Comparison of ground TEM and VTEM responses over kimberlites in the Kalahari of Botswana*

Ed Cunion

doi:10.1071/EG09019

RESEARCH ARTICLE

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Comparison of ground TEM and VTEM responses over kimberlites in the Kalahari of Botswana^*

Ed Cunion

+ Author Affiliations

- Author Affiliations

63 Woodlawn Avenue, Auburn, Maine, ME 04210, USA. Email: edcunion@yahoo.com

Exploration Geophysics 40(4) 308-319 https://doi.org/10.1071/EG09019
Submitted: 8 April 2009 Accepted: 29 October 2009 Published: 7 December 2009

Abstract

Kalahari cover greater than 60 m thick precludes indicator sampling from identifying individual kimberlite intrusions in the Kokong kimberlite field of Botswana. Employing concurrent multidisciplinary geophysical surveying methods is the exploration technique for the discovery of kimberlites. Time Domain Electromagnetic (TEM) surveying is an effective technique for the prioritization of aeromagnetic and gravity signatures. Diagnostic discrete conductive TEM signatures are usually returned from kimberlites overlain by up to 120 m of Kalahari cover. Following the success of kimberlite identification by ground TEM, a VTEM helicopter time domain survey was flown over the Kokong field to increase the TEM coverage in this prospective kimberlite terrain. A comparison of responses over covered kimberlites traversed by both TEM survey methods and their comparative effectiveness for kimberlite identification is presented.

Key words: Kalahari, kimberlite, magnetic, petrophysics, survey, TEM, VTEM.

Acknowledgements

Thanks go to Rio Tinto Africa/Europe for providing the logistical support for the geophysical work referenced in this paper, and for allowing the subsequently generated data and findings to be published. Thanks also go to Condor Consulting of Denver Colorado for suggesting this paper be written, and for providing examples and explanations of their VTEM processed products. The Botswana Geological Survey (BGS), Tiyapo Ngwisanyi in particular, explained the protocols on the publishing of geophysical information collected in Botswana. Thanks also go to BGS Chief Geologist Johannes Tsimako, then with Rio Tinto, for helping the writer get the Kokong geophysical program off the ground out in the field at its inception.

References

Cumming B. , 1985, Final report on work completed PL32/77 (Kang North), PL 33/77 (Kang South), PL17/78 (Kang West), PL 18/78 (Kang East) and PL 25/79 (Kang North West) from January 1978 to December 1982, Bulletin No. B212 (2436), Falconbridge Explorations Botswana (Pty) Ltd.

da Costa, A. J. M., 1989, Palmietfontein kimberlite pipe, South Africa, A case history: Geophysics 54, 689–700.
| Crossref | GoogleScholarGoogle Scholar | Hansen J. , and Finney W. , 1980, Interpretation report airborne electromagnetic survey, Barringer INPUT survey of the Kang areas A, B, and C, Botswana for Falconbridge Botswana (Pty) Ltd.

Hinks D. , 2003, Borehole logging of Kokong targets Botswana: unpublished Rio Tinto report.

Hinks D. , McIntosh S. , and Lane R. , 2004, A comparison of the Falcon^® and Air-FTG™ airborne gravity gradiometer systems at the Kokong Test Block, Botswana, In: Airborne Gravity 2004 – Abstracts from the ASEG-PESA Airborne Gravity 2004 Workshop: Geoscience Australia Record, 2004/18, 125–134.

Jansen J. , and Witherly K. , 2004, The Tli Kwi Cho Kimberlite Complex, Northwest Territories, Canada: A Geophysical Case Study: 74th Annual Mtg Soc. Expl. Geophy. Tech Prog (Ext. Abstr): Denver, CO. 231 147–1149.

MacInnes S. and Raymond M. , 2001, STEMINV Documentation – Smooth Model TEM Inversion, V.3.00: Zonge Engineering and Research Organization.

Macnae, J. C., 1979, Kimberlite and exploration geophysics: Geophysics 44, 1395–1416.
| Crossref | GoogleScholarGoogle Scholar |

Macnae, J. C., 1995, Applications of geophysics for the detection and exploration of kimberlites and lamproites: Journal of Geochemical Exploration 53, 213–243.
| Crossref | GoogleScholarGoogle Scholar | CAS |

Macnae, J. C., King, A., Stolz, N., Osmakoff, A., and Blaha, A., 1998, Fast AEM data processing and inversion: Exploration Geophysics 29, 163–169.
| Crossref | GoogleScholarGoogle Scholar |

West, G. F., Macnae, J. C., and Lamontagne, Y., 1984, A time-domain EM system measuring the step response of the ground: Geophysics 49, 1010–1026.
| Crossref | GoogleScholarGoogle Scholar |

^* ^*Presented at the 20th ASEG Geophysical Conference and Exhibition, February 2009.