Cape Lambert

Western Australia, WA, Australia

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The Cape Lambert magnetite iron deposit is located 15 km south-west of the Indian Ocean port of Cape Lambert, <10 km south of the new port of Ankatell, and 5 km west of the town of Wickham in north-western Western Australia (#Location: 20° 43' 8"S, 117° 5' 31"E).

This deposit is hosted within banded iron formations of the Cleaverville Formation, part of the 3.05 to 3.02 Ga Gorge Creek Group in the granite-greenstone terrane of the Palaeo- to Mesoarchaean core of the Pilbara craton.

The oldest rocks within the Pilbara Craton represent 3.80 to 3.53 Ga crust (seen in rare exposures of gneissic granite and gabbroic anorthosite), which was widely exposed throughout the evolution of the craton. These rocks are intruded and overlain by a granite-greenstone terrane, characterised by a regional outcrop pattern of ovoid granitic domes separated by arcuate belts of volcanosedimentary rocks that define the greenstone belts, representing at least eight successive volcanic cycles. The oldest sequence in the greenstone belt stratigraphy is the 15 to 20 km thick Pilbara Supergroup, which has been subdivided into the lower, dominantly volcanic, 3.53 to 3.42 Ga Warrawoona Group, comprising up to four sub-groups separated by disconformities, and intruded by 3.53 to 3.46 and 3.45 to 3.42 Ga granitoid supersuites. The Warrawoona Group is unconformably overlain, after a 75 m.y gap, by the 3.35 to 3.31 Ga Kelly and 3.25 to 3.24 Ga Sulphur Springs Groups, represented in the area by intermediate to felsic volcanic and sedimentary rocks, including the uppermost Pincunah Banded-iron Member which hosts significant magnetite deposits (e.g., Iron Bridge). The Kelly and Sulphur Springs groups are separated by an ~60 m.y. gap. Each of the gaps was preceded by deformation and metamorphism, and accompanied by subaerial erosion and deposition of shallow water sediments, e.g., the Strelley Pool stromatolitic dolomites at the base of the Kelly Group. These processes had established a thick continental crust by 3.23 Ga (Hickman and Van Kranendonh, 2012).

A major rifting event that occurred between 3.23 and 3.16 Ga, split this crust into three continental microplates, the main East Pilbara terrane, and the Karratha and Kurrana terranes to the NW and SE respectively, each separated by NE-trending basins that included oceanic-like crust. Initially these basins were filled with passive margin clastic rocks, followed by thick successions of pillow basalt and komatiitic basalt eruptions, accompanied by intrusion of ultramafic and mafic dykes and sills of the 3.18 Ga Dalton Suite (Hickman and Van Kranendonh, 2012).

Between 3.16 and 3.07 Ga, NW-SE compression and convergence caused part of the oceanic crust of the northwest basin to be thrust across the Karratha Terrane, to produce the Regal Terrane. To the SE, subduction of the same oceanic crust produced the intra-oceanic arc Sholl Terrane between 3.13 and 3.11 Ga, and by 3.07 Ga, the convergence culminated in the accretion of the Karratha, Sholl and Regal terranes to form the West Pilbara Superterrane. At the same time, collision of this superterrane with the East Pilbara Terrane resulted in major deformation and widespread granitic intrusion of the Prinsep Orogeny (Hickman and Van Kranendonh, 2012).

Following the Prinsep Orogeny, crustal relaxation, extension, and moderate subsidence led to the development of the 3.05 to 2.93 Ga De Grey Superbasin across most of the northern Pilbara Craton. The succession within this superbasin unconformably overlies both the East Pilbara Terrane and the West Pilbara Superterrane. Over the latter, it is composed of three basins, each separated by an unconformity, namely: i). the basal 3.05 to 3.02 Ga Gorge Creek Basin containing the Gorge Creek Group banded iron formation and clastic sediments; ii). the 3.01 to 2.99 Ga Whim Creek Basin (volcanic rocks); and iii). the 2.97 to 2.94 Ga Mallina Basin (sandstone, wacke and shale). Deposition was terminated by the major deformation North Pilbara and Mosquito Creek orogenies between 2.94 and 2.90 Ga and post-orogenic intrusion of the highly fractionated Split Rock Supersuite granites between 2.89 and 2.83 Ga, after which the craton remained stable until ~2.78 Ga (Hickman and Van Kranendonh, 2012).

The ~1000 to 1500 m thick Cleaverville Formation, in the lower sections of the Gorge Creek Group, which can be correlated over an east-west interval of >300 km, and >100 km north-south, hosts significant iron deposits, both magnetite and hematite, where it overlies both the East Pilbara Terrane (e.g., Yarrie-Mount Goldsworthy and Ridley-Pardoo) and in the West Pilbara Superterrane (e.g., Cape Lambert). This unit is composed of metamorphosed chert and banded iron formation, with minor felsic volcaniclastic rock, shale and siltstone. In the northern East Pilbara Terrane, the Gorge Creek Group unconformably overlies the Warrawoona Group following a 100 Ma hiatus, while to the south it rests on the Kelley and Sulphur Springs groups. In the Cape Lambert area of the West Pilbara Superterrane, it overlies ocean floor basalts of the Regal Terrane (Hickman and Van Kranendonh, 2012).

Little detail of the lithology and ore within the Cleaverville Formation at Cape Lambert have been encountered. The host-BIF is enclosed within basalts, and the deposit covers an area of ~9 x 2 km, striking north-south and dipping gently to the east. Individual intersections of ore grade BIF appear to vary from ~40 to as much as 120 m in thickness. The ore appears to be a well banded (<1 to >5 cm) magnetite-silica rock, with thin shale interbands. The principal ore mineral is magnetite. Test work suggests a >66% Fe concentrate can be produced (Cape Lambert Iron Ore Ltd, 2008).

In most of the other deposits within the East Pilbara Terrane, mineralisation is associated with the Nimingarra Iron Formation, which represents the lower section of the Cleaverville Formation, that, in turn, occurs in the lower part of the Gorge Creek Group (see the Yarrie, Mt Goldsworthy and Pardoo, Ridley records for information on these deposits and the occurrence of ore).

Mineral resources, as at 31 January, 2008 (Cape Lambert Iron Ore Ltd, 2008) were:
    Indicated resource - 979 Mt @ 31.4% Fe, 2.25% Al2O3, 40.2% SiO2, 0.03% P, 0.14% S, 5.95% LOI.
    Inferred resource - 577 Mt @ 30.8% Fe, 2.22% Al
2O3, 41.0% SiO2, 0.03% P, 0.13% S, 7.38% LOI.
    TOTAL resource - 1.556 Gt @ 31.2% Fe, 2.24% Al
2O3, 40.5% SiO2, 0.03% P, 0.13% S, 6.04% LOI.

The project was acquired by MCC Australia Sanjin Mining Pty Ltd in 2008-09. Little further information is available since then, other than that the WA Department of Minerals and Petroleum (2013) reports that the project is backed by a JORC compliant resource of 1.9 Gt of iron ore with an unspecified grade.

Ore was planned to be exported at a rate of 15 Mtpa from 2016 via the port of Anketell, ~12 km west of Cape Lambert and <10 km north of the deposit (WA Department of Minerals and Petroleum, 2013).

The most recent source geological information used to prepare this summary 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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