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.

Inversion of magnetic anomaly on rugged observation surface in the presence of strong remanent magnetization

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. J11-J19 ◽  
Author(s):  
Shu-Ling Li ◽  
Yaoguo Li
Keyword(s):  
Remanent Magnetization ◽  
Country Rock ◽  
Magnetization Vector ◽  
Magnetic Data ◽  
Magnetization Direction ◽  
Equivalent Source ◽  
Total Magnetization ◽  
Amplitude Inversion ◽  
Amplitude Data ◽  
And Inversion

We study the inversion of magnetic data acquired over a rugged observation surface and where the buried source bodies have strong remanent magnetization that leads to unknown total magnetization directions. These factors pose significant challenges for processing and inversion of such data. To tackle the challenges from both a rugged observation surface and an unknown magnetization direction, we propose a strategy through the joint use of the equivalent source technique and 3D amplitude inversion to obtain 3D magnetization strength. We use equivalent source processing to calculate the amplitude data in the space domain because the use of the wavenumber-domain method is invalid due to large variations in the data elevation. We then carried out an amplitude inversion to generate a 3D subsurface distribution of the magnitude of the total magnetization vector. The results from a synthetic example and aeromagnetic data in Daye Mine in China showed that this approach is effective and images the magnetic units whose contact zones with the limestone country rock host the mineralization. The method is general and can be applied to a variety of cases with similar challenges.

Susceptibility and remanent magnetization inversion of magnetic data with a priori information of the Köenigsberger ratio

2020 ◽  
Vol 221 (2) ◽  
pp. 1090-1109
Author(s):  
Shuang Liu ◽  
Xiangyun Hu ◽  
Boxin Zuo ◽  
Henglei Zhang ◽  
Meixia Geng ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Remanent Magnetization ◽  
Magnetization Vector ◽  
Northwest China ◽  
Natural Remanent Magnetization ◽  
Gradient Algorithm ◽  
Magnetic Data ◽  
Preconditioned Conjugate Gradient ◽  
Data Set ◽  
Discrete Values

SUMMARY Magnetic susceptibility and natural remanent magnetization of rocks are useful parameters to study geological structures and geodynamic processes. Traditional widely used algorithms for the inversion of magnetic data can recover the distribution of the apparent susceptibility or total magnetization intensity, but do not provide information on the remanent magnetization. In this paper, we propose a framework to directly invert for the magnetic susceptibility and the natural remanent magnetization vector using surface or airborne magnetic data, assuming that the Köenigsberger ratio of the rock is known or approximately deducible. The susceptibility and remanence are computed using two different approaches: (1) the susceptibility, intensity, and direction of the remanent magnetization are continuously recovered for each discretized cell and (2) the remanence direction is assumed to be uniform in each subzone and is iteratively computed as discrete values. Both processes are implemented using the preconditioned conjugate gradient algorithm. The method is tested on three synthetic models and one field data set from the Zaohuohexi iron-ore deposit, Qinghai Province, northwest China. The results of the continuous inversion show the trend of the remanent magnetization directions, while the discrete inversion yields more specific values. This inversion framework can determine the source bodies’ geometry and position, and also provide superposed and comprehensive information on the natural remanent magnetization, which may be useful to investigate geological bodies bearing stable primary remanent magnetization.

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>

A New Method of Cross-Correlation by Magnetic Dipole for Estimating Magnetization Direction under the Influence of Remanent Magnetization

2014 ◽  
Vol 644-650 ◽  
pp. 3459-3462 ◽  
Author(s):  
Lei Shi ◽  
Liang Hui Guo ◽  
Feng Yi Guo
Keyword(s):  
Correlation Coefficient ◽  
Magnetic Dipole ◽  
Remanent Magnetization ◽  
Cross Correlation ◽  
New Method ◽  
Magnetic Data ◽  
Dipole Source ◽  
Total Field ◽  
Magnetization Direction ◽  
Total Magnetization

Processing and interpretation of magnetic data usually require information of total magnetization direction. However, under the effects of remanent magnetization, total magnetization direction is different from induced magnetization direction, which makes data processing and interpretation complexity. In this paper, we present a new method by cross-correlation of magnetic dipole source for determination of magnetization direction from relatively isolated and approximate equiaxial-shape magnetic total field anomaly. This method calculates cross-correlation coefficient between observed magnetic total field anomaly and theoretical magnetic total field anomaly caused by a magnetic dipole source, by using a set of varying parameters of positions and total magnetization direction of dipole source for trial and error. The corresponding magnetization direction of maximum correlation coefficient is regarded as estimated total magnetization direction. Test on synthetic data indicates that this method reliably and effectively estimates the magnetization direction from relatively isolated and approximate equiaxial-shape magnetic total field anomaly.

Estimating the Magnetization Direction of Sources through Correlation between Reduced-to-Pole Anomaly and Normalized Source Strength

2014 ◽  
Vol 644-650 ◽  
pp. 3793-3796
Author(s):  
Liang Hui Guo ◽  
Rui Gao ◽  
Guo Li Zhang
Keyword(s):  
Geomagnetic Field ◽  
Remanent Magnetization ◽  
Cross Correlation ◽  
Synthetic Data ◽  
Field Direction ◽  
Magnetic Data ◽  
Source Strength ◽  
Magnetization Direction ◽  
New Approach ◽  
Total Magnetization

Under the effects of remanent magnetization, total magnetization direction is different from geomagnetic field direction, which makes magnetic data processing and interpretation complexity. In this paper, we present a new approach for estimating the total magnetization direction of sources via cross-correlation between the reduced-to-pole anomaly and the normalized source strength (who is less sensitive to remanent magnetization). The geomagnetic field direction is used to calculated the normalized source strength, while various assumed total magnetization directions are used to calculated the RTP anomalies. The maximum correlation between the RTP anomalies and the normalized corresponds to the estimated total magnetization direction. Test on synthetic data showed that the new approach is simple and effective.

Mitigating remanent magnetization effects in magnetic data using the normalized source strength

Geophysics ◽  
2013 ◽  
Vol 78 (3) ◽  
pp. J25-J32 ◽  
Author(s):  
Mark Pilkington ◽  
Majid Beiki
Keyword(s):  
Magnetic Field ◽  
Remanent Magnetization ◽  
Field Data ◽  
Magnetic Data ◽  
Magnetization Distribution ◽  
Source Strength ◽  
Inversion Algorithm ◽  
Data Set ◽  
Magnetic Field Data ◽  
The Magnetic Field

We have developed an approach for the interpretation of magnetic field data that can be used when measured anomalies are affected by significant remanent magnetization components. The method deals with remanent effects by using the normalized source strength (NSS), a quantity calculated from the eigenvectors of the magnetic gradient tensor. The NSS is minimally affected by the direction of remanent magnetization present and compares well with other transformations of the magnetic field that are used for the same purpose. It therefore offers a way of inverting magnetic data containing the effects of remanent magnetizations, particularly when these are unknown and are possibly varying within a given data set. We use a standard 3D inversion algorithm to invert NSS data from an area where varying remanence directions are apparent, resulting in a more reliable image of the subsurface magnetization distribution than possible using the observed magnetic field data directly.

scholarly journals Integrated Geological and Geophysical Mapping of a Carbonatite-Hosting Outcrop in Siilinjärvi, Finland, Using Unmanned Aerial Systems

2020 ◽  
Vol 12 (18) ◽  
pp. 2998
Author(s):  
Robert Jackisch ◽  
Sandra Lorenz ◽  
Moritz Kirsch ◽  
Robert Zimmermann ◽  
Laura Tusa ◽  
...  
Keyword(s):  
Hyperspectral Image ◽  
Mineral Exploration ◽  
Mine Planning ◽  
Machine Learning Algorithms ◽  
Magnetic Data ◽  
Unmanned Aerial Systems ◽  
Data Set ◽  
Ground Truth Data ◽  
Mapping Approach ◽  
Aerial Systems

Mapping geological outcrops is a crucial part of mineral exploration, mine planning and ore extraction. With the advent of unmanned aerial systems (UASs) for rapid spatial and spectral mapping, opportunities arise in fields where traditional ground-based approaches are established and trusted, but fail to cover sufficient area or compromise personal safety. Multi-sensor UAS are a technology that change geoscientific research, but they are still not routinely used for geological mapping in exploration and mining due to lack of trust in their added value and missing expertise and guidance in the selection and combination of drones and sensors. To address these limitations and highlight the potential of using UAS in exploration settings, we present an UAS multi-sensor mapping approach based on the integration of drone-borne photography, multi- and hyperspectral imaging and magnetics. Data are processed with conventional methods as well as innovative machine learning algorithms and validated by geological field mapping, yielding a comprehensive and geologically interpretable product. As a case study, we chose the northern extension of the Siilinjärvi apatite mine in Finland, in a brownfield exploration setting with plenty of ground truth data available and a survey area that is partly covered by vegetation. We conducted rapid UAS surveys from which we created a multi-layered data set to investigate properties of the ore-bearing carbonatite-glimmerite body. Our resulting geologic map discriminates between the principal lithologic units and distinguishes ore-bearing from waste rocks. Structural orientations and lithological units are deduced based on high-resolution, hyperspectral image-enhanced point clouds. UAS-based magnetic data allow an insight into their subsurface geometry through modeling based on magnetic interpretation. We validate our results via ground survey including rock specimen sampling, geochemical and mineralogical analysis and spectroscopic point measurements. We are convinced that the presented non-invasive, data-driven mapping approach can complement traditional workflows in mineral exploration as a flexible tool. Mapping products based on UAS data increase efficiency and maximize safety of the resource extraction process, and reduce expenses and incidental wastes.

A new method for determination of magnetization direction

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. L69-L73 ◽  
Author(s):  
Neal Dannemiller ◽  
Yaoguo Li
Keyword(s):  
Large Deviation ◽  
Three Dimensional ◽  
Vertical Gradient ◽  
Data Interpretation ◽  
Magnetic Data ◽  
Data Sets ◽  
Magnetization Direction ◽  
Total Magnetization ◽  
Total Gradient

The characterization and interpretation of magnetic anomalies rely upon knowledge of the total magnetization direction. Magnetization is usually assumed to consist solely, or primarily, of induced magnetization. The presence of strong remanent magnetization can alter the direction significantly and consequently adversely affect the interpretation, leading to erroneous sizes or shapes of causative bodies. Therefore, it is imperative to have some understanding of the total magnetization direction. We propose a method based upon the correlation between two quantities in magnetic data interpretation: the vertical gradient and the total gradient of the reduced-to-pole (RTP) field. This method is tested on both synthetic and field data sets. The results show that the method is effective in a variety of situations, including those with two-dimensional and three-dimensional dipping bodies and a field example that has a large deviation between the inducing field direction and the total magnetization direction.

Visual saliency and potential field data enhancements: Where is your attention drawn?

2014 ◽  
Vol 2 (4) ◽  
pp. SJ9-SJ21 ◽  
Author(s):  
Yathunanthan Sivarajah ◽  
Eun-Jung Holden ◽  
Roberto Togneri ◽  
Michael Dentith ◽  
Mark Lindsay
Keyword(s):  
Visual Attention ◽  
Image Enhancement ◽  
Feature Detection ◽  
Saliency Detection ◽  
Visual Saliency ◽  
Data Interpretation ◽  
Detection Algorithm ◽  
Magnetic Data ◽  
Data Set ◽  
Potential Field Data

Interpretation of gravity and magnetic data for exploration applications may be based on pattern recognition in which geophysical signatures of geologic features associated with localized characteristics are sought within data. A crucial control on what comprises noticeable and comparable characteristics in a data set is how images displaying those data are enhanced. Interpreters are provided with various image enhancement and display tools to assist their interpretation, although the effectiveness of these tools to improve geologic feature detection is difficult to measure. We addressed this challenge by analyzing how image enhancement methods impact the interpreter’s visual attention when interpreting the data because features that are more salient to the human visual system are more likely to be noticed. We used geologic target-spotting exercises within images generated from magnetic data to assess commonly used magnetic data visualization methods for their visual saliency. Our aim was achieved in two stages. In the first stage, we identified a suitable saliency detection algorithm that can computationally predict visual attention of magnetic data interpreters. The computer vision community has developed various image saliency detection algorithms, and we assessed which algorithm best matches the interpreter’s data observation patterns for magnetic target-spotting exercises. In the second stage, we applied this saliency detection algorithm to understand potential visual biases for commonly used magnetic data enhancement methods. We developed a guide to choosing image enhancement methods, based on saliency maps that minimize unintended visual biases in magnetic data interpretation, and some recommendations for identifying exploration targets in different types of magnetic data.

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