EM Applications in Mining

INDUSTRY APPLICATIONS OF EM — BASE METAL ANDENVIRONMENT

S.N.Sheard *, E.Brand **, T.Ritchie*

* MIM Exploration** University of Queensland

INTRODUCTION

Electromagnetic surveying has been a very important part of basemetal exploration in thelast four decades, although it has been used prior to that (Broughton Edge, A.B. andLaby, T. H, 1931). In the 1970 s, EM came of age as a prospecting tool and was usedextensively in an attempt to locate economic massive sulphides. In particular, the TimeDomain systems began to dominate in countries like Australia, which had incredibleprospecting potential but difficult (electrically conductive) overburden. At this stage theart of interpretation was confined to nomograms and some, now simple, predictiveformulae. Discoveries were made, and experimental EM surveys over deposits, such asTeutonic Bore in Western Australia, showed the potential of EM as a tool to define orebodies (Fritz, F.P., Sheehan, G.M., 1984).

In the 1980 s equipment became microprocessor based and the interpretation moved from1D to simple 2D. This gave a greater confidence in the interpretation and also started thebirth of EM as a mapping tool. Unfortunately the cost of surveys in the air and the limitedcover per dollar cost on the ground, still minimised its use, other than as a prospectingtool. An area that certainly bloomed in this era was the more concentrated use of downhole electromagnetics (DHEM). This very important use of EM allowed explorers towiden the search radius of boreholes, when used in the search of massive sulphides. Thisdecade also saw the innovative use of controlled source audio-frequency magnetotellurics(CSAMT) systems evolving and attempts to use audio-frequency magnetotelluricmeasurements (AMT) to search deep below the surface.

The next decade saw better utilisation of airborne technologies for mapping techniquesboth in mineral and environmental use. The equipment became increasingly smarter andthe use of 3D algorithms enabled better interpretations to be made both in ground andairborne technologies. In the airborne sector a desire to build and fly a heliborne timedomain system that could match and possibly outperform the standard airborne systems,invigorated a technological race. On the ground better use of Magnetotelluric systems formineral prospecting and profile mapping occurred, and DHEM three componenttechnology was embraced. The advent of powerful PC s and quality graphics capabilitieshas led to better, faster processing, rapid 2D interpretations and good integrated displays.

In the last four years it would appear that even more advances have occurred in all theabove avenues, however it is considered that the focus of electromagnetic utilisation hasbecome mapping, particularly in the environmental arena. In order to provide more than

anecdotal evidence, a review of papers with references to EM has been undertaken. Inthis study 112 papers were reviewed from global publications and the results tabulated.See Table 1. The subjects covered were sorted by the following categories - Mapping —Airborne, Ground, Marine and Magnetotellurics / Geological and Environmental; Directdetection or discovery; Case histories; Equipment; Theoretical Modelling — 2D and 3D,and R&D ; Oil Gas Coal; and Ground Penetrating Radar.

Table 1 Number of articles in the subject categories since 1998.

Broad EM Category Sub-Category Application Number ofArticles

Geological 7Airborne EMEnvironmental 7Geological 5Ground EMEnvironmental 16Geological 1Marine EMEnvironmental 1

Magnetotellurics 4

Mapping

TOTAL 41Direct Detection orDiscovery

8

11Case Histories

Equipment 5Theoretical Modelling andResearch and Development

42

Oil, Gas and Coal 1Ground Penetrating Radar 4

TOTAL NUMBER OF ARTICLES 112

The table shows a preponderance of electromagnetics as a mapping tool, and thatresearch into modelling algorithms continues aggressively. The references to these papersare attached in the appendix. Anecdotally it is thought that such a four year tally ofarticles a decade ago would have contained a considerable R&D component, a largernumber of case histories / discoveries, minimal mapping and very few environmentalarticles.

EQUIPMENT

Airborne:

Recently the Airborne geophysical industry has undergone a significant shakedown withFUGRO Airborne Surveys dominating the market and controlling the majority offrequency and time domain systems currently in use. The two commercial time domainfixed wing systems are MEGATEM and TEMPEST with SPECTREM being the onlyother system, owned and operated by Anglo American Inc.. Unfortunately all threesystems universally employ the same geometry of the bird trailing the aircraft, with allcontaining a 3 component receiver. This is not considered the most optimal geometrydue to its asymmetry, which makes interpretation somewhat difficult. Other problems arecaused by the height of the transmitter and receiver above the ground and hence theunderlying geology, which causes loss of power into the ground and even furtherdiminutive receiver signals. Current systems attempt to minimise this power effect byincreasing moment in the transmitter, either by increasing the number of turns of thetransmitter loop or increasing the transmitter current. All these options have the net effectof increasing weight and thus cost.

The improved time-domain AEM system — MEGATEM, is based upon GEOTEMtechnology. The system can operate at waveform frequencies from 12.5 Hz to 90 Hz andcan acquire both dB/dt and B-field data in three orthogonal directions (2 horizontal axesand 1 vertical axis). The transmitter dipole moment (transmitter power) claims to be byfar the largest of any operating AEM system, with a transmitter loop area of 406 squaremetres, four or five turns and a dipole moment of over one million ampere metressquared.

.The FUGRO website www.fugro.nl claims that in 1999, Noranda Inc. undertook acomplete evaluation of existing AEM technology in order to determine the most effectiveAEM system to reevaluate the Abitibi Mining district in Quebec, Canada. This wasachieved by systematically surveying, with each AEM system, a test grid which includedthree known deposits at different depths. The results indicated MEGATEM to be themost effective system and a MEGATEM survey was flown in late 1999 to reevaluate theMatagami mining camp. As follow up of this survey, the Perseverance Deposit wasdiscovered in March 2000. A discussion on this discovery can be found on the web site.

Ironically FUGRO Airborne Surveys are also the owner of the TEMPEST technologywhich in the same web site claims The quality detail and accuracy of TEMPEST data

reveals geological and structural information that cannot be matched by other airbornetechniques.

In rather another twist the Anglo American Inc. system SPECTREM also claims TheSpectrem system is arguably the most advanced AEM system in existence. This a quotefrom their web site www.spectrem.co.za.

In Heliborne systems advances have been largely in the time domain areas where, forexample HOISTEM ( see the GPX web site www.gpx.com.au ) is now beingcommercially offered. They claim Hoistem’s power into the ground and small footprintcompares with the best ground EM systems. It surpasses in penetration and definition allcurrent airborne systems.

The tried and tested frequency domain systems are still being employed and offer goodservice. The data quality for one-off mapping exercises, such as near surface structuralmapping, is good. They do have a common problem in that the systems are prone to drift,and when employed for accurate quantitative work, for example interpreting theconductivity of ground water salinity over repeat surveys in order to identify changes incomposition, they exhibit problems. The systems need to be stabilised if they are to beused accurately in the future.

There are currently signs of a possible new-age of AEM systems emerging in Canada.McPhar Geophysics Pty. Ltd is developing three new systems. The HAWK, a fixed wingmulti-frequency (200Hz — 25kHz) system, the SCORPION, a multi-waveform digitalTDEM heli-borne system and ELFMAg, an airborne natural magnetic field system are allinteresting developments.

Ground Systems

Ground electromagnetic surveys are undertaken in a variety of forms using a variety ofequipment. In basemetal exploration fixed loop and moving loop EM surveys, wherethe transmitter loop is either fixed or moves with respect to receiver, are still commonlyused to prospect for good conductors. Generally equipment capable of measuringmultiple channels are employed. Examples include the Zonge Engineering GDP32 (www.zonge.com ), SMARTEM ( www.emit.iinet.net.au/smartem.htm ), UTEM(www.sjgeop.bc.ca/sj_utem.html ), the PROTEM (www.geonics.com ) and the CRONEsystem (www.cronegeophysics.com ). All these systems are proven performers and alloperate in down hole mode.

Apart from the traditional EM surveys, other methods have become more commonplacefor mineral prospecting, including Controlled Source Audio Magnetotellurics (CSAMT)pioneered by Zonge and Continuous Profiling MT by EMI (Torres-Verdin, C,. Bostick,F.X., 1992). Both methods have the capability of deep penetration. Latterly MIMDAS(Sheard, S.N., Ritchie, T.J., Rowston, P.A., 2002) the MIM propriety system, is alsoconducting such surveys but generally in conjunction with Induced Polarisation surveyswhich adds another dimension to the results.

PROCESSING AND INTERPRETATION

Modern EM data can be subjected to a large number processing and interpretationtechniques that vary from the simple 1D to complex 3D and time consuming code. In allforms, forward and inversion modelling techniques are available. There are a plethora ofR&D institutions undertaking this work, notable of which are the groups from theUniversity of British Columbia (UBC) lead by Doug Oldenberghttp://www.geop.ubc.ca/ubcgif/ and Art Raiche s [email protected] from CSIRO in Sydney. Researchers from these groups are developing forwardand inverse code for the solution of the full 3D multi-frequency EM problem. At thesame time attempts are being made to deliver usable code by developing them on parallelplatforms — the so-called computing clusters .

MAPPING

Electromagnetic surveying is an excellent mapping technique as it is a true 3D mappingtool. By measuring the received signals at different frequencies or in a time sequence,allows the conductivity at depth to be computed. The accuracy and ease of computationdepends on the source geology configuration, however with reasonable assumptions adepth-based image known often as a conductivity depth image (CDI), can be constructed.If measurements are taken at close enough intervals a 3D image can be formed.

The best examples of the use of EM in mapping, are generally in airborne systemsbecause of their more extensive coverage. The applications are really still in theirinfancy. In the mineral industry, even though the value of mapping is often talked about,the extent of use is not like that of magnetics. This is due to a number of reasons, such as— the expense: the cost of surveys are about 5 - 10 times that of magnetics; the results areconsidered by many as a mostly a direct detection tool, and thus Government agencies donot undertake the surveys as it is perceived that it can provide companies with unfairadvantages if anomalies are identified on tenements controlled by the company.Unfortunately the different properties identified — conductivity — do not appear yet to bewidely recognized as a truly useful mapping parameter.

In environmental applications it is becoming an acceptable tool as the connectionbetween increased conductivity of contaminated waters, saline ground water, leakagefrom tailing dams or acid mine drainage has been well documented. Thus wellconstrained airborne EM surveys have become a very useful part of environmentalmapping technology, a good example of this is shown by Rutley and Fallon (SEGConference, Calgery, 2000).

As noted above ground systems are generally not often considered as an aerial mappingtool, because of the lack of coverage, however the data is often interpreted as profiles,which is ultimately 2D mapping, as well as a method of accurately targeting drill holes.

No summary of recent developments in this category would be complete withoutmentioning the work of Steve Constable and his Seafloor Electromagnetic MethodsConsortium. http://mahi.ucsd.edu/Steve/Who else would have the courage to throw US$35,000 worth of working instrumentationoverboard into 600m of water? This group has successfully deployed MT equipment onthe sea floor and mapped the base of salt and looked beneath basalt flows, areas that havetraditionally defied the best efforts of the seismic technique.

DISCOVERY

Today there are a number of operating mines or major deposits whose detection can bedirectly attributed to the follow up of EM anomalies. Examples include the Ernest Henrycopper-gold deposit in NW Queensland, Australia, and the Voisey Bay nickle-copper-cobalt deposit in the NW Territories, Canada. The Ernest Henry deposit was discoveredby the drilling of a surface TEM anomaly (Webb, M., Rowston, P., 1995), while theVoisey Bay deposit was discovered via airborne EM surveys (Crebs, T.J., 1996).

Indeed it could be said that the method was developed to assist prospectors locateconductors and it has been very successful.

An application which has also added enormous value to the drill hole, is downhole EM. Itis very difficult to calculate that value, but in the basemetal hunt it enlarges the radius ofsearch from the drill hole diameter of 10 to 20cm to a radius of 100 — 500m, dependingon hole depth and conductivity. This has a great impact when drilling under the depth ofinvestigation of surface systems. Indeed some companies design deep drill holes so as tomaximise the use of deep downhole EM.

CONCLUSION

The base metal mining industry continues to use electromagnetics techniques as a frontline tool for exploration. It is now used extensively to map below the earth s surface, andas such is now often used as a supplement to magnetic images, as it can provide betterresolved depth information. This aspect is now being used in shallow environmentalapplications and this area of use is growing.

There is still considerable effort going into R&D to define more robust and fasterschemes to process and interpret data, with 3D interpretation being foremost inResearchers minds.

REFERENCES

Brouhgton Edge, A. B. and Laby,T.H., 1931, The Principles and Practice of GeophysicalProspecting.

Creb, T.J., 1996, Discovery geophysics of the Voisey s Bay Ni-Cu-Co deposit, Labrador,Canada: , SEG; International Exposition & 66th Annual Meeting, Technical Program,Expanded Abstracts with Authors’ Biographies. Society of Exploration Geophysicists(SEG) November 10-15, p. 617-618.

CRONE GEOPHYSICS, Crone Geophysicshttp://www.cronegeophysics.com [Accessed 5 May 2002]

Fritz, F.P., Sheehan, G.M., 1984, The Geophysical Signature of the Teutonic Bore Cu-Zn-Ag Massive Sulphide Deposit, Western Australia: Exploration Geophysics 15, 127-142.

FUGRO 2002, MEGATEM/MEGATEMII

http://www.fugroairborne.com/ProductsServices/airborne/megatem.shtml [Accessed 5May 2002]

FUGRO 2002, TEMPEST — Digital Time Domain EMhttp://www.fugroairborne.com/ProductsServices/airborne/tempest.shtml [Accessed 5May 2002]

GEONICS, Time Domain Electromagneticshttp://www.geonics.com/tdem.html [Accessed 5 May 2002]

GPX: Geophysical Exploration Services, HOISTEMhttp://www.gpx.com.au [Accessed 5 May 2002]

Rutley, A., Fallon, G., 2000, Electromagnetic surveys for environmental applications atmining operations — an Argentinean and Australian perspective: SEG, Focus on theFuture. SEG International Exposition and Seventieth Annual Meeting; ExtendedAbstracts: 2000 Technical Program, 70th annual meeting, Calgary, Canada, August 6 —11, p. 1239-1242.

Sheard, S.N., Ritchie, T.J., Rowston, P.A., 2002, MIMDAS — A Quantum Change inSurface Electrical Geophysics: 2002 PDAC Conference, Canada.

SJ Geophysics Ltd., TEM Time Domainhttp://www.sjgeop.bc.ca/sj_utem.html [Accessed 5 May 2002]

SMATREM 2000, Electromagnetic Imaging Technology: SMARTem V GeophysicalReceiver Systemhttp://www.emit.iinet.net.au/smartem.htm [Accessed 5 May 2002]

SPECTRUM AIR, The SPECTRUM System

http://www.spectrem.co.za [Accessed 5 May 2002]

Torres-Verdin, C,. Bostick, F.X., 1992, Principles of Spatial Surface Electric FieldFiltering in Magnetotellurics: Electromagnetic Array Profiling (EMAP): Geophysics 57,603-622

Webb, M., Rowston, P., 1995, The geophysics of the Ernest Henry Cu-Au Deposit(N.W.) Qld: Exploration Geophysics 26, 51-59.

ZONGE 2001, Geophysical Receivers: The GDP-32II Multi-Function Receiverhttp://www.zonge.com/grgdp322.htm [Accessed 5 May 2002]

Index for Electromagnetic Papers.

DatePublished

Title and Author(s) Source Subjects Covered

1998 Beyond Bump Finding — airborne electromagneticsfor mineral exploration in regolith dominatedterrains

Green, A., Munday, T., Worral, L.

Exploration Geophysics 29 (1-2), 199-203

The paper suggests that AEM methods are potentiallymore effective at mapping geology through coverthan the traditional method of aeromagnetics,especially when the magnetic signal is quiet.

1998 Case Study: The evolution of Airborne TimeDomain Electromagnetic Applications forGeological mapping; a Noranda Perspective

Gingerich, J., Schaefer, M., Lemieux, J.


GEOTEMDEEP surveying over Noranda s San Jose,Arizona and Sol porphyry deposits showed that EMcould reliably identify known subsurface bedrockfeatures.

1998 Airborne conductivity mapping of the BathurstMining Camp

Keating, P.B., et al.


HEM surveys have been conducted over the BathurstMining Camp, Canada, in order to determinesubsurface conductivity and supplement detailedgeological mapping.

1998 Improving the management of dryland salinity inAustralia through the national airborne geophysicsproject

Coppa, I., Woodgate, P., Webb, A.


EM surveys will be used to determine the threedimensional variability in regolith conductivity, andhelp in the determination of spatial variability in soilcharacteristics.

1998 Landslide surveys in Tertiary soft rock areas usingHEM

Konishi, N.


HEM is used to detect and delineate landslidesassociated with cohesive soil, collapsed soil orweathered zones in areas of Tertiary soft rocks. .

1998 Helicopter EM mapping of saltwater intrusion inEverglades National Park, Florida

Fitterman, D.V., Deszcz-Pan, M.


HEM surveys are being used in Florida to determinethe saltwater-freshwater interface in order to assist informulating management polices for the restorationof the Everglade ecosystem.

1998 Sea ice thickness mapping by airborne and groundEM methods

Soininen, H. et al.


EM methods have been used over the Baltic Sea todetermine sea ice thickness. It was determined thatfor high resolution, low coverage surveys, groundEM techniques were the most successful, while AEMis preferred for large area coverage.

1998 Geophysical response of the Silver Swan NickelSulphide deposit, Western Australia

Amann, W.J., Pietil , R.


Downhole EM used to direct deep drilling.

1998 Minesite groundwater contamination mapping

Buselli, G., Hwang, H.S., Lu, K.


TEM was able to accurately determine waterablelevels and aquifer resistivity.

1998 Application of TEM in Taiwan

Chen, C.


Case Study One discusses a survey over the SWcoast of Taiwan, which was used to identify fresh-water-saturated sand and/or gravel sediments.Case Study Two located in E Taiwan identified aelectrical discontinuity that was interpreted torepresent the known suture trace on the surfacebetween the Philippine sea and the Eurasian plates.Case Study Three was situated over the urbanisedTaipei Basin, in which the study was able to imagebasement tomography and delineate probable faults.

1998 An Application of reverse coupling to increasesignal strength beneath conductive sediments-MiitelMine, Kambalda, W.A.

Elders, J., Wellington, A.


DHEM prime geophysical tool for delineatingsulphidic ore zones. Reverse coupling was usedsuccessfully to overcome the adverse interferenceeffects of the overlying pyrrhotitic sediments.

1998 The delineation of Cornet West by detailedunderground DHEM

Mutton, P.


DHEM has been used extensively to delineate thehighly conductive nickel sulphide bodies, and EMmodelling has resulted in a highly constrained andvery detailed geological model.

1998 Examination of the gravity and electromagneticsurvey methods applied to coal exploration in thearea of the Southern Gunnedah Basin

Nakano, O., et al.


TEM surveys conducted and the results show goodcorrelations between the known sedimentarythickness and structure.

1999 Effective exploration in covered terrains usingelectrical Geophysics

Ritchie, T., Sheard, N.

Australian Institute ofGeoscientists, Bulletin 28 99-103

The paper discusses the indirect methods required foreffective exploration using electrical geophysics.These methods include MIM s MIMDAS hardware,and software. The paper also looks at a number ofexamples including MT, IP, and the Eloise, Cu-Agprospect.

2000 Geoelectrical structure of the central zone of Pitonde la Fournaise volcano (R union)

L nat, J., et al.

Bulletin of Volcanology 62 (2)75-89

TEM studies were conducted in order to obtainreliable 1-D models of the resistivity distributionwithin the of Piton de la Fournaise volcano. 2-Dcross-sections were obtained by interpolatingbetween the 1-D models. The results showed highlyconductive zones which were interpreted as majorlithology changes at depth, which are unexpected fora shield volcano such as Piton de la Fournaise.

2000 A synthesis of electromagnetic studies in theLithoprobe Alberta Basement Transect: constraintson Paleoproterozoic indentation tectonics

Boerner, D.E., et al.

Canadian Journal of EarthSciences 37 (11) 1509-1534

EM surveys of the crust and upper mantle in theWestern Canadian Sedimentary Basin have revealedtwo conductivity anomalies that have beeninterpreted as being related to Paleoproterozoictectonic processes.

2000 A summary of electromagnetic studies on theAbitibi-Grenville transect

Boerner, D.E., et al.

Canadian Journal of EarthSciences 37 (2-3) 427-437

EM surveys have identified a number of conductivitysignatures that can be genetically linked toPrecambrian tectonic processes.

2000 Case studies of electrical and electromagneticmethods applied to mapping active faults beneaththe thick quaternary

Suzuki, K., et al.

Engineering Geology 56 (1-2)29-45

Electrical and electromagnetic methods includingcontrolled source audio-frequency magnetotellurics(CSAMT) have been used to study the geologicalstructure around active faults. In this case study, allgeophysical results were verified by drilling andtrenching. It was found that the CSAMT was aneffective method for defining an outline of geologicastructures around a fault to a depth of severalhundred meters.

2000 Geophysical investigations of large landslides in theCarnic Region of southern Austria

Mauritsch, H., et al.

Engineering Geology 56 373-388

EM surveys were conducted in order to delineate theexpected high resistivity country rock to the lowresistivity within the sliding mass. Other geophysicasurveys, including IP and seismic were conducted,and the EM results correlated well with the resultsobtained from those surveys.

2000 Transient Electromagnetic Survey of a Landslideand Fault, Santa Susanna Mountains, SouthernCalifornia

Cummings, D.

Environmental and EngineeringGeoscience 6 (3) 247-254

The paper discusses the TEM survey conducted tomap the thickness of the landslide and the location ofthe Santa Susanna Fault, under the landslide. Fourboreholes drilled confirm the thickness and depth tofault agree to within 5% of the geologicalinterpretations of the TEM data.

2000 Modelling the airborne electromagnetic response ofa vertical contact

Annetts, D., et al.


AEM can fail in circumstances, where the results canimply the presence of false conductors or resistorsthat mask the response of a genuine conductor. Thepaper shows that the use of multiple-component datasets utilising the inherent directional dependencequalities of AEM prospecting systems can be used tominimise the interpretational errors in the presence olateral conductivity contrasts.

2000 Analytical computation of EM field components ina uniform half-space

Sykes, M.


The paper discusses the use of Hankel transformsenumerated using expressions based on modifiedBessel functions of the first and second kind, toproduce results of up to four orders of magnitudemore accurately than that commonly obtained fromdigital filters.

2000 EM-coupling removal from time-domain IP data

Fullagar, P.K., Zhou, B., Bourne, B.


A fast an simple procedure has been developed toremove EM-coupling from time-domain IP data. Themethod is based on representing the EM-coupling asa half-space decay. The paper discusses the methodsapplication to dipole-dipole IP data from the Yandalgreenstone belt in Western Australia.

2000 The effect of magnetic anomalies on transientelectromagnetic data

Sattel, D.


The effect of magnetically polarisable material onTEM responses is discussed using data calculated fora layered earth model and a sphere in free-space. Thresults showed that TEM systems are only marginallyeffected by magnetic permeability on the surfacelayer. The results for the sphere model showed thatTEMPEST data is sensitive to magnetic permeabilityvariations exceeding 0.2µ0, but only for conductiveand sizeable structures.

2000 Current channelling in time-domain airborneelectromagnetic data

Reid, J., Macnae, J.


Typical approximate or nomogram methods for AEMmodelling only takes into account vortex induction ina conductive target, however this is only valid if thehost medium contains a poorly conductive target, orif measurements are taken at long decay times. In thcase of the target being wholly or partly embeddedinto a conductive host, current channelling mayenhance its response relative to that of vortexinduction.

2000 Efficient solution of full domain 3Delectromagnetic modelling problems

Xiong, Z., Raiche, A., Sugeng, F.


Current EM modelling of 3D conductive targets canbe improved by combining the already used bi-conjugate method with a restarted minimal residualcorrection. Other preconditioning techniques are alsoemployed to speed up the solver even more. Thepaper suggests that numerical results havedemonstrated the efficiency of the approaches.

2000 An example of 3D conductivity mapping using theTEMPEST airborne electromagnetic system

Lane, R., et al.


TEMPEST AEM system is designed to measure theinformation required to derive accurate, high-resolution 3D conductivity estimates of thesubsurface. The paper discusses the characteristics othe TEMPEST system with regard to data collectedfrom Walford Creek, Queensland.

2000 Braodband (ULF-VLF) surface impedancemeasurements using MIMDAS

Garner, S.J., Thiel, D.


EM radiation from distant, discrete, ground-to-cloudlightning return-strokes can be recorded asatmospherics using both electric and magnetic fieldantennas. The relationship between the orthogonalhorizontal electric and magnetic field signatures atthe receiver is directly related to the surfaceimpedance of the Earth at that point. Transformingfrom time-domain to frequency-domain allows forthe calculation of the surface impedance over afrequency range. From this, resistivity v. depthmodels can be developed.

2000 Airborne electromagnetic bathymetry of SydneyHarbour

Vrbancich, J., Hallett, M., Hodges, G.


An AEM survey utilising the helicopter-borneDIGHEM system, was carried out over lower PortJackson, Sydney Harbour, in order to determine theviability of AEM as a system to provide accuratebathymetry data in shallow seawater, down to 30m.The survey showed that AEM was a promising toolfor low-resolution bathymetry studies, to rapidlysurvey shallow coastal waters.

2000 Electromagnetic investigation of the Eyre Peninsulaconductivity anomaly

Popkov, I., et al.


The paper discusses seafloor and land MT data thatwas collected in order to delineate the strike anddepth extent of a zone of highly electricalconductivity, known as the Eyre PeninsularAnomaly.

2000 Horses for (conductive) courses: DHEM andDHMMR

Bishop, J., Lewis, R., Stolz, N.


A test drillhole magnetometric resistivity (DHMMR)survey was carried out to compare its effectiveness todrillhole electromagnetics (DHEM). It wasdiscovered that DHMMR well defined a zone ofshallower matrix sulphides, which were weaklydetected by the earlier DHEM surveys. In contrastthe DHMMR did not respond well to the massivesulphides, while they were clearly defined by theDHEM survey.

2000 The role of geophysics in the discovery anddelineation of the Cosmos Nickel Sulphide Deposit,Leinster Area, Western Australia

Craven, B., et al.


TEM played a critical role in the discovery of theCosmos Nickel Sulphide Deposit. The discoverydrillhole was the initial test of a late-time TEManomaly. Modelling of late-time fixed loop dataindicated the dip of the source. The limited depthextent of the conductor was confirmed by subsequentdrilling and DHEM.

2000 The Maggie Hays and Emily Ann nickel deposits,Western Australia: A geophysical case study

Peters, B., Buck, P.


A fixed-loop TEM survey delineated an excellentresponse, which when drilled, resulted in thediscovery of the Maggie Hays. A moving-loop TEMsurvey also resulted in the discovery of the blind,high-grade Emily Ann Deposit, north of MaggieHays and at a depth of 120m.

2000 Electromagnetic methods applied to exploration fordeep nickel sulphides in the Leinster Area, WesternAustralia

Stolz, E.


The paper discusses the application of TEM to thediscovery of a number of nickel sulphide deposits inthe Leinster Area, Western Australia.

2000 The use of ground EM systems to accurately assessalt store and help define land management optionsfor salinity management

Bennett, D.L., George, R.L., Whitfield, B.


The paper discusses the application of four Geonicsinstruments to salinity investigations. It was foundthat the instruments are all reliable and theinformation they generate is reproducible.

2000 Fractures rock geophysical studies in the ClareValley, South Australia

Wilson, T., et al.


EM surveys were conducted, along with othergeophysical methods, in order to evaluate thepresence of electrical anisotropy and heterogeneity,associated with fractured rock aquifers.

2000 Petrophysical characterisation of parna usingground and downhole geophysics at Marinna,central New South Wales.

Munday, T.J., et al.


Geophysical studies, including ground EM surveys,have been conducted in order to characterise parna,an aeolian sediment of dominantly clay size, thatcontributes to a significant component of the regolithin western NSW.

2000 Resistivity imaging of shallow salt withmagnetotellurics as an aid to prestack depthmigration

Dan Boer, E., et al.

First Break 18 (1) 19-26 Time Domain EM and Controlled Source Audio-Frequency Magnetotellurics were used tosuccessfully image the top of salt domes, whereearlier seismic imaging had failed.

2000 A Numerical Solution For ElectromagneticScattering by a Plate in a Conductive Media

Sedl k, V.

Geological Carpathica 51 (5),204-205

Abstract discusses a new integral solution formulatedusing the Galerkin method, and applied to the EMresponse over a thin conducting plate, in a stratifiedmaterial.

2000 On large-scale flow structures in a gravel-bed river

Buffin-B langer, T., Roy, A.G., Kirkbride, A.D.

Geomorphology 32 417-435 EM current meters were used to measure streamwiseand vertical velocities in order to map large-scaleflow structures in gravel-bed rivers.

2000 An electromagnetic modelling tool for the detectionof hydrocarbons in the subsoil

Carcione, J.M., Seriani, G.

Geophysical Prospecting 48231-256

EM is an appropriate tool for hydrocarbonexploration due to the difference in both effectivepermittivity and conductivity of the subsoil andhydrocarbon. The paper discusses the developmentof a model and for EM properties, its verificationwith experimental data, and the Ground PenetratingRadar forward-modelling algorithm that computesthe radargrams of a typical hydrocarbon spill.

2000 The assessment of marine gas hydrates throughelectrical remote sounding: Hydrate without BSR?

Yuan, J., Edwards, R.N.

Geophysical Research Letters 27(16) 2397-2400

Transient electric dipole-dipole EM techniques havebeen utilised to map the marine gas hydrates on theCascadia margin. Gas hydrates are important todocument as they are a possible hydrocarbonresource, a hazard to drilling and a source of majorgreen-house gas.

2000 Determining bed boundaries from inversion on EMlogging data using general measures of modelstructure and data misfit

Zhang, Z., et al.

Geophysics 65 (1) 76-82 The paper suggest a new method for determining bedboundaries by carrying out a 1-D nonlinear inversionof EM logging data.

2000 Automatic 1-D inversion of magnetotelluric data:Finding the simplest possible model that fits thedata

Pedersen, L.B., Gharibi, M.

Geophysics 65 (3) 773-782 The paper demonstrates that automatic layeredinversion of plane-wave EM data can be carried outby modifying the standard least squares inversionschemes.

2000 An efficient data-subspace inversion method for 2-D magnetotelluric data

Siripunvaraporn, W., Egbert, G.

Geophysics 65 (3) 791-803 The paper presents a new algorithm for theregularised 2-D inversion of MT data. It is based onthe OCCAM method, which achieves minimisationby using some variant on the linearised Guass-Newton method. The new method, referred to asDASOCC, is based on expressing the solution as alinear combination of rows of the sensitivity matrixsmoothed by the model covariance, and thentransforming the linearised inverse problem from theM-dimensional model space to the N-dimensionaldata space.

2000 3-D electromagnetic modelling and nonlinearinversion

Xie, G., et. al.

Geophysics 65 (3) 804-822 The paper describes a new algorithm for 3-D EMinversion that utilises global integral and localdifferential equations for both the forward andreverse problems.

2000 CSAMT exploration at Sellafield: Characterisationof a potential radioactive waste disposal site

Unsworth, M.J., Lu, X., Don Watts, M.

Geophysics 65 (4) 1070-1079 Long-term disposal sites of radioactive waste in anunderground repository requires a detailed geologicaevaluation of the potential site. CSAMT has beenused at Sellafield in Great Britain, and was found toprovide the best information on subsurface structure.

2000 Understanding LOTEM data from mountainousterrain

H rdt, A., M ller, M.

Geophysics 65 (4) 1113-1123 The paper discusses the effect of topography on theEM response. It was seen that the total effect oftopography is a combination of four distortions of thecorresponding responses for flat terrain.

2000 The realisable resistive limit: A new concept formapping geological features spanning a broad rangeof conductances

Smith, R.S.

Geophysics 65 (4) 1124-1127 The realisable resistive limit (RRL) allows for realtime-domain AEM data to be input into a nonlinearinversion scheme and used to estimate an apparentconductance. RRL is calculated using on-time data.A map of RRL can show many structural featuresthat are not evident on a map of conductance derivedfrom off-time data.

2000 Reconstruction of 1-D conductivity from dual-loopEM data

Zhang, Z., et al.

Geophysics 65 (4) 492-501 Inversions of EM data from different coilconfigurations can provide independent informationregarding the structure of the subsurface. The paperdiscusses a 1-D algorithm developed that can invertdata from horizontal coplanar, vertical coplanar,coaxial and perpendicular coil geometry s, eitherseparately or together.

2000 Two years of magnetotelluric measurements inAbitibi, western Qu bec, using a telephone line

Langlois, P., Chouteau, M.C., Bolduc, L.

Geophysics JournalInternational 140 (3) 509-520

A two year survey of continuous magnetotelluricmeasurements were collected and have allowed thestudy of two important phenomena effecting MTmeasurements: static shift and the noise. It wasdiscovered that the longer the telluric dipole the lessstatically shifted the resistivity curves. However itwas also noted that static shifts can still be presentdue to geological structures causing anomaliesexhibiting wavelengths similar to that of the dipolelength. The study also relates an observedrelationship between the coherence and the mainimpedance components, expressed in terms of asignal to noise ratio.

2000 Interpretation of long-offset transientelectromagnetic data from the Odenwald area,Germany, using two-dimensional modelling

H rdt, A., et al.


Because standard 1-D inversions typically fail in thepresence of near-surface conductive anomalies, andmultidimensional inversion codes are not routinelyavailable, the only possible interpretation techniqueis trial-and-error forward modelling. The paperdiscusses the interpretation of long-offset TEM datausing 2-D finite difference modelling.

2000 Geoelectromagnetic induction in a heterogeneoussphere: a new three-dimensional forward solverusing a conservative staggered-grid finite differencemethod

Uyeshima, M., Schultz, A.


The paper presents a conservative staggered-gridfinite difference method for computing theelectromagnetic induction response of an arbitraryheterogeneous conducting sphere by external currentexcitation. The paper suggests that this method isappropriate as the forward solution for the problem odetermining the electrical conductivity of the Earth sdeep interior.

2000 Characterisation of the magnetotelluric tensor interms of its invariants

Weaver, J.T., Agarwal, A.K., Lilley, F.E.M.


The paper discusses the definition of themagnetotelluric impedance tensor in terms of sevenindependent parameters. The parameters arealgebraically related, and have been chosen in such away as to have a clear representation on a Mohrcircle diagram, and also to reveal the geoelectricalproperties of the earth near the site where theimpedance data was collected.

2000 Fast Imaging of TDEM data based on S-inversion

Tartaras, E., et al.

Journal of Applied Geophysics43 (1) 15-32

S-inversion involves interpreting TDEM soundingdata by using the thin sheet model approach. Theapproach takes the EM response measured at thesurface of the earth and at every time delay ismatched to a thin sheet model. The conductivitychange with depth is then obtained using theconductance, S, and depth, d, of the equivalent thinsheet. The paper discusses two numerical techniquesfor determining the parameters of the thin sheet.These methods are the differential S-transformationand the regularised S-inversion.

2000 Investigations of geoelectric signatures athydrocarbon contamination site

Atekwana, E.A., Sauck, W.A., Werkema Jr., D.D.

Journal of Applied Geophysics44 (2-3) 167-180

Geoelectric techniques were used to investigate theelectrical properties of a light non aqueous phaseliquid (LNAPL) contaminant plume that resultedfrom 50 years leakage into a glacio-fluvial geologicsetting. GPR, EM, surface and in situ resistivitymethods were all utilised. The paper suggests thatthe results of combined in situ data and surfacegeoelectrical measurements can successfullycharacterise the distribution of conductive zones thatmay be associated with the biodegradation of theLNAPL in the subsurface.

2000 Integration of shallow reflection seismics and timedomain electromagnetics for detailed study of thecoastal aquifer in the Nitzanim area of Israel

Shitvelman, V., Goldman, M.


TDEM and seismic surveys were used to define thestructure and quality of the coastal aquifer in theNitzanim area of Israel. The TDEM survey was ableto identify an area of salt-water contamination, butwas often unable to delineate fresh water aquifersbeneath impermeable layers. However the combinedsurvey meant that greater resolution of the TDEMdata was possible by including additional layersidentified by the seismic survey.

2000 Evaluation of small-loop transient electromagneticsoundings to locate the Sherwood Sandstoneaquifer and confining formations at well sites in theVale of York, England

Meju, M.A., Fenning, P.J., Hawkins, T.R.W.


Shallow depth TEM soundings have been used tomap geological formations under a thick cover ofglacial drift deposits, in northern England.Modelling has shown that the Triassic SherwoodSandstone and overlying sedimentary rocks arediscernible from the TEM data. The survey though,was unable to accurately measure the upper 5-8m ofthe section. The paper therefore suggests that infuture surveys, TEM should be combined with shortspread-length DC resistivity soundings, in order toaccurately map the top layer.

2000 Improvement in TDEM sounding interpretation inpresence of induced polarisation. A case study inresistive rocks of the Fogo volcano, Cape VerdeIslands

Descloitres, M., et al.


A TDEM survey was conducted over the caldera ofthe Fogo volcano, Cape Verde Islands, in order todelineate low resistivity structures related togroundwater. Negative values in the early timetransient data were obtained, and provided aninteresting interpretational problem. The papershows that modelling using different TDEM data setsis essential to recover the electrical structure of thearea.

2000 Comparison of methods for estimating earthresistivity from airborne electromagneticmeasurements

Beard, L.P.


Because earth resistivity measurements fromfrequency-domain AEM data can vary by two ordersof magnitude depending on the half-space estimationmethod used, this paper makes comparisons betweenthe different methods used. Methods used includelook-up tables (quadrature-sensor and In-phase-quadrature), and inverse methods.

2000 Detection of welding in pyroclastic flows withground penetrating radar: insights from field andforward modelling data.

Rust, A.C., Russell, J.K.

Journal of Volcanology andGeothermal Research 95 (1-4)23-34

GPR is used to delineate welded portions ofpyroclastic flow by testing interpretations of fieldGPR and numerical modelling.

2000 Imaging the subsurface stratigraphy in the Ubehebehydrovolcanic field (Death Valley, California)using ground penetrating radar

Cagnoli, B., Russell, J.K.

Journal of Volcanology andGeothermal Research 96 (1-2)45-56

GPR was used to map subsurface images of thebasaltic base surge deposites in the Ubehebehydrovolcanic field, Death Valley, California. Datacollected included the lower stratigraphic boundaryof the pyroclastic deposits, and their thicknesses canbe estimated.

2000 Buried paleo-channels on the New Jerseycontinental margin: channel porosity structuresfrom electromagnetic surveying

Evans, R.L., et al.

Marine Geology 170 (3-4) 381-394

A marine EM survey has been used to provide bulkporosity estimates to depth, in order to place porosityconstraints on the nature of the infill and the contrastin physical properties across channel boundries.

2000 Coseismic piezoelectric effects due to a dislocationAn analytic far and early-time field solution in ahomogeneous whole space

Ogawa, T., Utada, H.

Physics of the Earth andPlanetary Interiors 121(3-4)273-288

Piezoelectricity is a property arising from the crystalanisotropy of substances. Piezoelectric substancescreated an EM field variations related to temporalvariations in the stress field. Thus, due to theabundance of piezoelectric substances in the earth scrust, it would be a reasonable assumption to expect coseismic piezoelectric EM phenomenon. The paperdiscusses the fundamental characteristics anddetectability of coseismic EM signals.

2000 Airborne Electromagnetic Bathymetry: AnOverview of Several Australian Surveys WithImplications for Maritime Defence in LittoralWaters

Vrbancich, J.

Preview 85 (1) 21-24 AEM can be used as a rapid tool for measuringseadepth and sediment properties in shallow water.This information can be utilised by the RoyalAustralian Navy, in application to minecountermeasures operations, amphibious operations,hydrographic reconnaissance and anti-submarinewarfare.

2000 Ground penetrating radar application in a shallowmarine Oxfordian limestone sequence located onthe eastern flank of the Paris Basin, NE France

Dagallier, G., et al.

Sedimentary Geology 130 (3-4)149-165

GPR was carried out on the Upper JurassicLimestone on the eastern flank of the Paris Basin, inNE France, in order to delineate geologicallymeaningful stratifications in the shallow subsurface.The GPR survey was able to identify severaldepositional units.

2000 Electromagnetic surveys for environmentalapplications at mining operations — an Argentineanand Australian perspective

Rutley, A., Fallon, G.

SEG, Extended Abstracts: 2000Technical Program, 70th annualmeeting, Calgary, Canada 1239-1242

The paper discusses two case studies in which EMsurveys have been able to define fluid migration fromtailings dams. The case studies include, Alumbrera,Argentina, and Ravenswood, Australia. Bothairborne and ground EM surveys were conducted atAlumbrera, and were able to clearly define thelocation and characteristics of the tailing dam fluids.Only AEM surveys were conducted at Ravenswood,however it was also able to define fluid migrationpathways that were not previously identified.

2000 The quest for the Holy Grail in mining geophysics:A review of the development and application ofairborne EM systems over the last 50 years

Witherly, K.

The Leading Edge 19 (3) 270-274

The paper discusses six AEM systems developedincluding a brief history of each system sdevelopment, its application and discovery success.The six systems discussed are INCO, TGS, INPUT,DIGHEM, The UniCoil and SPECTREM.

2001 Mapping Lost or Abandoned Pipes and Utilities atTwo Former Refinery Sites in Michigan

Mwanda, K., Sauck, W.

AAPG Bulletin 85 (8), 1537-1538

Abstract discusses the ability of EM to delineatebetween different types of pipes (ie. Steel andreinforced concrete.

2001 Finding Shallow Hydrocarbons with ElectricalGeophysical Methods at a Former Refinery Site

Sauck, W., Werkema, D.

AAPG Bulletin 85 (8), 1538 Shallow hydrocarbons, situated high in anunsaturated zone at a former refinery site, wereidentified by a dual coil EM induction system.

2001 Investigation of groundwater contamination usingelectric and electromagnetic methods at an openwaste-disposal site: a case study from Isparta,Turkey

Karlik, G., Ali Kaya, M.

Environmental Geology 40 (6)725-731

Very low frequency EM (VLF-EM) techniques wereemployed to collect fast and inexpensive informationregarding the spread of groundwater contaminants inIsaprta, Turkey.

2001 Airborne EM Applied to Sulphide Nickel —Examples and Analysis

Wolfgram, P., Golden, H.


The paper discusses a number of AEM systems andlooks at their ability to delineate the target. Theconclusion reached was that systems with lower basefrequency and wider transmitter pulse gave the bestresults.

2001 Tritton Copper Deposit, Girilambone NSW. AGeophysical Discovery

Collins, S.


The Tritton deposit was discovered by a moving-loopTEM survey.

2001 Galvanic excitation of the Cadjebut Pb-Zn ore body

Theodoridis, J.A., Asten, M.W.


Numerical modelling was used to investigate theresults of a DHTEM test survey at the Cadjebut ore-body. The response from the inductively well-coupled near-loop contained, unexpectedly, nosignature of the known ore-body, while the responseto the off-set loop contained a prominent negativeintersection anomaly. The modelling showed theimportance of offset loops to the production ofdetectable current channelling effects.

2001 The geophysical characteristics of the Trilogymassive sulphide deposit, Ravensthorpe, WesternAustralia

Sampson, L., Bourne, B.


The Trilogy deposit has a subtle AEM anomaly overthe known mineralisation, but ground EM defines themineralisation more clearly and strongly. Also theAEM anomaly was weak when compared to that ofthe conductive phyllites elsewhere in the region.

2001 Exploring through cover — the integratedinterpretation of high resolution aeromagnetic,airborne electromagnetic and ground gravity datafrom Grant s Patch area, Eastern GoldfieldsProvince, Archaean Yilgarn CratonPart A: Mapping geology using airborneelectromagnetics (TEMPEST)

Worrall, L., et al.


The conductivity distribution over the Grant s PatchArea, was determined by TEMPEST AEM data, andcompared with conductivity values derived fromground EM data and borehole induction logs.Information derived from the AEM data hassignificantly improved the understanding of thegeology in the Grant s Patch Area.

2001 Exploring through cover — the integratedinterpretation of high resolution aeromagnetic,airborne electromagnetic and ground gravity datafrom Grant s Patch area, Eastern GoldfieldsProvince, Archaean Yilgarn CratonPart C: Combining geophysical methods for aholistic exploration model

Meyers, J.B., et al.


AEM was incorporated into a geophysical survey ofthe Grant s Patch Area, in order to obtain ageophysical pattern map , which is relativelyinexpensive when compared to drilling. The patternmap increases the success rate of identifyingmineralised structures and fluid pathways at the earlystages of an exploration program.

2001 Geophysical characteristics of Salinisation at CapePortland, NE Tasmania

Howlett, A., Roach, M.J., Reid, J.E.


An integrated geophysical study, including the use ofEM-31 and TEM, on the salinisation at CapePortland, has mapped the distribution of saline areas,identified constrictions in the hydrogeologicalbasement and a possible source, store and transportmechanism for the salt.

2001 Application of the EM-31 terrain conductivitymeter in highly-conductive regimes

Reid, J.E., Howlett, A.


The paper discusses the limitations of the EM-31terrain conductivity meter due to the effects of skindepth attenuation.

2001 Filling in the gaps — validation and integration ofairborne EM data with surface and subsurfaceobservations for catchment management — anexample from Bendigo, Victoria, Australia

Lane, R., Heislers, D., McDonald, P.


An AEM survey flown over the Kamarooka studyarea north of Bendigo was used to map the thicknessof Tertiary and Quaternary cover overlying Paleozoicbasement, by resolving the transition frommoderately conductive cover to resistive basement.

2001 Electromagnetic imaging of a transpressionaltectonics in SW Iberia

Almeida, E., et al.

Geophysical Research Letters 28(3) 439-442

MT data was collected along a 200km long profileline in order to image the geological structures acrossthree major geotectonic units in SW Iberia.

2001 Mapping of the resistivity, susceptibility andpermittivity of the earth using a helicopter-borneelectromagnetic system

Huang, H., Fraser, D.C.

Geophysics 66 (1) 148-157 The paper discusses a method that allows for therecovery of resistivity, magnetic permeability anddielectric permittivity together from thetransformation of HEM data based on a half-spacemodel. The method shows that more credible resultscan be obtained from mapping resistivity, magneticpermeability and dielectric permittivity than ifpermeability and permittivity are ignored.

2001 Random scattering in magnetotellurics

White, B.S., Kohler, W.E., Srnka, L.J.

Geophysics 66 (1) 188-204 The paper looks at the effects of fine-scalemicrostructure on scattering of the naturallyoccurring EM waves used in MT.

2001 Engineering and environmental geophysics at themillennium

Steeples, D.W.

Geophysics 66 (1) 31-35 The paper briefly discusses the applications ofgeophysical techniques to engineering andenvironmental situations, and includes a section ofEM methods.

2001 Case History: The use of geophysical prospectingfor imaging active faults in the Roer Graben,Belgium

Demanet, D., et al.

Geophysics 66 (1) 78-89 EM along with other geophysical methods were usedto image active faults in the Roer Graben, Belgium.The data obtained was able to delineate structureseffectively, and these were checked by trenching.

2001 Cross-borehole delineation of a conductive oredeposit in a resistive host — experimental design

Johnson, D., et al.

Geophysics 66 (1) 824-835 The finite-difference time-domain method is used forhigh-resolution full-wave analysis of cross-boreholeEM surveys of buried nickel sulfide deposits. Themethod is compared to a number of other analyticalmethods for simple cases, but its versatility is evidenin its ability to analyse complex geological structures

2001 A comparison of performances of linearised andglobal nonlinear 2-D inversions of VLF and VLF-Relectromagnetic data

Kaikkonen, P., Sharma, S.P.

Geophysics 66 (2) 462-475 The performances of linearised (local) and globalnonlinear joint 2-D inversions of both very lowfrequency (VFL) and VFL resistivity electromagneticmeasurements are analysed.

2001 Modelling of the EM inductive-limit surfacecurrents

King, A., MacNae, J.C.

Geophysics 66 (2) 476-481 The inductive limit of an EM anomaly can be easilycomputed compared to the calculation required todevelop a full 3-D model. When hundreds of localanomalies may be identified during one days flying,it is essential to have a fast and computationallyinexpensive method to interpret the anomalies. Theinductive-limit modelling algorithm facilitates thisneed.

2001 Finite-element analysis of controlled-sourceelectromagnetic induction using Coulomb-gaugedpotentials

Badea, E.A., et al.

Geophysics 66 (3) 786-799 The paper discusses a 3-D finite-element solutionthat has been applied to controlled-source EMinduction problems in heterogeneous electricallyconducting media. The method is general and can beadapted for controlled-source EM modelling inmining, groundwater and environmental geophysics.

2001 A comparison of data from airborne, semi-airborne,and ground electromagnetic systems

Smith, R.S., Annan, A.P., McGowen, P.D.

Geophysics 66 (5) 1379-1385 A small conductive massive sulfide body nearSudbury, Ontario, Canada, was used as the target tocompare airborne and ground EM systems with anew experimental EM system that utilises a ground-based transmitter and an airborne receiver.

2001 3-D electromagnetic anisotropy modelling usingfinite differences

Wang, T., Fang, S.

Geophysics 66 (5) 1386-1398 The paper discusses the finite-difference method tosimulate multicomponent EM tools in a 3-Danisotropic formation.

2001 Direct inversion of the apparent complex-resistivityspectrum

Xiang, J., et al.

Geophysics 66 (5) 1399-1404 The paper presents a direct inversion method forparameter estimation based on multifold least-squares estimation.

2001 Electromagnetic induction in a layered earth witharbitrary anisotropy

Yin, C., Maurer, H.-M.

Geophysics 66 (5) 1405-1416 When EM surveys are conducted over regions ofsteeply dipping strata, then the traditional model forinterpreting geoelectromagnetic data, the layeredisotropic earth model, is inadequate. This papersuggests a new model, which handles anisotropy s,and apparent resistivities for CSAMT and the EMfield in the earth are calculated for this model.

2001 The Fourier transform of controlled-source time-domain electromagnetic data by smooth spectruminversion

Mitsuhata, Y., et al.


The paper outlines the Fourier transform algorithmdeveloped to estimate the frequency-domainresponses reliably from the time-domain data. Thealgorithm utilises a least-squares inversion with asmoothness constraint. The paper suggests that thealgorithm can handle time-domain data with a varietyof delay times, and is also effective for analysingnoisy data.

2001 Electrical resistivity structure of the Valu Fa Ridge,Lau Basin from marine controlled-sourceelectromagnetic sounding

MacGregor, L., Sinha, M., Constable, S.


The Valu Fa Ridge is a spreading back arc centre ofintermediate spreading rate. EM data was collectedand interpreted using a combination of 1-D and 2-Dforward modelling and inversion.

2001 Mapping Coastal Aquifers by Joint Inversion of DCand TEM Soundings — Three Case Histories

Albouy, Y., et al.

Ground Water 39 (1) 87-97 The paper discusses the results obtained fromindividual DC and TEM data inversions, and then themore tightly constrained model obtained from a jointinversion of both DC and TEM soundings.

2001 A Joint TEM-HLEM Geophysical Approach toBorehole Siting in Deeply Weathered GraniticTerrains

Meju, M.A., et al.

Ground Water 39 (4) 554-567 The paper discusses the application of frequency-domain horizontal loop and single loop transient EMsurveys to the identification of concealed aquiferousfracture zones.

2001 Moisture Effects on the Dielectric Properties ofSoils

Curtis, J.O.

IEEE Transactions onGeoscience and Remote Sensing39 (1) 125-128

The paper discusses laboratory experimentsconducted in order to determine the dielectricproperty data and related EM wave propagationparameters for a broad range of soil textures.

2001 Electromagnetic response of outburst-prone coal

Lui, Mingju., He, X.

International Journal of CoalGeology 45 (2-3) 155-162

The electromagnetic response of coal is thephenomenon in which an EM field can affect theemission rate of gas from coal. Laboratory researchwas conducted in order to gain knowledge of coaland gas outbursts and explore effective measures foroutburst prevention and control. Lab researchincluded testing the EM response of a variety of coaland relating it to the coal s outburst proneness.

2001 Full 3-D inversion of electromagnetic data on PC

Sasaki, Y.


The paper describes an attempt to carry out full 3-Dinversions of synthetic frequency-domain EM data ona Personal Computer.

2001 Improved and new resistivity-depth profiles forhelicopter electromagnetic data

Siemon, B.


The paper discusses the improvement on HEM databy the calculation of more accurate apparentresistivities by using better approximations; thecentroid depth is redefined as the sum of the apparendepth and half of the apparent skin depth; severalalgorithms are developed which are more sensitive toresistivity variations with depth.

2001 Analysis and interpretation of anomalousconductivity and magnetic permeability effects intime domain electromagnetic data Part I: NumericalModelling

Pavlov, D.A., Zhdanov, M.S.


The paper discusses the effects of magnetisation ontime domain EM data. The model the paperdescribes is a 3-D code based on finite-differencemethod, and is used to study the transient EM fieldpropagation through a medium containing bodies ofanomalous conductivity and magnetic permeability.The result was that the combination of anomalousconductivity and permeability increased significantlythe anomalous time domain EM response comparedto that of purely conductive or purely magneticanomalies.

2001 Analysis and interpretation of anomalousconductivity and magnetic permeability effects intime domain electromagnetic data Part II: Sµ-inversion

Zhdanov, M.S., Pavlov, D.A.


The paper follows on from Part I, and develops anew method of time domain EM data interpretation,allowing for the simultaneous reconstruction of bothelectrical and magnetic properties of the rocks. Sµ-inversion provides useful information regardingsubsurface conductivity and magnetic permeabilitydistributions.

2001 An accidental geophysical discovery of an Iron Agearchaeological site on the western shore of LakeBaikal

Kozhevnikov, N.O., Kharinsky, A.V, Kozhevnikov,O.K.


Slowly decaying transients during a TEM survey,near the village of Chernorud, Russia, baffledsurveyors until soil thrown out of a gopher burrownear the survey site was identified as containing slagand charcoal fragments from suggested ancientmetallurgical activity.

2001 Groundwater contamination monitoring withmultichannel electrical and electromagneticmethods

Buselli, G., Lu, K.


Ground based TEM surveys have been conductedover the Ranger Mine in the Northern Territory, inorder to determine if any seepage from the structuresdesigned to hold ore processing tailings, is occurringThe TEM results were able to resolve geologicalstructure relevant to the hydrogeological processesthat can effect seepage over time.

2001 Geophysical Response of Porphyry SystemMineralisation at the Dam Prospect, Temora, NewSouth Wales

Dean, T.J.

Preview 92 (1) 28-32 The paper discusses the recent suggestions thatground EM methods are being made obsolete byimproving time-domain AEM technology. A studyover the Dam Prospect in NSW is considered. Theresults from air and ground TEM surveys over thesite suggest that while the airborne TDEM methodswere successful in locating the orebody, groundTDEM was still required to fully establish thedeposit s extent and position.

2001 Environmental Geophysics Shows its Paces

Dent, D.

Preview 94 (1) 32-34 The paper discusses the applications of geophysicalmethods to the mapping of salt in the near surface. Anumber of geophysical methods are discussed in thepaper, including AEM.

2001 Laboratory measurements of electromagnetic wavevelocity in layered sands

Chan, C.Y., Knight, R.J.

Water Resources Research 37(4) 1099-1105

The velocity of an EM wave through a system oflayered geological materials is determined by thevelocities and volume fractions of the individuallayers and the ratio between the wavelength of theEM wave and the average layer thickness. Theexperiment showed that a 20% velocity changeoccurs when the thickness of the layers are changed,with the volume fraction of the fine and coarse sandsheld constant.

2001 Monitoring pumping test response in a fracturesaquifer using ground-penetrating radar

Tsoflias, G.P., Halihan, T., Sharp, J.M.

Water Resources Research 37(5) 1221-1229

Ground Penetrating Radar (GPR) is an non-invasive,high frequency EM method employed to monitor theresponse of a permeable subhorizontal fracture planein a well-characterised, fractured, carbonate aquifer.

2002 MIMDAS — A Quantum Change in SurfaceElectrical Geophysics

Sheard, S.N., Ritchie, T.J., Rowston, P.A.

2002 PDAC Conference The paper discusses the development and use ofMIM s MIMDAS system. MIMDAS is anacquisition system with a 24-bit distributed array,which can measure data from any sensor type, and iscapable of expansion to in excess of 100 channels.

2002 Environmental China — Ground EM for MappingSoil Salinity in China

Pettifer, G., Jingsong, Y., Guangming, L.

Preview 96 (1) 13-15 Salinity is a major threat to the quality of water andagricultural production in China. Ground EM is usedas a tool for mapping salinity, in order for a greaterunderstanding of the extent of salinity.

2002 Improved Near Surface Mapping in GroundwaterStudies: Application of Fast-Sampling Time-Domain EM Surveying Methods

Hatch, M., et al.

Preview 96 (1) 25-29 The paper discusses the use of ground TDEM torapidly produce data with a better resolution of thetop 15-50m than originally possible. The papersummarises the results from three studies including,the changing hydrogeological environment around aground-water disposal basin, the water mobility in anevolving dryland salinity system, and finally theextent of acid-mine drainage in an area around anabandoned mine.

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EM Applications in Mining