In‐mine applications of the radio‐wave method in the Sudbury igneous complex

Stevens, Kevin M.; Watts, Anthony H.; Redko, G.

doi:10.1190/1.1815587

Cited by 11 publications

(9 citation statements)

References 2 publications

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“…Conversely, a cross-borehole radar would provide velocity data controlled by the dielectric permittivity, associated with the water content and lithology, whereas a trade-off of RIM when compared to radar is that arrival time measurement for the dielectric permittivity (relevant for lithology mapping) is not available. The relative phase difference data of the EMRE system contain information on the slowness, which has been applied in the estimation of dielectric permittivity [24,25]. Dense receiver stations allow the compilation of reasonably smooth tomographic images.…”

Section: Discussionmentioning

confidence: 99%

“…Error bars are included and they are a result of the accuracy specification of the device. International Journal of Geophysics is a Russian-based device [24] that simultaneously operates at a maximum of four frequencies: 312.5, 625, 1250, and 2500 kHz ( Figure 5(a)) [25]. Thus, the survey time is reduced by measuring all frequencies simultaneously.…”

Section: Rim Instrumentmentioning

confidence: 99%

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Characterization of Geotomographic Studies with the EMRE System

Korpisalo

2014

International Journal of Geophysics

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Posiva Oy carries out research and development on spent nuclear fuel disposal in Finland. The repository will be constructed deep in the crystalline bedrock of Olkiluoto island in Eurajoki. Posiva Oy and ANDRA (France) have cooperated actively in examining methods for revealing properties of granitic bedrock. One of the considered methods was an electromagnetic cross-borehole survey, and RIM measurements were conducted in 2009. Olkiluoto migmatitic bedrock has undergone polyphasic ductile-brittle deformation and resistivity in the bedrock varies strongly in range of tens to tens of thousands of Ωm. Field work was successfully performed in one borehole pair. The results are presented in this paper. The tomographic reconstruction of the borehole section is based on the far-field approximation of the electric field. The results prove that the method can be used between boreholes to delineate and follow sulphide-bearing horizons. The detected low and high resistivity zones and their apparent shapes and orientations are in fair agreement with geological and other geophysical results. The obtained information can be used, for example, in assessing the integrity of the rock mass, as the increased electrical conductivity is often associated with rock mass deformation (clay and water bearing fractures, sulphide and graphite bearing zones).

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Section: Discussionmentioning

confidence: 99%

Section: Rim Instrumentmentioning

confidence: 99%

Characterization of Geotomographic Studies with the EMRE System

Korpisalo

2014

International Journal of Geophysics

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“…Thus, the first RT survey at McConnell demonstrated the potential of radio imaging to map sulfide bodies in highly resistive host rocks. The results were sufficiently encouraging to prompt further RT investigations in the Sudbury area by INCO (McDowell and Verlaan, 1997) and, more recently, by Falconbridge (Stevens and Redko, 2000).…”

Section: Discussionmentioning

confidence: 86%

“…The utility of radio imaging in metalliferous exploration and mining is currently under investigation. Radio frequency methods in the 10 kHz to 1 MHz band have already enjoyed some success in this context, e.g., Nickel and Cerny (1989), Anderson and Logan (1992), Thomson et al (1992), Wedepohl (1993), Zhou et al (1998), and Stevens and Redko (2000). RT can deliver higher resolution than traditional borehole EM systems, both by virtue of its higher frequencies and because the radio transmitter can be lowered down a borehole, closer to the target.…”

Section: Introductionmentioning

confidence: 99%

Radio tomography and borehole radar delineation of the McConnell nickel sulfide deposit, Sudbury, Ontario, Canada

Fullagar¹,

Livelybrooks

Zhang

et al. 2000

GEOPHYSICS

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In an effort to reduce costs and increase revenues at mines, there is a strong incentive to develop highresolution techniques both for near-mine exploration and for delineation of known orebodies. To investigate the potential of high-frequency EM techniques for exploration and delineation of massive sulfide orebodies, radio frequency electromagnetic (RFEM) and ground-penetrating radar (GPR) surveys were conducted in boreholes through the McConnell massive nickel-copper sulfide body near Sudbury, Ontario, from 1993Ontario, from -1996 Crosshole RFEM data were acquired with a JW-4 electric dipole system between two boreholes on section 2720W. Ten frequencies between 0.5 and 5.0 MHz were recorded. Radio signals propagated through the Sudbury Breccia over ranges of at least 150 m at all frequencies. The resulting radio absorption tomogram clearly imaged the McConnell deposit over 110 m downdip. Signal was extinguished when either antenna entered the sulfide body. However, the expected radio shadow did not eventuate when transmitter and receiver were on opposite sides of the deposit. Two-dimensional modeling suggested that diffraction around the edges of the sulfide body could not account for the observed field amplitudes. It was concluded at the time that the sulfide body is discontinuous; according to modeling, a gap as small as 5 m could have explained the observations. Subsequent investigations by INCO established that pick-up in the metal-cored downhole cables was actually responsible for the elevated signal levels.Both single-hole reflection profiles and crosshole measurements were acquired using RAMAC borehole radar systems, operating at 60 MHz. Detection of radar reflections from the sulfide contact was problematic. One coherent reflection was observed from the hanging-wall contact in single-hole reflection mode. This reflection could be traced about 25 m uphole from the contact. In addition to unfavorable survey geometry, factors which may have suppressed reflections included host rock heterogeneity, disseminated sulfides, and contact irregularity.Velocity and absorption tomograms were generated in the Sudbury Breccia host rock from the crosshole radar. Radar velocity was variable, averaging 125 m/µs, while absorption was typically 0.8 dB/m at 60 MHz. Kirchhoffstyle 2-D migration of later arrivals in the crosshole radargrams defined reflective zones that roughly parallel the inferred edge of the sulfide body.The McConnell high-frequency EM surveys established that radio tomography and simple radio shadowing are potentially valuable for near-and in-mine exploration and orebody delineation in the Sudbury Breccia. The effectiveness of borehole radar in this particular environment is less certain.

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“…The first steps in examining wave propagation below the Earth's surface were taken at the beginning of the 20th century. During an intensive period of development in electronics and device techniques, RIM has become a potential prospecting method, for instance for the delineation of massive sulphide deposits, where the rock becomes gradually more conductive towards the centre of the mineralization [2][3][4][5][6]. Operating in the transmission mode, the system must have a separate transmitter and receiver antenna, and the system is referred to as bistatic.…”

Section: Introductionmentioning

confidence: 99%

Borehole Antenna Considerations in the EMRE System: Frequency Band 312.5-2500 kHz

Korpisalo¹

2013

TOGEOJ

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Abstract:The ElectroMagnetic Radiofrequency Echoing (EMRE) system is utilized in radiofrequency imaging (RIM) measurements between two deep boreholes. It is based on radiowave attenuation, making it possible to reconstruct the attenuation distribution of the borehole section (tomogram). The main parts of the EMRE system are a continuous wave (CW) transmitter and superheterodyne-type receiver. The insulated dipole antennas are the transducers between the device and environment, or together they form a transmission line. The system is bistatic because the antennas are placed in separate boreholes.When an antenna is situated in a dissipative medium, e.g. in a deep borehole, its performance becomes highly environmentally sensitive. Direct measurements of the feed-point current and radiative characteristics are impossible, and numerical models must therefore be used to investigate the borehole effects. A generalized transmission line model of an insulated antenna is a simple and useful way to examine the antenna-related properties. A drawback is that the borehole water must be excluded from the models due to the high wave number of water. The commercial simulation package FEKO is a numerical modelling package and a powerful tool when constructing more realistic antenna and borehole models. FEKO models and transmission line models (WKG, CHEN) were compared and the results coincided in the frequency band of 312.5-2500 kHz. According to the FEKO studies, the influence of borehole water and the location of the antenna in the borehole, i.e. centric or eccentric, did not appear to have a significant effect. The scattering parameter s 11 , the ratio of forward and returned power, is a useful antenna parameter to estimate the power level that is radiated from the antenna to the surrounding rock. According to the FEKO models, the highest measurement frequency (2500 kHz) of the EMRE system seems to suffer the most under the borehole conditions due to the low values of s 11 (~-2dB). The performance level of the system determines the maximum distances (translumination distance) at which the signals are still detectable. According to the results using a simplified measurement geometry, the EMRE system can operate at distances of <1000 m when the host rock has resistivities of >10 000 Ωm and the lowest frequency of 312.5 kHz is used. At minor distances of 400-600 m, the system operates well at all frequencies.

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In‐mine applications of the radio‐wave method in the Sudbury igneous complex

Cited by 11 publications

References 2 publications

Characterization of Geotomographic Studies with the EMRE System

Characterization of Geotomographic Studies with the EMRE System

Radio tomography and borehole radar delineation of the McConnell nickel sulfide deposit, Sudbury, Ontario, Canada

Borehole Antenna Considerations in the EMRE System: Frequency Band 312.5-2500 kHz

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