1887
Geophysical Signatures of West Australian Mineral Deposits
  • ISSN: 2202-0586
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Abstract

Magnetite-rich banded iron-formations (BIFs) exhibit characteristic magnetic properties, including strong anisotropy. Interpretation of the geological structure of BIF units from the associated magnetic anomalies is complicated by anisotropy of susceptibility and, frequently, by remanent magnetisation. The timing of remanence acquisition relative to folding exerts a crucial influence on the form of the anomalies. Neglect of susceptibility anisotropy and remanence can lead to large errors in interpreted dips and thicknesses of BIF units. The effective susceptibility of BIFs parallel to bedding exceeds the susceptibility normal to bedding, typically by a factor of 2 to 4. Bedding-parallel susceptibilities of magnetite-rich BIFs are typically 0.5 to 2.0 SI (0.05-0.16 G/Oe). Remanence directions in BIFs usually lie close to the bedding plane. Koenigsberger ratios (Q) of BIFs vary widely, but characteristic values can often be determined for individual units. Q values in the range 1 to 2 are common. The magnetisations of the haematite-rich supergene-enrichment iron ores are much lower than those of their BIF precursors.

Magnetic properties of outcropping BIFs are usually greatly modified by weathering, which substantially decreases the bulk susceptibility, the degree of anisotropy and the remanence intensity. Deeper and more intense weathering of BIFs is encouraged by faulting and can be associated with reduced magnetic response over intensely faulted zones.

The remanence of BIFs from the Hamersley Basin is carried by late diagenetic to low-grade metamorphic magnetite after primary haematite. At Wittenoom and Paraburdoo, the remanent magnetisation of Brockman Formation BIFs is pre-folding, whereas in an area of higher metamorphic grade, the Turner Syncline, the remanence of the BIFs is probably post-folding. Aeromagnetic signatures over the Turner Syncline clearly reflect anisotropy and remanence.

Anisotropy and remanence effects are also evident in observed magnetic signatures over Archaean BIFs in the Yilgarn Block. Magnetic property measurements on samples from the Mount Magnet area and elsewhere confirm the high anisotropy and strong remanent magnetisations of these rocks.

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1994-12-01
2026-01-24

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References

  1. BATH G.D., 1962. Magnetic anomalies and magnetizations of the Biwabik Iron-formation, Mesabi area, Minnesota. Geophysics27, 627-650.
  2. BLOCKLEY J.G., 1990. Iron ore. In Geology and Mineral Resources of Western Australia. Geological Survey of Western Australia, Memoir3, 163-189.
  3. CHAMALAUN F. H. & DEMPSEY C.E., 1978. A survey of the magnetic properties of the banded iron formations, Hamersley Province, W.A. Department of Earth Sciences, Flinders University, Publication78/4, 51 pp.
  4. CLARK D.A. & SCHMIDT P.W., 1986a. Magnetic properties of the banded-iron formations of the Hamersley Group, W.A. CSIRO Division of Mineral Physics and Mineralogy, Restricted Investigation Report1638R, 92 pp.
  5. CLARK D.A. & SCHMIDT P.W., 1986b. Geological structure and magnetic signatures of Hamersley BIFs. CSIRO Division of Mineral Physics and Mineralogy, Restricted Investigation Report1639R, 62 pp.
  6. EMBLETON B.J.J., ROBERTSON W.A. & SCHMIDT P.W., 1979. A survey of magnetic properties of some rocks from northwestern Australia. CSIRO Division of Mineral Physics Investigation Report129, 46 pp.
  7. EMERSON D.W., CLARK D.A. & SAUL S.J., 1985. Magnetic exploration models incorporating remanence, demagnetisation and anisotropy: HP41C hand-held computer algorithms. Exploration Geophysics16, 1-122.
  8. HARMSWORTH R.A., KNEESHAW M., MORRIS R.C., ROBINSON C.J. & SHRIVASTAVA P.K., 1990. BIF-derived iron ores of the Hamersley Province. In Hughes F.E. (ed.), Geology of the Mineral Deposits of Australia and Papua New Guinea, pp. 617-642. Australasian Institute of Mining and Metallurgy, Melbourne.
  9. JAHRENS C.E., 1963. Magnetic susceptibility of bedded iron formation. Geophysics28, 756-766.
  10. KLEIN O, 1983. Diagenesis and metamorphism of Precambrian banded-iron formations. In Trendall A.F. & Morris R.C. (eds), Iron-Formation: Facts and Problems. Developments in Precambrian Geology6, 417-469.
  11. MORRIS R.C, 1980. A textural and mineralogical study of the relationship of iron ore to banded iron-formation in the Hamersley Iron Province of Western Australia. Economic Geology75, 184-209.
  12. MORRIS R.C, 1983. Supergene alteration of banded-iron formation. In Trendall A.F. & Morris R.C. (eds), Iron-Formation: Facts and Problems. Developments in Precambrian Geology6, 513-534.
  13. MORRIS R.C, 1985. Genesis of iron ore in banded iron formation by supergene and supergene-metamorphic processes - a conceptual model. In Wolf K.H. (ed.), Handbook of Strata-Bound and Stratiform Ore Deposits13, 73-235.
  14. PORATH H. & CHAMALAUN F.H., 1968. Palaeo-magnetism of Australian haematite ore bodies, II, Western Australia. Geophysical Journal of the Royal Astronomical Society15, 253-264.
  15. SCHMIDT P.W. & CLARK D.A., in press. Palaeo-magnetism and magnetic anisotropy of Protero-zoic banded-iron formations and iron ores of the Hamersley Basin, Western Australia. Precam-brian Research.
  16. SMITH R.E., PERDRIX J.L & PARKS T.C., 1982. Burial metamorphism in the Hamersley Basin, Western Australia. Journal of Petrology23, 75-102.
  17. SYMONS D.T.A. & STUPAVSKY M., 1979. Magnetic characteristics of the iron formation near Tema-gami, Ontario. Ontario Geological Survey, Miscellaneous Paper87, 133-147.
  18. SYMONS D.T.A. & STUPAVSKY M., 1980. Magnetic anomaly type curves and paleomagnetism of Algoman-type iron formation near Temagami, Ontario. Ontario Geological Survey, Miscellaneous Paper93, 215-219.
  19. SYMONS D.T.A., QUICK A.W. & STUPAVSKY M., 1981. Magnetic and paleomagnetic characteristics of the Archaean iron formation and host rocks at the Adams mine, Ontario. Ontario Geological Survey, Miscellaneous Paper98, 293-307.
  20. TRENDALL A.F., 1983. The Hamersley Basin. In Trendall A.F. & Morris R.C. (eds), Iron-Formation: Facts and Problems. Developments in Precambrian Geology6, 513-534.
  21. TRENDALL A.F., 1990. Hamersley Basin. In Geology and Mineral Resources of Western Australia. Geological Survey of Western Australia, Memoir3, 163-189.
  22. TRENDALL A.F. & BLOCKLEY J.G., 1970. The iron associations of the Precambrian Hamersley Group, Western Australia, with special reference to the associated crocidolite. Geological Survey of Western Australia, Bulletin119, 336 pp.
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  • Article Type: Research Article
Keyword(s): Banded iron-formation; banded iron-formation-hosted gold deposits; Hamersley Basin; magnetic anisotropy; magnetisation; Murchison Province; petrophysics; supergene-enrichment iron ore

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