Research

12 pages, 4386 KiB

Open AccessArticle

Deep Structure of Epithermal Deposits in Youxi Area: Insights from CSAMT and Dual-Frequency IP Data

by Huanyin He, Jinrong Wang, Wu Wen, Rencong Tian, Jiansui Lin, Weiqiang Huang and Yabin Li

Minerals 2024, 14(1), 27; https://doi.org/10.3390/min14010027 - 25 Dec 2023

Viewed by 843

Epithermal deposits represent a significant category of gold occurrences, with their subsurface structure playing a key role in reserve assessments. Fujian Province, characterized by extensive Mesozoic volcanic activities, stands out as a noteworthy region for shallow hydrothermal mineralization in China. This paper focus [...] Read more.

Epithermal deposits represent a significant category of gold occurrences, with their subsurface structure playing a key role in reserve assessments. Fujian Province, characterized by extensive Mesozoic volcanic activities, stands out as a noteworthy region for shallow hydrothermal mineralization in China. This paper focus on the Youxi area within Fujian Province, employing the dual-frequency induced polarization method (DFIP) and controlled-source audio-frequency magnetotelluric method (CSAMT) to investigate the target ore. The DFIP results revealed predominant northeast-oriented zones with high polarizability and notable apparent resistivity. The CSAMT data were inverted using the SCS2D software. Two-dimensional resistivity profiles reveal a three-layer electrical structure, comprising subsurface banded rhyolites influenced by fault zones, intermediate-low resistivity sandstone layers, and deep-seated high-resistivity conglomerates. The resistivity gradient zones and highly polarizable locations align closely with known local faults. We interpreted these resistivity gradient zones as prospective target areas for mineralization, a hypothesis subsequently validated by drilling results. Combining geochemical analyses of epithermal gold deposits with the electrical resistivity structure, we propose an explanatory model for the mechanism of the formation of epithermal gold–silver deposits in the Youxi area. The magmatic hydrothermal fluids ascended along the fault, underwent convection-driven interaction with meteoric waters, and subsequently metasomatized the host rocks. This integrated approach provides valuable insights into the geological processes governing epithermal gold–silver deposit formation in the Youxi region. Full article

(This article belongs to the Special Issue New Concept of Using Geophysical Data in Mineral Exploration, Depth Estimation and Structural Mapping)

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18 pages, 10919 KiB

Open AccessFeature PaperArticle

Three-Dimensional Forward Modeling of Transient Electromagnetic Method Considering Induced Polarization Effect Based on Spectral Element Method

by Xiaonan Zhang, Liangjun Yan, Xin Huang, Lei Zhou, Xinyu Wang and Xiaoyue Cao

Minerals 2024, 14(1), 24; https://doi.org/10.3390/min14010024 - 25 Dec 2023

Viewed by 835

Abstract

The transient electromagnetic method (TEM) is widely used in the exploration of mineral, petroleum, and geothermal resources due to its sensitivity to low-resistivity bodies, limited site constraints, and strong resistance to interference. In practical applications, the TEM often uses a long wire source [...] Read more.

The transient electromagnetic method (TEM) is widely used in the exploration of mineral, petroleum, and geothermal resources due to its sensitivity to low-resistivity bodies, limited site constraints, and strong resistance to interference. In practical applications, the TEM often uses a long wire source instead of an idealized horizontal electric dipole (HED) source as the excitation source. This is due to the complex external conditions and the relatively large distance between the receiving zone and the transmitter source. Compared to the HED, the long wire source can provide a larger excitation current, generating stronger signals to meet the requirements of a higher signal-to-noise ratio or deeper exploration. It also produces longer-duration signals, thereby providing better resolution. Additionally, for the interpretation of TEM data, three-dimensional forward modeling plays a crucial role. However, the mature traditional TEM forward method is based on a simple, sometimes inappropriate model, as it is well established that the induced polarization (IP) effect is widely present in the deep earth, especially in oil and gas reservoirs. The presence of the IP effect results in negative responses in field data that do not conform to the traditional theoretical decay law of TEM, which can significantly impact data processing and inversion results. To address this issue, a TEM forward modeling method considering the IP effect based on the spectral element method (SEM) has been developed in this study. Firstly, starting from the Helmholtz equation satisfied by the time domain electric field, we introduce the Debye model with polarization information into the forward modeling by utilizing the differential form of Ohm’s law. As a result, we derive the boundary value problem for the time domain electric field that considers the induced polarization effect. Using Gauss–Lobatto–Legendre (GLL) polynomials as the basis functions, the SEM is employed to discretize the governing equations at each time step and obtain spectral element discretization equations. Then, temporal discretization equations are derived using the second-order backward Euler formula, and the linear system of equations is solved using the Pardiso direct solver. Finally, the electromagnetic responses at any time channel are obtained via SEM interpolation and numerical integration, thereby achieving three-dimensional TEM forward modeling considering the IP effect. The results indicate that this method can effectively reflect the spatial distribution of polarizable subsurface media. It provides valuable references for studying the polarization parameters of subsurface media and performing a three-dimensional inversion of TEM data considering the induced polarization effect. Full article

(This article belongs to the Special Issue New Concept of Using Geophysical Data in Mineral Exploration, Depth Estimation and Structural Mapping)

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0 pages, 8464 KiB

Open AccessArticle

Noise Characteristics and Denoising Methods of Long-Offset Transient Electromagnetic Method

by Yang Xu, Xingbing Xie, Lei Zhou, Biao Xi and Liangjun Yan

Minerals 2023, 13(8), 1084; https://doi.org/10.3390/min13081084 - 14 Aug 2023

Cited by 1 | Viewed by 1084 | Correction

Abstract

The advantages of the long-offset transient electromagnetic method include deep detection and sensitive response to resistivity anomalies. It is widely used in underground mineral resources exploration, fluid identification in petroleum reservoirs, hydraulic fracturing, and dynamic residual oil and gas monitoring. After the primary [...] Read more.

The advantages of the long-offset transient electromagnetic method include deep detection and sensitive response to resistivity anomalies. It is widely used in underground mineral resources exploration, fluid identification in petroleum reservoirs, hydraulic fracturing, and dynamic residual oil and gas monitoring. After the primary field signal is turned off, grounded electrodes or coils are used to observe the secondary eddy field. The secondary field signal decays quickly and has a large dynamic range and a wide frequency band but is easily affected by various natural and human electromagnetic interferences. Therefore, noise reduction and distortion correction are important issues in the processing of transient electromagnetic data. This paper proposes a systematic noise interference suppression process. Multi-period and positive–negative bipolar signal stackings were used to remove random noise and suppress DC offset signals. Then, a time-domain inverse digital recursive method was applied to remove characteristic frequency signals, e.g., power frequency signals and their harmonic interference. A standard noise-free signal was constructed through forward modeling simulation and verified by adding different types of noise. Finally, high-quality transient electromagnetic secondary field attenuation signals were obtained through overlapping windowing technology. We applied this algorithm to obtain electromagnetic data from dynamic monitoring of hydraulic fracturing in Fuling shale gas and from a copper–iron metal mine in Daye City, demonstrating its effectiveness. Full article

(This article belongs to the Special Issue New Concept of Using Geophysical Data in Mineral Exploration, Depth Estimation and Structural Mapping)

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18 pages, 11947 KiB

Open AccessArticle

Multi-Scale Potential Field Data Integration Using Fuzzy C-Means Clustering for Automated Geological Mapping of North Singhbhum Mobile Belt, Eastern Indian Craton

by Santosh Kumar, Rama Chandrudu Arasada and Gangumalla Srinivasa Rao

Minerals 2023, 13(8), 1014; https://doi.org/10.3390/min13081014 - 29 Jul 2023

Cited by 3 | Viewed by 998

Abstract

Fuzzy C-Means (FCM) clustering is an unsupervised machine learning algorithm that helps to integrate multiple geophysical datasets and provides automated objective-oriented information. This study analyzed ground-based Bouguer gravity and aeromagnetic datasets using the FCM clustering algorithm to classify lithological units in the western [...] Read more.

Fuzzy C-Means (FCM) clustering is an unsupervised machine learning algorithm that helps to integrate multiple geophysical datasets and provides automated objective-oriented information. This study analyzed ground-based Bouguer gravity and aeromagnetic datasets using the FCM clustering algorithm to classify lithological units in the western part of the North Singhbhum Mobile Belt, a mineralized belt in the Eastern Indian Craton. The potential field signatures of clusters obtained using FCM correlate remarkably well with the existing surface geology on a broad scale. The cluster associated with the highest gravity signatures corresponds to the metabasic rocks, and the cluster with the highest magnetic response represents the mica schist rocks. The cluster characterized by the lowest gravity and magnetic responses reflects the granite gneiss rocks. However, few geological formations are represented by two or more clusters, probably due to the close association of similar rock types. The fuzzy membership scores for most of the data points in each cluster show above 0.8, indicating a consistent relationship between geophysical signatures and the existing lithological units. Further, the study reveals that integrating multi-scale geophysical data helps to disclose bedrock information and litho-units under the sediment cover. Full article

(This article belongs to the Special Issue New Concept of Using Geophysical Data in Mineral Exploration, Depth Estimation and Structural Mapping)

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15 pages, 3861 KiB

Open AccessArticle

Exploratory Mapping of the Geothermal Anomalies in the Neoproterozoic Arabian Shield, Saudi Arabia, Using Magnetic Data

by Kamal Abdelrahman, Stephen E. Ekwok, Christian A. Ulem, Ahmed M. Eldosouky, Naif Al-Otaibi, Bashar Y. Hazaea, Saddam Ali Hazaea, Peter Andráš and Anthony E. Akpan

Minerals 2023, 13(5), 694; https://doi.org/10.3390/min13050694 - 19 May 2023

Cited by 5 | Viewed by 1781

Abstract

In this paper, certain areas of the Kingdom of Saudi Arabia (KSA) are assessed in order to map potential geothermal energy zones. To evaluate high-resolution aerial magnetic data, spectral depth analysis using a modified centroid approach was used. The calculated geothermal parameters were [...] Read more.

In this paper, certain areas of the Kingdom of Saudi Arabia (KSA) are assessed in order to map potential geothermal energy zones. To evaluate high-resolution aerial magnetic data, spectral depth analysis using a modified centroid approach was used. The calculated geothermal parameters were gridded in order to delineate the regions characterised by a shallow Curie point depth (CPD) and a high geothermal gradient (GG) as well as a high heat flow (HF). The CPD, GG and HF calculated from the analysed data varied in the ranges of 6.0–15.0 km, 40.0–100.0 °C/km and 90.0–270.0 mW/m², respectively. The obtained results show the concurrence of the positions of shallow CPD (<8.0 km), high GG (>83.5 °C/km) and high HF (>211.0 mW/m²). The geothermal systems that are oriented in the E–W direction are related to the Red Sea tectonics, the tectonic opening of the Red Sea/Gulf of the Suez Rift, hot subterranean anomalies and high enthalpy from radioactive granites. Likewise, the geologic structures (fractures and faults) related to the Red Sea tectonics serve as channels for the movement of hydrothermal fluids and the deposition of associated minerals. All in all, another geophysical study involving deep boreholes, and seismic, magnetotelluric, electromagnetic and geochemical data should be conducted to evaluate and estimate precisely the economic reserves of geothermal resources. Full article

(This article belongs to the Special Issue New Concept of Using Geophysical Data in Mineral Exploration, Depth Estimation and Structural Mapping)

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14 pages, 6340 KiB

Open AccessArticle

Characterization of Surface–Borehole Transient Electromagnetic Response in Electrical Anisotropic Media

by Haojin Li, Yurong Mao, Xinyu Wang, Liangjun Yan and Lei Zhou

Minerals 2023, 13(5), 674; https://doi.org/10.3390/min13050674 - 14 May 2023

Viewed by 1231

Abstract

When encountering sedimentary rocks with obvious laminations or fracture development zones, the conductivity of the conductive medium in different directions will change significantly, and the subsurface medium will exhibit macroscopic conductivity anisotropy. To analyze the impact of electrical anisotropy on the surface–borehole transient [...] Read more.

When encountering sedimentary rocks with obvious laminations or fracture development zones, the conductivity of the conductive medium in different directions will change significantly, and the subsurface medium will exhibit macroscopic conductivity anisotropy. To analyze the impact of electrical anisotropy on the surface–borehole transient electromagnetic exploration method, we used the finite element method to investigate the electrical anisotropy surface–borehole transient electromagnetic three-dimensional (3D) forward algorithm, in which we used a tetrahedral mesh to spatially discretize the time–domain Maxwell equation. Then, we discretized it using the second-order backward Eulerian difference method, and we obtained the fields through the PARDISO solver. The validity and correctness of the algorithm were verified through comparison of a one-dimensional (1D) anisotropic model, a complex three-dimensional (3D) isotropic model, and a three-dimensional (3D) anisotropic half-space model. A typical anisotropic geological model was constructed to analyze the effects of anisotropic strata and anomalies in the different principal axis directions on the surface–borehole transient electromagnetic response. The results show that the response of the anisotropic medium is related to the direction of the transmitting source, and the response pattern is complex and volatile. The electrical anisotropic anomaly does affect the amplitude, which should be given special attention when performing surface–borehole transient electromagnetic inversion interpretation. Full article

(This article belongs to the Special Issue New Concept of Using Geophysical Data in Mineral Exploration, Depth Estimation and Structural Mapping)

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20 pages, 5868 KiB

Open AccessArticle

An Integrated Geophysics and Isotope Geochemistry to Unveil the Groundwater Paleochannel in Abydos Historical Site, Egypt

by Abdelbaset M. Abudeif, Gamal Z. Abdel Aal, Nessreen F. Abdelbaky, Mohamed H. Ali and Mohammed A. Mohammed

Minerals 2023, 13(1), 64; https://doi.org/10.3390/min13010064 - 30 Dec 2022

Viewed by 1466

Abstract

The scientific controversy among archaeologists about the existence of paleochannels under the Abydos archaeological site, Sohag, Egypt connecting the Osirion (cenotaph of Seti I) with the Nile River has been explained in this study. This study is an attempt to address [...] Read more.

The scientific controversy among archaeologists about the existence of paleochannels under the Abydos archaeological site, Sohag, Egypt connecting the Osirion (cenotaph of Seti I) with the Nile River has been explained in this study. This study is an attempt to address this issue using integrating a near-surface geophysical approach with stable isotopic geochemistry on this site. Particularly, the stable oxygen and hydrogen isotopes on the water samples collected from the surface and the groundwater in the study area were analyzed and interpreted. The isotopes result showed that the Osirion water is a mixture of three different types of water: Old Nile Water (ONW) before the construction of the High Dam, Recent Nile Water (RNW) after the construction of the High Dam, and Paleowater (PW) from deeper aquifers. Field observations of the Osirion and nearby water cannot explain the presence and direction of this water. Therefore, the next step in this study is determining the location and the direction of the paleochannel connecting the Osirion with the Nile River which was proven using the electric resistivity tomography (ERT) technique. By using the results of the isotope of all types of water near the Osirion and its surrounding wells and the water of the Nile River, in addition to the near-surface geophysical measurements, the results indicated that the 3D view of the ERT data revealed a prospective paleochannel in the direction of the northeast and its location, where this channel is in charge of providing groundwater from the Nile River to the Osirion location. Full article

(This article belongs to the Special Issue New Concept of Using Geophysical Data in Mineral Exploration, Depth Estimation and Structural Mapping)

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26 pages, 10027 KiB

Open AccessArticle

Reservoir Quality Prediction of Gas-Bearing Carbonate Sediments in the Qadirpur Field: Insights from Advanced Machine Learning Approaches of SOM and Cluster Analysis

by Muhammad Rashid, Miao Luo, Umar Ashraf, Wakeel Hussain, Nafees Ali, Nosheen Rahman, Sartaj Hussain, Dmitriy Aleksandrovich Martyushev, Hung Vo Thanh and Aqsa Anees

Minerals 2023, 13(1), 29; https://doi.org/10.3390/min13010029 - 24 Dec 2022

Cited by 23 | Viewed by 2353

Abstract

The detailed reservoir characterization was examined for the Central Indus Basin (CIB), Pakistan, across Qadirpur Field Eocene rock units. Various petrophysical parameters were analyzed with the integration of various cross-plots, complex water saturation, shale volume, effective porosity, total porosity, hydrocarbon saturation, neutron porosity [...] Read more.

The detailed reservoir characterization was examined for the Central Indus Basin (CIB), Pakistan, across Qadirpur Field Eocene rock units. Various petrophysical parameters were analyzed with the integration of various cross-plots, complex water saturation, shale volume, effective porosity, total porosity, hydrocarbon saturation, neutron porosity and sonic concepts, gas effects, and lithology. In total, 8–14% of high effective porosity and 45–62% of hydrocarbon saturation are superbly found in the reservoirs of the Eocene. The Sui Upper Limestone is one of the poorest reservoirs among all these reservoirs. However, this reservoir has few intervals of rich hydrocarbons with highly effective porosity values. The shale volume ranges from 30 to 43%. The reservoir is filled with effective and total porosities along with secondary porosities. Fracture–vuggy, chalky, and intracrystalline reservoirs are the main contributors of porosity. The reservoirs produce hydrocarbon without water and gas-emitting carbonates with an irreducible water saturation rate of 38–55%. In order to evaluate lithotypes, including axial changes in reservoir characterization, self-organizing maps, isoparametersetric maps of the petrophysical parameters, and litho-saturation cross-plots were constructed. Estimating the petrophysical parameters of gas wells and understanding reservoir prospects were both feasible with the methods employed in this study, and could be applied in the Central Indus Basin and anywhere else with comparable basins. Full article

(This article belongs to the Special Issue New Concept of Using Geophysical Data in Mineral Exploration, Depth Estimation and Structural Mapping)

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16 pages, 12979 KiB

Open AccessArticle

A Novel Enhanced Total Gradient (ETG) for Interpretation of Magnetic Data

by Korimilli Naga Durga Prasad, Luan Thanh Pham, Anand P. Singh, Ahmed M. Eldosouky, Kamal Abdelrahman, Mohammed S. Fnais and David Gómez-Ortiz

Minerals 2022, 12(11), 1468; https://doi.org/10.3390/min12111468 - 20 Nov 2022

Cited by 9 | Viewed by 2013

Abstract

Edge detection techniques identify the horizontal extents of the underground geological bodies and work well in association with magnetic as well as seismic data. Even though the detected edges might not be a lithological contact, they offer first-hand information regarding various rocks that [...] Read more.

Edge detection techniques identify the horizontal extents of the underground geological bodies and work well in association with magnetic as well as seismic data. Even though the detected edges might not be a lithological contact, they offer first-hand information regarding various rocks that ultimately offers an extra argument for existing tectonics. Most of the edge enhancement techniques depend either on the horizontal gradient or total gradient of the potential fields. As of now, no single edge detection filter performance is best in all conditions. The study proposes a novel edge detection filter called “ETG-Enhanced Total Gradient” that combines the derivatives of the analytic signal (AS) (in the third dimension). The maximum amplitude of the AS is less dependent of the direction of magnetization and is critical in mapping the borders of the buried magnetic sources beneath the Earth. As the ETG filter is based on the total gradient of the field, there is no need to apply reduction to the pole process on the magnetic data. One limitation of the method is that the filter is unable to perform better at the corners where the other conventional methods miserably failed. The filter’s behavior is examined and validated using 2D and 3D synthetic magnetic data. The reliability of the ETG filter is examined by applying it to the magnetic data of the Seattle uplift region, USA. A new structural map of the region is generated by using the proposed ETG filter. The observed peak response of the ETG filter is well correlated with major tectonic features such as the Seattle Fault Zone (SFZ), Hood Canal Fault (HCF), and Dewatto Fault (DF). Full article

(This article belongs to the Special Issue New Concept of Using Geophysical Data in Mineral Exploration, Depth Estimation and Structural Mapping)

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