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The location of the goafs in many abandoned coal mines in the Ordos Basin is unknown, which causes risks for current mines. The transient electromagnetic (TEM) method is the main geophysical tool used to detect the goaf, but this can have problems due to factors such as EM interference and topographic influences. Discussion is presented of the optimal loop size for goaf detection by TEM in the Ordos Basin, transmission frequency, suppression of electromagnetic noise, and corrections for local topography. Numerical simulation results of primary and secondary fields show that the most powerful abnormal signal can be obtained for the common 100 m deep goaf of the Ordos Basin by using a loop at least 240 m × 240 m. Time compensation and a polynomial fitting algorithm can be used to separate and weaken the EM noise. The terrain height difference mainly affects TEM depth parameters, which can be modified to correct the topographic influence by considering the lateral continuity of the sedimentary strata. Exploration results from three study areas in the Shenfu Dongsheng coalfield, where many small coal mines have been mined by bord and pillar methods, suggest that detection results were consistent with those obtained by drilling results., The location of the goafs in many abandoned coal mines in the Ordos Basin is unknown, which causes risks for current mines. The transient electromagnetic (TEM) method is the main geophysical tool used to detect the goaf, but this can have problems due to factors such as EM interference and topographic influences. Discussion is presented of the optimal loop size for goaf detection by TEM in the Ordos Basin, transmission frequency, suppression of electromagnetic noise, and corrections for local topography. Numerical simulation results of primary and secondary fields show that the most powerful abnormal signal can be obtained for the common 100 m deep goaf of the Ordos Basin by using a loop at least 240 m × 240 m. Time compensation and a polynomial fitting algorithm can be used to separate and weaken the EM noise. The terrain height difference mainly affects TEM depth parameters, which can be modified to correct the topographic influence by considering the lateral continuity of the sedimentary strata. Exploration results from three study areas in the Shenfu Dongsheng coalfield, where many small coal mines have been mined by bord and pillar methods, suggest that detection results were consistent with those obtained by drilling results.

Red Dog, in Alaska, mines a sediment-hosted polymetallic massive sulphide deposit with reserves of over 143 000 000 tonnes grading 16.1% Zn, 4.3% Pb and 83 g/t Ag. The Red Dog main deposit and part of the Aqqaluk deposit were extensively surveyed using CSAMT (controlled source audio-frequency magnetotellurics) in 1981. In 1997, the data from the main deposit was reinterpreted using a 2-D smoothed model inversion technique, and the Aqqaluk deposit was surveyed using an in-loop TEM method. Discussion is presented of the relationship of the EM response to the distribution of Zn mineralisation, which required an understanding of the relationship between the distribution of pyrite, galena and sphalerite. Microscopically correlation was non-existent to poor, for 5-ft intersections there was poor correlation, but megascopically there was a positive correlation., Red Dog, in Alaska, mines a sediment-hosted polymetallic massive sulphide deposit with reserves of over 143 000 000 tonnes grading 16.1% Zn, 4.3% Pb and 83 g/t Ag. The Red Dog main deposit and part of the Aqqaluk deposit were extensively surveyed using CSAMT (controlled source audio-frequency magnetotellurics) in 1981. In 1997, the data from the main deposit was reinterpreted using a 2-D smoothed model inversion technique, and the Aqqaluk deposit was surveyed using an in-loop TEM method. Discussion is presented of the relationship of the EM response to the distribution of Zn mineralisation, which required an understanding of the relationship between the distribution of pyrite, galena and sphalerite. Microscopically correlation was non-existent to poor, for 5-ft intersections there was poor correlation, but megascopically there was a positive correlation.

The emphasis of the book is on concepts, methods, exploration strategy and interpretation, covering material mainly applicable to general exploration of deep and shallow basins, exploration of the Earth's deep crust and propsecting for oil and gas, geothermal reservoirs and groundwater. Techniques used specifically in search of metallic sulphides are excluded. Field examples and case studies are given with the methods, not separately. The list of references has been kept to about 190 and there is a glossary and an index to subjects and place-names. Following introductory chapters on the place and role of electrical methods and the electrical properties of sedimentary rocks, there are four main sections on direct current resistivity methods, natural-source electromagnetic methods, controlled-source electromagnetic methods and the possibilities for direct detection of petroleum., The emphasis of the book is on concepts, methods, exploration strategy and interpretation, covering material mainly applicable to general exploration of deep and shallow basins, exploration of the Earth's deep crust and propsecting for oil and gas, geothermal reservoirs and groundwater. Techniques used specifically in search of metallic sulphides are excluded. Field examples and case studies are given with the methods, not separately. The list of references has been kept to about 190 and there is a glossary and an index to subjects and place-names. Following introductory chapters on the place and role of electrical methods and the electrical properties of sedimentary rocks, there are four main sections on direct current resistivity methods, natural-source electromagnetic methods, controlled-source electromagnetic methods and the possibilities for direct detection of petroleum.

Sampling practices are an important aspect of geophysical exploration survey design. The selection of survey parameters should ensure that the signal to noise ratio is optimised, while minimising survey cost. Sampling considerations for any geophysical method include: the size of the target; the scale of observation; aliasing associated with station and line spacing; the nature and extent of overburden; and data presentation. As a guide to survey design the specifics are discussed for three geophysical techniques in common use in mineral exploration: the magnetic method; transient electromagnetics; and induced polarisation., Sampling practices are an important aspect of geophysical exploration survey design. The selection of survey parameters should ensure that the signal to noise ratio is optimised, while minimising survey cost. Sampling considerations for any geophysical method include: the size of the target; the scale of observation; aliasing associated with station and line spacing; the nature and extent of overburden; and data presentation. As a guide to survey design the specifics are discussed for three geophysical techniques in common use in mineral exploration: the magnetic method; transient electromagnetics; and induced polarisation.

This volume includes 41 papers and summaries of two afternoon-workshops on Instrumentation and on Interpretation are printed in the order of presentation. Topics covered include: logging applications, calibration aspects, EM methods, applied potential methods, acoustic methods, magnetic methods, and new methods. The last category includes borehole radar, magnetometric resistivity, gravity, x-ray and other nuclear methods. The five papers from the earlier Mineral Logging Workshop concern inverse filtering of gamma ray logs, borehole IP, EM, resistivity and seismic measurements, and log calibration and quality control., This volume includes 41 papers and summaries of two afternoon-workshops on Instrumentation and on Interpretation are printed in the order of presentation. Topics covered include: logging applications, calibration aspects, EM methods, applied potential methods, acoustic methods, magnetic methods, and new methods. The last category includes borehole radar, magnetometric resistivity, gravity, x-ray and other nuclear methods. The five papers from the earlier Mineral Logging Workshop concern inverse filtering of gamma ray logs, borehole IP, EM, resistivity and seismic measurements, and log calibration and quality control.

The Elura ore body is a massive Zn-Pb-Ag sulphide body with reserves of 27 million tonnes of ore with an average grade of 8.3% Zn, 5.6% Pb, 140g/tonne Ag, occurring in deeply weathered siltstones. The papers presented at the symposium cover the exploration, discovery, evaluation and testing of the orebody using the following methods: gravity, magnetic and aeromagnetic, electrical methods including mise a la masse, induced polarisation including spectral IP surveys, magnetic induced polarisation and magnetometric resistivity, electromagnetic methods including TURAM and the airborne DIGHEMII, transient electromagnetic methods, and seismic refraction. Discussions of the techniques used are also reported., The Elura ore body is a massive Zn-Pb-Ag sulphide body with reserves of 27 million tonnes of ore with an average grade of 8.3% Zn, 5.6% Pb, 140g/tonne Ag, occurring in deeply weathered siltstones. The papers presented at the symposium cover the exploration, discovery, evaluation and testing of the orebody using the following methods: gravity, magnetic and aeromagnetic, electrical methods including mise a la masse, induced polarisation including spectral IP surveys, magnetic induced polarisation and magnetometric resistivity, electromagnetic methods including TURAM and the airborne DIGHEMII, transient electromagnetic methods, and seismic refraction. Discussions of the techniques used are also reported.

The following papers are presented: From the past to the future - new directions for exploration geophysics, by Mudge S., p.1-4, 1 ref.; Recent developments in gravity measurements - implications and potential uses, by Swain C., p.5-8, 8 refs.; Introduction to the interpretation of induced polarisation surveys using 3D inversion modelling, by Elliott G., p.9-13, 4 refs.; Ground electromagnetics - the basics and recent developments, by Peters W.S., p.15-32, 11 refs.; Airborne EM, alternative methods and new modelling - recent advances, by Farquhar-Smith D.B., p.33-36, 6 refs.; Radar and borehole logging in the mine environment - bet you thought that it didn't work! by Turner G., Osman N., Mason I. and Hatherly P., p.37-45, 13 refs. (includes examples from gold, nickel and coal mines); A new approach to DHTEM in holes drilled down-dip, by Amann W.J., p.47-52; Old MacDonald needs a geophysicist, by Street G., p.53-55, 2 refs. (discusses the use of airborne geophysics in land management for mapping salt hazards, groundwater sources and soil profiles); Fixed-wing time domain airborne EM systems in Australia - status 2001, by Lane R., p.57-62, 13 refs.; Conductivity depth imaging - new views under conductive regolith using TEM data, by Asten M.W., p.63-64, 2 refs.; and Borehole MMR and TEM for the detection of weak conductors, by Asten M.W., p.65-69, 11 refs., The following papers are presented: From the past to the future - new directions for exploration geophysics, by Mudge S., p.1-4, 1 ref.; Recent developments in gravity measurements - implications and potential uses, by Swain C., p.5-8, 8 refs.; Introduction to the interpretation of induced polarisation surveys using 3D inversion modelling, by Elliott G., p.9-13, 4 refs.; Ground electromagnetics - the basics and recent developments, by Peters W.S., p.15-32, 11 refs.; Airborne EM, alternative methods and new modelling - recent advances, by Farquhar-Smith D.B., p.33-36, 6 refs.; Radar and borehole logging in the mine environment - bet you thought that it didn't work! by Turner G., Osman N., Mason I. and Hatherly P., p.37-45, 13 refs. (includes examples from gold, nickel and coal mines); A new approach to DHTEM in holes drilled down-dip, by Amann W.J., p.47-52; Old MacDonald needs a geophysicist, by Street G., p.53-55, 2 refs. (discusses the use of airborne geophysics in land management for mapping salt hazards, groundwater sources and soil profiles); Fixed-wing time domain airborne EM systems in Australia - status 2001, by Lane R., p.57-62, 13 refs.; Conductivity depth imaging - new views under conductive regolith using TEM data, by Asten M.W., p.63-64, 2 refs.; and Borehole MMR and TEM for the detection of weak conductors, by Asten M.W., p.65-69, 11 refs.

Extended abstracts are presented in English or Russian with short abstracts of each paper/poster in the other language. Topics include: PC analysis of digital geoscience data; trace elements in diamond pathfinder minerals; nonparametric interpolation for geochemical pattern recognition; chrome spinel in Ni-Cu prospecting; soil geochemistry/hydrology and lake water in Lapland; exploration geochemistry in arid, high Central Asia; kimberlite indicator mineral sampling, Saskatchewan; environmental impacts of sulphide ore mines, Finland; platinum group metals exploration in alkaline complexes, NW Scotland; stream-water mapping in Wales; metallogenesis in Scottish Proterozoic rocks; source/drainage relationships over Lower Palaeozoic turbidites, UK; regional geochemical till data, south Finland; hydrogeochemical sampling; Archaean gold exploration, Ilomantsi, Finland; gold in topsoil/plants, Pahtavaara, Finland; heavy mineral prospecting for diamonds; marine sediments of the Western Arctic shelf; gold placers; heavy minerals on the Severnaya Zemlia islands/shelf; modelling dispersion haloes; geochemical exploration in Kola/Karelia; geological/geophysical techniques; buried placers in the Arctic; unexposed ore-generating structures; resources/prospecting in NW Russia; electrogeochemical exploration; U-REE-V deposits, Karelia; diamonds, East European platform; copper sandstones, Igarka; gold in Karelia; vectorial borehole magnetometry; electrical exploration, Baltic shield; bedrock diamonds; QSP magnetic exploration for subvertical bodies; lamproites in Kola/Karelia; the Kandagubsky carbonatites; bauxites in west Siberia; diamond in the Urals; the transient electromagnetic method; unconventional aerial/satellite mapping of basement; and Cu-Ni primary haloes., Extended abstracts are presented in English or Russian with short abstracts of each paper/poster in the other language. Topics include: PC analysis of digital geoscience data; trace elements in diamond pathfinder minerals; nonparametric interpolation for geochemical pattern recognition; chrome spinel in Ni-Cu prospecting; soil geochemistry/hydrology and lake water in Lapland; exploration geochemistry in arid, high Central Asia; kimberlite indicator mineral sampling, Saskatchewan; environmental impacts of sulphide ore mines, Finland; platinum group metals exploration in alkaline complexes, NW Scotland; stream-water mapping in Wales; metallogenesis in Scottish Proterozoic rocks; source/drainage relationships over Lower Palaeozoic turbidites, UK; regional geochemical till data, south Finland; hydrogeochemical sampling; Archaean gold exploration, Ilomantsi, Finland; gold in topsoil/plants, Pahtavaara, Finland; heavy mineral prospecting for diamonds; marine sediments of the Western Arctic shelf; gold placers; heavy minerals on the Severnaya Zemlia islands/shelf; modelling dispersion haloes; geochemical exploration in Kola/Karelia; geological/geophysical techniques; buried placers in the Arctic; unexposed ore-generating structures; resources/prospecting in NW Russia; electrogeochemical exploration; U-REE-V deposits, Karelia; diamonds, East European platform; copper sandstones, Igarka; gold in Karelia; vectorial borehole magnetometry; electrical exploration, Baltic shield; bedrock diamonds; QSP magnetic exploration for subvertical bodies; lamproites in Kola/Karelia; the Kandagubsky carbonatites; bauxites in west Siberia; diamond in the Urals; the transient electromagnetic method; unconventional aerial/satellite mapping of basement; and Cu-Ni primary haloes.

Methods have been developed to ensure safe mining of the 3153 working face in the Chengzhuang coal mine (Shanxi, China), which has an aquifuge thickness of only 20 m at the working floor. This involves detecting the distribution of the groundwater using the transient electromagnetic method, using a water injection experiment to test floor damage at different depths, followed by numerical simulation of floor damage thickness. Results showed that floor damage thickness decreases in the presence of backfilling and further thickens as the hanging roof area increases. Under cyclic loading, the tension and compression damage zones were found to be connected. As mining proceeded, compressive damage occurred first, followed by tensile damage, and the water resistance of the rock floor seriously deteriorated unless it was grouted. The deepest compression damage lagged behind the coal wall, while the point of maximum tensile damage was behind the deepest compression damage zone, which could cause water inrush behind the coal wall., Methods have been developed to ensure safe mining of the 3153 working face in the Chengzhuang coal mine (Shanxi, China), which has an aquifuge thickness of only 20 m at the working floor. This involves detecting the distribution of the groundwater using the transient electromagnetic method, using a water injection experiment to test floor damage at different depths, followed by numerical simulation of floor damage thickness. Results showed that floor damage thickness decreases in the presence of backfilling and further thickens as the hanging roof area increases. Under cyclic loading, the tension and compression damage zones were found to be connected. As mining proceeded, compressive damage occurred first, followed by tensile damage, and the water resistance of the rock floor seriously deteriorated unless it was grouted. The deepest compression damage lagged behind the coal wall, while the point of maximum tensile damage was behind the deepest compression damage zone, which could cause water inrush behind the coal wall.

A strategy to quantitatively evaluate the water content of aquifers was developed using transient electromagnetic (TEM) geo-electrical data and a database of generalised specific capacities obtained by pumping tests. Through regression analysis, a local (site-dependent) relationship was established between the generalised specific capacity and the aquifer’s average resistivity. According to the relationship, the quasi-generalised specific capacity can be obtained using TEM data from across the entire survey area. The methodology was tested (in Inner Mongolia) in a thick composite coal seam aquifer system with abundant water. By using the generalised specific capacities of 11 pumping wells and the average resistivities derived from TEM, a negative power function was established between the aquifer water volume and the area’s resistivity. Using the quasi-generalised specific capacity provided a clearer understanding. (Authors.), A strategy to quantitatively evaluate the water content of aquifers was developed using transient electromagnetic (TEM) geo-electrical data and a database of generalised specific capacities obtained by pumping tests. Through regression analysis, a local (site-dependent) relationship was established between the generalised specific capacity and the aquifer’s average resistivity. According to the relationship, the quasi-generalised specific capacity can be obtained using TEM data from across the entire survey area. The methodology was tested (in Inner Mongolia) in a thick composite coal seam aquifer system with abundant water. By using the generalised specific capacities of 11 pumping wells and the average resistivities derived from TEM, a negative power function was established between the aquifer water volume and the area’s resistivity. Using the quasi-generalised specific capacity provided a clearer understanding. (Authors.)

A free-space parametric model study of the Transient Electromagnetic (TEM) coincident loop technique has been undertaken, to provide a basic scheme for the interpretation of coincident loop anomalies and to provide insight on important survey design parameters. Experiments have been carried out to investigate the effects of changing geometrical relationships, target conductance, lateral resolution in the case of multiple thin dykes, and the masking influence of conductive overburden. The results confirm the advantages of the coincident loop technique in prospecting for large deep-seated ore deposits., A free-space parametric model study of the Transient Electromagnetic (TEM) coincident loop technique has been undertaken, to provide a basic scheme for the interpretation of coincident loop anomalies and to provide insight on important survey design parameters. Experiments have been carried out to investigate the effects of changing geometrical relationships, target conductance, lateral resolution in the case of multiple thin dykes, and the masking influence of conductive overburden. The results confirm the advantages of the coincident loop technique in prospecting for large deep-seated ore deposits.

Transient electromagnetic (TEM) measurements have been made with SIROTEM on five separate surveys over the Teutonic Bore orebody; initially before mining operations began and subsequently during different stages of the stripping of overburden from the mineral deposit. Results of the surveys are discussed., Transient electromagnetic (TEM) measurements have been made with SIROTEM on five separate surveys over the Teutonic Bore orebody; initially before mining operations began and subsequently during different stages of the stripping of overburden from the mineral deposit. Results of the surveys are discussed.

The relative sensitivities of the active and reactive components of a harmonic field are considered as well as that of transient fields to changes in the resistivity and dimensions of a conducting body. It is shown that the active and reactive components of a harmonic field have different resolving capabilities and, as such, different signal/noise ratios. The resolving capabilities of time and frequency domain techniques are compared in both high and low frequency ends of the spectrum, as well as early and late stages of the transient. The useful signal and the "geologic noise" are approximated by two conducting bodies immersed in an otherwise non-conducting medium., The relative sensitivities of the active and reactive components of a harmonic field are considered as well as that of transient fields to changes in the resistivity and dimensions of a conducting body. It is shown that the active and reactive components of a harmonic field have different resolving capabilities and, as such, different signal/noise ratios. The resolving capabilities of time and frequency domain techniques are compared in both high and low frequency ends of the spectrum, as well as early and late stages of the transient. The useful signal and the "geologic noise" are approximated by two conducting bodies immersed in an otherwise non-conducting medium.

Mathematical treatments of the transient electromagnetic response of layered structures, such as conducting basements or overburdens, have been very simplistic in the past. A contribution is made towards a more thorough treatment of this phenomenon. In deriving results, great attention has been paid to the singularities in the spectrum of the transient electromagnetic field and consequently it has been shown that the approximation of a layer structure by a conducting slab breaks down due to disagreement over the position of these singularities., Mathematical treatments of the transient electromagnetic response of layered structures, such as conducting basements or overburdens, have been very simplistic in the past. A contribution is made towards a more thorough treatment of this phenomenon. In deriving results, great attention has been paid to the singularities in the spectrum of the transient electromagnetic field and consequently it has been shown that the approximation of a layer structure by a conducting slab breaks down due to disagreement over the position of these singularities.

The Laplace transform of the solution for TEM soundings over an N-layer earth is derived and its inversion using the Gaver-Stehfest algorithm is illustrated. The method is considerably more stable and computationally efficient than inversion using the discrete Fourier transform., The Laplace transform of the solution for TEM soundings over an N-layer earth is derived and its inversion using the Gaver-Stehfest algorithm is illustrated. The method is considerably more stable and computationally efficient than inversion using the discrete Fourier transform.

s of 45 papers are included on geophysical, electromagnetic, magnetic, seismic exploration and airborne surveys in Scandinavia., s of 45 papers are included on geophysical, electromagnetic, magnetic, seismic exploration and airborne surveys in Scandinavia.

A simple first-order interpretation scheme is proposed for the theoretical modelling of late-time transient EM anomalies. It has been shown that, to a first approximation, the transient behaviour of a thin plate can be represented by the first free-decay eigencurrent. All the principal qualitative features of TEM anomalies can be reproduced for any loop configuration: theoretical model responses have been generated for the common loop, separated loop and fixed transmitter loop geometries for a range of target dispositions. The study indicates that the fixed central transmitter configuration is preferable to both the common and separated loop geometries for deep mineral exploration, ease of interpretation and rapid areal coverage., A simple first-order interpretation scheme is proposed for the theoretical modelling of late-time transient EM anomalies. It has been shown that, to a first approximation, the transient behaviour of a thin plate can be represented by the first free-decay eigencurrent. All the principal qualitative features of TEM anomalies can be reproduced for any loop configuration: theoretical model responses have been generated for the common loop, separated loop and fixed transmitter loop geometries for a range of target dispositions. The study indicates that the fixed central transmitter configuration is preferable to both the common and separated loop geometries for deep mineral exploration, ease of interpretation and rapid areal coverage.

After five years developmental work by the Minerals Research Laboratories of CSRO, a new mineral prospecting tool-SIROTEM-has gone into commercial production in Australia and has won wide international acclaim for its performance and field reliability. The name SIROTEM stands for SCIRO Transient Electro-magnetics. The transient electromagnetics technique depends on the good electrical conducting properties of mineral orebodies as compared with their surrounding rocks and soil., After five years developmental work by the Minerals Research Laboratories of CSRO, a new mineral prospecting tool-SIROTEM-has gone into commercial production in Australia and has won wide international acclaim for its performance and field reliability. The name SIROTEM stands for SCIRO Transient Electro-magnetics. The transient electromagnetics technique depends on the good electrical conducting properties of mineral orebodies as compared with their surrounding rocks and soil.

Empirical field studies have been made in controlled mineral environments at Sourton Tors, Pen y Drum and Cyffty Pb-Zn lode, Llanrwst, with two commercial transient electromagnetic method systems: SIROTEM and Crone PEM. The test surveys have demonstrated the operational and coupling characteristics of the coincident, vertical and separated loop geometries, and also the type of TEM response to be expected for a variety of target situations. Advantages over traditional frequency-domain systems are source discrimination based on multispectral measurements, rapid depth and conductivity determinations and the suppression of geological noise., Empirical field studies have been made in controlled mineral environments at Sourton Tors, Pen y Drum and Cyffty Pb-Zn lode, Llanrwst, with two commercial transient electromagnetic method systems: SIROTEM and Crone PEM. The test surveys have demonstrated the operational and coupling characteristics of the coincident, vertical and separated loop geometries, and also the type of TEM response to be expected for a variety of target situations. Advantages over traditional frequency-domain systems are source discrimination based on multispectral measurements, rapid depth and conductivity determinations and the suppression of geological noise.

A finite-difference formulation of the coaxial-loop or wire-loop transient electromagnetic prospecting system is used to model the fields from a buried cylindrical conductor whose axis is coincident with that of the field. Solutions are obtained directly in the time domain and the formulation is implicit and two-dimensional in space. All calculations are carried out for a perfectly conducting basement, but the method can be used for a finitely conducting basement as well. Results for a buried cylindrical conductor show that there is a high degree of sensitivity to conductor size., A finite-difference formulation of the coaxial-loop or wire-loop transient electromagnetic prospecting system is used to model the fields from a buried cylindrical conductor whose axis is coincident with that of the field. Solutions are obtained directly in the time domain and the formulation is implicit and two-dimensional in space. All calculations are carried out for a perfectly conducting basement, but the method can be used for a finitely conducting basement as well. Results for a buried cylindrical conductor show that there is a high degree of sensitivity to conductor size.

A finite-difference solution and an integral alogrithm are developed for computing time domain electromagnetic fields generated by an arbitrary source located in horizontally stratified earth. The finite-difference problem is first solved for the kernel of an integral Bessel transform of the desired field and then inverse transformation is performed either by numerical integration or by linear filtering. A description of the appropriate algorithm as well as numerical results are presented for two cases: an axially symmetric source (a vertical magnetic dipole or a circular loop) placed on the surface of a horizontally layered section overlying either an insulating or an ideally conducting basement. In comparison with the conventional methods used for computing transient electromagnetic fields, the integral-finite-difference method is more universally applicable., A finite-difference solution and an integral alogrithm are developed for computing time domain electromagnetic fields generated by an arbitrary source located in horizontally stratified earth. The finite-difference problem is first solved for the kernel of an integral Bessel transform of the desired field and then inverse transformation is performed either by numerical integration or by linear filtering. A description of the appropriate algorithm as well as numerical results are presented for two cases: an axially symmetric source (a vertical magnetic dipole or a circular loop) placed on the surface of a horizontally layered section overlying either an insulating or an ideally conducting basement. In comparison with the conventional methods used for computing transient electromagnetic fields, the integral-finite-difference method is more universally applicable.

Discussion is presented of the successful role that AMIRA has played in the development of geophysical exploration techniques over the past 25 years. To be successful, projects must focus the right combination of cutting edge science and technology on a pressing problem for the industry. Since the early 1970s there have been about 50 collaborative research projects in the areas of geophysics and remote sensing, about 70% of which were on electromagnetic geophysics, remote sensing and magnetic petrology. The EM programme has seen the development of the SIROTEM instrument, sophisticated modelling software and new airborne technology. The most important remote sensing project was associated with the processing of satellite imagery and projects have helped the development of Landsat mapping and satellite remote sensing. A series of magnetic projects has helped develop the techniques of palaeomagnetic measurement and the interpretation of complex magnetic data sets., Discussion is presented of the successful role that AMIRA has played in the development of geophysical exploration techniques over the past 25 years. To be successful, projects must focus the right combination of cutting edge science and technology on a pressing problem for the industry. Since the early 1970s there have been about 50 collaborative research projects in the areas of geophysics and remote sensing, about 70% of which were on electromagnetic geophysics, remote sensing and magnetic petrology. The EM programme has seen the development of the SIROTEM instrument, sophisticated modelling software and new airborne technology. The most important remote sensing project was associated with the processing of satellite imagery and projects have helped the development of Landsat mapping and satellite remote sensing. A series of magnetic projects has helped develop the techniques of palaeomagnetic measurement and the interpretation of complex magnetic data sets.

Geophysical programmes supported by AMIRA have been successful in the advancement of image processing technology, the interpretation of magnetic and Landsat data, the development of SIROTEM and the creation of a comprehensive suite of software for the interpretation of geophysical prospecting data. AMIRA meetings and projects have also helped the world status of the Australian mineral geophysical industry by supplying the forum for networking, debate and cooperation. The future looks bright, with a very large cooperative focus on deep penetrating airborne electromagnetics designed to see through the difficult weathering conditions prevalent in Australia, a new initiative into airborne gravity surveying and the development of ARIES, a satellite designed for mineral exploration., Geophysical programmes supported by AMIRA have been successful in the advancement of image processing technology, the interpretation of magnetic and Landsat data, the development of SIROTEM and the creation of a comprehensive suite of software for the interpretation of geophysical prospecting data. AMIRA meetings and projects have also helped the world status of the Australian mineral geophysical industry by supplying the forum for networking, debate and cooperation. The future looks bright, with a very large cooperative focus on deep penetrating airborne electromagnetics designed to see through the difficult weathering conditions prevalent in Australia, a new initiative into airborne gravity surveying and the development of ARIES, a satellite designed for mineral exploration.

Girilambone lies in the western Lachlan Fold Belt, in Ordovician metasediments. Known significant Cu is within and near the base of the Tritton Formation, whose proximal greywackes and phyllites overlie the lower-energy scistose metasediments of the Girilambone Beds. Primary targets are oxidised and supergene minerals that can be treated at the solvent extraction-electrowinning plant. Known significant deposits of this kind lie close to massive pyrite and chalcopyrite bodies. A large number of areas with anomalous Cu have been outlined and drilling priorities assigned using geophysical methods. The transient electromagnetic method has recorded anomalous responses related to massive sulphides over the Girilambone mine, at Girilambone North, at Budgerygar and over the blind, 200 m deep Tritton deposit, where high-grade chalcopyrite with Au and Ag has been intersected and two massive sulphide lenses outlined., Girilambone lies in the western Lachlan Fold Belt, in Ordovician metasediments. Known significant Cu is within and near the base of the Tritton Formation, whose proximal greywackes and phyllites overlie the lower-energy scistose metasediments of the Girilambone Beds. Primary targets are oxidised and supergene minerals that can be treated at the solvent extraction-electrowinning plant. Known significant deposits of this kind lie close to massive pyrite and chalcopyrite bodies. A large number of areas with anomalous Cu have been outlined and drilling priorities assigned using geophysical methods. The transient electromagnetic method has recorded anomalous responses related to massive sulphides over the Girilambone mine, at Girilambone North, at Budgerygar and over the blind, 200 m deep Tritton deposit, where high-grade chalcopyrite with Au and Ag has been intersected and two massive sulphide lenses outlined.

Major modifications of electromagnetic sounding with artificial excitation of a field are described. The sounding problems of ore prospecting geophysics are considered. The comparative efficiency of applied sounding methods is demonstrated by modelling a two-layer medium and half-space containing a spherical inhomgeneity. Several examples of the application of EM sounding methods in the USSR are described., Major modifications of electromagnetic sounding with artificial excitation of a field are described. The sounding problems of ore prospecting geophysics are considered. The comparative efficiency of applied sounding methods is demonstrated by modelling a two-layer medium and half-space containing a spherical inhomgeneity. Several examples of the application of EM sounding methods in the USSR are described.

When prospecting for ore deposits in the presence of graphitised and sulphidised formations, induced polarisation proved to be the most efficient of the electrical pulse methods. IP involves the study of various time responses and non-linear effects over a wide time range., When prospecting for ore deposits in the presence of graphitised and sulphidised formations, induced polarisation proved to be the most efficient of the electrical pulse methods. IP involves the study of various time responses and non-linear effects over a wide time range.

The extensions of the Kalliokyla sulphide orebody, which differs clearly from the environment in conductivity, can be traced to depths of 200-400 m by TDEM. It suggests a marked augmentation of the potential ore reserves in the area. On account of the complex structures, the estimates are not reliable everywhere. Even so, new information has been obtained on the behaviour of the methods. TDEM with a coincident loop reveals details in the central parts of the area. The deep hole drilled in the eastern part of the area demonstrates that the depth estimates based on the layered earth model are too shallow. The borehole data and their interpretation, however, are in good agreement with the assumed structure. The fixed loop system gave better depth estimates when the large transmitter loop had been placed over the eastern interfering conductor to eliminate its influence., The extensions of the Kalliokyla sulphide orebody, which differs clearly from the environment in conductivity, can be traced to depths of 200-400 m by TDEM. It suggests a marked augmentation of the potential ore reserves in the area. On account of the complex structures, the estimates are not reliable everywhere. Even so, new information has been obtained on the behaviour of the methods. TDEM with a coincident loop reveals details in the central parts of the area. The deep hole drilled in the eastern part of the area demonstrates that the depth estimates based on the layered earth model are too shallow. The borehole data and their interpretation, however, are in good agreement with the assumed structure. The fixed loop system gave better depth estimates when the large transmitter loop had been placed over the eastern interfering conductor to eliminate its influence.

Model studies were made to provide a suite of curves illustrating the transient electromagnetic (TEM) response down drillholes through a conductive overburden into a resistive host, and through a conductive overburden overlying a conductive prism approximating the Elura orebody. The results show that at early sample times the overburden alone generates the near-surface signal. At depth the response of the orebody is complicated: it may add to or subtract from the overburden response, depending on the sample time and the transmitter-receiver and orebody geometry. Separate tests with the orebody in electrical contact with the overburden and with the orebody insulated from it indicate, for this simple model, that there is only a marginal increase in the orebody response when it is in contact with the overburden. Comparison of the model curves with field observations obtained from SIROTEM down-hole surveys at Elura enable the bulk resistivity of the overburden and orebody to be determined., Model studies were made to provide a suite of curves illustrating the transient electromagnetic (TEM) response down drillholes through a conductive overburden into a resistive host, and through a conductive overburden overlying a conductive prism approximating the Elura orebody. The results show that at early sample times the overburden alone generates the near-surface signal. At depth the response of the orebody is complicated: it may add to or subtract from the overburden response, depending on the sample time and the transmitter-receiver and orebody geometry. Separate tests with the orebody in electrical contact with the overburden and with the orebody insulated from it indicate, for this simple model, that there is only a marginal increase in the orebody response when it is in contact with the overburden. Comparison of the model curves with field observations obtained from SIROTEM down-hole surveys at Elura enable the bulk resistivity of the overburden and orebody to be determined.

The use is described of transient electromagnetic (TEM) imaging for looking into or through solid rock to discover high-grade nickel sulphide deposits. Details are given of the development of a new set of operational tools which have increased the effectiveness of the technique. Application of the technique to underground exploration at the Long-Victor mine in Western Australia is described. The use of TEM for surface exploration and the development of low-temperature superconducting interference devices with improved discrimination are discussed., The use is described of transient electromagnetic (TEM) imaging for looking into or through solid rock to discover high-grade nickel sulphide deposits. Details are given of the development of a new set of operational tools which have increased the effectiveness of the technique. Application of the technique to underground exploration at the Long-Victor mine in Western Australia is described. The use of TEM for surface exploration and the development of low-temperature superconducting interference devices with improved discrimination are discussed.

The two highgrade Flying Fox massive-sulphide T1 and T5 deposits were discovered in 2003 and 2004 from follow-up drilling of unresolved geological and geophysical targets located within a few hundred metres of the mined-out Flying Fox. More than 80 000 t Ni has been delineated and drilling between the deposits has located additional high-grade mineralisation at T4, showing that the ore system extends deeper than 1 km, to the current limit of drill testing. The discoveries resulted from recognition of the modifying effects of tectono-metamorphic processes at Flying Fox, building on a sound understanding of the primary controls of nickel sulphide deposits. Key factors contributing to the success were: recognising that three deep exploration holes had not tested the prospective basal contact; the indication by downhole TEM surveys of untested conductors in a favourble geological setting; and an aggressive follow-through exploration programme that tested areas previously downgraded by a perceived lack of encouraging results., The two highgrade Flying Fox massive-sulphide T1 and T5 deposits were discovered in 2003 and 2004 from follow-up drilling of unresolved geological and geophysical targets located within a few hundred metres of the mined-out Flying Fox. More than 80 000 t Ni has been delineated and drilling between the deposits has located additional high-grade mineralisation at T4, showing that the ore system extends deeper than 1 km, to the current limit of drill testing. The discoveries resulted from recognition of the modifying effects of tectono-metamorphic processes at Flying Fox, building on a sound understanding of the primary controls of nickel sulphide deposits. Key factors contributing to the success were: recognising that three deep exploration holes had not tested the prospective basal contact; the indication by downhole TEM surveys of untested conductors in a favourble geological setting; and an aggressive follow-through exploration programme that tested areas previously downgraded by a perceived lack of encouraging results.

In the Stawell corridor of western Victoria, regional magnetic and gravity data plus results from various electrical methods have led to the detection of several mineralised systems without surface expression. Petrophysical measurements on core samples and geophysical logging of drillholes have been essential to interpreting the geophysical data and have also contributed to further understanding of the mineralising processes., In the Stawell corridor of western Victoria, regional magnetic and gravity data plus results from various electrical methods have led to the detection of several mineralised systems without surface expression. Petrophysical measurements on core samples and geophysical logging of drillholes have been essential to interpreting the geophysical data and have also contributed to further understanding of the mineralising processes.

Reaction of groundwater with tailings at the disused Brukunga pyrite mine in South Australia causes the formation and discharge of sulphuric acid. The possibility of using geophysical methods to characterise variations in depth to the water table and to map preferred groundwater flow paths has been considered. Three methods were studied: transient electromagnetic (TEM) sounding, direct current (DC) sounding and profiling and self potential (SP) profiling. Results from the TEM and DC soundings show that the DC method could determine layer boundaries at shallow depths (less than 10 m) while the TEM method can resolve deeper structures. Joint use of data from both gives a more complete and accurate geoelectric section. The voltages measured with SP profiling were small and it was difficult to determine any preferred channels of groundwater flow., Reaction of groundwater with tailings at the disused Brukunga pyrite mine in South Australia causes the formation and discharge of sulphuric acid. The possibility of using geophysical methods to characterise variations in depth to the water table and to map preferred groundwater flow paths has been considered. Three methods were studied: transient electromagnetic (TEM) sounding, direct current (DC) sounding and profiling and self potential (SP) profiling. Results from the TEM and DC soundings show that the DC method could determine layer boundaries at shallow depths (less than 10 m) while the TEM method can resolve deeper structures. Joint use of data from both gives a more complete and accurate geoelectric section. The voltages measured with SP profiling were small and it was difficult to determine any preferred channels of groundwater flow.

The Portuguese polymetallic sulphide deposit was located in 1992 in strongly altered acid tuffs under 130 m of Cainozoic sediments. Exploration began in 1994 to determine the complex geometry of the orebody and to locate other targets in the area. Work included additional gravity exploration and reprocessing of data, electromagnetic exploration, induced polarisation, testing of audiomagnetotelluric exploration, TEM sounding to estimate the depth of the basement and detect conductors, and airborne magnetic exploration. Around 10 500 m of exploration drilling also took place on 12 gravity anomalies. The deposit's structure was elucidated and three types of mineralisation identified: massive, banded, fine-grained complex sulphides with interesting Pb and Zn contents and zones of penalty Cu-Au enrichment, stockwork mineralisation with "clean" base metals and silicified auriferous shear zones with arsenopyrite., The Portuguese polymetallic sulphide deposit was located in 1992 in strongly altered acid tuffs under 130 m of Cainozoic sediments. Exploration began in 1994 to determine the complex geometry of the orebody and to locate other targets in the area. Work included additional gravity exploration and reprocessing of data, electromagnetic exploration, induced polarisation, testing of audiomagnetotelluric exploration, TEM sounding to estimate the depth of the basement and detect conductors, and airborne magnetic exploration. Around 10 500 m of exploration drilling also took place on 12 gravity anomalies. The deposit's structure was elucidated and three types of mineralisation identified: massive, banded, fine-grained complex sulphides with interesting Pb and Zn contents and zones of penalty Cu-Au enrichment, stockwork mineralisation with "clean" base metals and silicified auriferous shear zones with arsenopyrite.

Magnetometry is most widely used, as ultramafic rocks have a high magnetic susceptibility. Induced magnetisation helps in predicting the shape of an anomaly, but other non-kimberlitic bodies will be detected as well. They can be distinguished by comparing their fields with those theoretically produced by pipes, but modelling shows that while the fields of discs and vertical pipes are easily distinguished, inclination such as that introduced by a crater can cause confusion. There is also the problem of non-magnetic kimberlites. The use of electrical and electromagnetic exploration methods is more recent, the latter including both frequency-domain and transient methods. Such methods only give clear responses where there is a strong difference in resistivity between kimberlites and their host rocks. The electrical conductivity of kimberlites also results from both shallow and deep-seated effects, with the magnetisation of the weathered upper parts of pipes reduced relative to the unweathered lower portions. Where weathered "yellow ground" is absent, kimberlites give a much stronger conductive signal. The electrical conductivity has not been sufficiently studied, and conflicting data from the results of electrical sounding have been published., Magnetometry is most widely used, as ultramafic rocks have a high magnetic susceptibility. Induced magnetisation helps in predicting the shape of an anomaly, but other non-kimberlitic bodies will be detected as well. They can be distinguished by comparing their fields with those theoretically produced by pipes, but modelling shows that while the fields of discs and vertical pipes are easily distinguished, inclination such as that introduced by a crater can cause confusion. There is also the problem of non-magnetic kimberlites. The use of electrical and electromagnetic exploration methods is more recent, the latter including both frequency-domain and transient methods. Such methods only give clear responses where there is a strong difference in resistivity between kimberlites and their host rocks. The electrical conductivity of kimberlites also results from both shallow and deep-seated effects, with the magnetisation of the weathered upper parts of pipes reduced relative to the unweathered lower portions. Where weathered "yellow ground" is absent, kimberlites give a much stronger conductive signal. The electrical conductivity has not been sufficiently studied, and conflicting data from the results of electrical sounding have been published.

Time-domain electromagnetic methods have led to some exciting deep-seated base metal discoveries in the 1980s. The technology of this method is described., Time-domain electromagnetic methods have led to some exciting deep-seated base metal discoveries in the 1980s. The technology of this method is described.

TEMIX is a transient electromagnetic forward and inverse modelling program for personal computers. It provides a method of computing the forward TEM response of a layered earth to central loop sounding measurements and also the inverse solution for transient electromagnetic sounding data in terms of later resistivities and thickness., TEMIX is a transient electromagnetic forward and inverse modelling program for personal computers. It provides a method of computing the forward TEM response of a layered earth to central loop sounding measurements and also the inverse solution for transient electromagnetic sounding data in terms of later resistivities and thickness.

A computer program that analyses INPUT transient electromagnetic geophysical data quickly and accurately is introduced., A computer program that analyses INPUT transient electromagnetic geophysical data quickly and accurately is introduced.

Because of an extremely long history of weathering in Australia, new techniques are being developed to see through a leached conductive overburden up to 200m in thickness. SIROTEM, a portable multichannel transient electromagnetic system can see through conductive magnetic weathered material whereas SIROTOPE is a lead isotope geochemical technique which can use soils, water, rocks and drill core to discriminate between barren and mineralised rocks in a particular province. Both techniques have met with considerable success and enable reliable decisions to be taken before drilling expenditure thereby decreasing risks and obtaining maximum value for exploration expenditure., Because of an extremely long history of weathering in Australia, new techniques are being developed to see through a leached conductive overburden up to 200m in thickness. SIROTEM, a portable multichannel transient electromagnetic system can see through conductive magnetic weathered material whereas SIROTOPE is a lead isotope geochemical technique which can use soils, water, rocks and drill core to discriminate between barren and mineralised rocks in a particular province. Both techniques have met with considerable success and enable reliable decisions to be taken before drilling expenditure thereby decreasing risks and obtaining maximum value for exploration expenditure.

A theoretical model study to assess the influence of irregular terrain on common loop and separated loop transient electromagnetic anomalies is presented. Differences in loop-target distance and orientation can accentuate anomalies observed over hills, and suppress those recorded in valleys. In many cases, the diffusive behaviour of TEM anomalies with increasing delay time provides the only basis for resolving interpretational ambiguities caused by topographic variations., A theoretical model study to assess the influence of irregular terrain on common loop and separated loop transient electromagnetic anomalies is presented. Differences in loop-target distance and orientation can accentuate anomalies observed over hills, and suppress those recorded in valleys. In many cases, the diffusive behaviour of TEM anomalies with increasing delay time provides the only basis for resolving interpretational ambiguities caused by topographic variations.

Theoretically exact type curves are presented to show the effect on response shape of changing dip, strike, transmitter-receiver separation, depth of burial and target conductance. Relatively small dip variations produce a marked asymmetry in response shape. For steeply dipping conductors, strike can be determined from the cross-over width of the anomaly. The curves illustrate the dynamic character of the transient process, and suggest how the spatial disposition and quality of large sheet conductors might be inferred from the extent of peak-amplitude displacement with time, and rate of eddy-current diffusion. A generalised interpretation scheme is proposed on dimensionless response characteristics which will facilitate the rapid determination of conductor dip, conductance and depth of burial for any time regime., Theoretically exact type curves are presented to show the effect on response shape of changing dip, strike, transmitter-receiver separation, depth of burial and target conductance. Relatively small dip variations produce a marked asymmetry in response shape. For steeply dipping conductors, strike can be determined from the cross-over width of the anomaly. The curves illustrate the dynamic character of the transient process, and suggest how the spatial disposition and quality of large sheet conductors might be inferred from the extent of peak-amplitude displacement with time, and rate of eddy-current diffusion. A generalised interpretation scheme is proposed on dimensionless response characteristics which will facilitate the rapid determination of conductor dip, conductance and depth of burial for any time regime.

A first order numerical approximation is used to investigate the late-time geometric response characteristics of the inline and broadside exploration techniques, when profiling over a thin finite conductor embedded in a resistive host rock. The interpretational and operational attributes of the two configurations for differing target-loop geometrics, including changes in conductor dip, strike, depth, traverse off-set and loop separation are compared. It is shown that broadside geometry offers some interpretational advantages, but the inline configuration has a greater depth of investigation, and is more suited to routine applications., A first order numerical approximation is used to investigate the late-time geometric response characteristics of the inline and broadside exploration techniques, when profiling over a thin finite conductor embedded in a resistive host rock. The interpretational and operational attributes of the two configurations for differing target-loop geometrics, including changes in conductor dip, strike, depth, traverse off-set and loop separation are compared. It is shown that broadside geometry offers some interpretational advantages, but the inline configuration has a greater depth of investigation, and is more suited to routine applications.

Comparative studies of different transient electromagnetic loop configurations have been made in a controlled mineral environment. The operational and interpretational advantages of the common, separated inline, and fixed transmitter loop profiling techniques are analysed with respect to their response characteristics and detection capabilities. Laboratory and computer-aided theoretical simulations show that peak amplitude, response minima, and cross-over points are all important interpretative clues for estimating the location, attitude, and physical extent of the target mineralisation. However such features are non-unique and profiling with more than one target-loop geometry is advisable to minimise interpretational ambiguities. It is shown that improved signal-to-noise ratios and detection limits are achievable with the fixed central transmitter loop system but in resistive terrains large loops and earlier channel information are needed for the detection of poor conductors at depth., Comparative studies of different transient electromagnetic loop configurations have been made in a controlled mineral environment. The operational and interpretational advantages of the common, separated inline, and fixed transmitter loop profiling techniques are analysed with respect to their response characteristics and detection capabilities. Laboratory and computer-aided theoretical simulations show that peak amplitude, response minima, and cross-over points are all important interpretative clues for estimating the location, attitude, and physical extent of the target mineralisation. However such features are non-unique and profiling with more than one target-loop geometry is advisable to minimise interpretational ambiguities. It is shown that improved signal-to-noise ratios and detection limits are achievable with the fixed central transmitter loop system but in resistive terrains large loops and earlier channel information are needed for the detection of poor conductors at depth.

EM, IP, gravity and magnetic geophysical test results were assessed to judge the contribution each method might make towards further discoveries of graphite-associated uranium occurrences. The best drill targets were proven to be discontinuities in graphitic conductors and localities where the latter are intersected by fracture zones in the Athabasca. The tests demonstrated that the preferred combination of geophysical surveys is horizontal loop EM to locate graphite conductors in the basement and VLF-EM to locate the fractures., EM, IP, gravity and magnetic geophysical test results were assessed to judge the contribution each method might make towards further discoveries of graphite-associated uranium occurrences. The best drill targets were proven to be discontinuities in graphitic conductors and localities where the latter are intersected by fracture zones in the Athabasca. The tests demonstrated that the preferred combination of geophysical surveys is horizontal loop EM to locate graphite conductors in the basement and VLF-EM to locate the fractures.

Inappropriate instrument parameters of a TEM receiving system can lead to false anomalies. Criteria are given for selecting the lower cut-off frequency of the high-pass filter. An approximative formula is established to calculate the natural frequency of the receiving coil, and a simple and effective method is introduced to correct the systematic error caused by the delay effect of the receiving coil on the transient signals., Inappropriate instrument parameters of a TEM receiving system can lead to false anomalies. Criteria are given for selecting the lower cut-off frequency of the high-pass filter. An approximative formula is established to calculate the natural frequency of the receiving coil, and a simple and effective method is introduced to correct the systematic error caused by the delay effect of the receiving coil on the transient signals.