Overview
Hamersley Iron, a wholly owned subsidiary of Rio Tinto has operations located in the Pilbara region of Western Australia. Hamersley has a 100% interest in each of its mines with the exception of Channar, which is a joint venture with Hamersley owning 60% and a subsidiary of China Iron and Steel Industry and Trade Group Corporation owning 40% and Eastern Range which is owned 54% by Hamersley and 46% by Shanghai Baosteel Group Corporation.
The operations include six mines: Paraburdoo, Mount Tom Price, Marandoo, Brockman and Nammuldi mines, all located in Western Australia.
Location
The Pilbara region is located in the northwest of Western Australia, approximately 1,100km north of Perth, extending from the Indian Ocean to the Northern Territory border, the Pilbara covers more than 500,000 square kilometres.
Geology
The Pilbara region is located in the northwest of Western Australia, approximately 1,100km north of Perth. The region contains the 80,000 square km Hamersley Iron Province. The geology of the Province is characterized 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.
The Hamersley Group is approximately 2.5km thick. It contains several large units of Banded Iron Formation (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.
The BIF layers have been deformed by geological processes, and eroded by weathering resulting in the geological formations that we see today.
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
Each mine has its own drill and blast team. Hamersley has a total of eight diesel-electric rotary drills, with tricone bits. The blast holes are up to 381mm diameter, and drilled in patterns that optimise blasting fragmentation (with 7 to 11 m separation between holes, usually). The hole depth varies with bench height and there is subdrilling to 2.5 m. The drill cuttings are sampled for each hole, logged by mine geologists, then chemically analysed. The Geologists later use the sample data to estimate the average crusher feed head-grade for each mining block.
The blast holes are charged with ANFO (ammonium nitrate fuel/oil mixture). The charge per hole depends on hole depth, diameter and ore hardness. Blast sizes range from about 60kt of broken ground produced, to more than 1Mt.
Operators use hydraulic shovels and excavators, rope shovels (diesel-electric) and large front-end loaders.
Trucks, with capacities of up to 220t, haul the ore to primary crushers and the waste to dumps.
Each mine, except Yandicoogina, produces both lump (-31.5 +6.3 mm) and fines (-6.3 mm). Yandicoogina produces fines (-9.5 mm). After two or three stages of crushing and screening, the products are blended onto stockpiles at each mine, then loaded onto trains.
At Mount Tom Price, about 8 Mt/year of high grade ore is recovered from low grade ore that comes from mixtures of hematite and internal shale bands, footwall shale or low grade stockpiles. The processes used are heavy medium and gravity separation. At Paraburdoo, the fines are upgraded by removing the ultrafines (-0.01 mm) with wet screens and hydrocyclones.
Mount Tom Price, Paraburdoo/Channar, Marandoo and Brockman No 2 mines are treated as one mine. Each Lump and fines stockpile contains ore from every mine except Yandicoogina, in proportions and grades that match the short-term mine plan. All products are sampled automatically before they are stockpiled. We use the sampling data to monitor quality as the stockpiles are built. This ensures the quality matches our target for each mine's contribution to the blend. This system is centrally managed and runs 24 hours a day.
The next stage is blending each mine's ore onto the stockpiles at the Dampier port, and doing it so it meets the quality targets for shipment. Blended products from each mine are added to product stockpiles at each port terminal. Further blending gives a well-homogenised final lump or fines product. The product is ready for shipment when the full pile is built. Automatic sampling takes place just before ship loading. Hamersley's Yandi (HIY) product is also blended at the port to improve quality variability. The ore comes from a single mine, with tight grade control at the mine prior to homogenisation via stockpiling at the port.
Processing
There are 2 upgrading plants in operation at Hamersley. Mount Tom Price operates a concentrator which upgrades regular ore to high grade ore which is then reintegrated back into the stockpiles. Paraburdoo operates a fines processing plant.
The Paraburdoo fines processing plant treats the -6.3mm part of the ore stream from the crushing and screening plant. These fines are wetscreened at 0.6 mm. The -0.6mm fraction is then pumped to a two-stage hydrocyclone which performs a classification of the ore constituents and further improves the fine-ore quality by removing the ultrafines (-0.01mm).
Ultrafines contain a high proportion of impurities (gangue) - particularly alumina, silica and phosphorus. So the fines product that emerges from the plant (up to 85% mass recovery) has lower impurities as well as less ultrafines. Final dewatering reduces moisture as much as possible by conventional mechanical methods.
After dewatering, the products are stacked and blended alongside the lump ore on the blending stockpiles. The dewatering is completed by draining the fines on a specially designed stockpile area. The drainage water is recovered and recycled to the plant. Everything is done to ensure that as much free moisture is removed from the fines as possible.
Because of the complexity of the Paraburdoo deposits and the importance of product-blending at the mine, a sophisticated stockpiling and reclaiming system was designed. There are two pairs of stockpiles (about 300kt each) with chevron stacking and a full-face bridge reclaiming system.
A reclaimer loads the ore trains. The loading station has a pair of load-cell mounted bins, and a hydraulic indexer moves the ore wagons through the station.
At Mount Tom Price, the crushing and screening plant (the high grade ore processing plant) has three crushing stages, a primary surge stockpile, and scalping and product screens.
Lower grade, shaly ore (normally less than 60% Fe) is a mixture of liberated hematite and shale which requires cleaning via a concentrator. Approximately 11Mt of this ore is mined each year. It is scalped before it enters the primary crusher, with the +200mm fraction (about 10%) joining the high grade stream.
The undersize goes to a surge stockpile. It becomes feed to the concentrator, where it is crushed, wet-screened, and put through Heavy Medium Separation (HMS) and gravity separation (spirals). The heavy-medium output is a suspension of finely ground ferrosilicon (FeSi) in water. The spirals were added in 2001 as a direct replacement for the Wet High Intensity Magnetic Separators. This introduction has improved throughput, capacity and recovery. The concentrator generates approximately 8Mt/year of beneficiated product (60% lump, 40% fines) and has a mass recovery of 70%. It contributes approximately 40% of the total Mount Tom Price ore products.
All product streams in the high grade plant and the concentrator are sampled automatically, then processed and analysed promptly at the site laboratory. The operations staff therefore have frequent assay results. Those results play a decisive part in our product blending and quality control systems, and are also used for ore reconciliation.
Lump ore from the high grade plant and concentrator are stacked on separate stockpiles above the rail tunnels. The ore wagons are hauled through the tunnels and manually loaded using clamshell gates.
Fines products from both plants are stacked together on three 150kt stockpiles. These blended fines are reclaimed by a bucket wheel reclaimer then moved by belt conveyor to a bin above a manually-operated train loading station.
