Extraction of Mineralization-Related Anomalies from Gravity and Magnetic Potential Fields for Mineral Exploration Targeting: Tongling Cu(–Au) District, China

2018 ◽  
Vol 28 (2) ◽  
pp. 461-486 ◽  
Author(s):  
Gaoshen Tao ◽  
Gongwen Wang ◽  
Zhiqiang Zhang
2021 ◽  
Author(s):  
Alexey Shklyaruk ◽  
Kirill Kuznetsov ◽  
David Arutyunyan ◽  
Ivan Lygin

<p>At the stage of small and medium-scale geological and geophysical studies, in addition to seismic exploration, methods of potential fields (gravimetry and magnetometry) are usually actively used. These methods, in contrast to the profile seismic observations, taking into account modern satellite and aviation technologies, provide a high-quality areal density and magnetic characteristics of the study area. The main tasks of modern gravimetry and magnetometry include the task of constructing areal models, contrasting in density and magnetization of surfaces. Among a large number of algorithmic solutions, the most effective are methods using an integrated approach, in which seismic data on the morphology of reflecting horizon is used as a reference.</p><p>Reconstruction of the structural surface morphology by geophysical data can be considered as the problem of finding the relationship between the input information (potential fields, geophysical data, and available a priori information) and the desired surface. To assess the dependence, it is proposed to use the reference plots on which both input and output data are presented. Currently, one of the trends in solving such problems is methods based on neural networks. Neural networks can be of various configurations (feedforward networks, radial-basis function networks, backpropagation networks, convolutional networks, etc.), have a different number of layers and neurons.</p><p>In this research, we consider the test and real-world example. A site with a known position of the sedimentary cover bottom is considered as a test model. To verify and compare the algorithms, the gravity and magnetic effects of the layer are calculated. The gravity and magnetic fields were supplied to the input to the algorithms for constructing regression dependence and training the neural network. An incomplete model of the sedimentary cover was supplied to the input for training neural networks. The task was to restore the missing part. The parameter of the standard deviation of the original and reconstructed model was less than 2% for all types of neural networks.</p><p>As a real model, a site was considered where basement cover is only partially available. It was obtained as a result of seismic interpretation. All available geological and geophysical data were used to reconstruct the horizon. Models obtained using reconstruction algorithms can be additional information for further detailed description of the geological structure.</p><p>It should be noted that since neural networks help to find complex functional relationships between field parameters and attributes of the studied environment, they could be used in the tasks of complex interpretation of geological and geophysical data.</p>


Geophysics ◽  
2011 ◽  
Vol 76 (4) ◽  
pp. L29-L34 ◽  
Author(s):  
Zhen Jia ◽  
Shiguo Wu

We summarized and revised the present forward modeling methods for calculating the gravity- and magnetic-field components and their partial derivatives of a 2D homogeneous source with a polygonal cross section. The responses of interest include the gravity-field components and their first- and second-order partial derivatives and the magnetic-field components and their first-order partial derivatives. The revised formulas consist of several basic quantities that are common in all the formulations. A singularity appears when the observation point coincides with a polygon vertex. This singularity is removable for the gravity formulas but not for the others. The compact forms of the revised formulas make them easy to implement. We compare the gravity- and magnetic-field components and their partial derivatives produced by a 2D prism whose polygonal cross section approximates a cylinder with the corresponding analytical fields and partial derivatives of the cylinder. The perfect fittings presented by both data sets confirm the reliability of the updated formulas.


Geophysics ◽  
1988 ◽  
Vol 53 (3) ◽  
pp. 365-374 ◽  
Author(s):  
R. O. Hansen ◽  
Xiaomu Wang

Models based on homogeneous polyhedral bodies offer great flexibility in representing the potential fields of complex geologic sources. However, existing expressions for the gravity and magnetic fields of such bodies suffer from two disadvantages. First, the surface of the body must be specified as a set of triangular facets, which makes input to a modeling program rather awkward. Second, each facet of the body must be rotated into a special position, which generates substantial computational overhead and makes the analytic expressions difficult to interpret. In this paper, Pedersen’s Fourier transform expressions for the potential fields due to homogeneous polyhedral bodies are recast in a simpler, coordinate‐invariant form. The resulting expressions are then rewritten as a sum of contributions from each vertex of the body. This greatly simplified form is used as the basis for a modeling program that is substantially faster and more straightforward than existing programs. Furthermore, the analytic expressions promise to be useful for further investigation of an inverse method based on polyhedral‐body models.


Geophysics ◽  
1966 ◽  
Vol 31 (5) ◽  
pp. 949-962 ◽  
Author(s):  
H. P. Ross ◽  
P. M. Lavin

Recent studies have shown that many rocks of the earth’s crust have a substantial component of remanent magnetization. Extensive sampling is required to determine adequately the remanent vector from small samples. A field technique has been developed (and tested on model data) for the in‐situ determination of the resultant (induced+remanent) magnetic vector of bulk volumes of rock, using a combined analysis of the gravity and magnetic fields of a disturbing body (Poisson’s Theorem). The potential fields are sampled adequately at a limited expenditure of time and effort in the field by utilizing the geometry of two‐dimensional bodies. The major limitation to the analysis is the removal of regional gradients and the estimation of the base levels of anomalies. Combined gravity and magnetic surveys were conducted over six diabase bodies in the Triassic Basin of Pennsylvania. The results of these surveys indicate a resultant direction of magnetization given approximately by: declination 2° W, inclination 41 degrees below the horizon. The corresponding direction of natural remanent magnetization has a declination of 1° W and an inclination of 28 degrees. The ratio of remanent to induced magnetization for the diabase is approximately two. These results have been used to provide a better interpretation of magnetic survey data over a magnetite deposit in the Triassic Basin.


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