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3 pages, 179 KiB

Open AccessEditorial

Editorial for Special Issue “Geophysics for Mineral Exploration”

by Michael S. Zhdanov

Minerals 2021, 11(7), 692; https://doi.org/10.3390/min11070692 - 28 Jun 2021

Cited by 3 | Viewed by 1907

Abstract

Exploration geophysics plays a major role in unlocking mineral reserves [...] Full article

(This article belongs to the Special Issue Geophysics for Mineral Exploration)

Research

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20 pages, 6171 KiB

Open AccessEditor’s ChoiceArticle

Recovering Magnetization of Rock Formations by Jointly Inverting Airborne Gravity Gradiometry and Total Magnetic Intensity Data

by Michael Jorgensen and Michael S. Zhdanov

Minerals 2021, 11(4), 366; https://doi.org/10.3390/min11040366 - 31 Mar 2021

Cited by 14 | Viewed by 2812

Abstract

Conventional 3D magnetic inversion methods are based on the assumption that there is no remanent magnetization, and the inversion is run for magnetic susceptibility only. This approach is well-suited to targeting mineralization; however, it ignores the situation where the direction of magnetization of [...] Read more.

Conventional 3D magnetic inversion methods are based on the assumption that there is no remanent magnetization, and the inversion is run for magnetic susceptibility only. This approach is well-suited to targeting mineralization; however, it ignores the situation where the direction of magnetization of the rock formations is different from the direction of the induced magnetic field. We present a novel method of recovering a spatial distribution of magnetization vector within the rock formation based on joint inversion of airborne gravity gradiometry (AGG) and total magnetic intensity (TMI) data for a shared earth model. Increasing the number of inversion parameters (the scalar components of magnetization vector) results in a higher degree of non-uniqueness of the inverse problem. This increase of non-uniqueness rate can be remedied by joint inversion based on (1) Gramian constraints or (2) joint focusing stabilizers. The Gramian constraints enforce shared earth structure through a correlation of the model gradients. The joint focusing stabilizers also enforce the structural similarity and are implemented using minimum support or minimum gradient support approaches. Both novel approaches are applied to the interpretation of the airborne data collected over the Thunderbird V-Ti-Fe deposit in Ontario, Canada. By combining the complementary AGG and TMI data, we generate jointly inverted shared earth models that provide a congruent image of the rock formations hosting the mineral deposit. Full article

(This article belongs to the Special Issue Geophysics for Mineral Exploration)

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17 pages, 4325 KiB

Open AccessArticle

Combined Magnetic, Transient Electromagnetic, and Magnetotelluric Methods to Detect a BIF-Type Concealed Iron Ore Body: A Case Study in Gongchangling Iron Ore Concentration Area, Southern Liaoning Province, China

by Jianfei Fu, Sanshi Jia and Ende Wang

Minerals 2020, 10(12), 1044; https://doi.org/10.3390/min10121044 - 24 Nov 2020

Cited by 9 | Viewed by 3335

Abstract

The detection and evaluation of concealed mineral resources deep in metallic mines and in the surrounding areas remain technically difficult. In particular, due to the complex topographic and geomorphic conditions on the surface, the detection environments in these areas limit the choices of [...] Read more.

The detection and evaluation of concealed mineral resources deep in metallic mines and in the surrounding areas remain technically difficult. In particular, due to the complex topographic and geomorphic conditions on the surface, the detection environments in these areas limit the choices of detection equipment and data collection devices. In this study, based on metallogenic theory and the metallogenic geological characteristics of banded iron formation (BIF)-type iron ores, equipment for surface geophysical surveys (i.e., the high-precision ground magnetic survey method, the transient electromagnetic method, and the magnetotelluric method) and data collection devices capable of taking single-point continuous measurements were employed to detect the concealed iron ore bodies in the transition zone CID-1 between the Hejia and Dumu iron deposits in the Gongchangling iron ore concentration area in the Anshan-Benxi area (Liaoyang, China), a representative area of BIF-type iron ores. The results showed that an optimal combination of these geophysical survey methods accurately determined the anomalous planar spatial locations and anomalous profile morphologies of the concealed iron ore bodies. On this basis, we determined their locations, burial depths, and scales. Two anomalous zones induced by concealed iron ore bodies, YC-1 and YC-2, were discovered in zone CID-1. Two concealed iron-bearing zones, one shallow (0–150 m) and one deep (300–450 m), were found in YC-1. A 100 m scale drilling test showed that the cumulative thickness of the shallow iron-bearing zone was over 23.6 m. Full article

(This article belongs to the Special Issue Geophysics for Mineral Exploration)

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16 pages, 6909 KiB

Open AccessArticle

Geophysical Prospecting for Groundwater Resources in Phosphate Deposits (Morocco)

by Fatim-Zahra Ihbach, Azzouz Kchikach, Mohammed Jaffal, Driss El Azzab, Oussama Khadiri Yazami, Es-Said Jourani, José Antonio Peña Ruano, Oier Ardanaz Olaiz and Luis Vizcaíno Dávila

Minerals 2020, 10(10), 842; https://doi.org/10.3390/min10100842 - 24 Sep 2020

Cited by 10 | Viewed by 3929

Abstract

The Moroccan phosphate deposits are the largest in the world. Phosphatic layers are extracted in open-pit mines mainly in the sedimentary basins of Gantour and Ouled Abdoun in Central Morocco. The purpose of this study was to prospect and evaluate the water potential [...] Read more.

The Moroccan phosphate deposits are the largest in the world. Phosphatic layers are extracted in open-pit mines mainly in the sedimentary basins of Gantour and Ouled Abdoun in Central Morocco. The purpose of this study was to prospect and evaluate the water potential of aquifers incorporated in the phosphatic series using the following geophysical methods: Magnetic resonance sounding (MRS), electrical resistivity tomography (ERT), time-domain electromagnetics (TDEM), and frequency-domain electromagnetics (FDEM). The objective was, on the one hand, to contribute to the success of the drinking water supply program in rural areas around mining sites, and on the other hand, to delimit flooded layers in the phosphatic series to predict the necessary mining design for their extraction. The use of geophysical methods made it possible to stratigraphically locate the most important aquifers of the phosphatic series. Their hydraulic parameters can be evaluated using the MRS method while the mapping of their recharge areas is possible through FDEM surveys. The results obtained in two selected experimental zones in the mining sites of Youssoufia and Khouribga are discussed in this paper. The application of the implemented approach to large phosphate mines is in progress in partnership with the mining industry. Full article

(This article belongs to the Special Issue Geophysics for Mineral Exploration)

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25 pages, 8252 KiB

Open AccessArticle

Spectral Induced Polarization Survey with Distributed Array System for Mineral Exploration: Case Study in Saudi Arabia

by Fouzan A. Alfouzan, Abdulrahman M. Alotaibi, Leif H. Cox and Michael S. Zhdanov

Minerals 2020, 10(9), 769; https://doi.org/10.3390/min10090769 - 30 Aug 2020

Cited by 12 | Viewed by 3539

Abstract

The Saudi Arabian Glass Earth Pilot Project is a geophysical exploration program to explore the upper crust of the Kingdom for minerals, groundwater, and geothermal resources as well as strictly academic investigations. The project began with over 8000 km² of green-field area. [...] Read more.

The Saudi Arabian Glass Earth Pilot Project is a geophysical exploration program to explore the upper crust of the Kingdom for minerals, groundwater, and geothermal resources as well as strictly academic investigations. The project began with over 8000 km² of green-field area. Airborne geophysics including electromagnetic (EM), magnetics, and gravity were used to develop several high priority targets for ground follow-up. Based on the results of airborne survey, a spectral induced polarization (SIP) survey was completed over one of the prospective targets. The field data were collected with a distributed array system, which has the potential for strong inductive coupling. This was examined in a synthetic study, and it was determined that with the geometries and conductivities in the field survey, the inductive coupling effect may be visible in the data. In this study, we also confirmed that time domain is vastly superior to frequency domain for avoiding inductive coupling, that measuring decays from 50 ms to 2 s allow discrimination of time constants from 1 ms to 5 s, and the relaxation parameter C is strongly coupled to intrinsic chargeability. We developed a method to fully include all 3D EM effects in the inversion of induced polarization (IP) data. The field SIP data were inverted using the generalized effective-medium theory of induced polarization (GEMTIP) in conjunction with an integral equation-based modeling and inversion methods. These methods can replicate all inductive coupling and EM effects, which removes one significant barrier to inversion of large bandwidth spectral IP data. The results of this inversion were interpreted and compared with results of drill hole set up in the survey area. The drill hole intersected significant mineralization which is currently being further investigated. The project can be considered a technical success, validating the methods and effective-medium inversion technique used for the project. Full article

(This article belongs to the Special Issue Geophysics for Mineral Exploration)

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13 pages, 3491 KiB

Open AccessArticle

The Efficient 3D Gravity Focusing Density Inversion Based on Preconditioned JFNK Method under Undulating Terrain: A Case Study from Huayangchuan, Shaanxi Province, China

by Qingfa Meng, Guoqing Ma, Taihan Wang and Shengqing Xiong

Minerals 2020, 10(9), 741; https://doi.org/10.3390/min10090741 - 22 Aug 2020

Cited by 12 | Viewed by 2457

Abstract

Since polymetallic ores show higher anomalies in gravity exploration methods, we usually obtain the position and range of ore bodies by density inversion of gravity data. The three-dimensional (3D) gravity focusing density inversion is a common interpretation method in mineral exploration, which can [...] Read more.

Since polymetallic ores show higher anomalies in gravity exploration methods, we usually obtain the position and range of ore bodies by density inversion of gravity data. The three-dimensional (3D) gravity focusing density inversion is a common interpretation method in mineral exploration, which can directly and quantitatively obtain the density distribution of subsurface targets. However, in actual cases, it is computation inefficient. We proposed the preconditioned Jacobian-free Newton-Krylov (JFNK) method to accomplish the focusing inversion. The JFNK method is an efficient algorithm in solving large sparse systems of nonlinear equations, and we further accelerate the inversion process by the preconditioned technique. In the actual area, the gravity anomalies are distributed on the naturally undulating surface. Nowadays, the gravity inversion under undulating terrain was mainly achieved by discretizing the ground into unstructured meshes, but it is complicated and time-consuming. To improve the practicality, we presented an equivalent-dimensional method that incorporates unstructured meshes with structured meshes in gravity inversion, and the horizontal size is determined by the gradient of observed gravity and terrain data. The small size meshes are adopted at the position where the terrain or gravity gradient is large. We used synthetic data with undulating-terrain to test our new method. The results indicated that the recovered model obtained by this method was similar to the inversion method of unstructured meshes, and the new method computes faster. We also applied the method to field data in Huayangchuan, Shaanxi Province. The survey area has complicated terrain conditions and contains multiple polymetallic ores. Based on the high-density characteristics of polymetallic ore bodies in the area, we calculate the field data into 3D density models of the subsurface by the preconditioned JFNK method and infer six polymetallic ores. Full article

(This article belongs to the Special Issue Geophysics for Mineral Exploration)

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19 pages, 6228 KiB

Open AccessArticle

Magnetic Survey for Iron-Oxide-Copper-Gold (IOCG) and Alkali Calcic Alteration Signatures in Gadarwara, M.P, India: Implications on Copper Metallogeny

by P.V. Sunder Raju and K. Satish Kumar

Minerals 2020, 10(8), 671; https://doi.org/10.3390/min10080671 - 29 Jul 2020

Cited by 3 | Viewed by 8481

Abstract

A government airborne geophysical survey flown in the late 1970s detected a large Magnetic anomaly at Gadarwara, Madhya Pradesh, in north-central India. Deep drilling indicates that the oval-shaped Magnetic anomaly is caused by underlying Magnetite-bearing banded iron formation belonging to the Mahakoshal Formation [...] Read more.

A government airborne geophysical survey flown in the late 1970s detected a large Magnetic anomaly at Gadarwara, Madhya Pradesh, in north-central India. Deep drilling indicates that the oval-shaped Magnetic anomaly is caused by underlying Magnetite-bearing banded iron formation belonging to the Mahakoshal Formation of Archean to Early Proterozoic age. The anomaly is hosted in a tectonic rift zone (Narmada-Son Lineament). After drilling alluvium up to 312 m thick, rocks intersected to depths of 612 m provided core samples for research. Broadly speaking, the samples contain banded hematite jaspilite (BHJ) and banded Magnetite (BM) iron formation with pervasive carbonate alterations. Three vertical diamond drill holes were drilled along a 1.4 km long N-S transect across the center of the geophysical anomaly. DDH-1, near the northern edge of the anomaly, went through 309 m of alluvium before intersecting bedrock and then cored 303 m of bedrock for a total depth of 612 m. Copper mineralization with appreciable amounts of cobalt, zinc, molybdenum, silver, rare earth elements, uranium and other elements was intersected. The litho-units are highly oxidised and intensely brecciated with hydrothermal overprinting of Na-K metasomatism alteration mineralogy. The second borehole, DDH-2 failed as the core drilling bit stuck in the alluvium and further drilling was abandoned, whereas the third borehole DDH-3 didnot intersect a Magnetite-hematite association and cored only siltstone. Two-dimensional model studies suggest that the signature of high Magnetic anomaly is at a depth of 0.4 km from the surface, with a width of 3.5 km, dipping at 45

^{\circ}

in a northerly direction. The causative body has a Magnetic susceptibility of 0.0052 C.G.S. units, suggestive of a hematite with quartz veinlets lithology. Based on predictive Magnetic exploration models for Iron-Oxide-Copper-Gold (IOCG), such deposits can be inferred from geological observations combined with petrophysical data and forward modelling of the observed Magnetic signatures. This paper reports a prospective IOCG-like mineralization style hosted in a rift (Narmada-Son) type of tectonic environment. Full article

(This article belongs to the Special Issue Geophysics for Mineral Exploration)

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18 pages, 7181 KiB

Open AccessEditor’s ChoiceArticle

Three-Dimensional Regularized Focusing Migration: A Case Study from the Yucheng Mining Area, Shandong, China

by Yidan Ding, Guoqing Ma, Shengqing Xiong and Haoran Wang

Minerals 2020, 10(5), 471; https://doi.org/10.3390/min10050471 - 22 May 2020

Cited by 2 | Viewed by 2196

Abstract

Gravity migration is a fast imaging technique based on the migration concept to obtain subsurface density distribution. For higher resolution of migration imaging results, we propose a 3D regularized focusing migration method that implements migration imaging of an entire gravity survey with a [...] Read more.

Gravity migration is a fast imaging technique based on the migration concept to obtain subsurface density distribution. For higher resolution of migration imaging results, we propose a 3D regularized focusing migration method that implements migration imaging of an entire gravity survey with a focusing stabilizer based on regularization theory. When determining the model parameters, the iterative direction is chosen as the conjugate migration direction, and the step size is selected on the basis of the Wolfe–Powell conditions. The model tests demonstrate that the proposed method can improve the resolution and precision of imaging results, especially for blocky structures. At the same time, the method has high computational efficiency, which allows rapid imaging for large-scale gravity data. It also has high stability in noisy conditions. The developed novel method is applied to interpret gravity data collected from the skarn-type iron deposits in Yucheng, Shandong province. Migration results show that the depth of the buried iron ore in this area is 750–1500 m, which is consistent with the drilling data. We also provide recommendations for further mineral exploration in the survey area. This method can be used to complete rapid global imaging of large mining areas and it provides important technical support for exploration of deep, concealed deposits. Full article

(This article belongs to the Special Issue Geophysics for Mineral Exploration)

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17 pages, 11838 KiB

Open AccessArticle

Three-Dimensional P-wave Velocity Structure of the Zhuxi Ore Deposit, South China Revealed by Control-Source First-Arrival Tomography

by Yunpeng Zhang, Baoshan Wang, Guoqing Lin, Yongpeng Ouyang, Tao Wang, Shanhui Xu, Lili Song and Rucheng Wang

Minerals 2020, 10(2), 148; https://doi.org/10.3390/min10020148 - 09 Feb 2020

Cited by 8 | Viewed by 4400

Abstract

The Zhuxi ore deposit, located in Jiangxi province, South China, is the largest tungsten reserve in the world. To better understand the geological structure and distribution of orebodies, we conducted a high resolution three-dimensional P-wave velocity tomography of the uppermost 0.5 km beneath [...] Read more.

The Zhuxi ore deposit, located in Jiangxi province, South China, is the largest tungsten reserve in the world. To better understand the geological structure and distribution of orebodies, we conducted a high resolution three-dimensional P-wave velocity tomography of the uppermost 0.5 km beneath the Zhuxi ore deposit and adjacent area. Our velocity model was derived from 761,653 P-wave first arrivals from 998 control-source shots, recorded by a dense array. As the first 3D P-wave velocity structure of the Zhuxi ore deposit, our model agrees with local topographic and tectonic structures and shows depth-dependent velocity similar to laboratory measurements. The Carboniferous formations hosting the proven orebodies are imaged as high velocities. The high-velocity anomalies extend to a larger area beyond the proven orebodies, and the locations of high–low velocity boundaries are in accordance with the boundaries between the Neoproterozoic formation and the Carboniferous–Triassic formation. Seismic tomography reveals that high-velocity anomalies are closely related to the mineralized areas. Our results are helpful for further evaluating the total reserves and suggest that seismic tomography can be a useful tool for mineral exploration. Full article

(This article belongs to the Special Issue Geophysics for Mineral Exploration)

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17 pages, 6528 KiB

Open AccessArticle

Novel Approach to Modeling the Seismic Waves in the Areas with Complex Fractured Geological Structures

by Nikolay Khokhlov and Polina Stognii

Minerals 2020, 10(2), 122; https://doi.org/10.3390/min10020122 - 30 Jan 2020

Cited by 27 | Viewed by 3192

Abstract

This paper presents a novel approach to modeling the propagation of seismic waves in a medium containing subvertical fractured inhomogeneities, typical for mineralization zones. The developed method allows us to perform calculations on a structural computational grid, which avoids the construction of unstructured [...] Read more.

This paper presents a novel approach to modeling the propagation of seismic waves in a medium containing subvertical fractured inhomogeneities, typical for mineralization zones. The developed method allows us to perform calculations on a structural computational grid, which avoids the construction of unstructured grids. For the calculations, the grid-characteristic method is used. We also present a comparison of the proposed method with the one described at earlier works and discuss the areas of its practical application. As an example, the numerical results for a cluster of subvertical fractures are given. A new approach for modeling fractures makes it quite easy to incorporate fractured objects into the seismic models and perform calculations without using algorithms on unstructured and curved grids. Full article

(This article belongs to the Special Issue Geophysics for Mineral Exploration)

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19 pages, 6975 KiB

Open AccessArticle

Parallel Simulation of Audio- and Radio-Magnetotelluric Data

by Nikolay Yavich, Mikhail Malovichko and Arseny Shlykov

Minerals 2020, 10(1), 42; https://doi.org/10.3390/min10010042 - 31 Dec 2019

Cited by 6 | Viewed by 3137

Abstract

This paper presents a novel numerical method for simulation controlled-source audio-magnetotellurics (CSAMT) and radio-magnetotellurics (CSRMT) data. These methods are widely used in mineral exploration. Interpretation of the CSAMT and CSRMT data collected over an area with the complex geology requires application of effective [...] Read more.

This paper presents a novel numerical method for simulation controlled-source audio-magnetotellurics (CSAMT) and radio-magnetotellurics (CSRMT) data. These methods are widely used in mineral exploration. Interpretation of the CSAMT and CSRMT data collected over an area with the complex geology requires application of effective methods of numerical modeling capable to represent the geoelectrical model of a deposit well. In this paper, we considered an approach to 3D electromagnetic (EM) modeling based on new types of preconditioned iterative solvers for finite-difference (FD) EM simulation. The first preconditioner used fast direct inversion of the layered Earth FD matrix (Green’s function preconditioner). The other combined the first with a contraction operator transformation. To illustrate the effectiveness of the developed numerical modeling methods, a 3D resistivity model of Aleksandrovka study area in Kaluga Region, Russia, was prepared based on drilling data, AMT, and a detailed CSRMT survey. We conducted parallel EM simulation of the full CSRMT survey. Our results indicated that the developed methods can be effectively used for modeling EM responses over a realistic complex geoelectrical model for a controlled source EM survey with hundreds of receiver stations. The contraction-operator preconditioner outperformed the Green’s function preconditioner by factor of 7–10, both with respect to run-time and iteration count, and even more at higher frequencies. Full article

(This article belongs to the Special Issue Geophysics for Mineral Exploration)

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