Airborne Geophysical Data Research Articles

Analytical hierarchical prospectivity mapping using integration of exploratory data in the Anarak region, Central Iran

This paper aims to show the kind of corporations, Analytical Hierachy Process (AHP) for determining significant weights of evaluation criteria with Technique for Order Preference by Similarity to Ideal (TOPSIS) and Simple Additive Weighting (SAW) methods for ranking of geo-dataset for Mineral Prospectivity Mapping (MPM) of Cu in Anarak region, Central Iran. This operation was carried out by integration of remote sensing, geophysical, geochemical and geological data. The Anarak region has a high potential for copper mineralization because the studied district is located in the NW of the Central East Iranian Microplate (CEIM) that is an important ore mineralized zone in Central Iran. The integration approaches are complex, Multi-Criteria Decision Making (MCDM), and knowledge-driven methods that they named AHP-TOPSIS and AHP-SAW. In addition, there are three variant models of TOPSIS method including conventional, adjusted and modified. The AHP has been carried out on geological/alteration data, structural data, airborne geophysical data and stream sediment geochemical layer in the studied area. These data are classified by fractal modeling for the generation of geo-dataset layers to a relationship of copper occurrences in the Anarak region. Consequently, the produced MPMs by the AHP-TOPSIS and AHP-SAW have adequately matching and sufficient correlation with copper mines and main copper deposits/occurrences in the Anarak region.

Stream Sediment Datasets and Geophysical Anomalies: A Recipe for Porphyry Copper Systems Identification—The Eastern Papuan Peninsula Experience

Airborne magnetic and radiometric datasets have, over the past few years, become powerful tools in the identification of porphyry systems which may host economic porphyry copper–gold–molybdenum ore bodies. Magnetisation contrasts with the unaltered host rocks, coupled with the elevated radiometric signature, compared to the host rock, makes identification of large-scale porphyry copper systems possible. Integrating these two different datasets with stream sediment data and other geochemical exploration methods results in a higher degree of confidence. Stream sediment data were analysed to see the distribution of copper and gold elements throughout the study area, located within the Eastern Papuan Peninsula of Papua New Guinea. Airborne geophysics data over the same area were also processed for magnetic and radiometric responses. The processing of the magnetic data revealed several magnetic anomalies related to concealed intrusive rock units, with associated radiometric signatures. The distribution of gold and copper anomalism was correlated with the geology and geophysical signatures. Results indicate varying degrees of correlation, with some areas showing a strong correlation between gold/copper occurrence and geophysical signatures, compared to other areas. Some factors that we believe impact the level of correlation may include tectonic history, volcanic cover, and weathering patterns. We recommend caution when applying multi-data exploration for porphyry copper systems.

Hydrogeophysical Characterization in a Volcanic Context From Local to Regional Scales Combining Airborne Electromagnetism and Magnetism

AbstractIn volcanic islands, a crucial step in managing watershed water resources is the characterization of groundwater aquifers from local to regional scales. Airborne geophysical data provide high‐resolution images down to hundreds of meters below the surface, over large areas. Yet, the production of an accurate interpretation of regional geophysical imagery may be time consuming or limited by the low density of geological and hydrological field observations. Here, we propose an approach combining airborne electromagnetic and magnetic data in order to reduce geophysical ambiguities and provide a multiscale hydrogeophysical characterization of Piton des Neiges volcano (Réunion Island). With limited calibration data, this methodology produces a geological model more accurate than using airborne electromagnetic data alone. Through the continuous coverage of both methods, we demonstrate the influence of volcanic unit geometries on groundwater flows within the critical zone and we highlight major structures impacting groundwater flows at both local and regional scales.

The Archean Pavas Block in Uruguay: Extension and tectonic evolution based on LA-ICP-MS U–Pb ages and airborne geophysics

The Pavas Block is an Archean/Paleoproterozoic inlier located in the central segment of Uruguay's Precambrian exposition. A new insight initiated due to the acquisition of airborne geophysical data and new U–Pb zircon dating. The correlation of Archean crustal inliers in the amalgamation of the South American Platform is one of the main objectives in the Precambrian geological investigation. Although Ediacaran lateral strike-slip shear zones controlled the Pavas Block, their ultimate boundaries are not clear. Furthermore, a pre-Neoproterozoic metasedimentary succession discordant on this block is often confused with Neoproterozoic ones. Correctly identifying these limits is a necessary task to modify wrong tectono-stratigraphic models. The airborne total count radiometric imaging and the horizontal derivative of the total magnetic field anomaly reduced to the pole at 1000 m elevation led to establishing the Pavas Block's dimensions, based on new structural interpretation. The filtered magnetic anomaly is concordant with the previous Bouguer anomaly indicating a westward virgation of the Pavas Block in the north. This inlier narrows through the Minas city and along the Sarandí del Yí shear zone. The Sierra de Sosa and Sierra Ballena shear zones were confirmed as lateral limits. The total count radiometric map highlights the presence of brittle-fault reactivation. The Archean La China Complex containing zircons from three periods (~3.3–3.1 Ga; 3.0; 2.8–2.7 Ga) is in the Pavas Block's centre. New U–Pb zircon geochronology provided six samples from different metagranitoids that yielded LA-ICPMS U–Pb zircon ages ranging between 3353 ± 9 Ma and 1839 ± 2 Ma. Its southern periphery shows more recent Archean and Orosirian metagranitoids. These rocks were later partially affected by Neoproterozoic deformation. The preservation of igneous textures, field relationships, and zircon textures suggested that younger Neoarchean intrusive granitoids emplaced within the basal granitic gneiss “La China” complex. The pre-Neoproterozoic metasedimentary cover intercalates with Neoproterozoic successions until the southern end of the Pavas Block against the Sarandí del Yí Shear Zone. Finally, one granitoid devoid of Archean inherited zircons yielded a concordant 207Pb/206Pb zircon age of 1999 ± 3 Ma (MSWD = 8.1) interpreted as magmatic crystallisation. This Orosirian K-feldspar granite is likely to set the southern border of the block in a transitional crust. The Pavas Block is limited from the Villa Serrana Block by a schist belt of Mesoproterozoic protoliths, and reports enough information to be interpreted as a suspect terrane.

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.

An Assessment of Water Sources for Heritage Listed Organic Mound Springs in NW Australia Using Airborne Geophysical (Electromagnetics and Magnetics) and Satellite Remote Sensing Methods

Discrete phreatophytic vegetation associated with organic mound springs is present in several places in the semi-arid Walyarta Conservation Park (Park) in northern Western Australia. The mound springs are heritage listed, having significant cultural and environmental significance. Increased industrial (mining and agriculture) development in the region, coupled with a growing demand for groundwater to support these developments, requires an enhanced understanding of how the springs operate and the source of water that sustains their presence. The springs are broadly believed to be situated on geological faults and receive groundwater from artesian sources. However, their association with deeper geological structures and aquifer systems, the focus of this study, is not well understood. This study employed regional- and finer-scale airborne geophysical data, including electromagnetics (AEM) and magnetics, to constrain the sub-basin-scale hydrogeology of the West Canning Basin in Western Australia and to detail tectonic deformation, sedimentological and hydrological processes. The AEM data were inverted using 1- and 2D methods to better define structural discontinuities in the Park, and the results identified the location of faults and other geological structures that were coincident with spring locations. A complementary analysis of spatiotemporal patterns of green vegetation was undertaken using remote sensing data. A model for the extent of green vegetation (in percent), calculated using a constrained linear spectral unmixing algorithm and applied to a select Landsat Thematic Mapper ™ image archive, showed the persistence of green vegetation aligned with interpreted fault systems through extended dry periods. These geophysical and remotely sensed datasets demonstrate that in the Park, the sedimentary aquifers and landscapes are highly compartmentalized and that this constrains aquifer distribution, groundwater quality and the location of wetlands and phreatophytic vegetation. Integrating key information from these datasets allows for the construction of a three-dimensional model that predicts the nature and extent of the critical zone which sustains perennial groundwater discharge within mound springs, drainages and wetlands and provides a framework to assess discharge rates, mixing and, ultimately, sensitivity to changed water availability.

Global $9.5 bn refinery catalyst market to 2027 by material (zeolites, metallic, chemical compounds), &application (FCC, alkylation, hydrotreating, hydrocracking)

This study presents the air-borne geophysical Gamma Ray Spectrometry data have been used for detecting the alteration zones related to hydrothermal activity. Areas enriched in potassium may indicate the existence of potassic alteration zone that is often associated with hydrothermal alteration accompanied by economic mineral deposits. The radioelements (K (%), eTh (ppm), and eU (ppm)) concentration distribution and the ratios of (K/eTh and K/eU) over the study area were presented. A Potassium Point anomaly map was obtained from the statistical treatment of the K (%), K/eU, and K/eTh spectrometric data. Anomalously High (X+3σ or more) areas were delineated and considered the most preferred areas for potassic alteration. If the maximum values exceed the (X+3σ) threshold, then (X+2σ) or (X+σ) is applied instead. Sixteen areas were delineated and suggested for the presence of potassic alteration. The F-Parameter of Efimov (K*(eU/eTh)) was also implemented as proved approach for delineating the most preferred areas for hydrothermal alteration. The result of the Potassium point anomaly mapping was compared to that of the F-Parameter technique that was used as reference for validating the results. The sixteen anomalous areas revealed from the Potassium point anomaly technique showed perfect correlation with the areas of highly anomalous F-parameter.Remote sensing study supported by field data and laboratory spectral analyses was also implemented in this study as another useful powerful cost-effective approach for alteration mapping. A field study was conducted; samples from the different observed alterations were collected. The spectral signatures of these samples were measured using the “ASD TerraSpec Halo mineral identifier” hand-held spectroradiometer. Spectral analyses were performed to obtain the spectral characteristics of the alteration zones of the study are. The end-members were identified through comparing the measured spectra against the United States Geological Survey (USGS) spectral library in ENVI v.5.1. software. The identified end-members include; Kaolinite, Sericite, Montmorillonite, Chlorite, Epidote and iron oxides. Subpixel Mixture Tuned Matched Filtering (MTMF) mapping technique was finally used for mapping the distribution of these end-members on ASTER nine Visible Near Infra-Red (VNIR) and Short Wave Infra-Red (SWIR) bands. The remote sensing data were validated as Semna gold mine and the identified alterations during the field study were successfully mapped by the remote sensing technique. Finally; Most of the delineated areas using the proposed Potassium point anomaly technique were also evidenced by the approached remote sensing technique. Moreover remote sensing suggested more alteration areas than did the gamma ray spectrometry data.

BASF and Siemens Energy to cooperate in the field of carbon management

This study presents the air-borne geophysical Gamma Ray Spectrometry data have been used for detecting the alteration zones related to hydrothermal activity. Areas enriched in potassium may indicate the existence of potassic alteration zone that is often associated with hydrothermal alteration accompanied by economic mineral deposits. The radioelements (K (%), eTh (ppm), and eU (ppm)) concentration distribution and the ratios of (K/eTh and K/eU) over the study area were presented. A Potassium Point anomaly map was obtained from the statistical treatment of the K (%), K/eU, and K/eTh spectrometric data. Anomalously High (X+3σ or more) areas were delineated and considered the most preferred areas for potassic alteration. If the maximum values exceed the (X+3σ) threshold, then (X+2σ) or (X+σ) is applied instead. Sixteen areas were delineated and suggested for the presence of potassic alteration. The F-Parameter of Efimov (K*(eU/eTh)) was also implemented as proved approach for delineating the most preferred areas for hydrothermal alteration. The result of the Potassium point anomaly mapping was compared to that of the F-Parameter technique that was used as reference for validating the results. The sixteen anomalous areas revealed from the Potassium point anomaly technique showed perfect correlation with the areas of highly anomalous F-parameter.Remote sensing study supported by field data and laboratory spectral analyses was also implemented in this study as another useful powerful cost-effective approach for alteration mapping. A field study was conducted; samples from the different observed alterations were collected. The spectral signatures of these samples were measured using the “ASD TerraSpec Halo mineral identifier” hand-held spectroradiometer. Spectral analyses were performed to obtain the spectral characteristics of the alteration zones of the study are. The end-members were identified through comparing the measured spectra against the United States Geological Survey (USGS) spectral library in ENVI v.5.1. software. The identified end-members include; Kaolinite, Sericite, Montmorillonite, Chlorite, Epidote and iron oxides. Subpixel Mixture Tuned Matched Filtering (MTMF) mapping technique was finally used for mapping the distribution of these end-members on ASTER nine Visible Near Infra-Red (VNIR) and Short Wave Infra-Red (SWIR) bands. The remote sensing data were validated as Semna gold mine and the identified alterations during the field study were successfully mapped by the remote sensing technique. Finally; Most of the delineated areas using the proposed Potassium point anomaly technique were also evidenced by the approached remote sensing technique. Moreover remote sensing suggested more alteration areas than did the gamma ray spectrometry data.

Using air-borne gamma ray spectrometry and remote sensing data for detecting alteration zones around Wadi Saqia area, Central Eastern Desert, Egypt

This study presents the air-borne geophysical Gamma Ray Spectrometry data have been used for detecting the alteration zones related to hydrothermal activity. Areas enriched in potassium may indicate the existence of potassic alteration zone that is often associated with hydrothermal alteration accompanied by economic mineral deposits. The radioelements (K (%), eTh (ppm), and eU (ppm)) concentration distribution and the ratios of (K/eTh and K/eU) over the study area were presented. A Potassium Point anomaly map was obtained from the statistical treatment of the K (%), K/eU, and K/eTh spectrometric data. Anomalously High (X+3σ or more) areas were delineated and considered the most preferred areas for potassic alteration. If the maximum values exceed the (X+3σ) threshold, then (X+2σ) or (X+σ) is applied instead. Sixteen areas were delineated and suggested for the presence of potassic alteration. The F-Parameter of Efimov (K*(eU/eTh)) was also implemented as proved approach for delineating the most preferred areas for hydrothermal alteration. The result of the Potassium point anomaly mapping was compared to that of the F-Parameter technique that was used as reference for validating the results. The sixteen anomalous areas revealed from the Potassium point anomaly technique showed perfect correlation with the areas of highly anomalous F-parameter.Remote sensing study supported by field data and laboratory spectral analyses was also implemented in this study as another useful powerful cost-effective approach for alteration mapping. A field study was conducted; samples from the different observed alterations were collected. The spectral signatures of these samples were measured using the “ASD TerraSpec Halo mineral identifier” hand-held spectroradiometer. Spectral analyses were performed to obtain the spectral characteristics of the alteration zones of the study are. The end-members were identified through comparing the measured spectra against the United States Geological Survey (USGS) spectral library in ENVI v.5.1. software. The identified end-members include; Kaolinite, Sericite, Montmorillonite, Chlorite, Epidote and iron oxides. Subpixel Mixture Tuned Matched Filtering (MTMF) mapping technique was finally used for mapping the distribution of these end-members on ASTER nine Visible Near Infra-Red (VNIR) and Short Wave Infra-Red (SWIR) bands. The remote sensing data were validated as Semna gold mine and the identified alterations during the field study were successfully mapped by the remote sensing technique. Finally; Most of the delineated areas using the proposed Potassium point anomaly technique were also evidenced by the approached remote sensing technique. Moreover remote sensing suggested more alteration areas than did the gamma ray spectrometry data.

The approach to construction and discretization of complex 3D models of geological media in software for airborne geophysical surveys maintenance

The paper presents a new approach to construction of complex geological models and generation of finite element meshes in order to perform 3D modeling and multidimensional processing of airborne geophysical data. The main principles of geological models construction are considered. They are based on defining geological models in terms of the subject field and take into account their main specifics: complex background media, curvilinear Earth surface relief and borders between the geological layers, complex shape of target objects, etc. We consider the necessary data structures and specifics of finite element mesh generation. The example of generation of the finite element mesh for a geological model typical of airborne geophysical surveys is shown.

Airborne geophysical data levelling based on variational mode decomposition

ABSTRACTA new technique is proposed to level airborne geophysical data based on the assumption that the level errors along the flight‐line direction have a distinguishable centre frequency. In the levelling method, airborne geophysical data from the entire survey area are corrected automatically after sorting the data into a group according to the measurement order. Variational mode decomposition is applied to the profile data to adaptively extract the level‐error component with distinct spectral bands. In airborne geophysical surveys, data in the anomalous region show visible peaks with strong gradients along the flight‐line direction, which would impact the decomposition. To minimize their effect on variational mode decomposition, the higher amplitude anomalies are grouped and discarded by K‐means clustering to obtain the real data level. The levelling method extracts the level errors of the entire survey area simultaneously, thus avoiding the regional error caused by strong noise, missing data or error transfer in the common levelling process. Moreover, the approach is automatic and applicable to both irregular and regular line patterns without the participation of staff members or tie‐line control. The levelling method may require much time when decomposition is performed on the extended survey area. We have applied the method to the airborne electromagnetic and magnetic data acquired by Geotech Limited to confirm its validity and have compared the obtained results with those based on the flight‐line correlation levelling algorithm.

Updated map of the mafic dike swarms of Brazil based on airborne geophysical data

Identification of mafic dike swarms and LIPs (Large Igneous Provinces) are of vital importance in geologic history because they provide information on geodynamics, mantle geochemistry, and paleomagnetism. These data provide key information for paleogeographic reconstructions with the aid of barcode matches and precise radiometric ages. Considering such issues, the Brazilian Precambrian shield can be used as a case for refining the cartography of the relevant intraplate activity (e.g., dikes, sills, flood basalts) in space and time.This work presents an updated map of Brazilian mafic dike swarms produced from airborne geophysical maps (Series 1000 – Geological Survey of Brazil). Linear and strong anomalies found on aeromagnetic maps using First Vertical Derivative of the Magnetic Field and Amplitude of the Analytic Signal were mapped on a GIS platform. The obtained data were compared to ternary radiometric maps and geological maps in order to exclude those that do not correspond to mafic dikes. The remaining structures - those believed to represent mafic dikes - were classified based on data compiled from the literature.The updated map exhibits more than 5000 elements, including dikes and magmatic suites, in which about 75% were geologically identified and divided into 60 dike swarms and 10 igneous suites and/or units. The dikes were grouped into sixteen extensional episodes from the Archean to the Cenozoic, although some are related to extension/transtension domains within regional compressive zones akin to orogenic settings. The most frequent records refer to the Proterozoic, representing intraplate episodes, some of them consistent with LIPs. The dataset also includes a large record of the Mesozoic age, which corresponds to major LIP events related to the opening of the Atlantic Ocean and the fragmentation of Gondwana.

Shortening history of the Neoproterozoic oroclinal bending in Paraguay belt, Central Brazil, based on structural interpretation of field work and high resolution aerogeophysical data

Different phases of the orogen's evolutionary history can be geometrically restored by identifying associated tectonic features in the thrust-and-fold belts in the foreland basin. The geometry and fold styles allow understanding the rate of crustal shortening of the Paraguay Belt Neoproterozoic oroclinal. We suggest that high resolution airborne geophysical data provides critical information to understand the tectonic history of Brasiliano fold belts. Geophysical studies integrated to structural analysis in field mapping may unveil the crustal architecture as well as the sequence of events of rocks exposed in two structural windows of the basement in the region of Planalto da Serra and Nova Xavantina, in the state of Mato Grosso, northern segment of the Paraguay Belt, Central Brazil.The evolutive history of rocks exposed southwards of the Amazonian craton margin represents extensional tectonics followed by the development of a passive margin. It is estimated that the original width of the depositional space was ~350 km during the formation of the hyperextended platform and, after the intense shortening during the Brasiliano orogenesis, the oroclinal was restricted to ~130 km wide, in the post-deformation phase. Planalto da Serra region is characterized by asymmetrical, harmonic folds with thickened hinge zones. They show variable styles between tight and isoclinal and form pairs of EW and NE anticlines and synclines. In Nova Xavantina structural window, the magnetic lineaments mark important lithospheric discontinuities represented by the Campinápolis (CAL) and General Carneiro (GCL) lineaments, which seem to be the deep basement faults that controlled the extension and where the rift axial zone developed. The Transbrasiliano Lineament (TBL) is a major shear zone that controls the secondary lineaments propagation, forming a network of folds and drag faults, with lateral escapes and vertical movement. Between the two main lineaments occurred the deposition of sediments and volcanic successions related to Nova Xavantina Metavolcanosedimentary Sequence representing a marginal ocean basin. The transition from EW trending features of the Paraguay Belt to NE trend Araguaia Belt lies within Nova Xavantina region and is marked by the direct influence of TBL. TBL is evident in the magnetic images, forming a mosaic of different crustal blocks and corresponding to various curvilinear shear zones with unidirectional trend N30-45E. It is composed of mega-sigmoids interlaced with mainly dextral kinematics, within shallow and deep levels.During the Neoproterozoic orogeny, a foreland basin system was formed in response to the flexural subsidence due to the tectonic inversion of the basin. Several depocenters were formed and served as accumulation sites for the deposition of sediments of the Alto Paraguay Group (Raizama, Sepotuba and Diamantino formations). Gravimetric data allowed individualization of the foreland basin system, which is characterized by four discrete depozones (back-bulge, forebulge, foredeep and wedge-top), between the Amazonian Craton and the inner structural zone.

The elemental potential study based on modern methods of geochemical and airborne geophysical data in Lahrud 1:100,000 sheet, NW Iran

هدف از این پژوهش، شناسایی ناهنجاری­های عنصری با استفاده از ترکیب مدل فرکتالی1 (فرکتال، ساختاری هندسی است که با بزرگ کردن هر بخش از این ساختار به­نسبت معین، همان ساختار نخستین به­ دست آید؛ به ­بیان دیگر، فرکتال ساختاری است که هر بخش از آن با کل­ آن همانند است. فرکتال در بسیاری از ساختارهای طبیعی مثل سنگ­ها، برف، رسوب­گذاری، برگ و تنه درختان، DNA و غیره دیده می­شود. هندسه فرکتال یا هندسه بعد چهارم یا هندسه طبیعت در تضاد کامل با هندسه اقلیدسی بعدهای اول تا سوم می­باشد. درواقع هندسه فرکتال تعریفی از نظریه بی­نظمی یا آشوب است). عیار-تعداد و آنالیز فاکتوری مرحله­ای نمونه­های رسوبات آبراهه­ای با داده­های ژئوفیزیک هوابرد برگه 1:100،000 لاهرود بود. منطقه مورد مطالعه در نوار آتش­فشانی البرز-آذربایجان واقع است. تمام عناصر اخلال کننده (مولیبدن، برلیوم، جیوه، سرب، نقره، استرانسیوم، سلنیوم و بیسموت) پس از اعمال چهار مرحله آنالیز فاکتوری حذف شدند و عناصر ارسنیک، آنتیموان، قلع، تنگستن، کبالت، منگنز، روی، تیتانیوم، باریوم، نیکل، کروم، طلا، مس و بور در پنج گروه طبقه­بندی شدند؛ مس و طلا در گروه چهار از مرحله چهارم قرار گرفتند. نمودار عیار-تعداد امتیازهای فاکتوری ترسیم و مقادیر آن­ها به­منظور تهیه نقشه­های جوامع ژئوشیمیایی، تعیین شد. مناطق ناهنجار عناصر فلزی در بخش­های شمال­غرب، مرکز و جنوب­غرب منطقه قرار دارند که نشان­دهنده هم­بستگی با مناطق دگرسان شده، گسل­ها و توده­های نفوذی می­باشد. با استفاده از داده­های ژئوفیزیک هوایی و تهیه نقشه­های مربوط به آن، توده ژرف­سنگ در جنوب­غربی، که توجیه کننده دگرسانی­ها و در نتیجه، ناهنجاری­هاست و هم­چنین مناطق قابل پی­جویی منطقه لاهرود شناسایی شد.

Geophysical-structural framework of the Campo Alegre basin (Santa Catarina State, southern Brazil)

Numerous syn- to post-collisional basins originated as a response to crust stabilization processes after the collisions between Apiaí, Curitiba and Luis Alves Cratons during the Neoproterozoic in Brazil. The late Neoproterozoic Campo Alegre Basin represents one of these so called transitional-stage basin in the southern Brazil. The structural record of this basin is an important clue for understanding the regional geological development after the Western Gondwana supercontinent agglutination. An integrated study of airborne geophysical data, ground gravimetry and structural analysis of the basin and its basement outlined its magnetic-structural framework and its tectonic evolution. Thus, it was possible to present a basin 3-event tectonic evolution history. The first event (E1) is marked by WNW and ENE normal faults as a response to conjugated extension stress fields (σ3 and σ2). The normal faults generated in (E1) conditioned the deposition of the coarse-grained basal deposits close to basin borders. A second event (E2) was recognized through EW normal faults and ENE-WSW right-lateral strike-slip faults on basin intermediate formations. Hydrothermalism from volcanism final fluids is associated with these faults, especially on the south portion. The last tectonic event (E3) that affected basin rocks is characterized by the reactivation of E1 normal faults as inverse and occurred in Mesozoic Era associated with South Atlantic Ocean opening. This event is also marked by NNW e EW strike-slips faults. Besides the gravimetric model and the magnetic interpretation, field data allow us to conclude that the nucleation of Campo Alegre Basin began as a conjugated rift system.

From Mesoarchean drips to modern–style tectonics in the Carajás Province, Amazonian Craton

The beginning of modern–style plate tectonics on Earth is not a consensus, but many authors suggest that it happened transitionally, from 3.2 to 2.5 Ga. In the Amazonian Craton, Brazil, the contrasting crustal architecture of the Rio Maria and the Carajás domains is marked by dome–and–keel and linear belt, respectively, which may represent a shift in the tectonic styles along the Mesoarchean to Neoarchean transition. Here, we discuss this hypothesis combining existing literature and an interpretation of airborne geophysical data for the Caracol Dome. This Archean TTG (Trondhjemite–Tonalite–Granodiorite) Dome shows a concentric lithological variation, with older 2.97–2.96 Ga trondhjemites at the edges and younger 2.95–2.92 Ga tonalites within the inner parts. The Caracol Dome exhibits a similar magmatic evolution to other Archean domes worldwide (e.g., Yalgoo and Mt. Edgar Domes), commonly interpreted as the record of vertical tectonics (e.g., drip–tectonics). However, the subsequent geological record in the Carajás Province is more likely related to the onset or transition to modern–style tectonics, such as large continental shelf sedimentation (Carajás Basin), steeply dipping linear shear zones with 2.76–2.73 Ga syn–tectonic intrusions and Neoarchean iron oxide–copper–gold (IOCG) mineralization. Finally, late Neoarchean to Paleoproterozoic tectonic events with new (and/or remobilized) IOCG deposits are also recorded in the Carajás Province.

Identification of impact cratering-related similarities based on airborne geophysical data and satellite images: the Cabeça de Sapo Structure, Parnaíba Basin, Northeast Brazil

This study was performed to identify and interpret airborne geophysical responses and landform features of the Cabeca de Sapo Structure (CSS), a 6 km-diameter circular structure located in northeastern Brazil, SW of the Maranhao State, suspected of having been formed by the impact of a solid body. The application of processing techniques addressed to enhance the images from the remotely sensed data (gamma-ray spectrometry, magnetic, Sentinel 2B and ALOS PALSAR) enabled the identification of two airborne geophysical responses (ring-shaped magnetic anomaly and radiometric patterns) and five landform features (A, B, C,D and E). The ring-shaped magnetic anomaly is related to a 5.4 km-diameter well-defined circular structure and the depth of its magnetic sources is estimated in 300 m. Those sources are unknown, but they probably occur due to layers of dolerite sills. The radiometric patterns identified seem to be related to the A and D landform features. Feature A is an elevated area at the center of CSS. The radiometric response (high eTh, eU, and low K) at the top of this area possibly reflects the weathering effect, while the radiometric response (high K and low eTh, eU) at the hillside is possibly from the lithotypes that have supported this elevation. Feature “D” is a 6 km – diameter circular elevated area that corresponds to the outer boundary of CSS. This boundary is characterized by increased eU counts, which may happen due to weathering-resistant mineral content (e.g. zircon) present in eolian sandstones. Features “C” and “E” are outside of CSS. The first is interpreted as plateau-shaped residual relief formed by differential erosion of basaltic rocks and sandstones and the second is interpreted as a flat-relief dominated by eolian sandstones. This flat-relief may represent the landscape that has not been affected by the formation process of CSS, while the affected internal region may be represented by feature “B”. The interpretations also have revealed that CSS shows some similarities with typical features of impact structures, namely: disruption of the magnetic field by a ring-shaped magnetic anomaly; central elevation surrounded by a raised outer rim; local control of drainage and; differences in the relief pattern of internal and external parts of the structure. Those similarities reinforce the possibility of an exogenous origin of CSS, but new studies are required to confirm or refuse such possibility.

Unveiling the 3D undercover structure of a Precambrian intrusive complex by integrating airborne magnetic and gravity gradient data into 3D quasi-geology model building

Mineral exploration under a thick sedimentary cover naturally relies on geophysical methods. We have used high-resolution airborne magnetic and gravity gradient data over northeast Iowa to characterize the geology of the concealed Precambrian rocks and evaluate the prospectivity of mineral deposits. Previous researchers have interpreted the magnetic and gravity gradient data in the form of a 2D geologic map of the Precambrian basement rocks, which provides important geophysical constraints on the geologic history and mineral potentials over the Decorah area located in the northeast of Iowa. However, their interpretations are based on 2D data maps and are limited to the two horizontal dimensions. To fully tap into the rich information contained in the high-resolution airborne geophysical data, and to further our understanding of the undercover geology, we have performed separate and joint inversions of magnetic and gravity gradient data to obtain 3D density contrast models and 3D susceptibility models, based on which we carried out geology differentiation. Based on separately inverted physical property values, we have identified 10 geologic units and their spatial distributions in 3D which are all summarized in a 3D quasi-geology model. The extension of 2D geologic interpretation to 3D allows for the discovery of four previously unidentified geologic units, a more detailed classification of the Yavapai country rock, and the identification of the highly anomalous core of the mafic intrusions. Joint inversion allows for the classification of a few geologic units further into several subclasses. We have demonstrated the added value of the construction of a 3D quasi-geology model based on 3D separate and joint inversions.

Characterization of a fractured aquifer through potential geophysics and physicochemical parameters of groundwater samples

The heterogeneity of fractured and karstic aquifers is generally ignored, and not having an understanding of the hydrogeological evolution and functioning of these could potentially result in wrong water resource management practices. The geophysical methods are useful tools for hydrogeological investigations, helping in the detection of porosity and permeability zones in the subsoil that are important properties in the aquifer characterization. The combination of these with the measurement in situ of the physicochemical parameters of the groundwater can offer a detailed knowledge of the aquifer system. The study was conducted in the municipality of Tula, Tamaulipas, Mexico, where airborne geophysical data were analyzed. Then, 17 groundwater sampling points were established to measure physicochemical parameters (pH, Electric Conductivity and REDOX) and ionic concentration, to associate structures with zones of recharge, transport or storage of groundwater. It was found that the area with the greatest potential for groundwater recharge is located at the N and NW of the study area, with structures trending N–S and NE–SW, which favor the flow of groundwater to the convergence zone, located to the S of the study area. Also, near to the convergence zona, a fracture system with perpendicular direction to the groundwater flow acts as a barrier and divides the aquifer. Due to the chemistry characteristics of the groundwater, it was concluded that the main contribution of groundwater is through structures crossing evaporite rocks of the Guaxcama Formation.

Mount Milligan alkalic porphyry Au--Cu deposit, British Columbia, Canada, and its AEM and AIP signatures: Implications for mineral exploration in covered terrains

Although alkalic porphyry Au--Cu deposits are much less common than their calc-alkalic counterparts, they represent attractive exploration targets both due to their occurrence as, locally concealed, clusters and their high Au contents. In this paper, the geology of the Mt. Milligan Au--Cu deposit, Canada, and its geophysical footprint on magnetic and AEM data is used as a case-study for the exploration and discovery of concealed alkalic porphyry Au--Cu deposits.The Cole-Cole parameters in the AEM data are extracted using an improved Airborne Induced Polarization (AIP) mapping algorithm. We propose that the subtle electromagnetic signatures of disseminated sulfides around the intrusive porphyry stocks at Mt. Milligan could be mapped by the mτ product, where m is AIP apparent chargeability, and τ the Cole-Cole time-constant, provided that the depths of the alteration zone does not exceed 75 m. The product is called Tau-Scaled Chargeability or TSC.In order to improve the exploration success in the search for concealed alkalic porphyry Au--Cu deposits, we propose to: (1) concentrate the exploration on known and well-endowed mineral districts; and (2) apply innovative digital data-processing techniques capable of extracting weak and subtle signatures from airborne geophysical data and, subsequently, to utilize DCIP ground surveys in the follow-up of anomalies, ideally in combination with enzyme-leach soil sampling.