Hamersley Basin Iron Province

Western Australia, WA, Australia

Main commodities: Fe
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The main iron ores of the Hamersley province are hosted with in the Archaean to Palaeoproterozoic volcanic and sedimentary sequence the Mount Bruce Supergroup which spans a time interval of over 400 Ma, from greater than 2770 Ma to near 2350 Ma. It rests unconformably on 3.50 to 2.80 Ga granitoids and greenstones that occupy the northern half of the Pilbara craton, and is overlain by the thick Wyloo Group sediments which comprise the remainder of the Hamersley province sequence continuing to near 1800 Ma.

For background on the continental setting of the Hamersley Province, see the separate Australian Iron Ore Deposits - Overview record.

The Mount Bruce Supergroup is in turn sub-divided into three Groups. The lowermost of these, the Fortescue Group, commences with an early phase of clastic sedimentary rocks and mafic volcanism (the ~2.77 Ga Bellary Formation), deposited in localised grabens, with associated doleritic intrusions. These were followed by extensive sandstones and conglomerates with interbedded rhyolitic to dacitic flows, tuffs and epiclastic rocks (the 500 to 2000 m thick, 2.75 Ga Hardy Formation) which thicken markedly from north to south, with near 50% of the thickness in the south being mafic sills. These rocks are overlain by the 2.69 to 2.63 Ga, Jeerinah Formation, which commences with a sequence of bimodal basaltic to andesitic and rhyolitic volcanic rocks, with mafic sills increasing southwards, followed by 100 to 150 m thick organic and sulphide rich fine clastic rocks, lesser dolomites and sandstones. These are, in turn locally followed by several thousand metres of basaltic to andesitic volcanic rocks with interbedded stromatolitic dolomites, shales, sandstones and conglomerates, and a similar thickness and mafic sill, the percentage of which increases from north to south.

The Fortescue Group is conformably overlain by the 2500 m thick Hamersley Group which hosts most of the main iron ore deposits of Western Australia. It is characterised by around 1000 m of laterally extensive banded iron formation representing three major episodes. The base of the Hamersley Group represents a change from a volcanic to chemical sedimentary environment, and is marked by the base of the Marra Mamba Iron Formation.

The basal, ~200 m thick Marra Mamba (2.60 Ga) and ~600 m thick medial Brockman Iron Formations are separated by ~750 m of carbonate, shale and minor chert of the Wittenoom, Mount Sylvia and Mount McRea Shale Formations (2.60 to 2.48 Ga). This passive sequence is followed, after the Brockman Iron Formation, by the third phase of iron formation deposition (the ~600 m thick Weeli Wolli Iron Formation) which was accompanied by intense 2.45 Ga bimodal volcanism and mafic sills (which locally account for up to 80% of the sequence), overlain by up to 800 m of felsic volcanics of the Woongarra Formation and the uppermost ~450 m thick Boolgeeda Iron Formation. Thickness variations in the Hamersley Group are only minor.

In more detail, the main iron formation bearing section of the Hamersley Group has been subdivided into the following units, from the base, The thicknesses shown below are as estimated in the Mount Tom Price-Brockman area:
Marra Mamba Iron Formation, (230 m thick)
  • Nammuldi Member - cherty BIF with occasional shale bands,
  • MacLeod Member - BIF with extensive interbedded shales and "podded" BIF horizons,
  • Mount Newman Member - BIF with thin shale bands,
Wittenoom Formation, (max. 700 m thick)
  • West Angelas Member - manganese-rich shale with minor BIF and chert bands,
  • Paraburdoo Member - dolomite, some of which is karstic,
  • Bee Gorge Member - calcareous shale and dolomite,
Mt Sylvia Formation (30 m thick) - mudstone, siltstone, chert, dolomite and BIF bands,
Mt McRae Shale (~50 m thick) - graphitic (2-8 wt.% TOC), pyritic (1-10 wt.% S) and chloritic shales interbedded with BIF, capped by the 12 m thick Colonial Chert Member,
Brockman Iron Formation, (620 m thick)
  • Dales Gorge Member - interbedded BIF and shale,
  • Whaleback Shale Member - interbedded shale, chert and BIF,
  • Joffre Member - BIF with minor shale bands,
  • Yandicoogina Shale Member - shale and BIF,
Weeli Wolli Formation (~600 m thick) - BIF (commonly jaspilitic), mudstone and siltstone with common interlayered metadoleritic sills,

The overlying Turee Creek Group is the youngest unit of the Mt Bruce Supergroup. The uppermost unit of the Hamersley Group, the Boolgeeda Iron Formation, passes conformably upwards into the thick basal Kungarra Shale of the 3000 to 5000 m thick Turee Creek Group which is basically a coarsening upwards clastic sequence in a choked basin - marking a major change from the starved basin of the Hamersley Group.

The top of the Mount Bruce Supergroup is separated from the overlying Lower Wyloo Group Beasley River Quartzites by a first order unconformity. The basal conglomerate includes clasts of Hamersley Group banded iron formations and very rare hematite. These coarse sediments pass upwards into finer clastics and mafic volcanics to the 2000 m thick 2209 Ma Cheela Springs Basalt which are followed by dolomites to the west, but are cut by the major unconformity that separates the Lower and Upper Wyloo Groups which cuts down as far as the Fortescue Group. A generation of NW trending folds developed at the close of the Lower Wyloo Group interacted with the Ophthalmia orogeny structures to form a series of domes and basins.

The Upper Wyloo Group was deposited above a major unconformity It was formed in an extensional basin and comprise up to 12 km of sediments which are overlain to the south by the poorly sorted clastics of the Ashburton Formation which includes bimodal volcanics dated at 1842 to 1828 Ma. The Upper Wyloo Group was terminated at the time of the intrusion of the 1790 Ma Boolaloo Granite.

The southern half of the Hamersley Group was deformed by the north-south compressive, ~2.45 to 2.2 Ga Ophthalmia orogeny, that formed an east-west trending, northward-verging, fold and thrust belt, characterised by south-dipping thrust faults and asymmetric to overturned folds, which decrease in intensity to the north. A generation of NW trending folds were developed during the ~1.80 to 1.65 Ga Ashburton Orogeny, at the close of the Lower Wyloo Group, interacting with the Ophthalmia fold belt structures to form a series of domes and basins.

Ores mined in the Hamersley province may be divided into (1) enriched, bedded ores and (2) channel iron deposits (CID) within extensive palaeo-channels tens of kilometres in length, now largely preserved as mesas.

The enriched bedded ores of the Hamersley Group are sub-divided into:
    i). extensive flat lying martite-goethite ores developed from both Marra Mamba and Brockman Iron Formations by deep supergene enrichment of precursor banded iron formations, mostly during the Mesozoic to Tertiary (e.g., Marandoo - 390 Mt @ 63% Fe; West Angelas - 515 Mt @ 61.8% Fe, Area C - 3.294 Gt @ 60.0% Fe). Ores developed from Marra Mamba Iron Formation, tend to have a higher proportion of ochreous goethite, which is more friable with a marked yellow colour, while those over the Brockman Iron Formation are generally brown and less friable;
    ii). high grade hematite, mostly martite and microplaty hematite, but little goethite, predominantly developed within the Brockman Iron Formation within the main WNW-ESE trending Ophthalmia fold belt of the Hamersley Range. These ores commonly occur to much greater depths (to more than 400 m) and account for the largest high grade deposits of the province (e.g., Mount Whaleback - >3.5 Gt @ >60% Fe; Mount Tom Price - 900 Mt @ 64% Fe). Enrichment of the primary iron formation is interpreted to be predominantly hypogene, and to have taken place in three stages (Taylor et al., 2001, Hagerman et al., various and others). The first involved low to moderate temperature (110 to 280°C), highly saline, bicarbonate-saturated brines from the underlying sedimentary successions (e.g., Wittenoom dolomite and evaporites), transported via faults to the BIFs to migrated laterally in large folds, between shale aquitards. These fluids removed silica, leaving a thinned residue, enriched in iron oxides (mainly magnetite), carbonates (mainly siderite), magnesium silicates and apatite. The second stage involved deeply circulating, low temperature (<110°C), oxidised, Na-rich meteoric waters that interacted with evaporites, prior to their interaction with the BIF, to oxidise the mainly magnetite-siderite assemblage to hematite-ankerite, and then stripped all carbonate, leaving highly porous and permeable iron ore bands composed of martite-microplaty hematite-apatite, interbedded with magnesium-rich shale bands. A third, purely supergene stage, most likely in the Mesozoic to Tertiary, coincident with the formation of the martite-goethite ores described above, converted magnesium silicates to a kaolinitic residue, greatly thinning the shale bands, destroyed apatite, and leached calcium and phosphorus from the ore. This three stage process produced a highly porous hematite ore with a characteristic microplaty texture, interbedded with kaolinitic shale containing significant aluminium and titanium, which retained their relative proportions throughout the upgrading process. The Marra Mamba martite-goethite ore sheet in the Chichester Range, north of the Ophthalmia fold belt, but associated with structures on the northern margin of the Hamersley Basin, overprints and is underlain by microplaty hematite mineralisation (e.g., Cloud Break and Christmas Creek);
    iii). magnetite-rich ores, mostly within the Brockman Iron Formation, occurring as a laminated, metamorphosed oxide-facies iron formation in which the original chert or jasper bands have been recrystallised into distinguishable grains of quartz and the iron is present as thin layers of hematite, magnetite or martite (e.g., Cape Preston - 2.185 Gt @ 22.1% MagFe and 31.3% Total Fe). At Cape Preston/Balmoral, the main host Joffre Member of the Brockman iron formation, has a condensed thickness of 300 m, compared to the regional 360 m. This suggests removal of components of the unit, possibly by similar hypogene fluids that leached silica and produced a magnetite-rich assemblage from BIFs as the first stage in the production of microplaty hematite ore, as described above.

The channel iron deposits (CID) mined in the Hamersley Province account for up to 40% of the total iron ore mined from the Hamersley Province of Western Australia. These deposits are of Miocene age and occupy meandering palaeochannels in a mature surface composed mainly of Archaean to Paslaeoproterozoic rocks containing iron formations. These palaeochannels are generally less than 1 km but can range to several kms in width and from 1 to more than 100 m thick. The Robe and Marillana/Yandi palaeochannels in the western and eastern Hamersley Province respectively contain the principal CID resources currently being mined. These two major CID channels extend over 100 to 150 km lengths, with the Robe system being up to 5 km wide. Known economic CID resources within the province exceed 10 Gt with grades of 56 to 58% Fe. The CIDs are dominated by goethitic granular facies, which are typically composed of ooids and lesser pisoids with hematite nuclei and goethite cortices, abundant goethitised wood/charcoal fragments and goethitic peloids, all cemented by goethite (Morris and Ramanaidou, 2007). The goethite was produced by chemically precipitated iron hydroxyoxides, derived from leaching of iron-rich soils in an organic environment. Common post depositional weathering produced secondary facies (Morris, 2007). In contrast, the often associated younger detrital ores, which are predominantly of Pliocene age, comprise colluvial/alluvial deposits of modified clasts of older proximal BIF mineralisation. These deposits are generally much more limited in total tonnage than the CID of BIF hosted hematite deposits.

The most recent source geological information used to prepare this summary was dated: 2002.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Bekker, A., Slack, J.F., Planavsky, N., Krapez, B., Hofmann, A., Konhauser, K.O. and Rouxel, O.J.,  2010 - Iron formation: the sedimentary product of a complex interplay among mantle, tectonic, oceanic, and biospheric processes: in    Econ. Geol.   v.105 pp. 467-508
Beukes N J and Gutzmer J,  2008 - Origin and Paleoenvironmental Significance of Major Iron Formations at the Archean-Paleoproterozoic Boundary: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore Reviews in Economic Geology   v15 pp 5-47
Clark, D.A. and Schmidt, P.W.,  1994 - IRON: Magnetic properties and magnetic signatures of BlFs of the Hamersley Basin and Yilgarn Block, Western Australia: in Dentith, M.C., Frankcombe, K.F., Ho, S.E., Shepherd, D.I. and Trench, A., (Eds.),  Geophysical Signatures of Western Australian Mineral Deposits, Australian Society of Exploration Geophysicists, Special Publications,   v.7 pp. 341 - 354
Clout J M F,   2006 - Iron formation-hosted iron ores in the Hamersley Province of Western : in    Trans. IMM (incorp. AusIMM Proc.), Section B, Appl. Earth Sc.   v115 pp 115-125
Clout, J.M.F. and Simonson, B.M.,  2005 - Precambrian iron formation and iron formation-hosted iron ore deposits: in Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R.J. and Richards, J.P. (eds.),  Economic Geology, 100th Anniversary Volume Society of Economic Geologists    pp. 643-679
Dalstra H and Guedes S  2004 - Giant Hydrothermal Hematite Deposits with Mg-Fe Metasomatism: A Comparison of the Carajás, Hamersley, and other Iron Ores: in    Econ. Geol.   v99 pp 1793-1800
Dalstra H J,   2006 - Structural controls of bedded iron ore in the Hamersley Province, Western Australia - an example from the Paraburdoo Ranges: in    Trans. IMM (incorp. AusIMM Proc.), Section B, Appl. Earth Sc.   v115 pp 139-145
Dalstra, H. and Rosiere, C.A.,  2008 - Structural controls on high-grade iron ores hosted by banded iron formation: A global perspective: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore, Reviews in Economic Geology,   v.15 pp. 73-106
Findlay D,  1994 - Diagenetic boudinage, an analogue model for the control on hematite enrichment iron ores of the Hamersley Iron Province of Western Australia, and a comparison with Krivoi Rog of Ukraine, and Nimba Range, Liberia: in    Ore Geology Reviews   v9 pp 311-324
Flis, M.F.,  2008 - Advances in geophysics applied to the search for banded iron formation-related, high-grade hematite iron ore: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore, Reviews in Economic Geology,   v.15 pp. 381-391
Hagemann SH, Rosiere CA, Lobato L, Baars F and Zucchetti M,  2005 - Controversy in Genetic Models for Proterozoic High-Grade, Banded Iron Formation (BIF)-Related Iron Deposits - Unifying or Discrete Model(s)?: in   Iron Ore 2005 Conference, Perth, WA, September 19-20, 2005 The AusIMM, Melbourne   Publication Series 8 pp. 67-71
Heim J A, Vasconcelos P M, Shuster D L, Farley K A and Broadbent G,  2006 - Dating paleochannel iron ore by (U-Th)/He analysis of supergene goethite, Hamersley province, Australia. : in    Geology   v34 pp 173-176
Kerr, T.L., O’Sullivan, A.P., Podmore, D.C., Turner, R. and Waters, P.,  1994 - IRON: Geophysics and iron ore exploration: examples from the Jimblebar and Shay Gap-Yarrie regions, Western Australia: in Dentith, M.C., Frankcombe, K.F., Ho, S.E., Shepherd, D.I. and Trench, A., (Eds.),  Geophysical Signatures of Western Australian Mineral Deposits, Australian Society of Exploration Geophysicists, Special Publications,   v.7 pp. 355-368
Lobato L M, Figueiredo e Silva R C, Hagemann S and Thorne W,  2008 - Hypogene Alteration Associated with High-Grade Banded Iron Formation-Related Iron Ore: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore Reviews in Economic Geology   v15 pp 107-128
Martin D McB, Li Z X, Nemchin A A, Powell C McA  1998 - A pre-2.2 ga age for giant Hematite ores of the Hamersley Province, Australia: in    Econ. Geol.   v93 pp 1084-1090
Miller, R. and Dransfield, M.,  2011 - Airborne Gravity Gradiometry and Magnetics in the Search for Economic Iron Ore Deposits: in   Proceedings, Iron Ore 2011 Conference, 11-13 July 2011, Perth, Western Australia, The Australasian Institute of Mining and Metallurgy, Melbourne,    pp. 109-116
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 : in    Econ. Geol.   v75 pp 184-209
Morris R C and Ramanaidou E R,  2007 - Genesis of the channel iron deposits (CID) of the Pilbara region, Western Australia: in    Australian J. of Earth Sciences   v54 pp 733-756
Taylor D, Dalstra H J, Harding A E, Broadbent G C, Barley M E,  2001 - Genesis of High-Grade Hematite Orebodies of the Hamersley Province, Western Australia: in    Econ. Geol.   v96 pp 837-873
Thorne W, Hagemann S, Vennemann T and Oliver N,   2009 - Oxygen Isotope Compositions of Iron Oxides from High-Grade BIF-Hosted Iron Ore Deposits of the Central Hamersley Province, Western Australia: Constraints on the Evolution of Hydrothermal Fluids: in    Econ. Geol.   v104 pp 1019-1035
Thorne W, Hagemann S, Webb, A and Clout, J,  2008 - Banded iron formation-related iron ore deposits of the Hamersley Province, Western Australia: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore Reviews in Economic Geology   v.15 pp. 197–221
Webb, A.D., Dickens, G.R. and Oliver, N.H.S.,  2003 - From banded iron-formation to iron ore: geochemical and mineralogical constraints from across the Hamersley Province, Western Australia: in    Chemical Geology   v.197 pp. 215-251

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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