Quality management in the Pilbara

In the Pilbara region of Western Australia, Rio Tinto Iron Ore's production process has been developed to deliver products with a high degree of chemical and physical consistency.

The production process relies on good planning to ensure suitable ore is available at the required time to be mined, processed and blended into iron ore products.

The production process generates product quality forecasts based on mine plans and schedules. Mine plans and schedules are developed from detailed geological models using scheduling software.  The geological models are developed from chemical assays taken from drill holes and extrapolated using geophysical and geological information techniques. 

This process predicts the grade of each mining block within each deposit.  The ore blocks are scheduled so that each mine delivers a known quality product at any time. 

Centralised teams ensure that individual mine schedules are integrated at the planning stage so that individual mines deliver the required quality at the required time to meet product quality requirements.  Each mine has its own planned production schedule, but the responsibility for product quality rests with a central team. The team organises work that ranges from mine grades and tonnage contributions to the blending product stockpiles at the port.

At an operational level, as ore blocks are drilled to allow blasting, material removed from the holes are logged and chemically analysed to provide more detailed information and ensure that the estimated block grade is close to the grade predicted by the modeling and scheduling process. 

Each mine regularly measures the quality of lump and fines products as part of each mine stockpile. This process allows for rapid feedback to the operations team about any variation from the planned stockpile quality.  The team can then make exact and timely corrections.

The main control elements for monitoring ore chemistry are iron (Fe), alumina (Al₂O₃), silica (SiO₂), phosphorus (P), manganese (Mn) and loss on ignition (LOI).

The quality of lump and fines railed from each mine is predicted before the ore arrives at the port. Statistical methods are used to ensure that product variability is minimised.

RTIO manages product quality at the port by making minor changes to the planned blend by adjusting the proportion of tonnage contributed by each mine.  The ability to make these adjustments depends on a flexible and responsive rail system that can deliver the required ore to the right location at the right time. 

Trains from the various mines are assigned to relevant product stockpiles to achieve the product specifications.  Product stockpiles are complete when they have been built to the required size using the assigned trains.

Stockpile blending occurs using chevron and windrow stacking methods to ensure that individual mine contributions are evenly blended throughout the entire stockpile. 

Operations use slewing or bridge reclaimers to reclaim products. This process ensures products are blended on to ships with low variability within the cargo.

Lump products are screened again at the port immediately prior to shipping, to control the fines content. These fines are blended into appropriate fines products. Detailed models predict the chemistry of the products to ensure that the final blended-fines stockpile conforms to product specification.

During shiploading, specialised sample stations and associated laboratories sample and analyse the blended products. Samples are taken on either a time basis or a tonnage basis to yield composite samples for analysis.  This process yields final quality data on products that RTIO send to customers.