism mirror the geometry of their causative normal faults. Thus, aeromagnetic residuals document many of the central Apennine normal faults that were active during the last ~3 Ma. Most prominent anomalies reflect basins formed after 0.7 Ma, as their magnetization is significantly higher than that of older continental basins. We conclude that rectilinear boundaries of most prominent anomalies reflect faults formed after 0.7 Ma, thus probably seismogenic. [ABSTRACT FROM AUTHOR]

This paper presents the analysis and interpretation of an aeromagnetic data of Ilesha area, (Sheet 243) sourced from Nigeria Geological Survey Agency. The area is located between 7.5oN and 8.0oN of latitude and longitude 4.5oE to 5.0oE. Two methods: Analytic Signal Method (ASM) and Local wavenumber (LWN) were used. These methods were used to process and analyse the data so as to generate the depth to magnetic sources as well as the source locations. The results obtained showed a shallower depth range limit for ASM between 0.348 km and 1.28 km, which is less than the result of LWN within the range of 0.478 km-1.51 km. The results also revealed more source locations in ASM result in comparison with LWN. The overall results of the methods have revealed the prospect of the lithology of the area for magnetic mineral exploration in the field of applied geophysics. Keywords: Aeromagnetic survey, Analytic signal, Magnetic Anomaly, Local wave number, lithology

Aeromagnetic surveys play an important role in geophysical exploration and many other fields. In many applications, magnetometers are installed aboard an aircraft to survey large areas. Due to its composition, an aircraft has its own magnetic field, which degrades the reliability of the measurements, and thus a technique (named aeromagnetic compensation) that reduces the magnetic interference field effect is required. Commonly, based on the Tolles−Lawson model, this issue is solved as a linear regression problem. However, multicollinearity, which refers to the case when more than two model variables are highly linearly related, creates accuracy problems when estimating the model coefficients. The analysis in this study indicates that the variables that cause multicollinearity are related to the flight heading. To take this point into account, a multimodel compensation method is proposed. By selecting the variables that contribute less to the multicollinearity, different sub-models are built to describe the magnetic interference of the aircraft when flying in different orientations. This method restricts the impact of multicollinearity and improves the reliability of the measurements. Compared with the existing methods, the proposed method reduces the interference field more effectively, which is verified by a set of airborne tests.

Aeromagnetic data coupled with Landsat ETM+ data and SRTM DEM have been processed in order to map regional hydrogeological structures in the basement complex region of Paiko, North Central Nigeria. Lineaments were extracted from derivative maps of aeromagnetic, Landsat ETM+ and SRTM DEM datasets. Ground geophysical investigation utilizing Radial Vertical Electrical Sounding (RVES) was established in nine transects comprised of four sounding stations which are oriented in three azimuths. Source Parameter Imaging (SPI) was employed to map average depths of structures from aeromagnetic dataset. Selected thematic layers which included lineaments density, lithologic structure, slope, drainage density and geomorphologic maps were integrated and modeled using ArcGIS to generate a groundwater potential map of the area. Groundwater zones were classified into four categories: Very good, good, moderate and poor according to their potential to yield sustainable water to drilled wells. The results from RVES survey reveal a close correlation to lineaments delineated from surface structural mapping and remotely sensed datasets. Hydrogeological significance of these orientations suggest that aeromagnetic data can be used to map relatively deep-seated fractures which are likely to be open groundwater conduits while remotely sensed lineaments and orientations delineated from the RVES survey may indicate areas of recharge. Regions with high lineament density attributable to thick regolith and highly fractured basement have better groundwater potential. Drill depths in this area should target a minimum of 80 m to ensure sufficient and sustainable supplies to drilled wells. The outcome of this study would act as information framework that would guide the siting of productive water wells while providing needed information for relevant agencies in need of data for the development of groundwater resources. [ABSTRACT FROM AUTHOR]

This paper presents the analysis and interpretation of an aeromagnetic data of Ilesha area, (Sheet 243) sourced from Nigeria Geological Survey Agency. The area is located between 7.5oN and 8.0oN of latitude and longitude 4.5oE to 5.0oE. Two methods: Analytic Signal Method (ASM) and Local wavenumber (LWN) were used. These methods were used to process and analyse the data so as to generate the depth to magnetic sources as well as the source locations. The results obtained showed a shallower depth range limit for ASM between 0.348 km and 1.28 km, which is less than the result of LWN within the range of 0.478 km-1.51 km. The results also revealed more source locations in ASM result in comparison with LWN. The overall results of the methods have revealed the prospect of the lithology of the area for magnetic mineral exploration in the field of applied geophysics. [ABSTRACT FROM AUTHOR]