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Qingchengzi is an important polymetallic mineral concentration zone in China. However, long-term mining has led to the depletion of proven reserves in the Qingchengzi ore concentration zone. Therefore, it is necessary to carry out prospecting in the periphery of the existing ore bodies. Taking into account the complex surface conditions of the Qingchengzi mining area, we carried out an airborne time-domain electromagnetic survey in this region and obtained a high-precision underground resistivity model which covers the whole area. The quasi-3D inversion result shows a good agreement with the surface geological information. After analyzing the relationship between the underground geological structures and the resistivity model, we constructed a geological model with the distribution of the main strata, the rock masses and the faults. The reconstructed resistivity distribution of the entire region added new knowledge to understand the geology of the Qingchengzi survey area. [ABSTRACT FROM AUTHOR]

Skywave refers to the electromagnetic wave reflected or refracted from the ionosphere and propagated in the form of a guided wave between the ionosphere and the Earth's surface. Since the skywave can propagate over large distances, it has been widely used in long-distance communication. This paper explores and demonstrates the feasibility of skywave for deep resource and energy exploration at depths of up to 10 km. Theoretical and technical advancements were accomplished in furthering skywave applications. A new solution method based on Green's function has been developed to study skywave propagation in a fully coupled lithosphere-air-ionosphere full space model. For the first time, the model allows one to study skywave distribution characteristics in the lithosphere containing inhomogeneity such as ore deposits or oil and gas reservoirs. This model also lays a foundation for skywave data processing and interpretation. On a parallel line, we have developed a multi-channel, broadband, low-noise, portable data acquisition system suitable for receiving skywave signals. Using the skywave field excited by a high-power fixed source located in central China, actual field surveys have been carried out in some areas in China including the Biyang depression of Henan Province. The initial results appear encouraging—the interpreted resistivity models prove to be consistent with those of seismic exploration and known geological information, and the exploration cost is only ∼1/4 to 1/10 that of seismic surveys. These initial successful applications of the skywave theory lay a solid foundation for further verification of the new method. [ABSTRACT FROM AUTHOR]

The North China Craton is the oldest continental block, and has suffered from large-scale lithospheric thinning and destruction, which in turn led to gold deposits in northern China. The decratonic gold deposits in the North China Craton became the most important gold deposits in China, and geophysical methods are key means to detect and discover gold deposits there. In this paper, based on the geological and petrophysical characteristics of the North China Craton, the geological model of the decratonic gold deposits is transformed into a geophysical model. At present, two methods of geophysical exploration of decratonic gold deposits are in use: rapid and efficient exploration on the scale of the ore concentration area, and large depth exploration on the scale of the deposit area. In detail, the airborne electromagnetic, magnetic and gravity methods are used to detect the shallow (1,500 m) anomaly area on the scale of the ore concentration area. Through the ground-controlled source electromagnetic and ground magnetotelluric methods, explorations for targets at significant depth (5,000 m) are carried out in the mining area. Then, taking the Liaodong ore concentration area as an example, geophysical methods are used to discover two prospecting areas around the Jianshanzi Fault in the Qingchengzi ore concentration area, Baiyun-Xiaotongjiapuzi deep prospecting area, and Qingchengzi deep prospecting area. Next, three prospecting areas are delineated around the Jixingou Fault in the Wulong mining area, Wulong deep prospecting area, Weishagou deep prospecting area, and Chang'an deep prospecting area. The anomalies in the ore concentration area and mining area are revealed by means of three-dimensional exploration methods, thereby providing technical support for the exploration of metal minerals such as decratonic gold deposits. [ABSTRACT FROM AUTHOR]

Taohemu deposit is a superlarge silver‐polymetallic deposit discovered in the Great Xing'an Range metallogenic belt of China in recent years. The deposit occurs in the terrestrial volcanic rock sequences of Late Jurassic age. The ore bodies consist mainly of rhyolitic tuffs, brecciated tuffs, and volcanic breccia bearing Ag‐Pb‐Zn mineralization, and are largely conformable with the surrounding layered volcanic and volcaniclastic rocks with a gradual transitional relationship manifesting as strata‐bounded features in general. The mineralization system appears to be generally controlled by a paleo‐volcanic chamber. It is suggested that the late volcanic hydrothermal fluids flowed within the permeable layers of rhyolitic pyroclastics consisting mainly of volcanic breccias and breccia‐bearing tuffs. This resulted in the formation of superlarge Ag‐Pb‐Zn polymetallic ore deposit metasomatism and fracture filling. The majority of the deposit occurs as shallowly dipping concealed ore bodies, as defined by sparsely distributed drill holes. Because of its short discovery history, new mineralization style and low degree of comprehensive research, the boundaries of most ore bodies have not been effectively delineated along vertical and lateral extensions. At present, it is crucial to strengthen the comprehensive studies on the deposit, conduct more detailed geological exploration, and establish the metallogenic and prospecting models. For this reason, we have designed and implemented long sections of magnetotelluric (MT) and controlled‐source audio magnetotelluric (CSAMT) sounding across the Taohemu ore field and obtained a large number of geological structures and valuable underground exploration results that provided reliable geophysical support for promoting deep resource exploration. Plain Language Summary: The geological structures associated with metallogenic system is usually covered by surface vegetation and Quaternary layer. Furthermore, surface mineralization is not relevant to deep ore bodies. To reveal the shape of ore bodies and geoelectrical structures in this study area, we applied geophysical electromagnetic methods to achieve this purpose. The results showed that the ore bodies are largely conformable with the surrounding rocks as strata‐bounded features in general tested by borehole information. The mineralization system appears to be generally controlled by a paleo‐volcanic chamber. Key Points: Underground geoelectric structures are imaged from MT and CSAMT exploration over Taohemu superlarge silver‐polymetallic deposit, Inner MongoliaOre bodies are conformable with surrounding volcanic and volcaniclastic rock with a gradual transitional relationship manifesting as strata‐bounded featuresThe mineralization system appears to be generally controlled by a paleo‐volcanic chamber [ABSTRACT FROM AUTHOR]

As an important branch of geophysical exploration method, the electromagnetic method with artificial source has advanced rapidly in the past decade. These methods are classified as airborne electromagnetic method, ground-air electromagnetic method, ground electromagnetic method, and marine electromagnetic method. Over the years, researchers in China have made significant improvement to the fundamental theory, forward modeling and inverse for series of electromagnetic detection methods. Conversely, significant progress was made in the development of corresponding equipment. The researched techniques and their developed equipment have been successfully utilized to detect underground targets as deep as 10 km. However, there is increasing need for deep resources exploration, urban subsurface study, and prediction, monitoring and detection of geological hazards. To meet the increasing need and catch up with the advanced international level of exploration technologies and developed equipment, there is urgent necessity and requirement to continue developing geophysical methods and the corresponding equipment. [ABSTRACT FROM AUTHOR]

Previously, the multi‐channel transient electromagnetic (MTEM) system has been successfully developed and applied to hydrocarbon reservoirs exploration on land and offshore environments in France. In order to explore the mineral resources buried at the depths up to 2,000 m in China, we developed a new MTEM system. In this paper, we present the components of the system, methods, principles, the parameters of the system, and the data interpretation method. To validate the effectiveness of the methodology and the developed system, we carried out an MTEM survey to locate the controlling faults of a gold deposit in the east of China. The survey contains 30 receivers distributed over 12‐km survey. By comparing the MTEM interpretation results with the known geological background, we find that MTEM methods can provide a good estimation of the ore‐controlling faults and this method could be a potential tool for the future deep mineral exploration. [ABSTRACT FROM AUTHOR]

With fast development of Chinese economy, a large amount of garbage have been produced. Especially, high level radioactive waste (HLRW) bring dangers to the security of human being. Finding a suitable site to dispose HLRW is a key management to government. A potential HLRW disposal site has been chosen in west north of China at first, however, it is necessary to understand whether there exist electrical structures inside the rock mass, whether the rock mass is intact or not. We applied the controlled source audio-frequency magnetotelluric method (CSAMT) to confirm that. Three-dimensional numerical modeling of finite difference method was performed for typical structure in the study area, and response characteristics were analyzed to confirm which actual frequency range can be chosen and what structure dimension can be detected. Then we laid out 14 parallel survey lines to carry out data acquisition. By analyzing typical sounding curves, combined with drilling information and the inversion results, we suggest that the rock is intact and suitable for building a repository, which is a good recommendation for government department. [ABSTRACT FROM AUTHOR]

To identify problematic geological structures which would be encountered when driving tunnels in the high mountainous area of South West China, a joint geophysical and engineering geological study was made. The tunnels will form part of a project to divert water from the Yangtze to the Yellow Rivers. A controlled source audio-frequency magnetotelluric method (CSAMT) was carried out in 2004 between the Ma-ke and Jia-qu rivers in high, steep terrain. The paper discusses the method of data collection, processing, and analysis for the West route. The faults/fractures identified will need to be taken into account in the design and construction of the tunnel. [ABSTRACT FROM AUTHOR]

We conducted broadband Magnetotelluric survey to obtain 2D lithospheric electrical structures of Alxa block through two NE-SE trending profiles, which revealed the electrical evidence of bidirectional subduction of Paleo-Asian Ocean with spatial difference beneath Enger Us fault belt. [Display omitted] • Lithospheric electrical structures of the Alxa block were imaged through two NW-SE BMT profiles. • There was bidirectional subduction of the Paleo Asian Ocean beneath the Enger Us fault belt. • The low resistivity bodies of the middle and upper crust in the northwest are related to large-scale horizontal nappe tectonics. • The high conductivity bodies that extend deep in the southeast are attributed to the partial melting. The Alxa Block, situated between the Tarim and North China cratons, is essential to understand the tectonics of northwest China. It has undergone several tectonic cycles, including rifting from northern Gondwana in Neoproterozoic, subduction-accretion of the Paleo-Asian Ocean during Paleozoic, and intracontinental deformation in Mesozoic. Broadband magnetotelluric data covering a frequency range of 320 Hz to ∼ 10000 s was collected along two NW-SE trending lines across major tectonic units of the Alxa region to investigate the deep structures of the Alxa Block. By applying the nonlinear conjugate gradient (NLCG) inversion approach, two-dimensional (2D) electrical resistivity models were obtained at a 100 km depth. These findings indicate that the Zhusileng-Hangwula and Zongnaishan-Shalazhashan tectonic zones have high resistivity in their lower crust and upper mantle, with an overall layered high-low–high resistivity pattern. The upper crust of the Nuru-Langshan tectonic zone is primarily characterized by high resistivity values, whereas the lower crust and upper mantle contain a large-scale low-resistivity (or conductive) zone that is likely the result of partial melting. The large-scale Early–Middle Jurassic nappe structures may be connected to sub-horizontal low-resistivity anomalies in the shallow strata, which are located up to 20 km below the Yagan and Zhusileng–Hangwula tectonic zones. Below the Engger Us fault, two low-resistivity bands are interpreted as the product of bidirectional subduction and final closure of the Paleo-Asian Ocean. The Alxa Block may have subducted southwards beneath the Ordos Block, as suggested by a clear low-resistivity anomaly between the two blocks. Furthermore, partial melting may have happened for high-conductivity bodies in the upper mantle based on the modified Archie formula's evaluation of their melting degree. [ABSTRACT FROM AUTHOR]

This paper deals with the study of multi-channel adaptive noise cancellation with a focus on its application in electromagnetic (EM) telemetry. We presented new variable step-size least mean square (LMS) techniques: regularized variable step-size LMS and regularized sigmoid variable size LMS, for electromagnetic telemetry data processing. Considering the complexity and spatial distribution of environmental noise, algorithms with multiple reference signals were used to retrieve transmitted EM signals. The feasibility of the regularized variable step size LMS algorithms with numerical simulation was analyzed and presented. The adaptive processing techniques were applied in the recovery of frequency and binary phase shift key modulated signal. The proposed multi-channel adaptive technique achieves fast convergence speed, low mean squared error and is shown to have good convergence characteristics compared to conventional methods. In addition to attaining good results from the multi-channel adaptive filter and performing the signal analysis in real-time, we implemented combined fast effective impulse noise removal techniques. The combination of median and mean filters was effective in removing a wide range of impulsive noises without distorting any other data points. Further, electromagnetic telemetry data were acquired during a drilling operation in Sichuan province, China, for real field application. Data processing workflow was designed for EM telemetry data processing based on the noise characteristics, simulation results and expected result for demodulation. To establish a comprehensive overview, a performance comparison of the acquisition array system is also provided. Conclusively, the introduced multichannel adaptive noise canceling techniques are very effective in recovering transmitted EM telemetry signals. [ABSTRACT FROM AUTHOR]

This paper deals with the study of multi-channel adaptive noise cancellation with a focus on its application in electromagnetic (EM) telemetry. We presented new variable step-size least mean square (LMS) techniques: regularized variable step-size LMS and regularized sigmoid variable size LMS, for electromagnetic telemetry data processing. Considering the complexity and spatial distribution of environmental noise, algorithms with multiple reference signals were used to retrieve transmitted EM signals. The feasibility of the regularized variable step size LMS algorithms with numerical simulation was analyzed and presented. The adaptive processing techniques were applied in the recovery of frequency and binary phase shift key modulated signal. The proposed multi-channel adaptive technique achieves fast convergence speed, low mean squared error and is shown to have good convergence characteristics compared to conventional methods. In addition to attaining good results from the multi-channel adaptive filter and performing the signal analysis in real-time, we implemented combined fast effective impulse noise removal techniques. The combination of median and mean filters was effective in removing a wide range of impulsive noises without distorting any other data points. Further, electromagnetic telemetry data were acquired during a drilling operation in Sichuan province, China, for real field application. Data processing workflow was designed for EM telemetry data processing based on the noise characteristics, simulation results and expected result for demodulation. To establish a comprehensive overview, a performance comparison of the acquisition array system is also provided. Conclusively, the introduced multichannel adaptive noise canceling techniques are very effective in recovering transmitted EM telemetry signals. [ABSTRACT FROM AUTHOR]

Equivalence causes non-uniqueness in interpretations of the grounded-wire transient electromagnetic method (TEM). Many different layered models may produce the same response curves practically. However, the conventional theory of equivalence is based on the three-layer geo-electric models while the earth may not be reducible to a simple three-layer structure. Therefore, it is important to perform research on equivalence based on more complex models to reduce the uncertainty the grounded-wire TEM interpretations. Here, we extend the theory of equivalence based on a multi-layer target in the grounded-wire TEM, consisting of SS-, HH-, and TT-type. The analysis of relative error is applied to investigate the effect of measured components and receiver locations on equivalence. The results show that equivalence of multi-model occurs when any of three conditions is satisfied: the longitudinal conductance is constant in the far area, the thickness of targets do not change, or the transverse conductance of a multilayer target remains unchanged. In order to largely resolve the effect of equivalence on data interpretation, a strategy combined with short-offset survey and joint inversion of the electric component and magnetic component is presented and verified by the field survey in Shanxi Province, China. • Equivalence causes non-uniqueness in interpretations of the grounded-wire TEM method. • The conventional theory of equivalence is based on the three-layer geo-electric models. • It is important to perform research on equivalence based on more complex models. [ABSTRACT FROM AUTHOR]

• The gold deposits of the Qingchengzi orefield are controlled by faults. • The Jianshanzi fault zone is the major ore-controlling structure. • A magnetotelluric study was undertaken along the The Jianshanzi fault suggesting excellent potential for new, deep-seated gold discoveries in the Qingchengzi orefield. The Liaodong Peninsula in northern China has undergone multi-stage magmatic and tectonic modifications, similar to those recorded by the Jiaodong gold province that is the largest gold-producing district in China, indicating that Liaodong Peninsula has great potential for new discoveries. However, no significant gold deposit has been discovered thus far at depths below 1.5 km, the typical depth of the gold-bearing system in the comparable Jiaodong gold province. This study focused on the Qingchengzi orefield on the northern Liaodong Peninsula. Qingchengzi recorded multiple post-magmatic hydrothermal gold-mineralizing events along the Jianshanzi fault zone, the main ore-controlling structure in the orefield. Given the potential for undiscovered, deep-seated gold mineralization along the Jianshanzi fault zone, we performed a magnetotelluric (MT) study designed to identify any deeper exploration targets. The surface electromagnetic prospecting (SEP) system, a portable instrument suitable for use in electromagnetically mountain environments, was employed for the purpose of acquiring the MT data. Shallow conductive anomalies identified in the vicinity of the Jianshanzi fault zone were tested by known drilling recorder. The survey not only helped to generate a detailed map of the deep geological architecture, but also allowed us to estimate the vertical extent of the known gold orebody to a depth of more than 2 km. [ABSTRACT FROM AUTHOR]

The Tianshan-Xingmeng Orogenic Belt (TXOB) is located in China's northern region, and is one of the country's most important Au-Pb-Zn-Ag-Mo-Cu metallogenic belts. This metallogenic belt is known to have good minerogenetic conditions and exploration potential. However, the engineering detection depths of the majority of the metal deposits are generally less than 300 m. Therefore, high precision geophysical detection techniques are necessary to achieve the required accurate detection results. Among the commonly used techniques, the Stratagem EH4 system has been found to be the better choice for the deep prospecting of the metal deposits in the TXOB. Furthermore, a good understanding of the physical characteristics of the different rock formations in the region is essential for effective and efficient geophysical prospecting. This study revealed that the resistivity values of the ore and rock formation walls were different. In previous related research, the EH4 Conductivity Image System, which is a system combining MT and CSAMT, has been successfully used for ore explorations in China. The results of the geophysical prospecting processes indicated that there was good exploration potential of the aforementioned system in the TXOB. In the current study, the hidden gold ore bodies of disseminated (altered rock-type) gold deposits within the study area were defined by resistivity values of less than 150–1000 Ωm. The concealed gold orebodies in the quartz-type gold deposits were confirmed by resistivity values of 300 Ωm. The mineralization anomalies of the epigenetic lead-zinc deposits were defined by the smaller resistivity values, which were lower than the 100–1000 Ωm range. [ABSTRACT FROM AUTHOR]