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Pardoo, Ridley |
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Western Australia, WA, Australia |
| Main commodities:
Fe
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Pardoo group of smaller direct shipping ore (DSO) hematite, and the large Ridley magnetite, deposits are distributed over an area of some 12 x 7 km in a complex S-shaped structure (representing a strike length of ~20 km), on the northern margin of the exposed Archaean Pilbara craton, some 75 km east of Port Hedland in northwestern Western Australia. Fourteen separate DSO, and one CID (channel iron deposit), resources have been identified at Pardoo (#Location: 20° 15' 6"S, 119° 8' 29"E).
As distinct from the major iron ore deposits of the late Neoarchaean to early Palaeoproterozoic Hamersley Basin, also on the Pilbara Craton, these mines are developed within the underlying Palaeo- to Mesoarchaean 3.4 to 2.9 Ga granite-greenstone terrane. The greenstone belt stratigraphy has been subdivided into the lower dominantly volcanic 3.5 to 3.3 Ga Warrawoona Group of the Pilbara Supergroup and the upper mainly-sedimentary, 3.05 to 3.02 Ga Gorge Creek Group which belongs to the De Grey Supergroup. The Warrawoona Group has been subdivided into three main (ultra)mafic-felsic volcanic cycles and is 9 to 18 km thick. Regional mapping suggests the Warrawoona and Gorge Creek groups evolved as a near continuous succession with only minor internal unconformities (e.g., at the base of the 3.31 Ga Budjan Creek Formation, which overlies the Warawoona Group, and is in turn unconformaby overlain by the Gorge Creek Group following an interval of deformation at 3.15 Ga). Further to the south (50 to 100 km), granitoid plutonism (3.32 to 3.29 Ga and 3.27 to 3.23 Ga) and deposition of ultramafic to felsic volcanics and cherts of the Kelly and Sulphurs Springs are recorded during the gap between the Warrawoona and Gorge Creek groups. The lower Gorge Creek Group followed an ~100 m.y. period of relative quiescence during which concentrations of banded iron-formation and siliciclastics were deposited. These rocks are followed by a thick sequence of basaltic rocks, lesser felsic tuffs and volcaniclastic rocks, and finally by post 2.9 Ga clastic rocks that constitute the remainder of the De Grey Group, mainly to the west (Van Kranendonh et al., 2002; Podmore, 1990; Waters, 1998; Hickman and Van Kranendonh, 2012).
Both the Warrawoona and Gorge Creek groups suffered their most intense tectonic imprint together as a result of granitic diapirism resulting in the emplacement of the regional Carlindi, Muccan and Warrawagine batholiths between 3.0 and 2.8 Ga, which separate the sequence into isolated greenstone belts. The Pardoo - Ridley deposits lie within the Ord Range greenstone belt, separated by a major fault from the contiguous Goldsworthy greenstone belt, which hosts the Mt Goldsworthy deposit within the same stratigraphic units. Older >3.44 Ga tonalite-trondhjemite-granodiorite (TTG) rocks underlie or intrude the lower Warrawoona Group, but also constitute substantial volumes of the Carlindi, Muccan and Warrawagine batholiths (Van Kranendonh et al., 2002; Podmore, 1990; Waters, 1998; Hickman and Van Kranendonh, 2012).
The Archaean basement is overlain to the north by the near horizontal Permian Paterson Formation sedimentary rocks, and by extensive Cretaceous sandstones and Tertiary to Recent
alluvium that obscures the bedrock geology away from the hills to the east and represent the western margin of the Anketell Shelf of the Canning Basin.
Mineralisation is associated with the Nimingarra Iron Formation which represents the lower section of the Cleaverville Formation, that occurs in the lower part of the Gorge Creek Group. The resistant character of the Cleaverville Formation has produced the lows hills of the Ord-Ridley Ranges. The lower Cleaverville formation comprises a cherty BIF, that has been replaced at surface by a thin goethite carapace, overlain by a stratigraphy consisting of BIF with occasional interbedded thin shale bands. A prominent, up to 30 m true thickness shale marker overlying a red-black BIF, can be traced laterally over most the northern synclinal limb of the S-shaped structure. Conformably overlying the BIFs of the Nimingarra Iron Formation, the stratigraphy of the Cleaverville Formation is characterised by a metasedimentary sequence of shales and quartzite (Nyquest and Kozikowski, 2009).
Iron enrichment zones are found at three main stratigraphic levels within the Cleaverville Formation, predominantly in the massive chert in the lower and upper margins of the Nimingarra Iron Formation, forming irregular pods with a distinct orientation to the bedding of the BIF. The chert in the BIF has been replaced leaving a platy texture within the enriched zone which is depleted in silica. These pods vary in size from lenses that are 10 to 15 m, up to several hundred metres in width, and up to 400 m in length. Goethite and goethite-chert occur in a massive chert unit of the lower Nimingarra Group at several locations (Nyquest and Kozikowski, 2009).
The margins of the enrichment pods are relatively sharp, being gradational over intervals of less than 2 to 5 m wide, but are irregular and often include inliers of primary BIF. Iron enrichment of the chert in the Nimingarra Iron Formation appears to be associated with a ferruginous regolith that underlies the Mesozoic sandstones of the Canning Basin. The identified DSO iron ore deposits in the area occur as scattered hardcap/crustal style goethite-haematite deposits (Nyquest and Kozikowski, 2009).
The total Measured + Indicated + Inferred resource of DSO at Pardoo in 2008 (Atlas Iron, 2011) was:
23.4 Mt @ 55.9% Fe (16.94 Mt @ 56.0% Fe remaining, 31 Dec., 2012).
This tonnage is part of a total resource of ~450 Mt @ 56% Fe, 7% SiO2, 2.3% Al2O3, 0.11% P, 9.2% LOI at five locations distributed over an area of 150 km radius of Port Hedland that together constitute the larger North Pilbara DSO operation (i.e., Pardoo; Wodgina - 53 Mt @ 56.2% Fe; Abydos - 22.2 Mt @ 56.7% Fe; Mt Webber - 76.9 Mt @ 57.2% Fe; and McPhee Creek - 260 Mt @ 56.2% Fe).
Several small pisolitic limonite and goethite deposits (e.g., Connie) with abundant limonite clay infill, are preserved at Pardoo as relatively thin (<15 m thick), flat lying cappings of limited aerial extent, overlying the bedrock sequence. They form low hills, and are interpreted to represent remnants of Tertiary drainage channels.
The Ridley magnetite deposit represents a zone in excess of 500 m wide within the steeply dipping (~70°S) Nimingarra Iron Formation, over a length of more than 1.5 km and to a depth of 250 m with an average in-situ resource grade of 36.5% Fe. The resources is open on both ends and at depth.
The total indicated + inferred JORC complaint resource at the Ridley magnetite deposit in November 2008 (Atlas Iron, 2013) was:
2.01 Gt @ 36.5% Fe, 39.3% SiO2, 0.08% Al2O3, 0.09% P, 0.05% S, 4.1% LOI.
Davis Tube concentration tests suggests that for this resource, the recovered concentrate would be a:
37.2% concentration factor with a grade of 68.9% Fe, 4.1% SiO2, 0.03% Al2O3, 0.01% P, 0.01% S, -2.7% LOI.
The total Probable reserve at the Ridley magnetite deposit in November 2008 (Atlas Iron, 2013) was:
970 Mt of ore @ 36.0% Fe, for a concentrate product of 330 Mt @ 68.3% Fe, 3.8% SiO2.
Operations commenced at Pardoo in October 2008 where a quality low-Al2O3 DSO product is extracted from a number of open pits, providing flexibility in blending. Ore is mined by a conventional truck-and-backhoe mining fleet, before being crushed and screened on site and delivered to Port Hedland, 75 km to the west, by covered road trains.
The most recent source geological information used to prepare this decription was dated: 2012.
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.
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