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18 January 2022 4 min read

BHP Olympic Dam in South Australia ©  BHP

Characterising Olympic Dam

Since the late 1980s, CSIRO's Diffraction, Mineralogy and Geochemistry unit has worked on, among many other projects, the giant Olympic Dam deposit in South Australia, an iron-oxide–copper–uranium–silver–gold (IOCG–U) deposit originally discovered by Western Mining in 1975 and acquired by BHP in 2005.

It contains more than 135 discrete minerals, including copper sulfides, uranium minerals and  valuable minor minerals containing zinc, lead, tin and tungsten.

Of these, 15 are critically important to characterise — mostly gangue minerals like chlorite, hematite and quartz — because they significantly impact processing, for example gelling events.

Mark Raven, Project Leader for CSIRO's Mineralogy and Geochemistry Characterisation unit has long ties with the project.

XRD analysis of smelter dust and slime

"Our initial consulting work began in 1990 for Western Mining to identify the mineral types (qualitative analysis) in smelter dust using X-ray diffraction (XRD), and then shortly after analysing the mineralogy of metallurgical slimes.

So far, we've received more than 60,000 samples through the laboratory, and analysed more than 15,000 samples for Olympic Dam using quantitative XRD (QXRD), which is worth around $3 million in contracts," says Raven.

"In 1991, standardless quantitative XRD analysis (QXRD) using the Rietveld Method became widely available, leading to more detailed information about mineral structure and identification.

"This innovation led CSIRO and partners to develop SIROQUANT, a commercialised user-friendly software based on the Rietveld Method, which we then used for improved analyses at Olympic Dam".

Flotation circuit at Olympic Dam for recovering copper-bearing sulfides. ©  Split Image Multimedia Pty Ltd

Geometallurgical analysis to aid processing

Raven's group works closely with Kathy Ehrig, BHP's Superintendent Geometallurgy for Olympic Dam, and her team, who developed a comprehensive geometallurgical program that aims to avoid 'processing surprises' from unknown ore characteristics, and to help predict the metallurgical performance across the plant.

They found that the complex breccia textures throughout the deposit disguises a rather simplistic geochemistry that can then be used to help predict the mineralogy of each mined ore-block.

Consequently, they were then in a much better position to predict the different mineral mixes more accurately across the processing plant and how each would respond to the metallurgical processes.

"The mineralogical problems we need to solve at Olympic Dam are complex and sometimes require results very quickly," Ehrig explains.

"The sample mineralogy can also be very challenging, ranging from routine ore samples though to tailings leach residues, various smelter products and electrolytic refinery slimes."

CSIRO has been involved in that 'no surprises' workflow now for many years.

Quantitative analysis for flotation, tailings, smelter and slag feed

"It wasn't until 2007 when BHP was planning open-cut operations that our quantitative analysis work really expanded, and they needed a group that could deliver consistent results," Raven said.

"Although an open-cut mine was never developed, we've continued to help BHP through most parts of their processing plant, including flotation, tailings, smelter and slag feed.

"We also get monthly composite samples for quality control of their on-site laboratory to make sure everything is going OK," he says

Ehrig is a great supporter of Raven's work at CSIRO.

"Mark has always provided superb XRD support for BHP’s Olympic Dam project. His expertise in quantitative XRD is world class, and I've relied on him to help solve our technical problems," praises Ehrig.

Origins of CSIRO mineral characterisation expertise

CSIRO's mineral analysis expertise began with Keith Norrish in 1946 with clay characterisation of soils, which then grew during the following 75 years to include rocks, ores and minerals for exploration and mining. It now also extends to analyses of industrial products and chemicals.

Halloysite nanotubes

Recently, the group has been analysing the mineral halloysite, a distinctive aluminosilicate clay mineral with a cylindrical or nanotube structure.

Halloysite nanotubes (HNTs) are emerging as an extremely versatile mineral for drug delivery, nanotemplating and nanocomposites, and perhaps most significantly as a potential absorbent for carbon‑dioxide capture.

Raven said the CSIRO team analysed around 3000 samples from kaolinite deposits over the last couple of years and are making great progress in identifying the clay using QXRD techniques.

Scanning electron microscopy (SEM) image of mixed kaolinite and halloysite

Putting the team to the test

Recognition of CSIRO's mineral characterisation proficiency has come from recent successes in the Reynolds Cup, a biennial global competition for accuracy in quantitative mineral analysis, with emphasis on clay mineralogy.

Each participating laboratory analyses three blind samples containing mineral mixtures commonly found in clay bearing rocks or soils.

"We came second last year, having won the Cup in 2010, and have done pretty well since with a couple of seconds, and thirds and fourths," says Raven.

Such successes underscores CSIRO's world-class mineralogical and geochemical characterisation capability and bestows Raven's team with great confidence in their techniques and mineral knowledge.

Automated mineral analysis

In the future,  Raven would like to see more automation in mineral identification.

"I see a future outcome for mineralogical analysis in using processes that are a lot more user friendly, but also developed specifically for different deposit types," Raven says.

"You could potentially develop an automated modular system for each deposit type, going from the ore stage, all the way through the processing steps and then to the final product, with each analysis step designed specifically for say the concentrates, the slag or the tailings."

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