Gudai-Darri, Koodaideri

Western Australia, WA, Australia

Main commodities: Fe
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The Gudai-Darri, previously Koodaideri iron deposits are located ~20 km north of the Yandicoogina mine, ~110 km NW of Newman, 45 km SW of the Cloudbreak mine and ~320 km SE of the port of Dampier in the Pilbara of Western Australia (#Location: 22° 31' 39"S, 119° 0' 29"E).

The deposits were discovered in the 1960s, at much the same time as Paraburdoo and Mount Tom Price. It underwent a major evaluation between 1969 and 1971, but had not been developed until the mine was opened in mid 2022.

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

The deposits are composed of both bedded and superficial detrital iron ores localised in and over the Brockman Iron Formation along the median plateau of the northeastern slopes of the Hamersley Range. The northeastern escarpment of the Range comprises two major steps that were formed by differential southward erosion of gently south dipping, alternating hard and less resistant units. The topography is a combination of rounded duricrust covered hills, 305 m above plain level and rolling step like plateaus, the result of Tertiary and Recent erosion that has also laterally dissected the steps into domains separated by wide, infilled, flat bottomed, gorges oblique to the strike of bedding (Baldwin, 1975).

The deposits and escarpment are located in the gently folded northern segment of the Hamersley Iron Province, on the northern limb of the Yandicoogina Syncline. The stratigraphy generally dips at 5 to 10°S. Large and small scale warping and drag folding results in a regional basin and dome structure, although there is a general absence of axial continuity with folds generally having an en echelon pattern with variable plunges and no dominant trend. Northeast trending cross fold axes are indicated along the escarpment front, which may control the distribution of the gorges. Faulting has resulted inonly minor deformation, and small scale jointing is prevalent (Baldwin, 1975).

The bedded ore is hosted within the Hamersley Group which is composed of interstratified banded Iron Formation (BIF), shale, chert and dolomite, with a dolerite dyke occupying a fault at the western end of the deposit area. Superficial detrital deposits found on the median step are interpreted to have been deposited up to and during the Tertiary, whilst Recent alluvium is occurs in drainage channels, and colluvium is being deposited along the escarpment slopes. Superficial calcrete and silcrete are locally deposited, as are massive colloidal cherts, the age of which is not known (Baldwin, 1975).

The members of the Brockman Iron Formation forms the higher levels of the escarpment. The basal Dales Gorge Member forms the median plateau between the two steps described above. It is composed of a normal BIF-shale macroband assemblage, although the total thickness is thinner than the province average. The overlying unmineralised Whaleback Shale Member occurs along the base of the southern high step and generally consists of three shale and two BIF units with an average total 'unmineralised' thickness of between 21 to 24 m. The succeeding Joffre Member forms the upper portion of the southern high step and comprises BIF with thin shaley partings and a total thickness similar to the province average (Baldwin, 1975).

Two styles of iron ore are represented, namely (after Baldwin, 1975):
i). Bedded iron ore - which is dominantly restricted to the Dales Gorge Member, although the upper BIF of the Mount McRae Shale may also be mineralised and is locally included within the orebodies. Minor mineralisation is found within the Whaleback Shale and Joffre Members. The orebodies are tabular, dipping at 5 to 10°S, but are 'planed off' by erosion across the dip, and consequently thin to the north, increasing in preserved thickness to the full stratigraphic thickness to the south. Unenriched BIF relicts are locally evident. At surface, the deposits have a rolling topography with altitudes in the centre of deposit area averaging 100 to 119 m above plain level. In the northern and central sections of the deposits, the footwall is Mount McRae Shale, whilst towards the south, the base of the ore transgresses away from the shale into unenriched Dales Gorge BIF. In the central parts of the deposits the ore averages ~58 m vertical thickness, although the thickest mineralisation is 168 m. The ore is composed of discrete layers that are an intimate mixture of fine grained hematite and fine grained dense and porous goethite, separated by thinner ferruginised shale bands that are generally hydrated at the surface to vitreous goethite. A vertical composite Fe grade and mineralogical zonation may usually be delineated within the orebodies.
Zone A - Vitreous goethite, lesser amounts of hematite, dense goethite, goethitic shale and shale, averaging 50 to 60% Fe. This zone includes a hardcap that varies from 2 to 40 m in thickness, averaging ~20 m;
Zone B - Mixed hematite-goethite, with subsidiary dense goethite, shale, goethitized shale, minor vitreous goethite and limonite. This ore is further subdivided into ore types depending on mineralogical and friability characteristics, ranging from hard (banded and massive hematite goethite, slumped broken and recemented in places), through intermediate (banded, slumped broken and recemented types), to soft (banded powdery or platey hematite). There is also a vertical relationship with the powdery type underlying the harder varieties. The zone generally averages >60% Fe;
Zone M - Shale, goethitic shale, and mixed hematite-goethite, which is an arbitrary subdivision of Zone B, occurring as a discontinuous, lower grade median band corresponding to a thickened group of shale macrobands;
Zone C - Shale, goethitic shale, dense goethite and mixed hematite-goethite. The transition from the overlying Zone B may contain 50 to 60% Fe.
ii). Detrital iron ore - composed of secondary superficial mixtures of unconsolidated hematite, goethite and BIF gravels, ferruginous pisolites, and consolidated canga and pisolitic goethite (Baldwin, 1975). The larger of the detrital iron deposits occur within palaeochannels or depressions within the basement, which is mainly comprised of units of the Wittenoom Formation. The deposits are considered to have been sourced from erosion of bedded iron deposits of the Brockman Iron Formation which outcrops on the high ground both upstream and immediately to the southwest. The known deposits generally occur beneath cover of variable thickness of up to 50 m, whilst the deposits themselves may have thicknesses in excess of 100 m in major palaeochannels and sinkholes (Reid et al., 2016).

The ore grade mineralisation is distributed over an 8.6 km strike length in a WNW-ESE direction, and an up to 2.8 km width across strike in a NNE-SSW) direction with a maximum depth of 100 m below the current topographical surface, averaging 75 m in depth. The cut-offs to determine ore are that High-Grade ore is ≥60% Fe; whilst for Brockman Process Ore is material that is ≥50% to <60% and ≥3% to < 6% Al2O3 within the Dales Gorge, Joffre or Footwall Zone (Rio Tinto JORC Report tabulation, March, 2015).

The Gudai-Darri/Koodaideri high grade ore averages 62% Fe, 6.0% LOI and 0.12% P. The hematitic ore is an intimate mixture of hematite, occurring as martite and specular hematite, and dense goethite in the hard ore zone, whilst the powdery ore is composed of porous hematite associated with friable limonite. This results in banding, similar to BlF, but with alternating mesobands of hematite-goethite and dense goethite, or hematite-limonite and friable limonite. Secondary surface hydration of the hematitic ores produces vitreous colloform goethite which varies from the dense goethite matrix (Baldwin, 1975).

Phosphorus in the Gudai-Darri/Koodaideri hematitic ore is distributed through the dense and vitreous (colloform) goethite, and is either absorbed into the surfaces of microcrystals or within the mineral lattice, with the late stage vitreous goethite containing higher P than the dense goethite. There is no apparent association between the phosphorus content and the gangue quartz and kaolin. Only negligible P minerals have been recognised, with traces of aluminium-iron phosphate and apatite detected in some samples, but only accounting for <5% of the P in the ore. The amount of P is therefore proportional to the dense goethite and friable limonite composition of the ore. Also, the higher the LOI the higher the P. The main source of significant P contamination is the shale interbeds within the ore (Baldwin, 1975).

It is postulated that structural features, including folding and faulting, dislocated the BIFs allowing the influx of enriching fluids which removed SiO
2 and deposited Fe as ferric oxide in the form of dense goethite. The removal of silica is believed to account for the reduction of thickness of the Dales Gorge Member from 114.6 m in unenriched BIF, to 73.5 m in the ore zones. The orebodies are localised in structural traps which slowed the flow of these solutions and allowed time for reactions. The goethite is interpreted to have either replaced the chert bands in the BIF or filled the voids left by their dissolution and depletion. Removal of silica is indicated by local accumulations of colloidal silica at the base of mineralisation, and by colloidal silica ~20 km to the north on the Fortescue flood plains, possibly deposited from waters draining the areas being enriched (Baldwin, 1975). As such supergene depletion and enrichment, mostly during the Mesozoic to Tertiary, is preferred at the martite-goethite rich Gudai-Darri in contrast to the hypogene enrichment at martite-microplaty hematite rich deposits such as Mount Tom Price (Baldwin, 1975).

In 1975 two main deposits had been delineated, as follows (Baldwin, 1975):
Deposit K58W14S, with surface dimensions of ~5180 x 2130 m, and an average surface height above plain level is 104 m. The ore strikes east-west with an overall dip of 4 to 13°S. It averages 53.5 m in thickness, increasing to the south, eventually lensing out into unaltered BIF.
  Proved reserves (non-JORC) - 228 Mt @ 62.2% Fe, 5.9% LOI, 2.7% SiO
2, 1.5% Al2O3, 0.114% P.
Deposit K75W15S, which forms an extensive plateau adjacent to K58W14S, with surface dimensions of ~3960 x 2130 m wide, with an average surface height above plain level of 116 m. The ore has an overall dip of 5 to 9°S and averages 60 m in thickness.
  Proved reserves (non-JORC) - 304 Mt @ 62.1% Fe, 6.3% LOI, 2.5% SiO
2, 1.5% Al2O3, 0.128% P.
• Other smaller deposits containing >60% Fe are known, while a further >1 Mt of ore averages between 50 and 60% Fe.

Mineral Resources and Ore Reserves (JORC compliant) at the end of 2019 (Rio Tinto Annual Report, 2019) were:
Ore reserves
  Gudai-Darri/Koodaideri Brockman ore, Proved Ore Reserves - 214 Mt @ 62.4% Fe;
    Probable Ore Reserves - 302 Mt @ 61.2% Fe.
  No Mineral Resources differentiated by deposit are attributed to Gudai-Darri.

NOTE: This description is largely based on Baldwin (1975), as no other more recent descriptions have been encountered. It is hoped that, like the reserves, the observations from the more recent drilling program have not significantly changed the geological interpretation of the deposit.

The most recent source geological information used to prepare this summary was dated: 1975.    
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:
Baldwin, J.T.,  1975 - Paraburdoo and Koodaideri Iron Ore Deposits and Comparisons with Tom Price Iron Ore Deposits, Hamersley Iron Province: in Knight, C.L., (Ed.), 1975 Economic Geology of Australia & Papua New Guinea, Monograph 5 The AusIMM, Melbourne   v.1 - Metals pp. 898-905.
Reid, J., Farrell, J., Pears, G., Jaunzems, A., Enright, M. and Haederle, M.,  2016 - Integrated Geological and Geophysical Interpretation for the Koodaideri Detrital Iron Deposits, Fortescue Valley, Western Australia: in   ASEG-PESA-AIG 2016, 25th Geophysical Conference and Exhibition, Interpreting the Past, Discovering the Future, August 21-24, Adelaide, Australia, ASEG Extended Abstracts    Issue 1, 9p.

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, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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