Some Positive thoughts about Negative TEM Responses

John Bishop; James Reid

doi:10.1071/ASEG2003ab014

ISSN: 2202-0586
E-ISSN:

oa Some Positive thoughts about Negative TEM Responses
Authors John Bishop^a and James Reid^b
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^a Mitre Geophysics Pty Ltd, , Australia, [email protected] ^b University of Tasmania, , Australia, [email protected]
Publisher: Australian Society of Exploration Geophysicists
Source: ASEG Extended Abstracts, Volume 2003, Issue ASEG2003 - 16th Geophysical Conference, Aug 2003, p. 1 - 4
DOI: https://doi.org/10.1071/ASEG2003ab014
- Published online: 01 Aug 2003

Abstract

Negative responses recorded during moving in-loop TEM surveys, where only positive data are expected, are a regular occurrence in TEM surveys. They are however generally poorly understood and little reported. In most cases, such negatives are ascribed to induced polarisation (IP) effects, but we suggest that there is at least one other cause of negative TEM response, one which is associated with very resistive terranes containing little if any polarisable material.

This paper presents some examples of this negative resistive response where there is little or no polarisable material present and where a source other than IP should be sought. A series of tests have been proposed to try and isolate the cause.

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References

Bishop, J.R., Enright, M.J., Hinks, J.D. and Kakebeeke, V.Q., 2001. A report on the 2001 SEM, DHEM and DHMMR surveys at Kakoulima, Guinea. RTME report.
Bishop, J.R., Hinks, J.D. and Mclntosh, S.M., 2002. Kakoulima: A Resistive Regime for EM. RTME report.
DAndrea, L., 2001, Interpretation and ground truthing of helicopter electromagnetic data, Zeehan, Western Tasmania. B. Sc. (Hons.) thesis, University of Tasmania.
Flis, M. A., Newman, G. A., and Hohmann, G. W., 1989, Induced polarisation effects in time-domain electromagnetic measurements: Geophysics, 54, 514-523.
Jansen, J.C. and Doyle, B.J., 1998. The Tli Kwi Cho kimberlite complex, Northwest Territories, Canada: a geophysical post mortum. In: Northwest Mining Association 1998 Practical Geophysics Short Course, edited by R.B. Ellis, R. Irvine and F. Fritz.
Kakebeeke, V.Q. and Mclntosh, S.M., 2000. Kakoulima, Guinea TEM survey. RTME report.
Smith, R. S., and West, G. F., 1989, Field examples of negative coincident-loop transient electromagnetic anomalies modelled with polarisable half-planes: Geophysics, 54, 1491-1498.
Weidelt, P., 1982, Response characteristics of coincident-loop transient EM systems: Geophysics, 47, 1325-1330.

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Article Type: Research Article

Keyword(s): kimberlites; negative responses; nickel; resistive terranes; ultramafics

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