Summary:
The Pilbara region comprises a large part of the ancient continental shield of Western Australia which is comprised of both Proterozoic and Archaean rocks.
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 of the 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.
The Marra Mamba Iron Formation is the lowermost unit of the Proterozoic Hamersley Group in the northwestern part of Western Australia.
The Marra Mamba Iron Formation varies considerably in thickness, as based on sections measured in the field; however, not enough drill hole data are available to provide a quantitative assessment of its thickness variation throughout the Hamersley Range.
Others report thicknesses that range from a minimum of 15 m to 183 m (Macleod, 1966) for sections in different parts of the Hamersley Range. The Marra Mamba lron Formation is underlain by the Jeerinah Formation which is the uppermost member of the Fortescue Group. This group may be as much as 3660 to 4270 m thick and consists of shales and cherts in the upper part.
Brockman 2, Brockman 4, Channar, Gudai-Darri, Tom Price, Paraburdoo and Western Turner Syncline: mineralisation is haematite/goethite mineralisation hosted within the banded iron formations of the Brockman Formation. Detrital deposits also occur at these sites. At Tom Price and Western Turner Syncline, some goethite/ haematite mineralisation hosted within the Marra Mamba Formation also occurs.
Marandoo and Silvergrass: mineralisation occurs as goethite/ haematite within the banded iron formations of the Marra Mamba Formation. Some detrital mineralisation also occurs.
Yandicoogina: goethite mineralisation occurs as pisolite ores within the paleo-channel of a channel iron formation.
Mineralisation at Eastern Range and Western Range occurs as haematite/goethite mineralisation hosted within the banded iron formations of the Brockman Formation.