Overview
The Robe River mines include the Pannawonica and West Angelas (commenced operations in 2002). The West Angeles Mine is located approximately 300 km southeast of Pannawonica.
Robe River operates two open pit mining operations in Western Australia. Mesa J is located in the Robe Valley, north of the town of Pannawonica. The mine produces Robe River fines and lump, which are pisolitic iron ore products. The West Angelas mine, opened in 2002, is located approximately 100 kilometres west of the town of Newman. The mine produces West Angelas fines and lump, which are Marra Mamba iron ore products. The crusher and port facilities are located at Cape Lambert in the Pilbara region.
Location
The Pilbara region is located in the northwest of Western Australia, approximately 1,100km north of Perth.
Geology
The region contains the 80,000 square km, Hamersley Iron Province. The geology of the Province is characterised by a 2,500 million years old group of late Archaean and early Proterozoic rock formations known as the 'Hamersley Group'.
The Hamersley Group was formed by chemical sedimentation of minerals in a marine (ocean) environment. The processes which formed the Hamersley Group occurred after volcanic activity introduced basalt rocks in the area. Sedimentary rocks like sandstones also occur in the group due to weathering and transportation of rocks which occurred during the period when the Hamersley Group was formed.
During the period of formation, layers of rock with different chemical composition were deposited. Iron-rich layers alternate with silica-rich layers in the rock formation. Occasionally these layers are interspersed with layers of sedimentary rock. This type of rock formation is called a Banded Iron Formation (BIF).
The Hamersley Group is approximately 2.5km thick. It contains several large units of BIF: rock with bands of iron minerals (magnetite and hematite) and gangue minerals (mostly carbonates, silicates and chert). Typically, unenriched BIF contains about 30 per cent iron by weight.
Bedded Iron Deposits
Where Banded Iron Formation (BIF) has been enriched by natural processes, these zones can become Bedded Iron Deposits. Many of the commercially important iron ore deposits in the Pilbara were formed by natural enrichment of BIF. These enriched deposits include the commercially viable ores in the Brockman and Marra Mamba Iron Formations.
The BIF in the Brockman and Marra Mamba Iron Formations was enriched to a high degree forming ore grade ore with more than 60 per cent iron. The natural processes that accomplished this (hypogene and supergene enrichment) involved circulating ground waters. Non-iron minerals in the BIF were largely replaced by hydrous iron oxides (notably goethite) and partly dissolved out. At the same time, magnetite in the BIF oxidised to hematite. Favourable climate and geological structures (folds and faults) stimulated the process. Sedimentary rocks that were interspersed with the BIF became shales.
In the Pilbara, other types of ore deposit exist, notably channel iron deposits, but these are derived from the original bedded iron formations.
Mining & Operations
Mining at Mesa J starts with drilling and blasting at the huge open pit. Blasting occurs several days each week to ensure availability of ore for up to two months ahead, allowing maximum grade control flexibility. Topsoil, removed to access the ore underneath, is preserved and re-established in mined-out areas as part of the company's rehabilitation and revegetation program.
Following blasting, conventional open pit mining methods are used to extract the ore. The broken material is loaded into large capacity haul trucks by hydraulic excavators and front-end loaders.
Ore is then hauled directly to the train load-out, while mixed waste is processed through the two Process Plants for ore recovery (ore is then conveyed to the train load-out) and waste is taken to waste dumps. Total material hauled at Mesa J is between 50Mt and 60Mt each year.
The newer West Angelas operation comprises an open pit mine, a crushing and screening ore processing plant producing lump and sinter fines iron ore with a capacity of 20 million tonnes per annum, as well as stockpiling, reclaiming and train-loading facilities
Processing
There are a number of stages of processing that ore undergoes depending on which mine it is sourced from.
Ore from West Angelas goes through a 2 stage crushing and screening process at the mine site producing one of two products: Marra Mamba lump ore of +6.3mm-31.5 mm and fines ore of -6.3mm. At the Cape, West Angelas ore is delivered to a hydraulic car positioner, which locates two cars in a new dual car dumper. The average car dumping rate is 9,000 tonnes per hour or about two cars every 90 seconds.
The ore is then conveyed to product stockpiles with a capacity of 8.5 million tonnes.
At Mesa J, ore is taken from the mine by haul trucks to Process Plant 1 which was commissioned in 1999. The plant processes sub-economic material, which was previously discarded, to reduce contaminants and retain onspecification ore suitable for further processing at Cape Lambert.
The second processing plant at the mine was commissioned in June 2001, following the success in value-added production of sub-grade ore through Process Plant 1. Process Plant 2 enables the processing of sub-grade ore to be increased by 1350 tonnes per hour. The combined production capacity at Mesa J is 2100tph.
Ore from both mines is transported by rail to Robe's Cape Lambert port operations. West Angelas is linked to the main rail line of Hamersley Iron via a 62-kilometre rail spur and the"northern link" connects the Hamersley rail network with the existing Robe line between Pannawonica and Cape Lambert.
Cape Lambert has been expanded to cater for West Angelas ore. This included construction of a new dual car dumper, expansion of stockpiling capacity to 8.5 million tonnes, new stackers and reclaimers, construction of a lump rescreening plant, an expansion in ship-loading capacity with installation of a new ship loader to allow dual ship loading and a wharf extension. Following completion of this work, the capacity of the port increased to a nominal 50 million tonnes per annum from the previous 32mtpa.
Ore cars are delivered to a hydraulic car positioner, which locates each car in a rotary car dumper above the primary crusher. Here material is crushed to a maximum 200mm. The average car dumping rate is 5,700 tonnes per hour, or about one car per minute.
Material from the primary crusher is conveyed to a 400,000 tonne capacity coarse ore stockpile. From there it is fed to conveyors beneath the stockpile, which take it to a series of crushers and screens in the processing plant. There, ore is processed into different products, including Mesa J sinter fines ore of -9.5mm and lump ore of +6.3mm-31.5mm.
After processing, the ore is stockpiled until its shipped.
