Geophysical Prospecting Methods Research Articles

Geological exploration of coal mine burnt rock and waterlogged area boundary based on transient electromagnetic and high-density electrical resistivity

The water-rich burnt rock may threaten the safe production of coal mines. Identifying the boundaries of burnt rock and the water-rich area is of great practical significance for the ensuring the safety of mining operations. Transient electromagnetic and high-density resistivity methods are commonly employed in geophysical exploration, such as for investigating the presence of groundwater or delineating boundaries of altered rocks. These methods are non-invasive and provide detailed information about subsurface conditions without the need for drilling or excavation. The Jiangjun Gobi No. 1 open-pit coal mine is situated in the Kalamaili fault zone and is characterized by a high groundwater content. In certain mining sites within the study area, the inflow of water reaches tens of thousands of cubic meters per day, which significantly impacts production and presents major risks. To accurately determine the boundaries of burnt rock and water accumulation areas in the Jiangjun Gobi No. 1 open-pit coal mine, this paper uses different geophysical prospecting methods based on the depth of the strata. The middle and deep parts are investigated using the high-resolution transient electromagnetic method, while the shallow parts are examined using the high-accuracy high-density electric method. Through analyzing the electrical characteristics of the study area, it is inferred that the low-resistivity area in the northwest represents a shallow surface water-rich region. This area extends continuously towards the northwest, is not trapped, and is supplied by surface water. The deep low-resistivity zone primarily consists of sandstone and coarse sandstone. It is inferred that the low-resistance area in the southern part of the study area is also a shallow surface water-rich region, extending towards the east and west sides, not trapped, and supplied by surface water. The deep low-resistivity zone mainly comprises a combination of sandstone, coarse sandstone, and burnt rock, with intermittent layers of mudstone and argillaceous sandstone. The boundary line of burnt rock (coal-bearing strata) is located in the south of the study area. The resistivity of burnt rock (coal-bearing strata) is higher than that of the surrounding rocks, and the resistivity of coal seams is slightly higher than that of sandstone with larger porosity. Estimating the boundaries of groundwater and altered rocks serves to prevent geological disasters and provides valuable information for mineral development and ecological protection.

Application of Borehole Geophysical Prospecting Method in Pile Foundation Detection of Existing Buildings

It is particularly important to find out the pile foundation of existing buildings for building safety protection and engineering construction safety during the development and utilization of urban underground space. As a non-destructive, efficient and economic method, the borehole geophysical techniques such as magnetic gradient method, ground penetrating radar method and parallel seismic test method are used to detect the pile foundation of existing buildings, which have obvious advantages. According to the combined abnormal characteristics such as "strong magnetic anomaly, electromagnetic wave in-phase axis change and diffraction wave anomaly at the pile end, P-wave velocity variation", the pile foundation length can be judged.

Geodynamics and Metallogeny of Copper in the Middle Zone of Central Kazakhstan and its Prospects

In the middle part of Central Kazakhstan there are linear copper-bearing riftogenic-orogenic zones of sublatitudinal strike (Spassk and Uspensk zones) with numerous sulfide and porphyritic deeply eroded deposits and ore occurrences of copper not currently presenting commercial interest due to insignificant reserves and Zhezkazgan basin conjugated with them in which first-rate deposits of cupriferous sandstones are located. Formation of sulfide deposits occurred in the process of riftogenesis, and porphyritic deposits were formed in orogeny. Copper was carried away by river waters together with broken rocks, minerals and organic matters from the mentioned zones with humid climate into arid littoral-deltoid areas of the Zhezkazgan sea basin in the Carboniferous-Permian, where water soluble copper compounds sedimented under the influence of hydrogen sulphide of biogenic sulfate-reduction. Gradual upthrusting of the north side of the basin shifted the riverbed in the undercurrent many times. This resulted in forming of deposits of different ages: from the Middle (The North group) and Middle-Upper Carboniferous (Zhezkazgan) to the Upper Permian (Taskora). It is possible that between the latter ones there are some large deposits localized in lenses of alluvial deposits controlled by paleofaults situated in multiple distances. To discover them a complex of geological and geophysical prospecting methods is proposed.

Aplicación de métodos eléctricos y electromagnéticos, combinados con el análisis de propiedades térmicas, a la caracterización y del recurso geotérmico de baja y media entalpía

The relationship between the thermal properties of the ground and the efficiency of geothermal installations located in the ground is well known. The different geologies and subsurface structures have a decisive influence on the behavior of a given location with respect to heat exchanges. The electrical and electromagnetic methods of geophysical prospecting can be useful in determining the compositions and structures present in a given area in order to be able to perform energy modeling that will help to design more precisely the ideal geothermal heat exchanger for that area. In this work we study the relationship, observed in different studies, between the geological structure and the electromagnetic magnitude measurements collected from these prospecting methods. Possibilities are also explored in contact with the idea of relating electromagnetic and thermal magnitudes in the search for new ideas to develop more accurate methods of geophysical prospecting of the geothermal resource.

Comprehensive Evaluation of Goaf Range in a Coal Mine with a Complex Terrain through CSAMT and an Activated-Carbon Method for Radon Measurement

Underground goaves were left in many mining areas due to the continuous exploitation of coal resources. These mining areas seriously affect the production safety of the mines and the safety of life and property of the surrounding residents. Enormous safety hazards will be generated if the goaf range is not accurately controlled. In this study, we proposed a method for the detection of goaves in coal mines with a complex terrain by combining controlled source audio-frequency magnetotellurics (CSAMT) and an activated-carbon method for radon measurement. The disadvantage of failing to interpret goaf depth for the activated-carbon method for radon measurement was compensated by the advantage of the capability of goaf-depth sounding for CSAMT. Subsequently, the reference for CSAMT data was provided by the immunity of the activated-carbon method for radon measurement to the influences of terrain, earth electricity, and EMF. On this basis, the proposed method was employed to detect the goaf of Houjiagou Coal Mine in Liulin County, China, and obtained reliable detection results. The feasibility of the comprehensive geophysical prospecting method in the complex terrain was verified and it provides a new reference for the detection method of goaves with other conditions.

Integrated Interpretation of Electrical Resistivity Tomography for Evaporite Rock Exploration: A Case Study of the Messinian Gypsum in the Sorbas Basin (Almería, Spain)

In this study, we conduct an investigation of the Sorbas Basin (Almería, Spain) on the Messinian gypsum unit using geophysical prospecting methods. Geophysical electrical resistivity tomography (ERT) methods were applied to study the subsurface of this gypsum unit, the exploitation of which could be of interest economically, with different commercial specifications for alabastrine and selenitic gypsums. For the interpretation of the different ERT images, the data for the surface geology, borehole cores, and seismic refraction conducted at a point within the ERT profiles were used. The results obtained from this investigation can be used as a reference for other similar studies in other regions. It was observed that selenitic gypsum is more resistive than alabastrine gypsum; therefore, the diagenetic processes of dehydration (anhydritization) and hydration (gypsification) increase the “percolation” phenomenon through possibly ensuring a greater connectivity of the shale matrix. Fracturing and moisture can be used to fully determine the resistivity of the purest and most resistive gypsum, to the point of considerably lowering the resistivity in an entire area affected by fracturing. The use of different tests with different lengths for the same profile can help one better understand the structure of the gypsum body in the subsurface, especially when there are shale intercalations or more- or less-pure levels of gypsum that do not reach a value of a few meters in thickness, because these thinner levels of a few meters are not defined in the ERT images when the test is performed at depths of up to 75 m.

Application of geophysical prospecting methods ERT and MASW in the landslide of Daofu County, China

Natural disasters such as debris flow caused by earthquakes seriously threaten the local infrastructure and economy, as well as the lives of people in the area. As the material source of debris flow, it has significance to accurately and effectively study the underground structure of the landslide to prevent debris flow disasters. A landslide has a complex structural system, and its underground characteristics play an important role in its stability. The early identification of fracture surfaces and unstable bodies, and assessment of potential hazards are essential for prevention and protection. The research object of this paper is a landslide that occurred in Yige Village, Xianshui Town, Daofu County, which is on the Xianshui River Earthquake Zone, an area subject to frequent earthquakes. In western Sichuan, the frequent occurrence of landslides has caused considerable economic losses. Developing methods for efficient and accurate risk assessment is a top priority. The Daofu landslide is a typical example of a landslide directly threatening the road below and forming a debris flow channel. The lithology is composed of Jurassic sedimentary rocks, such as marl and clay, covered by limestone. In this study, we combined traditional methods (drilling and field investigation) with two geophysical techniques, multichannel analysis of surface waves (MASW) and electrical resistivity tomography (ERT) to effectively determine the electrical characteristics, velocity characteristics and spatial structure of the landslide. It is found that the buried depth of the sliding surface of the landslide is about 16–20 m. The sliding body above the sliding surface forms a low velocity and low resistivity Quaternary cover. The rock mass below the sliding surface is Triassic Zhuwo Formation sandstone and slate with high velocity and high resistivity. According to comprehensive analysis, the landslide lacks sufficient stability under rainstorm. Our study shows that the use of MASW and ERT can quickly and effectively characterize the subsurface of landslides to assess landslide risk and prevent debris flow hazards.

On the possibility of using the methods of geophysical electrical exploration for current control of the quality of soil processing

Purpose. Improving the quality of tillage by creating an indicator of current control to be installed at the machine-tractor unit. Methods. Based on the analysis of methods of geophysical research of the earth’s crust, a method of current control of soil cultivation during technological operations is proposed. Results. Variants of block diagrams of integral indicators of the quality of execution of technological processes of soil cultivation using methods of geophysical electrical prospecting are proposed. Conclusions 1. To ensure the quality of soil cultivation, it is necessary to use continuous current control methods. 2. It is expedient to create an indicator of integral soil tillage quality control for installation on existing machine-tractor units using the existing theoretical developments of geophysical electrical prospecting. 3. Modern means of measuring and processing the results allow creating indicators of the current integrated quality control of soil cultivation. Keywords: machine-tractor unit, quality, tillage, geophysics, electric survey.

Evaluation of Compressive Geophysical Prospecting Method for the Identification of the Abandoned Goaf at the Tengzhou Section of China’s Mu Shi Expressway

Subsidence deformation of abandoned goafs can induce cracking, distortion and even collapse of surface buildings (structures), and thus, subsidence deformation poses a great threat. Accurate detection of the abandoned goaf location and overburden morphology is an important prerequisite for stability evaluation and scientific management of surface buildings (structures), and effective detection methods are bottlenecks for accurate detection. Taking the abandoned goaf in the Tengzhou section of China’s Mu Shi expressway as an engineering example, step-by-step detection, traditional detection and combination methods are used to determine the location of the underlying abandoned goaf and overburden morphology. First, we conduct disaster investigation on the expressway and surface within the affected area of the abandoned goaf and initially determine the detection area. Then, according to the principle that the detection range can be examined step-by-step from large to small, the high-density resistivity method is used for detection, and the high-resolution seismic method is further selected to analyze the target area. Then, based on the results of the resistivity method, the position of the abandoned goaf is evaluated with the high-resolution seismic method, and the distributions of the overburden subsidence, the water-filled fractured zone and the caving zone (the three belts) are determined. Finally, boreholes are drilled deep into the bottom of the abandoned goaf at specific locations and the distributions of the abandoned goaf and three belts are verified and corrected with drilling data, acoustic detection and borehole TV imaging technology, thereby providing accurate data on abandoned goafs for highway stability evaluation.

Revisiting Fara: Comparison of merged prospection results of diverse magnetometers with the earliest excavations in ancient Šuruppak from 120 years ago

AbstractAncient Šuruppak, today Fara, was one of the major Sumerian cities in Mesopotamia. It was situated along one of the ancient watercourses of the Euphrates River. Findings date it back to the Jemdet Nasr period around 3000 bc with a continuous occupation until the end of the Ur III period around 2000 bc. Fara was first explored and excavated by the Deutsche Orient‐Gesellschaft in the years 1902 and 1903 under the direction of Walter Andrae. Multiple excavation trenches with lengths up to 900 m transect the 1 km2 wide mound and are still visible today which enables us to georeference the excavation maps. Today, the 2.2 km2 wide archaeological area is dry and without any vegetation. Thousands of deep looting pits are covering the majority of mound which not only destroyed its upper metres but also challenge the application of geophysical prospection methods and their interpretation. The magnetometer prospecting of selected areas on and around the mound was carried out with three devices, two total field magnetometers and one gradiometer. The individual survey areas were combined in post‐processing by applying a high‐pass filter on the total field data sets and multiplying the vertical gradiometer data sets by a factor of two. This approach provides visually uniform magnetograms, despite being obtained by different devices, which simplifies subsequent visual interpretation. These magnetograms enable us to review, and to extend the results of the old excavations. The comparison show a good correlation in accuracy to the old drawings and positive identification of the already excavated features with magnetometry. Highlights of the survey are the discovery of the city wall confirming its existence, the layout of a unique building complex in the centre of the mound, likely a temple, traces of canals inside the city and an evaluation of magnetometer prospection over a looted area.

Combining geophysical prospection and core drilling: Reconstruction of a Late Bronze Age copper mine at Prigglitz-Gasteil in the Eastern Alps (Austria).

Prehistoric mines are often too large and too deep for conventional archaeological excavations. Non-destructive and minimally invasive methods of prospection can help to overcome these limits. Our case study of a Late Bronze Age opencast mine (ca. 1050 to 780 BC) shows the potential of geophysical prospection methods combined with core drillings. For the reconstruction of this mine, we combined electrical resistivity and induced polarization (IP) tomography, seismic refraction tomography (SRT) and ground penetrating radar (GPR). The geophysical data were collected based on an orthogonal grid of 10 longitudinal and transverse profiles, laid out over an area of ~330 × 300 m. The profiles allowed a three-dimensional interpolation of the geological units, the mining dumps, the mining areas and the residual mineralization. Additionally, two deep cores were drilled to ground-truth the geophysical prospection results. They provided information about the stratification at intersections of the measurement grid, and this proved crucial for validating the interpreted geophysical profiles. Each geophysical method applied provided different information for the reconstruction of the site: the electrical resistivity tomography offered the best clues as to the locations of the geological units and the dumps, the seismic refraction tomography visualized the transition between the dump or backfill layers and the underlying bedrock, and the IP measurements revealed residual mineralization. The georadar measurements, on the other hand, did not contribute to the interpretation owing to the limited depth of penetration. Based on the combination of borehole and geophysical data, it was possible to develop a hypothetical model of an open-pit mine for copper ore that developed in three phases (mines A-C) during the Late Bronze Age. Without the control provided by the core drillings, one of the mining areas (mine A) could not have been correctly identified in the geophysical prospections.

Geoelectric, magnetic susceptibility, and geochemical survey as a tool to clarify the origin of Bronze Age water reservoirs at the Štěpánov hillfort, Czechia

Geophysical prospecting methods can reveal structures and objects connected with past settlement in a noninvasive manner and thus contribute significantly to understanding a fortified settlement’s function. It is challenging to discriminate properly between geogenic and anthropogenically influenced soil features. In highly magnetic soil that is locally influenced by water, this is not straightforward and more detailed study is needed. We propose to address this challenge by combined measurements of electrical resistivity tomography, magnetic susceptibility, and elements content on vertical soil profiles. Pedological description is completed by examining the content of soil organic matter (OM) and active soil reaction. We found this combination of methods to enable distinct identification of water reservoirs (WR) of artificial versus natural origin. Soils in the vicinity of the three WRs reflect physicochemical mineral changes by magnetic susceptibility (χ), its frequency dependence parameters (χFD, and χFD,%), and differences in element concentrations. The strongly magnetic Cambisol and Cambisol with gleying features at the Štěpánov hillfort reveal the best links between χF,χFD, and concentrations of the elements Fe, Mn, Ti, Sr, and Ca. The most enriched elements in soil were Pb, S, K, Rb, Si, and Zr compared to parent rock. Topsoil accumulates Pb and S originated from recent human activities. Zinc positively correlates with OM and magnetic parameters in the acropolis and near WR1. Stagnant water has a significant effect on links between magnetic susceptibility and element concentrations, but χ significantly correlates with Ti, Al, Ca, Sr, and Cr. This study provides new insight into the applicability of magnetic susceptibility for the identification of past settlement at highly magnetic sites in discriminating between natural and anthropogenic particles.

Dolní Věstonice – Vysoká zahrada: an Integrated Geophysical Survey of an Early Medieval Fortified Settlement

The fortified settlement at Dolní Věstonice – Vysoká zahrada belongs to the important Early Medieval centres connected with the establishment of the Přemyslid domain in Moravia. The site functioned as a local administrative and economic centre from about the middle of the 11th century to the end of the 12th century. In written historical sources it was known as Strachotíngrad (“Castrum Strachotín”). Between 1948 and 1986, several minor archaeological excavations were made at this site. Our work’s purpose was to gain new knowledge by deploying proven geophysical prospecting methods in archaeology. The first two of these methods, Electrical Resistivity Tomography (ERT) and Groundpenetrating radar (GPR) focused on the rampart. Within the third used method – magnetometry, we focused on the prospection of the inner area of the hillfort. Based on the results, it was possible to identify some of the construction features of the fortification and locate the course of the no longer existing rampart and several settlement structures. At the same time, the geophysical survey also made clear the overall plan of past archaeological excavations.

The Deserted Manor of Noer, Schleswig-Holstein, Germany. Geophysical Prospection Methods in Comparison

Manors are an important component of the cultural-economic history of Northern Germany and Southern Scandinavia. We present the results of a geophysical prospection that led to the identification of a previously unknown manor near the village of Noer, Schleswig-Holstein, Northern Germany. Although magnetic gradiometry provides a fast way to cover large areas, it does not provide accurate depth estimates, is affected by magnetic blanking and is unable to detect differences in water content. Therefore, we applied a combination of different geophysical methods to optimize the non-invasive reconstruction of the target and its surroundings not only with respect to building structures but also in relation to the surrounding landscape. In particular, a combination of magnetics, ground-penetrating radar (GPR), electromagnetic induction (EMI), electrical resistivity tomography (ERT), and soil samples were carried out to determine: (1) the object's exact location; (2) the building structure and state of preservation; and (3) any additional structures in the surrounding area. We detected a tripartite building of 22 by 27 m, with several inner walls, which was located underneath a topographic high on the surveyed field. The bulk structure is identifiable most clearly in the magnetic and EMI inphase component maps. GPR profiles and soil samples indicate flooring or foundations in part of the building. Their shallow depths of less than 2 m below the surface and debris clusters close to the surface indicate at least partial demolition. A surrounding wall was found about 5 m outside the building. The area in between shows no magnetic anomalies, lower resistivities in EMI and ERT, and low GPR reflection amplitudes. Soil samples suggest a moat or other water feature. Archaeological artifacts found at the location characterize the building as a 16th to 17th century brick manor. Other objects, like a suspected farmyard and access path could not be found. A comparison with historical sources suggest that the mansion is in relation to the manor Grönwohld. After a change of the owner it was degraded to a Meierhof, and subsequently the building decayed and was forgotten.

3-D Inversion of Gravity Anomalies by Combining Power-Spectrum Derived Adaptive Weighting and Cross-Gradient Regulation: Application to Molybdenum–Copper Deposit

Gravity measurement is an important geophysical prospecting method for mineral exploration. With most of the shallow ore deposits in China being exploited, the future targets for exploration will be aimed at the deep mineral resources about 4-km underground. To improve the resolving ability in the vertical direction of the 3-D density inversion to find deep-source minerals, we propose to achieve the inversion of gravity anomalies by combining power-spectrum derived adaptive weighting and cross-gradient regularization. First, spectral analysis is utilized to conduct the source-depth separation, and the adaptive weighting function is designed depending on the slope of the radial logarithmic power spectrum of the gravity anomaly, which can enhance the correspondence for the field sources with different depths to improve the vertical resolution relatively. Thus, each separated source with different depths could be given an adaptive weighting coefficient in each separated inversion. Second, the cross-gradient technique is introduced as a structural constraint in the objective function to further constrain the separated inversion process. By performing two-cuboid-source cases, it can be seen that this combination calculated approach has great potential to improve the quality of the inversion results. When examining the inversion of the actual gravity data from certain ore district in the west of Zhen’an, South Qinling, we speculate that a potential deep ore body would exist in the deposit via utilizing the recovered density model obtained by the proposed method.

Analysis of response characteristics of comprehensive geophysical prospecting technology in concealed water-bearing structures

The mine transient electromagnetic method and the mine direct current method were used to detect the abundant water at 1,144 m ahead of the track roadway on the 9101 working face in the Chaoyang Coal Mine. Low-resistance abnormal areas indicated by both methods were analyzed comprehensively for early warning of water hazards. The results showed that two low-resistance abnormal areas were indicated by the mine transient electromagnetic method and the existence of a low-resistance abnormal area was indicated by the direct current method. Both methods showed the existence of a low-resistance abnormal area ahead, delineating possible illegal mining areas of old kilns ahead, which were verified by drilling. The methods can indicate the direction for drilling. The case shows that the combination of different geophysical prospecting methods can eliminate their limitations and that comprehensive detection can reduce omissions, which has a good guiding significance for safe mine excavation.

SOME PROBLEMS OF ELECTRICAL GEOPHYSICAL PROSPECTING METHODS USED FOR EXPLORATION OF ORE DEPOSITS

Electrical geophysical prospecting methods are widely used at different stages of geological exploration. In the last two decades, new computer technologies and satellite navigation systems were successfully introduced in the geophysical industry. As a result, exploration technologies have improved, and new geophysical methods have been developed, such as electrical resistivity tomography (ERT) and spectral induced polarization (SIP) methods. An important role in ore geophysics is played by magnetotelluric (MT) methods. In this article, we focus on the issues of methodology and interpretation of electrical prospecting data for solving ore exploration problems. Special attention is paid to the induced polarization (IP) method that is most widely used in mineral exploration and mining industry as one of the most important and most dynamically developing techniques of ore geophysics. In addition, the issues of correct choices of survey scales and the use of automatic 2D and 3D inversion programs are considered.

Engineering application of fuzzy evaluation based on comprehensive weight in the selection of geophysical prospecting methods

Engineering application of fuzzy evaluation based on comprehensive weight in the selection of geophysical prospecting methods

Geophysical Assessment of Groundwater Vulnerability to Diesel Contamination at a Telecommunication Mast in Adebayo Area, Ado-Ekiti, Southwestern Nigeria

Abstract An appraisal of the groundwater vulnerability to contamination risk at Adebayo in Ado-Ekiti, Southwestern Nigeria, was carried out using the electrical resistivity method of geophysical prospecting. Two traverses of length 100 m each were established for both vertical electrical sounding (VES) and dipole-dipole. Six (6) Vertical Electrical Sounding (VES) and 2-D dipole-dipole profiling techniques of the electrical resistivity method were adopted for the geophysical investigation. The results show variations in resistivity values, depicting four to five geologic layers: the topsoil, laterite, weathered layer, fractured, and the fresh basement. It was observed from the correlation of the geoelectric section and 2-D resistivity image along traverse 1 (TR1) that the groundwater in the study area flows towards the southwestern part, and the fractured basement serves as a migration pathway to the diesel oil in the same direction as groundwater flow. The fractured basement (Well 2) with no lateritic cover has higher resistivity values compare to the fracture zone that was found directly under the mast which was overlain by the laterite. Comparing the resistivity values of Well 1 and 2, Well 2 that was drilled into the fractured basement has more traces of the contaminant than Well 1.

Review of Processing and Interpretation of Self-Potential Anomalies: Transfer of Methodologies Developed in Magnetic Prospecting

The self-potential (SP) method is one of the most inexpensive and unsophisticated geophysical methods. However, its application is limited due to the absence of a reliable interpreting methodology for the complex geological-environmental conditions. To exclude disturbances appearing in the SP method, a few ways for their removal (elimination) before quantitative analysis are presented. A brief review of the available interpretation methods is included. For the magnetic method of geophysical prospecting, special quantitative procedures applicable under complex physical-geological environments (oblique polarization, uneven terrain relief and unknown level of the normal field), have been developed. The detected common peculiarities between the magnetic and SP fields make it possible to apply the advanced procedures developed in magnetic prospecting to the SP method. Besides the reliable determination of the depth of anomalous targets, these methodologies enable the calculation of the corrections for non-horizontal SP observations and to determine the orientation of the polarization vector. For the classification of SP anomalies, is proposed to use a new parameter: the ‘self-potential moment’. The quantitative procedures (improved modifications of characteristic point, tangent techniques and the areal method) including the determination of the SP vector and SP moment, have been successfully tested on models and employed in real situations in mining, archaeological, environmental and technogenic geophysics. The obtained results indicate the effectiveness of the presented methodologies.