Exploration Geophysics Exploration Geophysics Society
Journal of the Australian Society of Exploration Geophysicists

The contribution of magnetite to the induced polarization response of the Centenary orebody*

Karen Pittard 1 2 Barry Bourne 1

1 Barrick Gold of Australia, 2 Mill St, Perth, WA 6000, Australia.

2 Email: kpittard@barrick.com.au

Exploration Geophysics 38(3) 200-207 http://dx.doi.org/10.1071/EG07020
Submitted: 1 August 2006  Accepted: 18 June 2007   Published: 19 September 2007


The Centenary gold deposit is a concealed ore body located 110 km north of Leonora, Western Australia. The orebody is associated with sulphides and is hosted in the magnetic portion of the Mount Pickering Dolerite. Due to its sulphidic nature, both gravity and induced polarisation (IP) were trialled soon after discovery.

The gravity survey showed major structures and delineated the host magnetic dolerite, and a trial dipole–dipole IP and resistivity survey detected a significant chargeability anomaly over Centenary. Interestingly, both forward and inverse models showed an IP anomaly that was broader than, and displaced from, mineralisation. Down hole IP and resistivity surveys also showed an elevated chargeability response shallower and broader than the intersected mineralised zone. Pyrite is the main sulphide associated with Centenary and is spatially related to gold mineralisation. These data therefore suggested that pyrite was not the sole contributor to the chargeability response of Centenary.

Petrophysical results, integrated with examination of thin sections, found that the five samples giving the highest chargeability response contained at least 5% pyrite and 5% magnetite, and at least 15% magnetite and pyrite combined. Samples with comparable amounts of pyrite, but less magnetite, gave a lower chargeability response. This supports a hypothesis that rocks containing both magnetite and pyrite at Centenary can generate a larger IP response than rocks containing pyrite or magnetite alone.

Key words: Centenary, greenstone, geophysics, induced polarisation, magnetics, gravity, pyrite, magnetite.


Bourne B. , 1999, Darlot/Centenary Geophysical Summary and Follow-up Proposal: Homestake Internal Memorandum (unpublished).

Clark D. A. , French H. H. , Lackie M. A. , and Schmidt P. W. , 1992, Rock Magnetism and Magnetic Petrology Applied to Geological Interpretation of Magnetic Surveys: Division of Exploration Geoscience, Inst. Minerals, Energy and Construction, Restricted Report 303R.

Forsyth A. , 1999, Petrophysical analysis of nickeliferous rocks at the Forrestania greenstone belt, Western Australia: B.Sc.(Honours) thesis (unpublished), Curtin University.

Krcmarov R. , Beardsmore T. J. , King J. , Kellett R. , and Hay R. , 2000, Geology, regolith, mineralisation and mining of the Darlot-Centenary gold deposit, Yandal belt: in Phillips, G. N., and Anand, R. R., (Eds). Yandal greenstone belt: Aust. Inst. of Geoscientists Bulletin 32, 351–373.

Pittard K. , 2001, The Contribution of Magnetite to the Induced Polarisation Response of the Centenary Orebody: B.Sc.(Honours) thesis (unpublished), Curtin University.

Wong J. 1979 An electrochemical model of the induced-polarization phenomenon in disseminated sulfide ores: Geophysics 44 1245 1265 doi:10.1190/1.1441005

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