The Hamersley Group

Introduction

Western Australia is the home to a number of mining regions. One of these regions is the Pilbara, located 1100km north of Perth. This region covers a vast area of approximately 510000 square-kilometres. Within this region there is an area of 80000 square-kilometres which is the Hamersley Iron Province. The Province is primarily made up of late Archaen and early Proterozoic rock formations approximately 2500 Ma. These rock formations are known as the Hamersley Group (www.riotintoironore.com).

Within the Pilbara there are two of the largest mining companies in the world who mine iron ore. Rio and BHP both have a number of operating mines located throughout the Pilbara. BHP has seven high-grade iron ore mines, with a few of these located near Newman. The biggest mine by far is the BHP operated open-cut mine of Mt Whaleback. Iron ore reserves, established by BHP, indicate they can sustain mining for another 30 years (www.bhpbilliton.com).

BHP exports its products to steelmakers in Japan, Korea, Taiwan, China, Europe and Australia. All products are exported through Port Hedland (www.bhpbilliton.com).

Content

History (BHP)

The Pilbara has a mining history dating back to the 1880s. Although back in this time the Pilbara was famous for gold not iron ore. It was due to the gold rush that the town of Port Headland was built in 1896. Yet it wasn't until 1957 that prospectors, Stan Hilditch and Charles Warman, discovered the first massive deposit of iron ore located at Mt Whaleback. This discovery was kept secret due to an embargo on iron ore exports. This was because the Australian government thought that iron ore was in short supply. In 1960 the Mt Newman iron ore project commenced due to the lifting of the embargo. This created the new town of Newman and the construction of a 426km railway to Port Hedland from Mt Whaleback (www.bhpbilliton.com).

Mt Goldsworthy Mining Associates started to established a mine and town in 1962 called Goldsworthy. They also built a railway to transport iron ore to the port at Finucane Island, Port Hedland, with the first shipment of iron ore occurring in 1966 (www.bhpbilliton.com).

Geology and Formation

Within the Pilbara there are a number of different styles of iron deposits. Each of these styles characterises a different iron deposit. These styles include Banded Iron Formation (BIF), Bedded Iron Deposits, Brockman Iron Deposits, Marra Mamba Iron Deposits, Channel Iron Deposits (CIDs) and Detrital Iron Deposits (DIDs) (www.riotintoironore.com).

One of the regions within the Pilbara, known as the Hamersley Group approximately 2.5km thick, formed in a marine environment due to chemical sedimentation of minerals. Volcanic activity forced basalt rocks into the area which formed the Hamersley Group. During formation layers of rock were deposited, with each layer having a different chemical composition. Layers alternated between iron-rich minerals (magnetite and hematitie) and silica-rich minerals with sporadic layers of sedimentary rock. This type of rock formation is called a Banded Iron Formation (BIF) (www.riotintoironore.com).

Geologists identified within the 2.5km thick BIF two important layer formations. These are the Brockman Iron Formation (620m thick) and the Marra Mamba Iron Formation (230m thick). The layers are commercially important as they are host to the larger iron ore deposits (www.riotintoironore.com).

Bedded Iron Deposits form when BIF has been naturally enriched. These deposits which have been naturally enriched also include the Brockman and Marra Mamba Iron Formations. The enrichment of Brockman and Marra Mamba Iron Formations was due to circulating ground waters, where non-iron minerals were replaced by hydrous iron oxides, with magnetite oxidising to hematite within the BIF. The sporadic sedimentary rocks located in the BIF were converted to shales. Geological structures, such as folds and faults, assisted these iron formations with ore grade within the BIF reaching 60% iron (www.riotintoironore.com).

The dominant iron mineral in Brockman Iron Deposits is usually hematite. The content of phosphorus, goethite (iron bearing oxide mineral) and physical characteristics vary in these deposits. This variation is due to the different levels of dehydration in goethite. These different levels also affect the residual phosphorus content. The levels of dehydration change the colour of these deposits. Colours range from blue grey for high levels of dehydration to grey-yellow-brown for lower dehydration levels (www.riotintoironore.com).

Marra Mamba Iron Deposits are similar to Brockman Deposits except have a higher proportion of goethite and lower phosphorus content. Typically the deposits are grey-yellow-brown (www.riotintoironore.com).

Unlike bedded deposits Channel Iron Deposits (CIDs) were formed due to meandering rivers. Bedded Iron Deposits were eroded and iron particles concentrated in these rivers. These deposits appear typically in two forms either as a low flat-topped hill or concealed under recent rocks. The thickness of these CIDs ranges between 5 to 40m. Ore is brown-yellow in colour with grains of rounded hematite locked in a goethite matrix. Channel Iron Deposits are unique to Western Australia (www.riotintoironore.com).

The eroding of Bedded Iron Deposits can also form Detrital Iron Deposits (DIDs). Ore fragments are eroded and are deposited in natural traps. These traps can be drainage channels or valleys formed by topography (www.riotintoironore.com).

These deposits can vary in texture as some are loose gravels and others are cemented naturally. This typically means that there is a high proportion of high quality lump, with the iron grade being highly dependant on the grade of the original particles which came from the Bedded Iron Deposits (www.riotintoironore.com).

Mining

Mining by BHP occurs at several different locations within the Pilbara mainly near the town of Newman. From these mines there are several products which BHP produce these include lump and fines from Yandi, Newman, Yarrie and Mining Area C. The ore from Mt Whaleback has the highest grade containing up to 68% iron (www.bhpbilliton.com).

Ore once blasted is then crushed from boulder size, 1.5m diameter, down to smaller lumps approximately 15-30cm. This ore then undergoes secondary crushing to reduce the size again down to pellet size. Once it has been crushed it is stockpiled ready for rail transport, while waste rock is left at the mine for future rehabilitation (www.bhpbilliton.com).

All ore is then transported by heavy haulage railway to ports located at Nelson Point and Finucane Island. These two ports are located either side of the harbour. Typically ore is unloaded, screened and crushed before being stockpiled ready for shipment. Unloading, screening and crushing processes all create dust which is controlled by water cannons. Stockpiles are arranged in different grades which can be mixed according to the grade required by the contract. Stockpiles are mixed and loaded onto conveyor systems which transport ore to ship loaders (www.bhpbilliton.com).

Expansion

Several future developments and expansion of mines controlled by BHP are planned for the future. An expansion of the Area C mine is planned with Products and Capacity Expansion, Accelerated Expansion and 5 Rapid Growth Projects (RGP) scheduled. One of the RGP is designed to increase capacity by 50 Mt to 205 Mt per annum which is scheduled for 2011. With all future development and growth BHP has stated that they must meet a number of commitments to they community. Commitments outlined include working with local communities to support sustainable development and to ensure needs are incorporated into growth (www.bhpbilliton.com).

Expansion of the mines requires adequate reserves and resources are available. To extend the life of mining in the Pilbara the size of the drilling group has been increased by 60%. This increase is to try and expand the resource and reserve base at Mt Whaleback, surrounding satellite mines, Area C corridor and Yandi corridor (www.bhpbilliton.com).

Discussion

The two major mining companies which operate in the Pilbara are BHP and Rio Tinto. The two companies both have large up to date infrastructure and rail networks put in place with significant resources and reserves in stock. This enables the companies to concentrate on increasing there resources and reserves by exploration and drilling, while not having to worry about expanding and or upgrading there production and or infrastructure as much.

Conclusions

The Pilbara is host to a number of various iron ore deposits. There are a number of companies who own and operate mines throughout the Pilbara. Two of these companies include BHP and RioTinto which export there products to several countries including Japan, Korea, Taiwan, China, Europe and Australia. The export of iron ore comes from several iron ore deposit types which include Banded Iron Formation (BIF), Bedded Iron Deposits, Brockman Iron Deposits, Marra Mamba Iron Deposits, Channel Iron Deposits (CIDs) and Detrital Iron Deposits (DIDs). The higher iron grades come from the Brockman and Marra Mamba Iron type Deposits.

References

  • www.bhpbhilliton.com viewed 10th October 2009
  • www.riotintoironore.com viewed 10th October 2009

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