Geophysical surveys at the Nkomati Mine, Mpumalanga, South Africa

Marco Nyoni; Bishop John

doi:10.1071/EG00521

ISSN: 0812-3985
E-ISSN: 1834-7533

Geophysical surveys at the Nkomati Mine, Mpumalanga, South Africa
Authors Marco Nyoni^a and Bishop John^b
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^a Marco Nyoni Anglovaal Mining Ltd, PO Box 62379, Marshalltown, 2107, South Africa, Phone: +2711 6340351, Facsimile: +2711 6340500, Email: [email protected] ^b John Bishop, Mitre Geophysics Pty Ltd, PO Box 974, Sandy Bay, Tasmania, 7006, Phone: (03) 6225 4556, Facsimile: (03) 6225 4553, Email: [email protected]
Publisher: Australian Society of Exploration Geophysicists
Source: Exploration Geophysics, Volume 31, Issue 3, Jun 2000, p. 521 - 530
DOI: https://doi.org/10.1071/EG00521
- Published online: 01 Jun 2000

Abstract

Nkomati Mine, a joint venture between Anglovaal Mining and Anglo American, exploits a magmatic Ni-Cu-Co-PGE massivesulphide deposit associated with the Uitkomst Complex, inMpumalanga, South Africa. The mineralisation consists of flatlyingmassive sulphides, which are magnetic, dense andconductive. Geophysics has been used to assist the explorationprogram for further resources. Methods that were tried includesurface magnetic, gravity and controlled source audiomagnetotelluric (CSAMT) surveys, plus downhole electromagnetic(DHEM) and downhole magnetometric resistivity (DHMMR)surveys.

The downhole methods were the most effective for deep targets. Because of the highly conductive nature of the sulphides, standardimpulse type time-domain DHEM did not give good results untiltransformed into step-type data. However, strong responses wereobtained from frequency-domain measurements. Since all of theholes were vertical, no useful cross component data could becollected and the location of the sources suffered from radialsymmetry. In contrast, the DHMMR was able to resolve on whichside of the hole the conductors lay.

CSAMT successfully defined the disseminated and massivemineralisation at depth. Surface magnetic and gravity surveys wereuseful for outlining relatively shallow mineralisation outside of themain complex. Qualitative interpretation, and modelling of thegravity and magnetic data, showed a good correlation with theCSAMT results.

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References

Bishop, J. R., 1998, Modelling of Geophysical Surveys proposed for the Nkomati Ni-Cu Mine: Unpublished report for Anglovaal Mining.
Bishop, J.R., Hatch, M., Asten, M., Carroll, N. and MacInnes, S., 1997. Finding sphalerite at Broken Hill with downhole magnetometric resistivity: Expl. Geophys., 28, 6–10.
Bishop, J.R. and Lewis, R.J.G., 1996. Introduction to the 1996 special volume on DHEM: Expl. Geophys., 27, 37–39.
Bishop, J.R., Lewis, R.J.G. and Stolz, E.M., 2000. Horses for (conductive) courses: DHEM and DHMMR: Expl. Geophys., 31, 192–199.
Kellett, R., Bishop, J.R. and Van Reed, E., 1993, The effects of source polarisation in CSAMT data over two massive sulphide deposits in Australia: Geophysics, 59, 1764–1772.
Kenyon, A.K., Attridge, R.L. and Coetzee, G.L., 1986, The Uitkomst nickel-copper deposit, Eastern Transvaal, in Anhaeusser, C.R. and Maske, S., Eds., Mineral deposits of Southern Africa: Geol. Soc. of South Africa, 1009–1019.
King, A., 1996, Deep drillhole electromagnetic surveys for nickel/copper sulphides at Sudbury, Canada: Expl. Geophys., 27, 105–118.
Lamontagne Geophysics, 1993. Manual for Multiloop 2, version 2.5.
Lewis, R.J.G., 1998, The art of DHMMR: AGR Pty Ltd publication.
Macnae, J. and Mutton, A., 1996, Can sulphides be discriminated from conductive slates? A case history at Dugald River: Expl. Geophys., 27, 119–130.
Watts, A., 1997. Exploring for nickel in the 90s, or ‘til depth us do part’, Gubins, A.G., Ed., Proceedings of Exploration '97, 1003–1013.
Woolfe, J. A. S., 1996, The Nkomati Joint Venture - a nickel mine in the making, Geol. Soc. of South Africa: Geobulletin, 39, 5–7.
Zonge, K., L. and Hughes, L.J., 1988, Controlled source audio-frequency magnetotellurics, in Nabighian, M., Ed., Electromagnetic methods in applied geophysics, Vol. 2, 713–809.

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Article Type: Research Article

Keyword(s): controlled source audio-frequency magnetotelluric; downhole magnetometric resistivity; nickel; Nkomati; Uitkomst; ultramafic

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Geophysical surveys at the Nkomati Mine, Mpumalanga, South Africa

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