Application Of Electromagnetic Methods Research Articles

Research on the Application of Electromagnetic Method in the Exploration of Altered Rock‐type Gold Deposits in the East Kunlun Metallogenic Belt

Research on the Application of Electromagnetic Method in the Exploration of Altered Rock‐type Gold Deposits in the East Kunlun Metallogenic Belt

Application of Electromagnetic Method in the Detection of Buried Karst Groundwater in the North-South Archaic Uplift, Ningxia, China

Abstract The North-South Archaic Uplift Karst Area, situated in the Ningxia Hui Autonomous Region, exemplifies the presence of underground karst formations in northern China. This work utilizes the regional hydrogeological survey to carry out geophysical investigations. The objective is to examine the resistivity qualities of layers and formations in order to investigate the attributes of subterranean karst water. The results indicate the existence of karst groundwater within the carbonate fault zone, covered by Quaternary loess with a high resistance and Neogene mudstone with a low resistance. The resistivity of the fault zone is relatively lower compared to the surrounding carbonate rock. The core principle of this rule can be concisely stated as “detect regions of high resistance within regions of low resistance, and detect regions of low resistance within regions of high resistance.” The electrical characteristics of the subterranean karst formation greatly aid in identifying ideal locations for investigating karst groundwater.

Using Low Frequency Ground and Downhole TDEM to explore for Massive Sulfide Mineralisation in the Carajás Mineral Province

SummaryThe Carajás Mineral Province in Brazil hosts the highest concentration of major IOCG deposits in the world. Airborne and ground electromagnetic (EM) methods are frequently applied when exploring for these deposits using relatively high operating frequencies (25Hz - 30Hz). This frequency range limits the survey to effectively detect shallow, weakly to moderately conductive sources.An airborne EM survey (VTEM) using a 30Hz base frequency has been flown by Falconbridge Ltd over the Pedra Branca deposit in 2005, identifying two discrete anomalies in the area. The high frequency nature of the VTEM system did not provide good depth resolution of the anomalies and follow-up ground EM surveys were conducted.An orientation fixed loop EM (FLTEM) survey was carried out at Pedra Branca to compare the effectiveness of using lower frequency (2Hz) ground EM against existing VTEM and previous high-frequency ground EM surveys. The application of EM methods using frequencies of 2Hz and below enables the detection of late time conductors by recording much later in time compared to high frequency systems. These typically detect stronger, deeper conductors which are commonly related to higher grade and/or thicker massive sulfide mineralisation.The results of this new survey significantly increased the resolution of the conductor. Modelling of the FLTEM data shows excellent correlation with the high-grade mineralisation surface, down to a depth of approximately 550m.An FLTEM survey was also completed over the Azevedo prospect and provided a significant improvement in resolution compared to the historical, poorly defined VTEM anomaly. The FLTEM data provided an 80m lateral adjustment to the initial anomaly, allowed detailed modelling, and reduced drill testing uncertainty.Ground and downhole EM surveys at lower frequencies are now being used extensively to effectively explore for massive sulfides with a greatly increased depth of investigation compared to historical airborne and ground EM surveys.

Application of electromagnetic methods in force sensing, with emphasis on micro, nano and pico ranges

This paper reviews, compares and classifies some precision electromagnetic methods used for measuring force and related quantities. Several sensing devices are described (magnetoresistive, magnetostrictive and hall elements) as well as complex equipment (AFM, EMFC and SQUID), covering a wide variety of applications in the range of micro-, nano- and piconewtons.

Application of Electromagnetic Method in Geothermal Investigation in the Inner Mongolia

Geothermal energy is an important type of renewable energy. It can be easily mined at low cost, and has the advantages of no pollution and recycling utilization. The exploitation of geothermal energy can bring about significant economic, social and environmental benefits. The base for geothermal energy exploitation is the exploration of geothermal field. Analysis of the geological background of regional structure and heat control, collect adjacent areas geological data in Inner Mongolia with the use of electromagnetic sounding.

Applications of Electromagnetic Methods in Selecting Ground Sites for Ultra High Voltage Power Plant

We present a combined electromagnetic method which consist of Audio Magnetotellurics (AMT) and Transient Electromagnetic method (TEM) to the utilize in the selecting sites for ultra high voltage power plant. The inversion profile gives the underground resistivity distribution for the power engineers to select proper ground site location. The result is satisfactory and some ground sites have been established already, indicating that electromagnetic method is suitable for selecting the ground site for ultra high voltage power plant.

Detection technology and application of electromagnetic method for hidden danger of water gushing at coal face

The principles, methods, technologies and application effects of several electromagnetic methods for the detection of the hidden danger of water gushing at the coal face were introduced. Also, emphasis was laid on expounding the methods, principles and effects of down-hole detections by electric transmission tomography and transient electromagnetic method. The potential of point power supplied in the underground homogeneous semi-space, as well as the response to a low-resistivity abnormal body in the homogeneous semi-space, was simulated by adopting 3-D finite element method to interpret the basic theory of the electric transmission tomography. The results of actual measurement show that the mine electromagnetic method is sensitive to water-bearing low-resistivity bodies and can play a unique role in detecting the hidden danger of water gushing at the coal face.

Biographies of the guest editors

Erika Luck was born in Leipzig, Germany in 1956. She received her diploma in Physics at the University of Leipzig in 1979 and her PhD in geophysics in 1982 (also at the University of Leipzig). From 1982 to 1991 she worked in the field of ‘deep seismic sounding’ at the Central Institute of Physics of the Earth at the Academy of Sciences in Potsdam, Germany. In 1992 she joined the University of Potsdam as a researcher. At this time she changed her topics and started research into the application of geophysical methods for the shallow subsurface. Between 1996 and 1997 she took part in the DEKORP-experiment ‘BASIN 96’ at the GFZ Potsdam (GeoForschungsZentrum). She went back to the University of Potsdam in 1997 and continued her studies in the field of applied geophysics. Her special interests are in near-surface investigations for archaeology, agriculture and soil sciences. Martin Muller has experience in geophysics, both in education and in research, that covers a broad range of applications from hydrogeophysics, environmental geophysics, geotechnical applications, civil engineering and volcanology. He performed research with geophysical methods ranging from electromagnetics, DC-geoelectrics, magnetics, gravity, seismics, ground-penetrating radar to nuclear magnetic resonance (NMR). His latest projects dealt with the application of geophysics in the saturated and the unsaturated zone, namely in agriculture and soil sciences, to assess water content and moisture dynamics. He studied geophysics at the University of Cologne, Germany and received his diploma for a thesis on magnetotellurics. In Cologne he continued with a PhD thesis on the application of electromagnetic methods to volcanoes, namely Mt. Merapi, Indonesia and Mt. Vesuvius, Italy. From 2000 until 2006 he was assistant professor at the Department of Applied Geophysics of the Technical University Berlin (TUB), Germany, as head of the rock physics laboratory and lecturer on petrophysics and well logging. During his years at TUB, he was also a project leader in projects dealing with the integration of geophysical techniques to derive the water content in soils and application of geophysics in agriculture. During the winter of 2006/2007, he was guest professor for applied geophysics and hydrogeophysics at the University of Vienna, Austria.

Open ended-coaxial Cable Measurements of Saturated Sandy Soils

The application of electromagnetic methods in the radar and micro-wave frequency band allows the fluid content of soils to be estimated; the heuristic or physically-based models permit to relate the observed electrical permittivity of the soils with the porosity and fluid saturation. The role of the effect of the free water and bound water in the overall electromagnetic behaviour of soils is discussed. The measurements of the complex electrical permittivity of samples with different fluid content were carried out using an open ended coaxial cable in the frequency range between 0.2 and 6 GHz. The data processing permitted to estimate the water content with good accuracy; the slight overestimate of the values with respect to the standard laboratory measures of the fluid content is due to the propagation of the experimental uncertainties and to the effect of the bound water.

Application of Electromagnetic Method for Mineral Prospecting in Al-Bayda Area, Yemen

أجري مسح كهرومغنطيسي في منطقة البيضاء ( جبل معبل ) لغرض التنقيب عن المعادن. تم رسم خارطة كهرومغنطيسية من القياسات الحقلية التي أجريت على أحد عشر خطا، وكان طول الخط 1300 متر ، مع مسافة بين الخطوط 100 متر، وكانت المسافة بين محطات القياس على كل خط 25مترا. رسمت منحنيات الكهرومغنطيسية من المعلومات الحقلية ، وقد فسرت نوعيا لتحديد الأنطقة الموصلة والمدفونة المحلية ، ومن ثم فسرت كميا لحساب أعماق المصادر المسببة لها ، وميلها ، والتوصيلية ، من خلال استخدام المنحنيات المعدة من قبل شركة سنتركس. لقد وجد بأن الأعماق تتراوح بين ( 30-66) مترا. إن معظم المصادر لها ميل حوالي (30) درجة جنوب شرق ، كما أن التوصيلية قد حسبت ووجدت بأنها تتراوح بين (3ـ60) سيمنس.

A Review Of Environmental Applications Of Quasi-Stationary Electromagnetic Techniques

Electromagnetic (EM) techniques are the most commonly used geophysical methods in mineral exploration. However, the use of EM measurements for environmental and engineering applications like the detection of contaminant plumes or the exploration of waste sites is relatively new. The reason for the success of the application of EM methods to environmental problems lies in the variation of conductivity caused by different geometry of pore fluids and clay contents in rocks, and by the presence of organic and inorganic contaminants. Many EM methods/instruments used for mapping near surface geology exist and nowadays they play a central role in environmental geophysics. In general, these methods can be classified in two blocks: EM methods using a plane wave source of excitation and EM methods using a controlled source like a magnetic dipole or a loop source. The Very Low Frequency (VLF, VLF-R) and Radiomagnetotelluric (RMT) methods are chosen as representative methods for plane wave techniques, while horizontal loop EM methods operating in low induction numbers (EM31, EM34) and Transient Electromagnetic methods (TEM) are chosen as representatives of magnetic dipole or loop source techniques. Basic principles, advantages and disadvantages of each technique as well as their connection to specific environmental problems will be discussed. Different successful applications of these methods are reported in the literature. However, this review will focus on three major subjects: waste site exploration, detection of contaminated earth layers, and groundwater exploration. Case histories are presented illustrating the suitability of EM methods for solving such problems.

The magnetic field perturbations produced by an ellipsoidal cavity in a uniform conductor

In the application of electromagnetic methods to the non-destructive testing of electrically conducting materials for cracks or inclusions an electric current is applied to the specimen and the presence of a flaw is indicated by the perturbations it produces in the electromagnetic field. A number of different variants of the method can be used. The presence of a flaw may be observed by measuring either electric or magnetic field perturbations and the nature of the interrogating field will be sensitive to the choice of frequency chosen for the applied current. It is well known that when alternating current is applied to conductors the current tends to be confined to a surface layer whose depth, δ, is measured by the length 1/(ωσμ) ½ where σ is the conductivity, μ is the magnetic permeability and ω the angular frequency. An important dimensionless parameter in the characterisation of the field perturbations is the ratio δ/ l , where l is a length typical of the flaw dimensions. The electromagnetic field is described as a thin-skin or a thick-skin field according as this ratio is small or large respectively. In practical applications there is a need to model both thin and thick-skin fields. In the examination of surface fatigue cracks in large scale structures fabricated by welding together ferrous steel members surface fatigue cracks with depths of order 1–10 mm have been interrogated with currents at 5–6 KHz at which the skin depth is of order 0·1 mm (Dover, Collins and Michael [1]).

Marine electromagnetic research

All aspects of Marine Electromagnetic Research have made important advances over the last few years: theoretical studies, instrument design and data from equipment on the bottom of the ocean. The seafloor results show that the depth to the conducting asthenosphere is greater under older lithosphere and thus the thickness of the lithosphere increases with age. To obtain greater resolution of the electrical conductivity structure of the upper layers, several controlled source systems were developed. The first observations indicate a decrease in conductivity a few kilometers below the seafloor. Improved theoretical response curves for the electromagnetic fields at an ocean-continent boundary are now available. The theoretical curves, combined with land and seafloor data from coastal regions, allow the effects of the electric currents induced in the seawater to be separated from those caused by currents in the tectonic structure at the continental margin. Of growing interest is the application of electromagnetic methods to determine oceanographic wave parameters. Recent studies have investigated meanders in ocean current patterns, the response of internal edge waves and the tidal effect. With the forseeable improvements in seafloor instrumentation it will be possible to investigate the conductivity structure of offshore basins and the hydrothermal deposits associated with spreading ridges.

Ice studies: Visit to the Radio Physics Laboratory of the Arctic and Antarctic Research Institute in Leningrad

In June 1977 I spent nearly a month in discussions on the application of electromagnetic methods to the study of ice with V. V. Bogorodskii and his associates at the Radio Physics Laboratory (RPL) of the Soviet Arctic and Antarctic Research Institute. This exchange was a clear instance of Soviet/American exchange in which the preponderance of benefit was on the American side. Bogorodskii and his associates were very generous with their time and knowledge—over 90% of the discussions concerned their work, much of it not yet published. Many of the types of experiments that are currently being considered for present and future development of radio glaciological systems in the United States have already been carried out by the Soviet investigators with the production of some interesting and important results. Furthermore, there are related investigations of interest, such as direct measurement of ice motion by laser interferometry, microwave surveys of the Arctic Ocean, and sounding of permafrost and dry sand.