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Down-hole magnetometric resistivity inversion for zinc and lead lenses localization at tobermalug, county Limerick, Ireland.

Bouchedda, Abderrezak; Giroux, Bernard; Allard, Michel (2017). Down-hole magnetometric resistivity inversion for zinc and lead lenses localization at tobermalug, county Limerick, Ireland. Journal of Applied Geophysics , vol. 137 . p. 25-33. DOI: 10.1016/j.jappgeo.2016.12.010.

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Résumé

The magnetometric resistivity (MMR) method consists of measuring the variation of magnetostatic field associated to current density variations. It is based on the principle that direct current flow between two electrodes takes the path of least resistance through the earth. Consequently, conductive or relatively conductive ore bodies such as massive, semi-massive to disseminated sulphides are preferentially energized, which increases the current density in their vicinity. MMR is more efficient than electromagnetic methods in the case of weak conductivity contrasts. To improve the signal to noise ratio the magnetic field can be measured in boreholes rather than on the surface. Down-hole magnetometric resistivity measurements have been conducted in Tobermalug prospect in County Limerick, Ireland. The survey was used as an alternative to down-hole electromagnetic to delineate subhorizontal zinc/lead mineralization lenses that can be poorly conductive. Two survey areas were investigated, DHMMR1 and DHMMR2. Interpretation is based on the regularized least-squares inversion of MMR data, in which the MMR forward problem is solved with a finite volume discretization of the electrostatic and magnetostatic equations. Inversion of synthetic data generated over two conductive horizontal discs model shows that conductive structures are well positioned but their extensions is biased along current electrodes orientation. Inversion of the field data allowed localizing a few conductive elongated targets. At DHMMR1, the conductivity is weaker and seems to be associated to disseminated mineralization. DHMMR2 contains a higher conductivity and more elongated target. It appears to be associated to semi-massive sulphides.

Type de document: Article
Mots-clés libres: MMR; zinc-Lead; inversion
Centre: Centre Eau Terre Environnement
Date de dépôt: 07 mai 2018 20:03
Dernière modification: 07 mai 2018 20:03
URI: http://espace.inrs.ca/id/eprint/6441

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