1887
Volume 31, Issue 1-2
  • ISSN: 0812-3985
  • E-ISSN: 1834-7533

Abstract

The effect of magnetically polarisable material on transient electromagnetic (TEM) responses is discussed using data calculated for a layered-Earth model and a sphere in free-space. The layered-Earth models are characterised by a resistive surface layer of elevated magnetic permeability to represent lateritic duricrust and ironstone. The corresponding results indicate that data measured by TEM systems such as SIROTEM, UTEM, QUESTEM and TEMPEST will only be marginally affected by the magnetic permeability of the surface layer. The sphere model is characterised by high conductivity and high magnetic permeability to represent a pyrrhotite-rich mineralisation. The corresponding TEMPEST responses as well as results from singular value decomposition analysis indicate TEMPEST data to be sensitive to magnetic permeability variations exceeding 0.2 μ , but only for conductive and sizeable structures.

TEMPEST data acquired crossing a banded iron formationrelated magnetic anomaly of 8000 nT were found to be devoid of any indication of magnetic induction. The anomaly was modelled with a dike-shaped polygon suggesting a magnetic permeability of 2.0 μ with the corresponding EM data indicating a zone of low conductivity. The EM responses caused by dragging the receiver coils through the associated magnetic gradient is removed by the stacking process, but is retrievable from the streamed data.

© 2000 ASEG
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2000-03-01
2026-01-14

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References

  1. Beard, L.P. and Nyquist, J.E., 1998, Simultaneous inversion of airborne electromagnetic data for resistivity and magnetic permeability: Geophysics, 63, 1556-1564.
  2. Buselli, G. and O'Neill, B., 1977, SIROTEM: a new portable instrument for multichannel transient electromagnetic measurements: Bull. Austral. Soc. Expl. Geophys., 8, 82-87.
  3. Clark, D.A., French, D.H., Lackie, M.A. and Schmidt, P.W., 1992, Magnetic petrology: application of integrated rock magnetic and petrological techniques to geological interpretation of magnetic surveys: Expl. Geophys., 23, 65-68.
  4. Clark, D.A. and Schmidt, P.W., 1994, Magnetic properties of BIFs, Hamersley Basin and Yilgarn, in Dentith, M.C., Frankcombe, K.F., Ho, S.E., Shepherd, D.I. and Trench, A., Eds., Geophysical signatures of Western Australian mineral deposits: Austral. Soc. Explr. Geophys., Special Publication, 7, 343-354.
  5. Dauth, C., 1997, Airborne magnetic, radiometric and satellite imagery for regolith mapping in the Yilgarn Craton of Western Australia: Expl. Geophys., 28, 199-203.
  6. Eskola, L., Puranen, R. and Soininen, H., 1999, Measurement of magnetic properties of steel sheets: Geophys. Prosp., 47, 593-602.
  7. Flis, M., Hawke, P. and McMillan, A., 1998, The application of multifrequency airborne electromagnetics to iron ore exploration: Expl. Geophys., 29, 254-258.
  8. Fraser, D.C., 1973, Magnetite ore tonnage estimates from an aerial electromagnetic survey: Geoexploration, 11, 97-105.
  9. Fraser, D.C., 1981, Magnetite mapping with a multicoil airborne electromagnetic system: Geophysics, 46, 1579-1593.
  10. Golub, G.H. and Reinsch, C., 1970, Singular value decomposition and least squares solutions, in Wilkinson, J. and Reinsch, C., Eds., Handbook for Automatic Computation, II, Linear Algebra, Springer-Verlag.
  11. Grant, F.S., 1985, Aeromagnetics, geology and ore environments, I. Magnetite in igneous, sedimentary and metamorphic rocks: an overview: Geoexploration, 23, 303-333.
  12. Guo, W., Dentith, M.C., Li, Z. and Powell, C.McA., 1998, Self demagnetisation corrections in magnetic modelling: some examples: Expl. Geophys., 29, 396-401.
  13. Habashy, T.M., Spies, B.R. and Groom, R.W., 1995, Computation of the electromagnetic response of a conductive sphere in a uniform conducting earth at arbitrary frequency: Schlumberger-Doll Research (unpublished).
  14. Johansen, H.K., 1977, A man/computer interpretation system for resistivity soundings over a horizontally stratified earth: Geophys. Prosp., 25, 667-691.
  15. Lane, R., Green, A., Golding, C., Owers, M., Pik, P., Plunkett, C., Sattel, D. and Thorn, B., 2000, An example of 3D conductivity mapping using the TEMPEST airborne electromagnetic system: Expl. Geophys., (this issue).
  16. Lane, R., Green, A., Hu,Y., Plunkett, C. and Price, A., 1998, Streamed data - a source of insight and improvement for time domain airborne EM: Expl. Geophys., 29, 16-23.
  17. Macnae, J., Emerson, D. and Sattel, D., 2000, Physical properties of the Lawlers regolith, W.A.: Expl. Geophys., (this issue).
  18. Newman, G.A., Hohmann, G.W. and Anderson,W.L., 1986, Transient electromagnetic response of a three-dimensional body in a layered earth: Geophysics, 51, 1608- 1627.
  19. NGA, 1998, GM-SYS v. 4.04: Gravity and magnetics modeling for windows and X-windows user's guide: Northwest Geophysical Associates Inc.
  20. Sattel, D., 1996, Resolving shallow conductivity structures in the Lawlers regolith and the feasibility of an EM gradiometer: Ph.D thesis, Macquarie Univ.
  21. Sattel, D., 1998a, Conductivity information in three dimensions: Expl. Geophys., 29, 157-162.
  22. Sattel, D., 1998b, Improving conductivity models using on-time EM data: Expl. Geophys., 29, 605-608.
  23. Smith, P. and Hall, D., 1995, Application of geophysics to the White Devil Gold Deposit, N.T.: Expl. Geophys., 26, 116-123.
  24. Sumner, J., 1998, Exploration geophysics in the North Kimberley Kimberlite Province of Western Australia: B.Sc Honours thesis, Curtin Univ.
  25. Tabbagh, A., 1986, Applications and advantages of the Slingram electromagnetic method for archaeological prospecting: Geophysics, 51, 576-584.
  26. Ward, S.H., 1961, The electromagnetic response of a magnetic iron ore deposit: Geophys. Prosp., 9, 190-202.
  27. West, G.F., Macnae, J.C. and Lamontagne, Y., 1984, A time-domain electromagnetic system measuring the step response of the ground: Geophysics, 49, 1010-1026.
  28. West, G.F. and Macnae, J.C., 1991, Physics of the electromagnetic induction exploration method, in Nabighian, M.N., Ed., Electromagnetic Methods in Applied Geophysics, 2: Soc. Expl. Geophys., 5-45.
  29. Zhang, Z. and Oldenburg, D., 1999, Simultaneous reconstruction of 1-D susceptibility and conductivity from electromagnetic data: Geophysics, 64, 33-47.
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  • Article Type: Research Article
Keyword(s): Airborne EM; inversion; magnetic induction; magnetic permeability; time-domain EM

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