6. Resistivity and Induced Polarization Methods

The major environmental and engineering applications of the self-potential method have been investigations of subsurface water movement. Specific uses have included mapping of seepage flow associated with dams, dikes, reservoir floors, and other containment structures; studies of general groundwater movement; and delineation of flow patterns in the vicinity of landslides, wells, faults, drainage structures, shafts, tunnels, and sinkholes. The method also has been used to a lesser extent for subsurface thermal investigations such as mapping of steam flood fronts and coal mine fires, and preliminary studies indicate that it could be used to help delineate chemical concentration gradients associated with subsurface contaminants. Self-potential anomaly amplitudes generated by such environmental and engineering sources tend to be lower than those seen in mineral and geothermal exploration, and spurious anomalies associated with the presence of man-made structures at most field sites often create very high noise levels. Therefore extreme care in the acquisition and reduction of field data, and recognition of characteristic fields associated with artificial and natural noise sources, are critical to the success of environmental self-potential investigations. Interpretation of self-potential data often is qualitative, using visual correlation between observed profile or contour patterns and known or suspected seepage flow paths or other sources. The use of available geometric source models, including charged points, lines, spheres, cylinders, and sheets, can provide useful first estimates of source depth and configuration. Computer programs based on analytical modeling techniques can be used to calculate self-potentials generated by subsurface gradients of pressure, temperature, or chemical concentration. If in-situ physical property parameters such as cross-coupling coefficients and hydraulic, thermal, and electrical conductivity are known or can be reasonably estimated, these techniques can provide useful information about the nature, location, and strength of self-potential sources.

In this study, we conducted an extensive geophysical survey to explore the potential of electrical resistivity methods in delineating deep ore deposits within between Koillismaa Intrusion and Näränkävaara intrusion, northeastern Finland. Preliminary investigations in 2022, including magnetic, gravity and audio-magnetotelluric (AMT) methods, along with drilling, uncovered significant anomalous structures in the survey area. Subsequent drilling of an exploration well provided positive lithological indications of a ultramafic igneous rock at more than 1.5 km depth, which are very likely of the same age as the layered intrusions in the area. Borehole data indeed revealed that the Archaean basement gneiss extends down to approximately 510 m, underlain by a granite dyke with interspersed thin layers of pyroxenite and peridotite. Notably, peridotite layers around 1500 m depth exhibited distinct magnetic and IP responses in core data.We employed electrical methods at the site, including electrical resistivity tomography (ERT) and induced polarization (IP). To cover a large-scale area, 25 transmitter dipoles, each 1 km long and using three different transmitter systems, were deployed and data were recorded at 119 receiver stations. This work presents the acquisition and preliminary results from the ERT-IP surveys. During the processing of ERT and IP data, we utilized full time-series data recorded across the four lowest main frequencies (from 0.0625 Hz to 8Hz) to capture voltage data in a steady state. Apparent resistivity data were derived from the stacked voltage data, while IP data were initially extracted from these decay curves of these stacked voltage data and subsequently processed in the frequency domain (outphasing). Analysis of the resistivity and IP responses revealed notable IP signals at depths exceeding 1.5 km. Meanwhile, the resistivity data indicated generally very high values, around 10,000 ohm-m, with complex variations observed near the surface. This study demonstrates the efficacy of ERT and IP methods in delineating deep-seated mineral deposits, with the deep-depths IP responses being particularly noteworthy.

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2002An algorithm for the three‐dimensional inversion of magnetotelluric dataAuthors: Colin G. FarquharsonDouglas W. OldenburgEldad HaberRoman ShekhtmanColin G. FarquharsonUBC‐Geophysical Inversion Facility, U. of British Columbia, Vancouver, Canada, Douglas W. OldenburgUBC‐Geophysical Inversion Facility, U. of British Columbia, Vancouver, Canada, Eldad HaberEMI‐Schlumberger, Richmond, CA, and Roman ShekhtmanUBC‐GIFhttps://doi.org/10.1190/1.1817336 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InReddit Permalink: https://doi.org/10.1190/1.1817336FiguresReferencesRelatedDetailsCited byHybrid mesh for magnetotelluric forward modeling based on the finite element method11 January 2023 | Scientific Reports, Vol. 13, No. 1Fast 3D simulation of magnetotelluric data in anisotropic media using a rational Krylov methodJunjun Zhou, Ningbo Bai, Xiangyun Hu, Tiaojie Xiao, and Zhidan Long17 October 2023 | GEOPHYSICS, Vol. 88, No. 6Processing of passive EM fields acquired during active-source airborne EM surveys4 February 2021 | Exploration Geophysics, Vol. 52, No. 6An efficient parallel algorithm for 3D magnetotelluric modeling with edge-based finite element6 July 2020 | Computational Geosciences, Vol. 25, No. 1A reduced order approach for probabilistic inversions of 3-D magnetotelluric data I: general formulation1 September 2020 | Geophysical Journal International, Vol. 223, No. 33D inversion of magnetotelluric data by using a hybrid forward-modeling approach and mesh decouplingDeniz Varılsüha11 September 2020 | GEOPHYSICS, Vol. 85, No. 5Subsurface Characterization of the Pennsylvanian Clare Basin, Western Ireland, by Means of Joint Interpretation of Electromagnetic Geophysical Data and Well‐Log Data9 July 2019 | Journal of Geophysical Research: Solid Earth, Vol. 124, No. 7Modeling sferic signals extracted from active-source AEM dataDaniel Sattel and Eric Battig27 August 2018Removal of galvanic distortion effects in 3D magnetotelluric data by an equivalent source techniqueWenwu Tang, Yaoguo Li, Douglas W. Oldenburg, and Jianxin Liu8 February 2018 | GEOPHYSICS, Vol. 83, No. 2The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study23 September 2016 | Geophysical Journal International, Vol. 207, No. 3Integration of controlled-source and radio magnetotellurics, electric resistivity tomography, and reflection seismics to delineate 3D structures of a quick-clay landslide site in southwest of SwedenChunling Shan, Mehrdad Bastani, Alireza Malehmir, Lena Persson, and Emil Lundberg12 January 2016 | GEOPHYSICS, Vol. 81, No. 13-D inversion of magnetotelluric data using unstructured tetrahedral elements: applicability to data affected by topography29 May 2015 | Geophysical Journal International, Vol. 202, No. 23D marine magnetotelluric modeling and inversion with the finite-difference time-domain methodSébastien de la Kethulle de Ryhove and Rune Mittet8 October 2014 | GEOPHYSICS, Vol. 79, No. 6Magnetotelluric static shift correction using an equivalent source techniqueWenwu Tang, Yaoguo Li, Douglas W. Oldenburg, and Jianxin Liu5 August 2014The inability of magnetotelluric off-diagonal impedance tensor elements to sense oblique conductors in three-dimensional inversion17 December 2013 | Geophysical Journal International, Vol. 196, No. 3Magnetotelluric 3-D inversion—a review of two successful workshops on forward and inversion code testing and comparison14 March 2013 | Geophysical Journal International, Vol. 193, No. 3Methods and algorithms for reconstructing three-dimensional distributions of electric conductivity and polarization in the medium by finite-element 3D modeling using the data of electromagnetic sounding8 May 2013 | Izvestiya, Physics of the Solid Earth, Vol. 49, No. 3The modeling of ZTEM data with 2D and 3D algorithmsDaniel Sattel and Ken Witherly25 October 2012Large-scale inversion of ZTEM dataElliot Holtham and Douglas W. Oldenburg9 July 2012 | GEOPHYSICS, Vol. 77, No. 4Electrical resistivity structure at the northern margin of the Tibetan Plateau and tectonic implications7 December 2011 | Journal of Geophysical Research, Vol. 116, No. B12Application of the 3D magnetotelluric inversion code in a geologically complex area9 June 2010 | Geophysical Prospecting, Vol. 58, No. 6Three‐dimensional inversion of MT and ZTEM dataElliot Holtham and Douglas W. Oldenburg21 October 2010Constructing piecewise-constant models in multidimensional minimum-structure inversionsColin G. Farquharson26 December 2007 | GEOPHYSICS, Vol. 73, No. 1Three‐dimensional forward modelling and inversion of Z‐TEM dataElliot Holtham and Douglas W. Oldenburg15 December 2008Constructing piecewise‐constant models in multi‐dimensional minimum‐structure inversionsColin G. Farquharson6 October 2006Three-Dimensional Electromagnetic Modelling and Inversion from Theory to ApplicationSurveys in Geophysics, Vol. 26, No. 6Three‐dimensional inversion of MT data from the Turquoise Ridge mine, NevadaColin G. Farquharson, Douglas W. Oldenburg, and Peter Kowalczyk3 January 2005 SEG Technical Program Expanded Abstracts 2002 ISSN (print):1052-3812 ISSN (online):1949-4645 Copyright: 2002 Pages: 2478 publication data© 2002 Copyright © 2002 Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished Online: 03 Jan 2005 CITATION INFORMATION Colin G. Farquharson, Douglas W. Oldenburg, Eldad Haber, and Roman Shekhtman, (2002), "An algorithm for the three‐dimensional inversion of magnetotelluric data," SEG Technical Program Expanded Abstracts : 649-652. https://doi.org/10.1190/1.1817336 Plain-Language Summary PDF DownloadLoading ...

HYDROGEOPHYSICS TECHNIQUES TO AQUIFER LOCATING AND MONITORING FOR INDUSTRIAL ZONE NORTH THANGLONG AND QUANGMINH, HANOI

This paper identifies the gold mineralization zone in X Village using the Induced Polarization and resistivity geoelectric method. The measurements were performed using the Wenner arrangement on six tracks, each separated by a distance of 235 meters and spaced 5 meters apart. The distribution of chargeability values was determined using the Induced Polarization method, while the distribution of resistivity values was determined using the resistivity geoelectric method at the research site. The identification results indicate that the suspected gold mineralization zone is on tracks 2 and 6. On track 2, the zone of suspected gold mineralization is suspected to be located 70-75 meters away from the starting point of measurement (point A). On track 6, it is located 65-75 meters away. The gold deposits are found in phyllite rocks that have undergone alteration, specifically philic, argillic, and silicified rock.

The aim of this study is to prove the effectiveness of two electrical geophysical prospecting techniques, namely electrical resistivity tomography (ERT) and induced polarization (IP), in locating thin vein structures of metal sulphides embedded in Palaeozoic materials underlying a sedimentary cover. For this purpose, a Quaternary basin known as La Garza was selected, located in the mining district of Linares-La Carolina (Southern Spain). Galena (PbS) veins appear abundantly throughout this area, hosted in the Palaeozoic granitic bedrock. The studied veins show thicknesses from 0.5 to 2.0 m, and most present a vertical planar distribution. The veins lose their continuity below the sedimentary cover due to normal fractures that control the subsidence of the basin. During the 1980s, geophysical research campaigns were carried out in La Garza using vertical electrical sounding and failed in detecting the hidden veins. For this reason, to carry out this study, a closed regular mesh was designed, composed by eight ERT and IP profiles, with variable lengths between 315 and 411 metres. An electrode spacing between 5 and 7 metres was selected, thus allowing the granite bedrock to be reached without significantly reducing the resolution capabilities of the method. Even though ERT and IP are well-known geophysical techniques for mapping ore deposits, this is a case study that shows the advantages of the simultaneous use of both techniques (ERT and IP), over their individual application. ERT allows for reconstructing the morphology of the basin and the fractures that control it due to high-resistivity contrast between the overlying sedimentary cover and the underlaying granitic basement. However, it cannot provide any insights about their degree of mineralization. At this point, it is the IP technique that makes it possible to differentiate which are the mineralized structures. Some of these fractures produce high (above 50 mV/V) and moderate (below 50 mV/V) chargeability values, suggesting the existence of several unexploited metal veins. Furthermore, the derived models enable researchers to analyse the morphology of this sedimentary basin controlled by normal faults.

Reverse time migration (RTM) is achieved by a forward and reverse time propagation of source and receiver wavefields respectively, followed by an imaging condition. The quality of the image from any RTM implementation depends directly on the method’s ability to separate the true reflection data from the backscattered correlation noise between the source and receiver wavefields. In this paper we demonstrate the application of an inverse scattering imaging condition that significantly reduces this backscattered correlation noise and results in a much higher quality subsurface image than is achieved by typical RTM imaging conditions.

Resistivity and induced polarization surveying were originally developed for mineral exploration but are now the of outcome new applications in the field of environmental and engineering geophysics. This paper describes an experimental setup used to carry out resistivity tomography and induced polarization tests (in the time domain) that are used in geological and geophysical surveys to characterize soil and rock. The test setup is carried out in the laboratory via the Tank model developed for this purpose. The paper describes a laboratory system used to study the influence of different contaminants in a small-scale soil stratum using two geophysical methods and describes how the behaviors of resistivity and chargeability result in contaminated and uncontaminated soils. The results of a geophysical survey were performed to identify a contaminator in the Tank model. Both techniques provided evidence of contamination. In general, the electrical resistivity method was better than the induced polarization method in providing distinct values for most kinds of contamination, Except for the contamination with salt water, both methods gave significant results.

Complex-conductivity imaging for the understanding of landslide architecture

Integrated airborne and ground geophysical studies were conducted in parts of Ilesha schist belt, southwestern Nigeria. The goal was to provide a useful guide for mineral prospecting, with the hope of considerably narrowing down the future search for mineral deposits within the study area. Aeromagnetic and aeroradiometric data were analyzed for the reconnaissance study. In addition, the reduction-to-equator transform, analytic signal, tilt derivative, and Euler deconvolution filters were applied to the aeromagnetic data to enhance shallow and deep geologic features. The aeroradiometric data were used to determine spatial variations in the concentrations of uranium (U), thorium (Th), and potassium (K) in near-surface rocks and to map spatial lithologic changes. The 2D-magnetic sections, radiometric profiles, inverted resistivity, and induced polarization (IP) sections were generated from the integrated geophysical data. The electrical resistivity tomography (ERT) results reveal the subsurface heterogeneity (to a depth of approximately 197 m) and varied geoelectric layers (topsoil, lateritic-clay, weathered rock, and basement rock). The IP sections show varying degrees of chargeability and features that suggest the presence of disseminated mineralized bodies concealed in some areas. The overburden thickness varies between 4 and 85 m as determined from the 2D-magnetic and electric resistivity sections. Anomalous peaks on profiles of elemental ratios (eTh/K, eTh/eU, and K/eU) correlate with the results of IP and ERT. Data sets are well correlated and highlight areas with relevant structural and lithologic signatures favorable for mineral deposition. The methodology adopted in our research is well adapted, and the interpretation techniques provided insight into regional and local lithostructural settings. These anomalous areas are suggested as targets for future exploration works.

The banded iron ore mineralization at Ero was investigated using aeromagnetic, resistivity and induced polarization (IP) methods with the aim of characterizing the deposit. Analysis of the aeromagnetic data involved the application of reduced-to-equator transformation, derivative filters, analytic signal and source parameter imaging techniques. Computer modelling of some of the identified anomalies was undertaken. The electrical resistivity and IP methods helped in discriminating between the iron ore and the host rock. The results showed that the banded iron formations (BIFs) were characterized by spherical analytic signal anomalies ranging from 0.035 nT/m to 0.06 nT/m within the granite gneiss and magnetic susceptibility of 0.007-0.014 SI. The iron ore had low chargeability (0.1-5.0 msec) and resistivity (1.5 × 102 to 2.5 × 103 Ωm). Structural features trending in the NE-SW, E-W, and NW-SE were identified, suggesting that the area had undergone many episodes of tectonic events. Depth to the BIF varied from the surface up to about 200 m. The chargeability response of the iron bodies suggested an average grade of 20%-40%, making the prospect for economic exploitation attractive.

Recently, two-dimensional resistivity inversion techniques have been widely used for mineral resource exploration, ground water exploration, and civil engineering purposes (for example Shima, 1990). On the other hand, induced polarization (IP) method has been used mainly for the metal resource exploration. Chargeability obtained by the IP method corresponds to the polarization or charging phenomenon of underground which usually caused by metal ores or clay minerals. The IP method is considered effective to explore clayish fracture zone for the civil engineering purposes. Joint inversion of resistivity and chargeability data is also expected to have better accuracy than conventional roversion of only resistivity (Iseki and Shima; 1992).

Karl E. Butler is an Associate Professor in the Department of Geology and Director of the Geological Engineering Program at the University of New Brunswick. He holds a BSc (1987) from Queen’s University, as well as MSc (1991) and PhD (1996) degrees in Geophysics from the University of British Columbia. From 1987 to 1989 he was employed in oil exploration with Chevron Canada Resources. His postdoctoral experience, prior to joining UNB in 1999, included electromagnetic modelling research at Lamontagne Geophysics Ltd and a study of electromagnetic effects associated with seismicity in mines carried out as a NSERC Industrial Research Fellow at Engineering Seismology Group Inc. His research interests include seismoelectric and electrical methods and, more generally, novel applications of high-resolution geophysics in hydrogeology, engineering and geological exploration. Luigi Sambuelli is Associate Professor of Applied Geophysics at the Politecnico di Torino. He holds an MSc in Mining (1982) from the Politecnico di Torino. From 1992 to 1995 he was Associate Professor in Applied Geophysics at the Universita di Cagliari. He was the scientific leader of the research ‘Experiments in the High-Frequency Georadar Band (0.9–2.5 GHz) for the Analysis of Ancient Historical Buildings’ within the ‘Cultural Heritage’ project of CNR and scientifically responsible for the European project ‘Holographic Ground Probing Radar System’. He has been invited lecturer at the International School of Applied Geophysics at the ‘Ettore Majorana’ Centre in Erice (Sicily) at the 8th European Meeting of Environmental and Engineering Geophysics in Aveiro, Portugal and at the School of Civil and Environmental Engineering (Georgia Tech, Atlanta, USA). Since 1997 he has been a member of EEGS and since 1988 he has been on the Editorial Board of European Journal of Environmental and Engineering Geophysics. From 2007 he has been a member of SEG and he is associate editor of Near Surface Geophysics. He is owner of one Italian patent and co-owner of two international patents. His main interests are the applications of geophysics to very small scales (non-destructive testing), to archaeology, tunnelling, geotechnics, the environment and hydrogeology.

In recent years, research into the use of geophysical methods for monitoring microbial activity within the subsurface has advanced. One of the most promising methods, induced polarization (IP), has indirectly shown sensitivity to changes in the presence of microbial cells and especially biofilms. The aim of this study is to conclusively show, and quantify if possible, the effect of biofilm accumulation on IP signals. To ensure the controlled formation of biofilm we created an “artificial” alginate gel biofilm, which was introduced into an experimental column at varying amounts. The IP response was measured throughout. Our initial results showed that the IP method is sensitive to biofilm accumulation, after a certain point, and could potentially be used to monitor such microbial structures remotely. Further research with real biofilms under more natural conditions is needed to validate our results.

DC resistivity and IP methods in acid mine drainage problems: results from the Copper Cliff mine tailings impoundments