Ores ain't ores

DIRECT ship iron ore mining used to be so simple. Drill, blast, dig, truck, crush, screen, load. However, ores are not what they used to be.
Ores ain't ores Ores ain't ores Ores ain't ores Ores ain't ores Ores ain't ores

CSIRO has developed textural classification tools to help iron ore miners work more effectively.

Noel Dyson

The Pilbara iron ore producers made their names on the back of high-grade, low-phosphorous ore for some decades.

The depletion of such ores means producers are starting to transition to increasing amounts of goethite-rich Marra Mamba, Channel Iron Deposit and hematite-goethite Brockman ores.

CSIRO Mineral Resources research group leader Keith Vining said the switch to increasingly goethitic ore types could have significant impacts at various points of the iron ore supply chain.

Most miners get a handle on the chemical composition of their ores but that, he argues, is not enough.

Vining said not understanding the texture of the ore could have ramifications for productivity and costs reductions across the iron ore value chain.

 “Ore bodies contain a wide range of ore textural types in differing proportions, which can vary significantly even at a local scale within the ore body,” he said.

“The different textures have distinct physical properties and behaviours that will impact grade, crushing, processing, bulk handling, sintering and blast furnace behaviour.

“The increased prevalence of goethitic ore coming from Australia’s mines means the need for a robust textural classification framework is growing.”

The CSIRO has a textural classification tools to help mines understand how different ore bodies will mine and process. It developed the process 20 years ago and has been validating and constantly refining the tool with iron ore miners.

There are three basic types of goethite: vitreous, brown and ochreous.

In bedded hematite-goethite ores ochreous goethite is dominant in the lower part of the orebody, including below the water table zones. Vitreous goethite occurs largely in deposit hardcap and is associated with localised and relatively high levels of aluminium and silica. 

Contrary to common perception, Vining said, chemical analysis typically showed low impurity levels associated with brown and ochreous goethite in Pilbara deposits.

Goethite ores can have an impact all the way through the mining process.

Hematite can be very hard while the goethite can be very soft, which can have a huge impact on blast plans and generation of fine ore.

Failing to understand the textural composition of the goethite can also impact the process plan and lead to downtime and reduced efficiency.

Vining said textural classification would allow mines to better predict where different types of goethite were present, allowing blending processes to be adjusted to address differences between ore types. 

It can also have an impact on shipping and the processing of the iron.

Vining said variability of ore textures could impact handling and transport options.

“For example, knowing which components of ore are associated with clay minerals or are inherently ‘sticky’ allow mine operators to adjust their processing to account for more complex ore transportation by mitigating the risk of screens, chutes, transfer points and rail cars getting blocked throughout the supply chain,” he said

“Similarly, understanding an ore’s moisture carrying capacity through textural classification can mitigate the risks associated with transportation.

“Mines with this information can develop blending strategies and adjust their handling systems to proactively manage moisture issues, instead of reactively adjusting to minimise output losses.”

CSIRO’s textural classification process can be implemented using a conventional light-optical microscope from Zeiss combined with CSIRO’s own specialist software.

This tool allows iron ores to be characterised using both mineralogy and texture.

“That can help you better understand your process,” Vining said.

Members of the CSIRO Mineral Resources team will be presenting at the Australian Institute of Mines and Metallurgy’s Iron Ore 2017 conference being held Perth Convention and Exhibition Centre from July 24-26.

The CSIRO ore textural classification system will be on display there too and CSIRO will be running workshops with Iron Ore 2017. Information on that can be found here.