Horses for (conductive) courses: DHEM and DHMMR

Bishop, John; Lewis, Ruth; Stolz, Ned

doi:10.1071/eg00192

Cited by 9 publications

(4 citation statements)

References 10 publications

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“…In contrast, the MMR technique is more appropriate because it can respond to highly conductive and to weakly conductive targets in a conductive host. For example, it was successfully used in Australian environments for poorly conducting metal sulphide targets, such as sphalerite rich bodies (Asten, 1988;Bishop et al, 1997) and nickel sulphide mineralisation (Bishop et al, 2000). Despite this advantage, MMR is not much used in mineral exploration (Godber and Bishop, 2007).…”

Section: Introductionmentioning

confidence: 97%

Down-hole Magnetometric Resistivity inversion for zinc and lead lenses localization at Tobermalug, County Limerick, Irland

Bouchedda¹,

Giroux²,

Michel

2015

SEG Technical Program Expanded Abstracts 2015

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Section: Introductionmentioning

confidence: 97%

Down-hole Magnetometric Resistivity inversion for zinc and lead lenses localization at Tobermalug, County Limerick, Irland

Bouchedda¹,

Giroux²,

Michel

2015

SEG Technical Program Expanded Abstracts 2015

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“…This suggests a complementary nature of MMR and BHEM methods in studying mineral deposits. The cross-hole magnetometric resistivity (source and receivers in distinct boreholes; Nabighian et al 1984) and down-hole magnetometric resistivity (DHMMR; source on surface extended along strike and borehole receivers; Asten 1988) methods have been used with success in mineral exploration and led to discoveries of ore deposits that did not generate anomalous BHEM signals (e.g., Bishop et al 1997Bishop et al , 2000. Field evidence (Asten 1988;Bishop et al 1997) and numerical simulations (Chen et al 2002) suggest that the sensitivity of DHMMR and surface MMR data, respectively, is limited to lateral distances / 500 m off the borehole or receiver site, whereas BHEM methods may be sensitive to a comparable or smaller region around the borehole.…”

Section: Other Borehole Electromagnetic Methodsmentioning

confidence: 99%

“…In typical BHEM surveys, transmitter loops with more than 200 m side length are deployed on the surface of the ground, and magnetic field data are collected in boreholes and on the surface (e.g., Boyd and Wiles 1984;Pantze et al 1986;Dyck 1991;Bishop et al 2000;Hattula and Rekola 2000;Spicer 2016). In order to illuminate deposits from different angles, and thus to determine dip angle, along-dip extent and along-strike extent, individual boreholes are surveyed using a combination of different transmitter loops (e.g., Asten 1996).…”

Section: Other Borehole Electromagnetic Methodsmentioning

confidence: 99%

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

Kalscheuer

Juhojuntti

Vaittinen³

2017

Surv Geophys

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A combination of magnetotelluric (MT) measurements on the surface and in boreholes (without metal casing) can be expected to enhance resolution and reduce the ambiguity in models of electrical resistivity derived from MT surface measurements alone. In order to quantify potential improvement in inversion models and to aid design of electromagnetic (EM) borehole sensors, we considered two synthetic 2D models containing ore bodies down to 3000 m depth (the first with two dipping conductors in resistive crystalline host rock and the second with three mineralisation zones in a sedimentary succession exhibiting only moderate resistivity contrasts). We computed 2D inversion models from the forward responses based on combinations of surface impedance measurements and borehole measurements such as (1) skin-effect transfer functions relating horizontal magnetic fields at depth to those on the surface, (2) vertical magnetic transfer functions relating vertical magnetic fields at depth to horizontal magnetic fields on the surface and (3) vertical electric transfer functions relating vertical electric fields at depth to horizontal magnetic fields on the surface. Whereas skin-effect transfer functions are sensitive to the resistivity of the background medium and 2D anomalies, the vertical magnetic and electric field transfer functions have the disadvantage that they are comparatively insensitive to the resistivity of the layered background medium. This insensitivity introduces convergence problems in the inversion of data from structures with strong 2D resistivity contrasts. Hence, we adjusted the inversion approach to a three-step procedure, where (1) (2) this inversion model from surface impedances is used as the initial model for a joint inversion of surface impedances and skin-effect transfer functions and (3) the joint inversion model derived from the surface impedances and skin-effect transfer functions is used as the initial model for the inversion of the surface impedances, skin-effect transfer functions and vertical magnetic and electric transfer functions. For both synthetic examples, the inversion models resulting from surface and borehole measurements have higher similarity to the true models than models computed exclusively from surface measurements. However, the most prominent improvements were obtained for the first example, in which a deep small-sized ore body is more easily distinguished from a shallow main ore body penetrated by a borehole and the extent of the shadow zone (a conductive artefact) underneath the main conductor is strongly reduced. Formal model error and resolution analysis demonstrated that predominantly the skin-effect transfer functions improve model resolution at depth below the sensors and at distance of $ 300-1000 m laterally off a borehole, whereas the vertical electric and magnetic transfer functions improve resolution along the borehole and in its immediate vicinity. Furthermore, we studied the signal levels at depth and provided specifications of borehole magnetic and elect...

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“…Downhole magnetometric resistivity (DHMMR) is becoming an increasingly popular method for the detection of weakly conductive, sulphidic mineralization (Bishop et al 1997;Bishop, Lewis and Stolz 2000). Unlike standard inductive EM methods, magnetometric resistivity (MMR) methods use frequencies sufficiently low so that the measured strength of the magnetic field is dominated by galvanic energization/current channelling.…”

Section: Introductionmentioning

confidence: 99%

A comparison of receiver technologies in borehole MMR and EM surveys

Elders

Asten

2004

Geophysical Prospecting

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A series of downhole magnetometric resistivity (DHMMR) and downhole electromagnetic (DHEM) surveys were conducted near Broken Hill, New South Wales, Australia, and at Zinkgruvan, Sweden, to determine how probe and receiver equipment choices affect the amount of noise visible in borehole MMR and EM data. Noise analyses performed on the data, using the standard deviation to gauge the relative noise levels between different probes and receiver systems, indicate that high noise levels in MMR data result primarily from the use of a three‐component EM probe, which has a reduced effective area and hence a higher noise floor compared with a single‐component EM probe. High noise, attributable to cultural sources such as nearby power lines, in either MMR or EM data can be reduced through the use of full‐waveform, multipurpose receiver systems. These systems allow for the use of tapered stacking, which is a more effective method of eliminating coherent noise associated with power‐line transients than the boxcar‐stacking method used by traditional receiver systems.

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Horses for (conductive) courses: DHEM and DHMMR

Cited by 9 publications

References 10 publications

Down-hole Magnetometric Resistivity inversion for zinc and lead lenses localization at Tobermalug, County Limerick, Irland

Down-hole Magnetometric Resistivity inversion for zinc and lead lenses localization at Tobermalug, County Limerick, Irland

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

A comparison of receiver technologies in borehole MMR and EM surveys

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