The Western Range Mine is subleased by Hamersley Iron (HI) to the Bao-HI Ranges Joint Venture, and hereafter referred to as Rio Tinto. The Bao-HI Ranges Joint Venture comprises:
• Ranges Mining Pty Ltd (54% participating interest) – a subsidiary of Rio Tinto; and
• Baosteel Australia Mining Company Pty Ltd (46% participating interest) – a subsidiary of the Shanghai Baosteel Group Corporation.
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Summary:
Mineralisation at Eastern Range and Western Range occurs as haematite/goethite mineralisation hosted within the banded iron formations of the Brockman Formation.
The Western Range 36W–50W and 55W–66W deposits are located within the Hamersley Basin of Western Australia, the host to some of the most significant iron ore deposits in the world. The Western Range 36W–50W and 55W–66W deposits mineralisation is primarily hosted by the Brockman Iron Formation with additional detrital mineralisation present.
The BIF is a member of the ~620 m thick Brockman Iron Formation which makes up part of the 2.63 2.45 Ga Hamersley Group. The Hamersley Group comprises almost 2.5 km of consecutive sedimentary and volcanic rocks located within the ca. 80,000 km2 Hamersley Province of the Pilbara craton in North West Australia, approximately 1100 km north of Perth. In the lower part, it consists of dolomite, shale and BIF, while the upper part consists of dolerite, various lava types and BIF with minor amounts of tuffs and shales. Underlying the Hamersley Group, is the 2.78–2.63 Ga Fortescue Group, which consists of flood basalts and rhyolites. These volcanics were laid down on the uplifted and eroded Pilbara block. This volcanic succession may contain remnants of a Large Igneous Province (LIP).
The Brockman Iron Formation ofthe Hamersley Group is divided into four sub-lithostratigraphic units, namely the lowermost Dales Gorge Member (BIF), the Whaleback Shale Member, the Joffre Member (BIF), and the uppermost Yandicoogina Shale Member. After deposition, these laterally extensive BIF have all experienced minor folding and basinal uplift along with low-grade regional metamorphism – from burial prehnite–pumpellyite facies to greenschist facies.
General consensus exists regarding the depositional model of the Brockman Iron Formation. According to this model, the succession was deposited on a large, stable, and clastic-starved, continental platform, which was influenced by episodic inputs of fine-grained tuffaceous detritus.
General Statements:
• The Western Range 36W-50W and 55W–66W deposits are typical high-phosphorus, martitegoethite Brockman type deposits.
• Mineralisation occurs within both the Dales Gorge and Joffre Members of the Brockman Iron Formation. Minor mineralisation also occurs in the Whaleback Shale, Yandicoogina Shale and Weeli Wolli Members.
• There is minor detrital mineralisation, which occurs as shallow fan shaped deposits to the south of the range and small canga deposits close to the range front.
• Western Range is bounded to the east by the 36W steep reverse fault and to the west by the 72W fault.
• There are numerous smaller scale faults trending northwest and east-northeast. Numerous dolerite dyke intrusions crosscut and overprint faults. There are also numerous dolerite sills in the area within the Whaleback Shale, Joffre, Yandicoogina Shale and Weeli Wolli Members.
• Several dolerite dykes bisect the area, and largely follow fault lines which tend to trend northwest to southeast.
• The major Joffre sill runs east to west across the area and is offset by the northwest-southeast trending faults.
• Approximately 90% of the Mineral Resource lies above the water table.
Deposit Specific Statements:
Western Range 36W-50W:
• Eighteen mapped faults lie within the Western Range 36W-50W deposit. The mapped faults have varying trend and throw.
• A minor sill lies within the Whaleback Shale 2 layer, but this is only present in the Western Range 36W-50W deposit.
• The Western Range 36W-50W deposit strikes approximately southeast – northwest with an along strike extent of approximately 6 km and a width of up to approximately 1 km. The mineralisation extends from surface to a depth of 200 m.
Western Range 55W-66W:
• Twenty-one mapped faults lie within the Western Range 55W–66W deposit. The mapped faults have varying trend and throw.
• The Western Range 55W-66W deposit strikes approximately east-west with an along strike extent of approximately 5 km and a width of up to approximately 1 km. The mineralisation extends from surface to a depth of 180 m.