Methods for determining remanent and total magnetisations of magnetic sources – a review

Clark, David

doi:10.1071/eg14013

Cited by 95 publications

(70 citation statements)

References 121 publications

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“…4c. These results confirm numerically what was pointed out by Clark (2014): confocal ellipsoids with properly scaled isotropic susceptibilities, no remanence and the same magnetic moment produce different magnetic fields at the same external points, unless the inducing field happens to lie along one of their axes. Farrar (1979) …”

Section: Confocal Ellipsoidssupporting

confidence: 79%

“…This ambiguity between confocal ellipsoids with the same magnetic moment has already been pointed out by Clark (2014). It occurs for the particular case in which the uniform inducing field is parallel to an ellipsoid axis and there is no remanence.…”

Section: Ambiguity Between Confocal Ellipsoids With the Same Magneticmentioning

confidence: 90%

“…This is a function of the body shape and gives rise to shape anisotropy (Uyeda et al, 1963;Thompson and Oldfield, 1986;Dunlop and Özdemir, 1997;Clark and Emerson, 1999;Tauxe, 2003). It is well established in the literature that the self-demagnetization can be neglected if the body has a susceptibility lower than 0.1 SI (Emerson et al, 1985;Clark et al, 1986;Eskola and Tervo, 1980;Guo et al, 1998Guo et al, , 2001Purss and Cull, 2005;Hillan and Foss, 2012;Austin et al, 2014;Clark, 2014). On the other hand, neglecting the self-demagnetization in geological bodies with high susceptibilities (> 0.1 SI) may strongly mislead the interpretation obtained from magnetic methods.…”

Section: Introductionmentioning

confidence: 95%

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Ellipsoids (v1.0): 3-D magnetic modelling of ellipsoidal bodies

Takahashi¹,

Oliveira²

2017

Geosci. Model Dev.

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Abstract. A considerable amount of literature has been published on the magnetic modelling of uniformly magnetized ellipsoids since the second half of the nineteenth century. Ellipsoids have flexibility to represent a wide range of geometrical forms, are the only known bodies which can be uniformly magnetized in the presence of a uniform inducing field and are the only finite bodies for which the selfdemagnetization can be treated analytically. This property makes ellipsoids particularly useful for modelling compact orebodies having high susceptibility. In this case, neglecting the self-demagnetization may strongly mislead the interpretation of these bodies by using magnetic methods. A number of previous studies consider that the self-demagnetization can be neglected for the case in which the geological body has an isotropic susceptibility lower than or equal to 0.1 SI. This limiting value, however, seems to be determined empirically and there has been no discussion about how this value was determined. In addition, the geoscientific community lacks an easy-to-use tool to simulate the magnetic field produced by uniformly magnetized ellipsoids. Here, we present an integrated review of the magnetic modelling of arbitrarily oriented triaxial, prolate and oblate ellipsoids. Our review includes ellipsoids with both induced and remanent magnetization, as well as with isotropic or anisotropic susceptibility. We also discuss the ambiguity between confocal ellipsoids with the same magnetic moment and propose a way of determining the isotropic susceptibility above which the self-demagnetization must be taken into consideration. Tests with synthetic data validate our approach. Finally, we provide a set of routines to model the magnetic field produced by ellipsoids. The routines are written in Python language as part of the Fatiando a Terra, which is an open-source library for modelling and inversion in geophysics.

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Section: Confocal Ellipsoidssupporting

confidence: 79%

Section: Ambiguity Between Confocal Ellipsoids With the Same Magneticmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 95%

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Ellipsoids (v1.0): 3-D magnetic modelling of ellipsoidal bodies

Takahashi¹,

Oliveira²

2017

Geosci. Model Dev.

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“…A second inversion was performed using Geosoft's magnetic vector inversion (Ellis et al, 2012) algorithm, however the resultant model was spatially near-identical to the susceptibility model, which leads to the interpretation that the magnetic geological bodies have no measurable magnetic remanence. The susceptibilities are approaching values (>0.005SI) where self demagnetisation may occur (Clark, 2014) but these effects were ignored in this study.…”

Section: Geophysical Modelmentioning

confidence: 99%

Magnetic modelling and geological modelling come together at the Kintyre uranium deposit

Fitzpatrick¹,

Large²

2015

ASEG Extended Abstracts

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“…If significant remanence is present in the target it is necessary to take into account the direction and intensity of the remanence when performing magnetic modelling, or inversions. Methods exist that allow the total magnetisation of isolated magnetic sources to be estimated (see Clark, 2014) and such methods should also be used when siting drill targets. These calculations and the measurement techniques discussed here are complementary and both should be used when remanent effects have been identified.…”

Section: Introductionmentioning

confidence: 99%

The Qmeter - a portable tool for remanence and susceptibility

Schmidt

2015

ASEG Extended Abstracts

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Methods for determining remanent and total magnetisations of magnetic sources – a review

Cited by 95 publications

References 121 publications

Ellipsoids (v1.0): 3-D magnetic modelling of ellipsoidal bodies

Ellipsoids (v1.0): 3-D magnetic modelling of ellipsoidal bodies

Magnetic modelling and geological modelling come together at the Kintyre uranium deposit

The Qmeter - a portable tool for remanence and susceptibility

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