Robe River, Mesas A and J

Western Australia, WA, Australia

Main commodities: Fe
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The Robe River pisolitic iron ores have been mined from a number of deposits near Pannawonica by Robe River Associates since 1972. The current long term operation in the district is the Mesa 'A' and Mesa 'J' deposit.   Pannawonica is some 190 km NW of Tom Price and 140 km SW of its export port, at Cape Lambert (#Location: 21° 40' 50"S, 116° 19' 10"E).

These deposits are resistant erosional remnants of large Channel Iron Deposits (CIDs). Mineralisation at Robe River consists of a series of mesas, mantled by hard goethitic pisolitic deposits of Tertiary age which occur on either side of the Robe River from Pannawonica Hill in an ESE direction for more than 35 km.   In general the mesas are from 46 to 62 m above the current flood plains of the river and have steep walls from recent erosion.   Most of the deposits are unconformably developed above the middle to upper Fortescue Group, particularly the basalts of the Mount Jope Member, although rocks of the Marra Mamba Iron Formation are found in the extreme south-west.   The unconformity between the basalts and pisolitic deposits is usually marked by a zone of white to grey kaolinitic clay.

Mesa 'J' is the largest of the deposits worked in the district, and is a pisolitic goethite-hematite ore with a grade of 57.2% Fe over a thickness of up to 50 m.   Overburden consists of thin soil horizons, clay and weathered goethite and sometimes calcrete, colluvium and alluvium which are usually thin but may be up to 15 m thick.   These are underlain by the main ore zone which is generally 5 to 40 m thick.   Typically the goethite-hematite pisolitic ore yields grades of 55-59% Fe, 0.04% P, 5 to 6% SiO2 and 2.5 to 3% Al2O3.   Discontinuous horizontal lenses of clay and claystone occur within the main ore horizon, while clay (alumina contaminant) occurs as an alteration product around joints and fracture.   Solution cavities up to several metres across are common, particularly below the water table.   The ore zone is usually stratified with a porous pisolitic texture and a dark brown metallic lustre.   Lower grade material is usually more friable with a high content of orange/yellow ochreous clay.

The pisolitic ores have a pisolitic to oolitic character.   Generally spherulites of oolitic dimensions (ie. less than 2 mm in diameter) tend to be of higher grade and more indurated.   Those with pisolitic sized concretions and up to 10 mm in diameter are of lower grade and higher in diluent and porosity.

The iron oxides goethite, limonite, hematite and maghemite are mixed in both the pisolites and ground mass.   In general pisolites have a hematitic core surrounded by thin concentric concretionary spheres of goethite, hematite and maghemite.   Diluents are usually minute particles of silica, generally more abundant in the outer shells.   The groundmass consists of colloform isotropic yellow to brown limonite or brownish-black goethite.   Minute cavities in more friable ores are often lined with opaline silica.

See the Hamersley Basin Iron Province record for the regional setting.

Channel Iron Deposit mineral resources and ore reserves at 31 December, 2012 (Rio Tinto 2012 annual report), were:
      Measured + indicated + inferred resources - 2785 Mt @ 57.1% Fe, plus
      Proved + probable reserves - 274 Mt @ 57.2% Fe
      TOTAL reserves + resources - 3.059 Gt @ 57.1% Fe
  Note:  Rio Tinto does not include reserves in resources.

The Robe River operation currently produces more than 30 Mt of ore per annum for export, with a total cumulative production since 1972 of more than 800 Mt of sinter fines and lump ore.   The mine is owned and operated by Robe River Iron Associates, an unincorporated joint venture of Rio Tinto Ltd (53%), Mitsui Iron Ore Development Pty Ltd (33%), Nippon Steel Australia Pty Ltd (10.5%) and Sumitomo Metal Australia Pty Ltd (3.5%). Ore is transport by private rail, 200 km to the Indian Ocean port of Cape Lambert, 40 km east of Karratha.

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:
Adair D L  1975 - Middle Robe River Iron Ore Deposits: in Knight CL (Ed.), 1975 Economic Geology of Australia & Papua New Guinea, Monograph 5 The AusIMM, Melbourne   v1 - Metals pp 943-945
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
Ramanaidou E R and Morris R C,  2007 - Channel Iron Deposits (CID) of the Hamersley Province (Western Australia): in   Proceedings, Iron Ore 2007 Conference, 20-22 August 2007, Perth, Western Australia The AusIMM, Melbourne,    pp. 175-178
Ramanaidou E R, Morris R C, Horwitz R C  2003 - Channel iron deposits of the Hamersley Province, Western Australia: in    Australian J. of Earth Sciences   v50 pp 669-690

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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