scholarly journals Drone-based magnetic and multispectral surveys to develop a 3D model for mineral exploration at Qullissat, Disko Island, Greenland

2021 ◽  
Author(s):  
Robert Jackisch ◽  
Björn Henning Heincke ◽  
Robert Zimmermann ◽  
Erik Vest Sørensen ◽  
Markku Pirttijärvi ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
High Resolution ◽  
3D Model ◽  
Mineral Exploration ◽  
Magnetization Vector ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Constant Thickness ◽  
Magmatic Body ◽  
Wide Range

Abstract. Mineral exploration in the West Greenland flood basalt province is attractive because of its resemblance to the magmatic sulphide-rich deposit in the Russian Norilsk region, but it is challenged by rugged topography and partly poor exposure for relevant geologic formations. On northern Disko Island, previous exploration efforts have identified rare native iron occurrences and a high potential for Ni-Cu-Co-PGE-Au mineralization. However, Quaternary landslide activity has obliterated rock exposure at many places at lower elevations. To augment prospecting field work under these challenging conditions, we acquire high-resolution magnetic and optical remote sensing data using drones in the Qullissat area. From the data, we generate a detailed 3D model of a mineralized basalt unit, belonging to the Asuk Member (Mb) of the Palaeocene Vaigat formation. A wide range of legacy data and newly acquired geo- and petrophysical, as well as geochemical-mineralogical measurements form the basis of an integrated geological interpretation of the unoccupied aerial system (UAS) surveys. In this context, magnetic data aims to define the location and the shape of the buried magmatic body, and to estimate if its magnetic properties are indicative for mineralization. High-resolution UAS-based multispectral orthomosaics are used to identify surficial iron staining, which serve as a proxy for outcropping sulphide mineralization. In addition, high-resolution UAS-based digital surface models are created for geomorphological characterisation of the landscape to accurately reveal landslide features. UAS-based magnetic data suggests that the targeted magmatic unit is characterized by a pattern of distinct positive and negative magnetic anomalies. We apply a 3D magnetization vector inversion model (MVI) on the UAS-based magnetic data to estimate the magnetic properties and shape of the magmatic body. By means of using constraints in the inversion, (1) optical UAS-based data and legacy drill cores are used to assign significant magnetic properties to areas that are associated with the mineralized Asuk Mb, and (2) the Earth’s magnetic and the paleomagnetic field directions are used to evaluate the general magnetization direction in the magmatic units. Our results indicate that the geometry of the mineralized target can be estimated as a horizontal sheet of constant thickness, and that the magnetization of the unit has a strong remanent component formed during a period of Earth’s magnetic field reversal. The magnetization values obtained in the MVI are in a similar range as the measured ones from a drillcore intersecting the targeted unit. Both the magnetics and topography confirm that parts of the target unit were displaced by landslides. We identified several fully detached and presumably rotated blocks in the obtained model. The model highlights magnetic anomalies that correspond to zones of mineralization and is used to identify outcrops for sampling. Our study demonstrates the potential and efficiency of using multi-sensor high-resolution UAS data to constrain the geometry of partially exposed geological units and assist exploration targeting in difficult, poorly exposed terrain.

Magnetization vector imaging for borehole magnetic data based on magnitude magnetic anomaly

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. D429-D444 ◽  
Author(s):  
Shuang Liu ◽  
Xiangyun Hu ◽  
Tianyou Liu ◽  
Jie Feng ◽  
Wenli Gao ◽  
...  
Keyword(s):  
Conjugate Gradient Method ◽  
Conjugate Gradient ◽  
Gradient Method ◽  
Magnetization Vector ◽  
Real Data ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Preconditioned Conjugate Gradient ◽  
Magnetization Direction ◽  
Magnetization Intensity

Remanent magnetization and self-demagnetization change the magnitude and direction of the magnetization vector, which complicates the interpretation of magnetic data. To deal with this problem, we evaluated a method for inverting the distributions of 2D magnetization vector or effective susceptibility using 3C borehole magnetic data. The basis for this method is the fact that 2D magnitude magnetic anomalies are not sensitive to the magnetization direction. We calculated magnitude anomalies from the measured borehole magnetic data in a spatial domain. The vector distributions of magnetization were inverted methodically in two steps. The distributions of magnetization magnitude were initially solved based on magnitude magnetic anomalies using the preconditioned conjugate gradient method. The preconditioner determined by the distances between the cells and the borehole observation points greatly improved the quality of the magnetization magnitude imaging. With the calculated magnetization magnitude, the distributions of magnetization direction were computed by fitting the component anomalies secondly using the conjugate gradient method. The two-step approach made full use of the amplitude and phase anomalies of the borehole magnetic data. We studied the influence of remanence and demagnetization based on the recovered magnetization intensity and direction distributions. Finally, we tested our method using synthetic and real data from scenarios that involved high susceptibility and complicated remanence, and all tests returned favorable results.

Comprehensive approaches to 3D inversion of magnetic data affected by remanent magnetization

Geophysics ◽  
2010 ◽  
Vol 75 (1) ◽  
pp. L1-L11 ◽  
Author(s):  
Yaoguo Li ◽  
Sarah E. Shearer ◽  
Matthew M. Haney ◽  
Neal Dannemiller
Keyword(s):  
Mineral Exploration ◽  
Three Dimensional ◽  
Canadian Arctic ◽  
Magnetization Vector ◽  
Magnetic Data ◽  
Inversion Algorithm ◽  
3D Inversion ◽  
Magnetization Direction ◽  
Direct Inversion ◽  
Amplitude Data

Three-dimensional (3D) inversion of magnetic data to recover a distribution of magnetic susceptibility has been successfully used for mineral exploration during the last decade. However, the unknown direction of magnetization has limited the use of this technique when significant remanence is present. We have developed a comprehensive methodology for solving this problem by examining two classes of approaches and have formulated a suite of methods of practical utility. The first class focuses on estimating total magnetization direction and then incorporating the resultant direction into an inversion algorithm that assumes a known direction. The second class focuses on direct inversion of the amplitude of the magnetic anomaly vector. Amplitude data depend weakly upon magnetization direction and are amenable to direct inversion for the magnitude of magnetization vector in 3D subsurface. Two sets of high-resolution aeromagnetic data acquired for diamond exploration in the Canadian Arctic are used to illustrate the methods’ usefulness.

Assessing and ameliorating edge effects in magnetic data transformations

2020 ◽  
Author(s):  
Peter Lelièvre ◽  
Dominique Fournier ◽  
Sean Walker ◽  
Nicholas Williams ◽  
Colin Farquharson
Keyword(s):  
Edge Effects ◽  
Mineral Exploration ◽  
Magnetization Vector ◽  
Magnetic Data ◽  
Separation Procedure ◽  
Magnetic Intensity ◽  
Source Inversion ◽  
Total Field ◽  
Equivalent Source ◽  
Amplitude Data

<p>Reduction to pole and other transformations of total field magnetic intensity data are often challenging to perform at low magnetic latitudes, when remanence exists, and when large topographic relief exists. Several studies have suggested use of inversion-based equivalent source methods for performing such transformations under those complicating factors. However, there has been little assessment of the importance of erroneous edge effects that occur when fundamental assumptions underlying the transformation procedures are broken. In this work we propose a transformation procedure that utilizes magnetization vector inversion, inversion-based regional field separation, and equivalent source inversion on unstructured meshes. We investigated whether edge effects in transformations could be reduced by performing a regional separation procedure prior to equivalent source inversion. We applied our proposed procedure to the transformation of total field magnetic intensity to magnetic amplitude data, using a complicated synthetic example based on a real geological scenario from mineral exploration. While the procedure performed acceptably on this test example, the results could be improved. We pose many questions regarding the various choices and control parameters used throughout the procedure, but we leave the investigation of those questions to future work.</p>

Ultra-lightweight integrated unmanned aerial systems for a wide range of geophysical magnetic exploration: a single system for high-precision archaeological surveys to rugged topography geological acquisitions

2021 ◽  
Author(s):  
Jeanne Mercier de Lépinay ◽  
Tristan Fréville ◽  
Baptiste Kiemes ◽  
Luis Miguel Sanabria ◽  
Bruno Gavazzi ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
High Precision ◽  
Adaptive Systems ◽  
Magnetic Measurements ◽  
Magnetic Sensor ◽  
Magnetic Data ◽  
Industrial Sectors ◽  
Wide Range ◽  
The Magnetic Field

<p>Magnetic mapping is commonly used in the academic and industrial sectors for a wide variety of objectives. To comply with a broad range of survey designs, the use of unmanned aerial vehicles (UAVs) has become frequent over the recent years. The majority of existing systems involves a magnetic acquisition equipment and its carrier (an UAV in this context) with no -or very few- connections between the two systems. Terremys is conceiving and optimizing UAVs specifically adapted for geophysical magnetic acquisitions together with the appropriate processing tools, and performs magnetic surveying in challenging environments. Terremys’ “Q6” system weights 2.5 kg in air, including UAV & instrumentation, and allows 30 min swarm or individual flights.</p><p>Rotary-wing UAVs are found to be the most adaptive systems for a wide range of contexts and constraints (extensive range of flights heights even with steep slopes). They offer more flight flexibility than fixed-wing aircrafts. One of the major problems in the use of rotary-wings UAVs for magnetic mapping is the magnetic field generated by the aircraft itself on the measurements. Towing the magnetic sensor 2 to 5 m under the aircraft reduces data positioning accuracy and decreases the performances of the UAV, which can be critical for high-resolution surveys. To overcome these problems, a deployable 1 m long boom is rigidly attached to the UAV. The UAV magnetic signal can be divided between 1-the magnetic field of the whole equipment and 2-a low to high frequency magnetic field mostly originating from the motors. The magnetization of the system is the principal source of magnetic noise. It is modelled and corrected by calibration-compensation processes permitted by the use of three-component fluxgate magnetometers. The time-varying noise depends on the motors rotational speed and is minimized by optimizing the UAV components and characteristics along with the boom’s length.</p><p>The final set-up is able to acquire magnetic data with a precision of 1 to 5 nT at any height from 1 to 150 m above ground level. The high-precision magnetic measurements are coupled with a centimetric RTK navigation system to allow for high-resolution surveying. The quality of the obtained data is similar to that obtained with ground or aerial surveys with conventional carriers and matches industrial standards. Moreover, Terremys’ systems merge in real-time data from all the aircraft instruments in order to integrate magnetic measurements, positioning information and all the UAV’s flight data (full telemetry) into a unique synchronized data file. This opens up many possibilities in terms of QA/QC, data processing and facilitates on-field workflows.</p><p>Case studies with diverse designs, flight altitudes and targets are presented to investigate the acquisition performances for different applications, as distinct as network positioning, archaeological prospecting or geological mapping.</p><p>The full integration of the magnetic sensor to the drone opens the possibility for implementation additional sensors to the system. The adjoining of other magnetic sensors would allow multi-sensors surveying and increases daily productivity. Diverse geophysical sensors can also be added, such as thermal/infrared cameras, spectrometers, radar/SAR.</p>

SPECTRAL ANALYSIS OF TOTAL MAGNETIC ANOMALIES OF STEP MODEL

Geophysics ◽  
1978 ◽  
Vol 43 (3) ◽  
pp. 634-636 ◽  
Author(s):  
M. V. Ramanaiah Chowdary
Keyword(s):  
Magnetic Properties ◽  
Spectral Analysis ◽  
Frequency Analysis ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Model Parameters ◽  
Considerable Success ◽  
Step Model ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Data

A great deal of interest has been shown in the frequency analysis of gravity and magnetic data originally suggested by Dean (1958). The application of this method for potential field problems has met with considerable success. The purpose of this note is to show that the interpretation of total magnetic anomalies due to a sloping step model, which represents a contact between zones having different magnetic properties in terms of model parameters, is less complicated in the frequency domain than in the spatial domain.

Mineral sources of magnetic anomalies: Insights from scanning magnetic microscopy

2020 ◽  
Author(s):  
Suzanne McEnroe ◽  
Zeudia Pastore ◽  
Nathan Church ◽  
Falko Langenhorst ◽  
Hirokuni Oda
Keyword(s):  
Thin Section ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Mapping Technique ◽  
Small Scale ◽  
Rock Samples ◽  
Mineral Phases ◽  
Natural Rock ◽  
Wide Range ◽  
Magnetic Microscopy

<p>Development in instrumentation and technology now allows for mapping of magnetic anomalies, caused by spatial variations in magnetization in the source materials, over a wide range of scales, from the millimeter mineral scale to the km crustal scale.</p><p>Traditional rock magnetic methods, used to investigate the magnetization in natural rock samples, are bulk measurements, which cannot be directly correlated to the individual mineral phases, or particles.  Scanning magnetic microscopy is a high-resolution mapping technique that allows for detailed investigation of the magnetization in natural rock samples. The technique generates a map of the magnetic field distribution over a planar surface of a rock sample with sub-millimeter resolution that can be used to correlate specific magnetic signals to the underlying mineralogy. This information is vital for an understanding of the origin of rock bulk behavior measured in both the laboratory, and in magnetic surveys.</p><p>Here we use 3D magnetic modeling to investigate the sources of the magnetic anomalies mapped over a sample thin section. The oxide grains in the thin sections are modeled using information from optical and electron microscopy (SEM and TEM) to constrain the source geometry, and with magnetic property data. The internal geometry of the oxide mineral phases (exsolution lamellae, intergrowths, symplectites) and compositions are constrained by EMP and TEM. </p><p>Magnetic scans aid in locating the magnetic sources, and resolving the different magnetic components contributing to the bulk rock properties.  By modeling the small-scale variations in the oxides the direction and intensity of the magnetic grains are determined.  Aeromagnetic and ground magnetic data from the sample locations are used in conjunction with thin section magnetic mapping. Thin section results can be up-scaled to compare with ground and aeromagnetic data.</p>

A paradigm shift in magnetic data interpretation: Increased value through magnetization inversions

2021 ◽  
Vol 40 (2) ◽  
pp. 89-98
Author(s):  
Yaoguo Li ◽  
Jiajia Sun ◽  
Shu-Ling Li ◽  
Marcelo Leão-Santos
Keyword(s):  
Paradigm Shift ◽  
Remanent Magnetization ◽  
Mineral Content ◽  
Mineral Exploration ◽  
Magnetization Vector ◽  
Data Interpretation ◽  
Magnetic Data ◽  
Data Set ◽  
Total Magnetization ◽  
Informational Value

Magnetic data are sensitive to both the induced magnetization in rock units caused by the present earth's magnetic field and the remanent magnetization acquired by rock units in past geologic time. Susceptibility is a direct indicator of the magnetic mineral content, whereas remanent magnetization carries information about the formation process and subsequent structural movement of geologic units. The ability to recover and use total magnetization, defined as the vectorial sum of the induced and remanent magnetization, therefore enables us to take full advantage of magnetic data. The exploration geophysics community has achieved significant advances in inverting magnetic data affected by remanent magnetization. It is now feasible to invert any magnetic data set for total magnetization. We provide an overview of the state of the art in magnetization inversion and demonstrate the informational value of inverted magnetization through a set of case studies from mineral exploration problems. We focus on the methods that recover either the magnitude of the total magnetization or the total magnetization vector itself.

Neotectonics and landscape characterization in the Gawler Craton, South Australia - Insights through high-resolution remote sensing

2020 ◽  
Author(s):  
Cericia Martinez ◽  
Ulrich Kelka ◽  
Ignacio Gonzalez-Alvarez ◽  
Carmen Krapf
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Mineral Exploration ◽  
Gravity Data ◽  
South Australia ◽  
Magnetic Data ◽  
Surface Features ◽  
Mineral Potential ◽  
Landscape Characterization ◽  
Digital Elevation

<p>The Gawler Craton hosts significant economic mineralization within South Australia. Due to limited outcrops, deeply weathered profiles, and the absence of a clear variety of landscape surface features, mineral exploration is particularly challenging in this part of Australia. Here we present a workflow of data processing and interpretation to understand the neotectonics and landscape characterization of this region. We explore the potential to delineate surface lineaments and features from newly acquired high-resolution datasets. We aim to automatically identify landform domains based on the analysed data and investigate whether deep seated tectonic lineaments manifest in recognizable surface expressions.</p><p>The data we analyse in this study comprises digital elevation, radiometric, magnetic, and gravity data. We assume that elevation and radiometric data relate to surficial landscape features, whereas gravity and magnetic data represent subsurface basement features. Linking the analysis of both surface and subsurface datasets can potentially yield information on the neotectonic activity, and the association between landforms and basement structures as potential zones of fluid migration. We will show how processed digital elevation data can be used for automatic classification of different landform domains.</p><p>In order to assess mineral potential zones in the area, we compare the generated lineament data in terms of their geometric and topological properties to examine whether there is consistency in the subsurface and surface layers. We postulate that through a line density map, we may be able to quantify a potential relationship between lineaments that are representative in both the surface and subsurface, indicating potential faults or large-scale lineament trends that may link mineral systems in the basement with the landscape surface features. Areas that exhibit large numbers of surface and subsurface lineaments might be areas of enhanced mineral potential. This study contributes to enhance the efficiency of mineral exploration protocols in areas under cover.</p>

scholarly journals Application of the Euler deconvolution 2D and 3D at the Pari syncline, internal area of the Paraguay Belt, Mato Grosso, Brazil

2021 ◽  
Vol 21 (3) ◽  
pp. 75-84
Author(s):  
Sérgio Raffael Silva Iocca ◽  
Sérgio Junior da Silva Fachin
Keyword(s):  
Magnetic Susceptibility ◽  
River Basin ◽  
Structural Control ◽  
3D Model ◽  
Mineral Exploration ◽  
Magnetic Data ◽  
Euler Deconvolution ◽  
Mato Grosso ◽  
High Level ◽  
2D And 3D

Among the several techniques that allow the estimation of mean depths from airborne geophysical magnetic data, the Euler deconvolution became popular due to the high level of reliability in the generated data. With the use of this tool, it is possible to study structures remotely at different crustal levels that may or may not contain mineralization, consequently being able to determine potential targets for mineral exploration or to study better its relation with the structural background. With the analysis of the magnetic susceptibility of subsurface and the inversion profiles of the magnetic data (Euler deconvolution 2D) were interpolate a 3D model of the region, that allowed to generate a descriptive suggestion of the geometry of the Pari syncline, located in the Cuiabá Group, in the northwestern portion of the Paraguay belt. It has a strong structural control in the context of the Pari River basin and a great auriferous potential, as evidenced by updated research and exploration data. The data applied in this paper were extract from the Cuiabá aerogeophysical project and previous mappings and have their mean depths correlated with the Cuiabá group.

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