Upgrading processes in BIF-derived iron ore deposits: Implications for ore genesis and downstream mineral processing

Abstract

Ore textures in Australian BIF-derived ores are quite complex and have formed the basis for ore genesis models, which includes hypogene upgrading or supergene upgrading then regional metamorphism for the microplaty hematite ores and supergene upgrading for the martite-goethite ores. Despite a high level of ore texture knowledge, little is known about the spatial distribution of ore textures within deposits or their relationship to downstream processing. This paper describes a new iron ore texture classification system to understand better the vertical textural zonation characteristics of Australian BIF-derived deposits, the interpreted role of recent supergene upgrading processes on modifying primary ore textures and their implications for downstream mineral processing. The iron ore textural classification scheme presented uses textural groupings defined on the basis of similarities in mineralogy, ore texture, porosity, mineral associations and hardness. The scheme is non-genetic and has been successfully applied to deposits in the Pilbara, Yilgarn and Gawler cratons. The main ore texture groups include dense martite/hematite, microplaty hematite, microplaty hematite-goethite, martite-goethite, goethite-martite and goethite-rich. Each group can be further subdivided into physically hard to softer subcategories. The ore textural groups can be divided into those interpreted to be associated with primary replacement of BIF and secondary textures resulting from more recent modification by near-surface hydration or dehydration processes. A schematic vertical section through BIF-derived deposits consists (from the surface) of detritals underlain by a carapace, both of which may have been eroded, followed by a hydrated zone with replacement of primary ore martite and microplaty hematite by vitreous goethite. The hydrated zone is underlain by 0·2-6 m thick zones of intense dehydration and textural infilling of porosity with hematite and hydrohematite. Immediately below the dehydration zone is a strong zone of leaching, where more porous and friable ore textures occur, followed underneath by a gradational contact with primary ore. Secondary supergene processes can impact on beneficiation with hydration and leaching resulting in more difficult density separations at the concentrator stage due to reductions in density differences between ore and gangue and loss of heavy media into pores. Supergene modification of primary BIF-derived ore textures can substantially change lump metallurgical properties, with hydration and dehydration favourably increasing lump yield, but reducing resistance to thermal shock whilst leaching will give the opposing outcome. The lump properties of ore textural groups appear to be relatively consistent within and between the iron ore deposits examined.

Keywords

BIF-DERIVED IRON ORE DEPOSITS TEXTURAL CLASSIFICATION SCHEME ORE GENESIS DOWNSTREAM MINERAL PROCESSING

Get full access to this article

View all access options for this article.

References

ARNAND

R. R.

and PINE

: Regolith geology of the Yilgarn Craton, Western Australia: implications for exploration, Aust. J Earth Sci., 2002, 49, 3–162.

BARLEY

M. E.

, PRICKARD

A. L.

and SYLVESTER

P. J.

: ‘Emplacement of a large igneous province as a possible cause of banded iron formation 245 billion years ago', Nature, 1997, 385, 55–58.

Box

, PHILLIPS

and CLOUT

J. M. E

: ‘Use of geological material types for predicting iron ore product characteristics', in Proc. 1t Japan-Australia Symp. on ‘Iron and Steelmaking’, Fuwa-Ward Symp., ISIJ, Kyoto University, 4–5 April 2002.

CLOUT

J. M. E

, FIRTH

B. A.

and O'CoNNoR

M. T.

: ‘New advances in beneficiation of iron ore', in Proc. Natl Conf. on ‘Iron making resources and reserves estimation' (ed. Misra

V. N.

and Dunlop

J. S.

), 177–183; 1997, Perth, AusIMM.

CLOUT

J. M. F.

: ‘The effects of ore petrology on down-stream processing performance: a review', in ‘Mine to Mill 1998 Conference', 43–50; 1998, Brisbane, AusIMM.

VAN

DORR

II : ‘Nature and origin of high-grade hem-atite ores of Minas Gerais, Brazil', Econ. Geol., 1965, 60, 1–46.

HARMSWORTH

R. A.

, KNEESHAW

, MORIUS

R. C.

, ROBINSON

C. J.

and Shrivastava : ‘BIE-derived iron ores of the Hamersley Province', in ‘Geology of the mineral deposits of Australia and Papua New Guinea' (ed. Hughes

E E.

), 617–642; 1990, Melbourne, AusIMM.

KNEESHAW

: Tilbara iron ore classification - a proposal for a common classification for BIE-derived supergene iron ore', Proc. Aust. Inst. Min. Metal!., 1984, (289), 157–162.

X. I.

, POWELL

C. McA.

and BOWMAN

: ‘Timing and genesis of Hamersley iron-ore deposits', Explor. Geophys., 1993, 24, 6312–6316.

10.

MARTIN

D. McB.

, LI

Z. X.

, NEMCHIN

A. A.

and POWELL

C. McA.

: ‘A pre-2.2 Ga age for giant hematite ores of the Hamersley Province, Australia?' Econ. Geol., 1998, 93, 1084–1090.

11.

McKENNA

D. M.

and HARMSWOR'TH

R. A.

: ‘Brockman No. 2 detritals iron ore deposit', in ‘Geology of Australian and Papua New Guinea mineral deposits, (ed. Hughes

F. E.

), 617–642; 1998, Melbourne, AusIMM.

12.

MORRIS

R. C.

: ‘A textural and mineralogical study of the relationship of iron ore to banded iron formation in the Hamersley Iron Province of Western Australia', Econ. Geol., 1980, 75, 184–209.

13.

MORRIS

R. C.

: ‘Genesis of iron ore in banded iron-formation by supergene and supergene-metamorphic processes — conceptual model, in ‘Handbook of strata-bound and strataform ore deposits', Vol. 13 (ed. Wolf

K. H.

), 73–235; 1985, Amsterdam, Elsevier.

14.

MORRIS

R. C.

: ‘A review of geological research on the iron ores of the Hamersley Iron Province', in ‘Publications of the 13th CMMI Cong., Geology and Exploration', Vol. 2 (ed. Berkman

D. A.

), 191–200; 1986, Melbourne, AusIMM.

15.

MORRIS

R. C.

: ‘Iron ores derived by the enrichment of banded iron-formation, in ‘The genesis of ores and petroleum associated with sedimentary siliceous deposits', (ed. Hein

J. R.

), 231–267; 1987, New York, Van Nostrand Reinhold.

16.

MORRIS

R. C.

: ‘Genetic modelling for banded iron-formation of the Hamersley Group, Pilbara Craton, Western Australia', Precamdruan Res., 1993, 60, 243–286.

17.

WEBB

, OLIVER

N. H. S.

and DICKENS

G. R.

: ‘Multistage evolution of high-grade hematite orebodies from the Hamersley Province, Western Australia', in ‘Iron Ore 2002 Conference', 91–94; 2002, Perth, AusIMM.