Airborne Geophysical Survey Research Articles

Tectonic structures of the Dome Fuji region, East Antarctica, based on new magnetic data

The Oldest Ice Reconnaissance (OIR) airborne geophysical survey in East Antarctica was flown over approximately 170,000 km2 of the Dome Fuji region in 2016/17. The survey’s results support new insights into the subglacial geology and its meaning for the tectonic histories of the supercontinents Rodinia and Gondwana. The new magnetic and radar-derived bed topography data are integrated with previously acquired magnetic and gravity data, allowing the mapping of crustal domains within and beyond the survey’s limits. The magnetic data reveal three distinct domains within the survey region, delineated by N–S oriented boundaries, partly aligned with gravity domains following upward continuation transformations for both datasets. Additionally, four primary sets of magnetic lineaments were identified, exhibiting correlations with topographic and gravity patterns. These correlations indicate the continuation of the Tonian Oceanic Arc Super Terrane (TOAST) southward of its previously known southern limit. Moreover, an E–W-trending magnetic anomaly, the Elbert magnetic anomaly, suggests the suture between the recently-proposed subglacial Valkyrie craton and the TOAST. Furthermore, the analysis reveals a broad scale shear zone, named here the OIR shear zone, which formed as a result of oblique collision of the Ruker and Valkyrie cratons during the amalgamation of Gondwana.

Application of High-Resolution Aeromagnetic and Gamma-ray Spectrometry Surveys for Litho-Structural Mapping in Southwest China

Airborne geophysical surveys serve as an effective tool for litho-structural mapping, providing extensive and high-resolution underground information. They offer vital data support for the interpretation and analysis of lithologies and structures, complementing surface geological mapping. In the study area of the Nanpanjiang-Youjiang metallogenic belt in southeast China, we obtained high-resolution aeromagnetic and gamma-ray spectrometry data covering an area of approximately 27,000 km2, which facilitated the conduct of litho-structural mapping. The total magnetic intensity, reduction to the pole, and directional derivative maps generated from the aeromagnetic data, efficiently identified concealed rocks and faults. Additionally, the total count, potassium, thorium to potassium ratio, and ternary maps generated from the airborne gamma-ray spectrometry data demonstrated advantages in distinguishing carbonate rocks from clastic rocks. They also provided more comprehensive geological information, refining the structural strike and location interpreted by the aeromagnetic data. The litho-structural map produced in this study significantly contributes to our understanding of the structures in the Nanpanjiang area and offers valuable guidance for successful mineral exploration endeavors.

Application of airborne geophysical survey data in a logistic regression model to improve the predictive power of geogenic radon maps. A case study in Castleisland, County Kerry, Ireland

In this study, a novel methodology was investigated to improve the spatial resolution and predictive power of geogenic radon maps. The data inputs comprise indoor radon measurements and seven geogenic factors including geological data (i.e. bedrock and Quaternary geology, aquifer type and soil permeability) and airborne geophysical parameters (i.e. magnetic field strength, gamma-ray radiation and electromagnetic resistivity). The methodology was tested in Castleisland southwest Ireland, a radon-prone area identified based on the results of previous indoor radon surveys. The developed model was capable of justifying almost 75 % of the variation in geogenic radon potential. It was found that the attributes with the greatest statistical significance were equivalent uranium content (EqU) and soil permeability. A new radon potential map was produced at a higher spatial resolution compared with the original map, which did not include geophysical parameter data. In the final step, the activity of radon in soil gas was measured at 87 sites, and the correlation between the observed soil gas radon and geophysical properties was evaluated. The results indicate that any model using only geophysical data cannot accurately predict soil radon activity and that geological information should be integrated to achieve a successful prediction model. Furthermore, we found that EqU is a better indicator for predicting indoor radon potential than the measured soil radon concentrations.

Three-Dimensional Inversion of Induced Polarization Effects in Airborne Time Domain Electromagnetic Data Using the GEMTIP Model

This paper discusses the physical and mathematical principles of the airborne induced polarization (IP) method. The possibility of extracting information about the IP properties of rocks from airborne survey data has become a subject of active research recently. We introduce a method for the joint inversion of the airborne EM data into the electrical conductivity and IP parameters based on the generalized effective-medium theory of induced polarization (GEMTIP). We also present the results of the inversion of the airborne EM data collected over the Echum Project Area, in Northwestern Ontario, Canada, into 3D conductivity and chargeability models. Obtaining IP physical property models from an airborne geophysical survey may result in a paradigm change in mineral exploration by pulling more information and value from airborne EM surveys.

Detection of potential hydrocarbon accumulations at Qaret El-Soda area, Western Desert, Egypt, based on airborne geophysical survey data

Airborne spectral gamma-ray survey data were processed using Th-normalization technique for oil and gas exploration in the Qaret El-Soda area, Western Desert of Egypt. This technique was applied to suppress the effects of surface lithology, which are the main factors influencing the variation of radioelement content in rocks. Normalization of K and U by thorium yielded residual potassium and residual uranium estimates. Possible occurrences of new hydrocarbon microseepages were determined by mapping low values of residual potassium and high values of residual uranium relative to potassium, which are indicated as DRAD values, which were obtained by subtracting residual potassium from residual uranium values (eUresid – Kresid). Lower residual values of K, which were associated with higher DRAD anomaly values, highlight areas of prospective hydrocarbon accumulations. The obtained results from quantitative analysis and interpretation of aeromagnetic data show sufficiently thick sediments, probably suitable for the accumulation of hydrocarbons. This means that the study area may possess a potential for hydrocarbon exploration if supported by other detailed geophysical and geochemical exploration techniques.

Mapping geological configuration using geophysics data: an investigative approach in targeting iron ore, gold mineralization and other commodities, a case study of Toko-Nlokeng area (Nyong Greenstone Belt, SW Cameroon)

ABSTRACT Regional geophysical data are important for detecting the presence of mineral deposits under cover. This study used geophysical data coupled with field geology of the Toko-Nlokeng area, Cameroon, to locate and map structures and lithologies as part of an exploration campaign for mineral deposits. The airborne geophysical survey in the Toko-Nlokeng area located in the Nyong complex revealed a predominantly EW striking highly folded series result of polyphase deformation of iron formations and host rocks divided into domains based on magnetic and radiometric character. The geophysical data indicate that major faults and shear zones strike NE-SW, with N–S striking units on the western margin and mainly E–W striking units in the rest of the area. These data suggest a major N–S thrust fault similar to the Borborema Province (NE Brazil) terrane marked by accretionary processes during the assembly of Western Gondwana. Several significant NE–SW striking shear zones are present. The data revealed many moderate to highly magnetic bodies that are interpreted as magnetite-bearing iron formation, mafic–ultramafic intrusions and flows, skarns, carbonatites and kimberlites. The magnetic and radiometric trends reveal the internal regional rock fabric and strike, and iron ore targets with magnetic anomaly up to 27,000 nT related to iron formations and other significant targets for gold, potassium (alteration) and uranium. The Toko-Nlokeng iron deposit is comprised of magnetite-bearing quartzite beds and is concordant with the surrounding host rocks and stands as one of a broad group of magnetite-dominated iron formations that occur throughout West and Central Africa. A new geological map was produced from mapped lithologies and microstructure characteristics of the iron formations, interpretations of the aeromagnetic data and structural features. The study results have important implications for regional exploration programs.

A comparison of airborne geophysical data over two magmatic nickel deposits

Historical exploration for economic nickel (Ni) mineralization has often targeted magmatic sulfide deposits in extensional settings. However, convergent-margin-hosted Alaskan-type complexes represent a potentially underexplored source of Ni. Case studies of the geophysical responses associated with two magmatic Ni deposits (one is typical, and one is associated with an Alaskan-type complex) are presented, and the results are compared. Data were assessed from historical and newly acquired airborne geophysical surveys that were collected over the Mayville property in southeast Manitoba and the Turnagain property in northern British Columbia. The properties were explored by Mustang Minerals Corporation and Giga Metals Corporation, respectively. Airborne electromagnetic (EM) and magnetic data were utilized to compare the two properties and the mineralized zones. The review showed that the Mayville magmatic sulfide deposit was directly detectible with EM methods, and the passive and active-source methods were complementary to one another. The EM data did not directly detect the Turnagain Alaskan-type deposit, but the magnetics data proved to be successful in defining the geologic framework. Implications for future targeting and exploration for economic Ni mineralization are considered.

Objective classification of high‐resolution geophysical data: Empowering the next generation of mineral exploration in Sierra Leone

AbstractIn 2019, a nationwide airborne geophysical survey of Sierra Leone was flown at 150 m nominal line spacing and 50 m nominal terrain clearance. Contractual deliverables included magnetic, radiometric and supporting data streams. The primary aim of the geophysical survey was to provide a national geoscientific benchmark for resource management by the National Minerals Agency and to encourage foreign investment in the rich mining potential of Sierra Leone. Geophysical interpretation is often highly subjective. This can be helpful when an interpreter is skilled in the project area and exploration targets being sought but can be constraining and even dangerous when exploring new areas, and for new commodities. Objective classification tools can challenge interpretive bias and enhance geological understanding, both locally and regionally. We present self‐organizing maps and neural network products generated from the Sierra Leone geophysical dataset which both confirm and challenge the validity of conventional, subjective interpretation workflows. We demonstrate the usefulness of self‐organizing maps as a tool for inferring complementary geological information and show some initial results of convolution neural network classification of a reduced‐to‐equator grid to locate magnetic lineaments in plan and in depth. Moreover, we show initial results of self‐organizing map clustering as a tool for joint analysis of multiphysics datasets and construction of a pseudolithological cluster map.

Агаарын геофизикийн судалгааны ажлын эдийн засгийн урьдчилсан тооцоо

There is still unexplored areas left in total surface of Mongolia by airborne geophysical survey. In today’s world, the necessity of airborne geophysical survey is increasing; Mongolian experts are in search of opportunities to explore the total surface area of the country using technological advances. Time frame required for research and cost analysis in comparison with other similar project are discussed in this article.

New high resolution aeromagnetic anomaly map of Türkiye and its various derivative-based maps

Since Türkiye's territory is mostly mountainous and forested, earth science studies in these areas have not been completed at an adequate level and with a satisfying resolution. However, due to the long time and cost of collecting measurements from land in large- and medium-scale studies and due to the inability to collect measurements in regular grid intervals in large-scale studies to be carried out on land, an airborne geophysical survey project was conducted in order to collect high-resolution magnetic and radiometric country-scale data. Total magnetic field and radiometry data were collected from the air between 2017 and 2022 within the scope of the country-wide Airborne Geophysics Surveys Project. The data collection flights were carried out in such a way as to follow the topography from an altitude of about 200 m above the ground. The flights were carried out considering the regular geometry of the flight profile and the general geological and tectonic structure of Türkiye in the direction of N-S with one-kilometer profile intervals. A total field magnetic anomaly map was obtained after applying the diurnal, tie line leveling, IGRF (model 2020), and differential reduction to magnetic pole (DRTP) corrections to the magnetic data. For the scope of this study, the total field magnetic anomaly and the regional total field magnetic anomaly maps were presented along with the structural boundary maps (tilt angle (TA), the total horizontal derivative (THDR) and the analytical signal (AS)) derived from these maps. During another stage of the study, the general tectonic structure of Türkiye and structural boundaries obtained from derivative-based maps (AS, TA, and THDR) were compared. General geophysical interpretation was also performed with magnetic-anomaly and derivative-based maps for the three regions characterized by high magnetic anomalies.

Country-wide exploration for graphite- and sulphide-rich black shales with airborne geophysics and petrophysical and geochemical studies

Black shales host critical raw materials such as graphite and cobalt and occur in the vicinity of many types of sulphide deposits. We report the procedure for country-wide mapping of graphite- and sulphide-rich rocks and the chemical and petrophysical data of 319 samples we selected from sulphide occurrences and mines in Finland. Even though black shales are rarely outcropped in glaciated and deeply weathered terrains, they can be traced with geophysical surveys.In the Precambrian of Finland, where the metamorphic grade varies from greenschist to granulite facies, systematic airborne geophysical surveys revealed stratigraphy-related, coupled magnetic and electrically conductive patterns. Electrical conductivity was related to the graphite and sulphide contents, producing continuous and bending electromagnetic anomaly patterns. The magnetic anomalies, if present, resulted from ferrimagnetic monoclinic pyrrhotite.The petrophysical properties of black shales varied in our sample set. The densities were mainly between 2700 and 3000 kg/m3, with the mean density ~ 2800 kg/m3, where the amount of graphite had a reducing effect on density whereas sulphides increased it. The average magnetic susceptibilities were about 6000·10−6 (SI), but they showed wide variation, depending on the abundance of ferrimagnetic monoclinic pyrrhotite. The electrical conductivity of black shales appeared to be positively related to the abundance of monoclinic pyrrhotite. Conductivity variation, 1–105 1/Ωm was based on laboratory determinations of apparent resistivities.We correlated an airborne magnetic and electromagnetic survey with petrophysical and chemical data from altogether 319 drill core samples containing >1 % graphitic C and >1 % S. The samples were selected during 2009–2011 from 102 drill cores all over Finland except for the Talvivaara–Outokumpu region, which was studied during previous projects. The black-shale-hosted Talvivaara Ni–Zn–Co–Cu deposit is currently being mined.The maximum graphite concentration in the country-wide sample set was 34.3 %, and the median value was 5.7 %, a lower value than reported from the Talvivaara black-shale-hosted sulphide deposit (7.6 %). S, Co, Cu, Fe and Ni concentrations were also lower in our sample set on average than in the Talvivaara ore. However, the maximum concentration in our sample set was 397 mg/kg for Co, 0.36 % for Cu, 40.8 % for Fe and 0.28 % for Ni.The developed black shale mapping procedure can be directly applied in other parts of the world in terrains with greenschist to granulite facies regional metamorphism. Information on basic petrophysical properties, i.e., density, magnetic and electric properties, are needed to explain geophysical anomalies. If the metamorphic grade is lower than greenschist facies and there is no graphite, sulphides will increase the electromagnetic properties. If ferrimagnetic pyrrhotite exists, susceptibility increases, as well as remanence.The black shale database covering the whole of Finland is used not only in exploration and bedrock mapping, but also in regional planning and for environmental risk analyses, because sulphide-rich black shales may cause acid rock drainage when exposed to weathering and the quality of surface water and groundwater may suffer from black shale bedrock and glacial till. The scale limitations given by airborne geophysics may request detailed studies in selected sites.

Digital soil mapping of peatland using airborne radiometric data and supervised machine learning – Implication for the assessment of carbon stock

Peatlands account for approx. 4.23 million km2 of the land surface of Earth and between 5 % and 20 % of the global soil carbon stock, however much uncertainty exists. The release of carbon from modified peatlands is significant and affects the global carbon balance. The importance of conservation and rehabilitation of peatlands is clear. Global estimates currently use national scale mapping strategies that vary depending on available resources and national interest. The most up-to-date methods rely on satellite remote sensing data, which detect peat based on a multiband spectral signature, or reflected radar backscatter. However, satellite data may not be capable of detecting peat under landcover such as pasture or forest. Airborne geophysical surveys provide relevant subsurface information to update or redefine peatland extent maps at a national scale. Radiometric surveys, which measure the naturally occurring geologically sourced potassium, uranium, and thorium, offer the largest potential. Modelling of gamma ray attenuation shows that peat has a distinctive attenuation signature, due to its low bulk density, when considering all recorded radiometric data. This study exploits this signature by combining airborne radiometric data in a machine learning framework and training an artificial neural network to detect those data which have been acquired over previously mapped peatlands. A ∼95 % predictability is achieved. The trained neural network can be then used to predict the extent of all peatlands within a region, including forested and agriculturally modified peatlands, and an updated peatland map can be produced. This methodology has implications for global carbon stock assessment and rehabilitation projects where similar datasets exist or are planned, by updating the extent and boundary positions of current peatlands and uncovering previously unknown peatlands under forestry or grasslands.

A step towards meeting battery raw material demand: the geology and exploration of graphite deposits, examples from northern Norway

Abstract In northern Norway, we have identified more than 40 occurrences of graphite through airborne geophysical surveys and follow-up fieldwork. Out of these, 29 have been investigated in detail using ground-based geophysical methods. For 21 of these occurrences, in combination with surface sampling, it is possible to estimate approximately the grade and tonnage of graphite. The graphite deposits are concentrated in two areas: the island of Senja and the Lofoten–Vesterålen islands. The aggregated tonnage and average graphite grade are 8.1 Mt and 12.6% graphite, respectively. Data collected from 17 international deposits show similar averages of 30.7 Mt and 10.8% graphite. Thus, the Norwegian deposits show a similar span in tonnage and grade and are most likely typical for graphite deposits worldwide. Similarly, and common elsewhere, the Norwegian graphite deposits in a succession of high metamorphic grade supracrustal rocks, comprising meta-arenites, carbonates and garnet- and pyroxene-bearing gneisses of variable composition. In parts, this succession is migmatized. Two bench-scale ore-dressing trials show that the graphite can be upgraded to market quality. Our work demonstrates a successful approach for locating and evaluating graphite deposits by combining nearly all the methods used in economic geology investigations.

The Relationship between Fe Mineralization and Magnetic Basement Faults using Multifractal Modeling in the Esfordi and Behabad Areas (BMD), Central Iran

AbstractMultifractal modeling is a mathematical method for the separation of a high potential mineralized background from a non‐mineralized background. The Concentration‐Distance to Fault structures (C‐DF) fractal model and the distribution of the known iron (Fe) deposits/mines seen in the Esfordi and Behabad 1:100,000 sheets from the Bafq region of central Iran are used to distinguish Fe mineralization based on their distance to magnetic basement structures and surface faults, separately, using airborne geophysical data and field surveys. Application of the C‐DF fractal model for the classification of Fe mineralizations in the Esfordi and Behabad areas reveals that the main ones show a correlation with their distance from magnetic basement structures. Accordingly, the distances of Fe mineralizations with grades of Fe higher than 55% (43% < Fe ≤ 60%) are located at a distance of less than 1 km, whereas for surfacial faults with grades of 43% ≤ Fe ≤ 60%, the distances are 3162< DF ≤ 4365 m from the faults. Thus, there is a positive relationship between Fe mineralization and magnetic basement structures. Also, the proximity evidence of Precambrian high‐grade Fe mineralization related to magnetic basement structures indicates syn‐rifting tectonic events. Finally, this C‐DF fractal model can be used for exploration of magmatic and hydrothermal ore deposits.

Improving spatial characterization of buried bedrock valleys through airborne frequency-domain electromagnetic, residual magnetic, and surface resistivity measurements

The development of a three-dimensional (3D) hydrogeologic site model requires detailed knowledge of an area's hydrostratigraphy, information typically obtained from core logs, historical well records, outcrop mapping, and/or surface geophysics. Due to the high cost of drilling, a 3D model may rely on various statistical techniques to interpolate lithological boundaries between points located tens of kilometers or more apart. This situation can result in poorly constrained or simplified lithostratigraphic models, with under-sampled features such as karst and buried bedrock valleys. The non-invasive nature of airborne geophysical surveys combined with its dense sampling capability can fill critical data gaps. This study evaluates the capacity of a helicopter borne frequency-domain electromagnetic (FDEM) and residual magnetic survey using the Resolve™ system over a buried bedrock valley incised in a multi-layered dolostone aquifer within a complex glaciated environment in an urban/agricultural region of southern Ontario, Canada. The resulting airborne data was evaluated against two high-resolution ground-based electrical resistivity transects oriented orthogonal to the valley, alongside a published Quaternary geological model. A comparison between our local geophysically-based model and the regional geological model shows that the airborne electromagnetic surveys can markedly improve characterization of bedrock valley morphology and Quaternary sedimentary unit architecture that is comparable to that obtained using high-resolution surface-based electrical resistivity measurements with 10 m electrode spacing. The scale of heterogeneity that can be resolved by the airborne survey reveals the level of petrophysical variability that can be seen within the valley infill. Our study demonstrates the potential of airborne FDEM surveys in semi-urban agricultural environments where detailed characterization of Quaternary sediment architecture and bedrock topography is needed to inform 3D groundwater flow system variability.

Mapped Predictions of Manganese and Arsenicin an Alluvial Aquifer Using Boosted Regression Trees.

Manganese (Mn) concentrations and the probability of arsenic (As) exceeding the drinking‐water standard of 10 μg/L were predicted in the Mississippi River Valley alluvial aquifer (MRVA) using boosted regression trees (BRT). BRT, a type of ensemble‐tree machine‐learning model, were created using predictor variables that affect Mn and As distribution in groundwater. These variables included iron (Fe) concentrations and specific conductance predicted from previously developed BRT models, groundwater flux and age estimates from MODFLOW, and hydrologic characteristics. The models also included results from the first airborne geophysical survey conducted in the United States to target an entire aquifer system. Predictions of high Mn and As occurred where Fe was high. Predicted high Mn concentrations were correlated with fraction of young groundwater (less than 65 years) computed from MODFLOW results. High probabilities of As exceedance were predicted where groundwater was relatively old and airborne electromagnetic resistivity was high, typically proximal to streams. Two‐variable partial‐dependence plots and sensitivity analysis were used to provide insight into the factors controlling Mn and As distribution in groundwater. The maps of predicted Mn concentrations and As exceedance probabilities can be used to identify areas where these constituents may be high, and that could be targeted for further study. This paper shows that incorporation of a selected set of process‐informed data, such as MODFLOW results and airborne geophysics, into a machine‐learning model improves model interpretability. Incorporation of process‐rich information into machine‐learning models will likely be useful for addressing a wide range of problems of interest to groundwater hydrologists.

Nested anisotropic geostatistical gridding of airborne geophysical data

Airborne geophysical surveys routinely collect data along traverse lines at sample spacing distances that are two or more orders of magnitude less than between-line separations. Grids and maps interpolated from such surveys can produce aliasing; features that cross flight lines can exhibit boudinage or string-of-beads artifacts. Boudinage effects can be addressed by novel gridding methods. Following developments in geostatistics, a nonstationary nested anisotropic gridding scheme is proposed that accommodates sampling and data anisotropy in geophysical surveys. Computation is reduced by including anchor points throughout the interpolation region that contain localized anisotropy information that is propagated throughout the survey area with a smoothing kernel. Additional anisotropy can be required at certain locations in the region to be gridded. A model selection scheme is proposed that uses Laplace approximations for determining whether increased model complexity is supported by the surrounding data. The efficacy of the method is shown using a synthetic data set obtained from satellite imagery. A pseudogeophysical survey is created from the image and reconstructed with this method. Two case histories are selected for further elucidation from airborne geophysical surveys conducted in Western Australia (WA). The first example illustrates improvement in gridding the depth of paleochannels interpreted from along-line conductivity-depth models of a regional airborne electromagnetic (AEM) survey in the Mid West WA region. The second example indicates how improvements can be made in producing grids of aeromagnetic data and inverted electrical conductivity from an AEM survey conducted in the Pilbara region. In both case histories, nested anisotropic kriging reduces the expression of boudinage patterns and sharpens crossline features in the final gridded products permitting increased confidence in interpretations based on such products.

Airborne geophysical surveys of the lower Mississippi Valley demonstrate system-scale mapping of subsurface architecture

The Mississippi Alluvial Plain hosts one of the most prolific shallow aquifer systems in the United States but is experiencing chronic groundwater decline. The Reelfoot rift and New Madrid seismic zone underlie the region and represent an important and poorly understood seismic hazard. Despite its societal and economic importance, the shallow subsurface architecture has not been mapped with the spatial resolution needed for effective management. Here, we present airborne electromagnetic, magnetic, and radiometric observations, measured over more than 43,000 flight-line-kilometers, which collectively provide a system-scale snapshot of the entire region. We develop detailed maps of aquifer connectivity and shallow geologic structure, infer relationships between structure and groundwater age, and identify previously unseen paleochannels and shallow fault structures. This dataset demonstrates how regional-scale airborne geophysics can close a scale gap in Earth observation by providing observational data at suitable scales and resolutions to improve our understanding of subsurface structures.

Using self-organizing maps in airborne geophysical data for mapping mafic dyke swarms in NE Brazil

Mapping widespread dyke swarms shed light on the tectonic processes that culminate in continental fragmentation, especially in the early phases of the crustal extension and magma emplacement. Airborne magnetic data are an effective geophysical tool to clarify the extent of dyke swarms in continental-scale areas due to the expressive magnetic contrast between magmatic bodies and host rocks. However, many geological features display similar magnetic patterns, making the qualitative interpretation of magnetic anomaly maps quite subjective and ambiguous. To improve and optimize the predictive mapping of dyke swarms, this research presents a multivariate analysis of airborne geophysical surveys, applying a Self-Organizing Maps (SOM) approach using two magnetic and three gamma-spectrometric variables. This semiautomatic technique has allowed an integrated spatial analysis and the classification of the lithological units based on their magnetic and gamma-spectrometric signatures. We applied the SOM method to investigate a set of mafic dyke swarms that intruded in the Neoproterozoic Borborema Province (BP), Parnaíba Basin (PB) and the São Francisco Craton (SFC) in NE Brazil. These dykes are part of a large magmatic event associated with the continental breakup, which formed the Equatorial Atlantic Ocean in the Early Cretaceous, denominated EQUAMP. First, the SOM hyperparameters were defined by running the algorithm in a representative area in the central part of the BP. This training test area worked as a SOM template through which all data from the area were processed. The SOM analysis identified seven different populations, according to responses found in the five geophysical input variables. Two of these populations were associated with the mafic dykes, reducing the ambiguity of the magnetic anomaly interpretation. These populations represent high SOM quantization error, which means that these groups are the most anomalous data, evidenced in airborne magnetic data. These results were checked during fieldwork, revealing that dyke swarms occur more widely than were previously known, throughout the BP intruding the SFC, and showing some occurrences embedded in the Paleozoic sedimentary infill of the eastern border of the PB.

Mineral Resources Tasmania: Regional airborne geophysical survey completed

The magnetic and radiometric survey on behalf of Mineral Resources Tasmania in collaboration with Geoscience Australia (GA), has now concluded. The contractors demobilised on 2 April, with data pro...