Grade-by-Size – focus on small size fractions

Extensive testing conducted found Western Australian Goldfields mine sites can add value to their operations by focusing on small size fractions.

Gold nuggetIn recent decades, the primary driver to maximise profitability of mining operations has been to mine and process as much material as possible to exploit economies of scale. This has led to bigger equipment, higher throughput plants and greater production but not necessarily efficient use of resources.

With the concerns of declining grades, more complex orebodies, greater haulage distances, higher energy costs and water usage, any approach that can alleviate the impact of these issues is highly desirable.

The Kalgoorlie-Boulder Mining Innovation Hub recently explored use of a preconcentration technique known as Grade by Size Deportment. This technique exploits the propensity for some ores to exhibit preferential breakage leading to concentration of minerals in specific size fractions.

Several sites within the Goldfields region showed significant potential for separation by size to provide value to their operations. This is particularly the case where either marginal grades are present or growing distances from face to surface, or from mine to mill, are subject to increasing transport costs.

Research and test work by the Hub show that natural grade by size deportment during coarse rock breakage and screening is a key lever for generating high-value coarse separation. This in turn can drive better productivity and returns for mine operators.

The Kal Hub, established in 2018 by the Cooperative Research Centre for Optimising Resource Extraction (CRC ORE), enables focused collaboration between researchers; mining equipment, technology and services suppliers; and mining companies to unlock value for Australian mining through technology development.

CRC ORE Chief Operating Officer Dr Luke Keeney said that the work conducted by the Hub was significant.

“In a short amount of time the Hub has been able to bring together some of the most innovative people in industry and research, enabling collaborative innovation to occur,” Dr Keeney said.

“This collaboration is good for the Goldfields, and for the wider mining industry, as it demonstrates the benefits mine sites can experience by deploying various aspects of Grade Engineering®, including grade by size deportment.”

Grade Engineering is a system-based methodology developed by CRC ORE designed to reject low value material early in the extraction value chain and pre-concentrate processing plant feed. A key lever for successful Grade Engineering is Grade-by-Size Deportment.

Hub Technical Advisor Dr Laurence Dyer explained the objective of the Grade-by-Size Deportment project was to undertake initial representative sample testing to determine natural deportment Response Rankings (RR) at a range of deposits in the Kalgoorlie-Boulder region.

“This project provided an introduction for industry participants to Grade Engineering and an indication of potential opportunities that Grade-by-Size deportment may present,” Dr Dyer said.

“A number of companies came on board and we were able to obtain diamond drill core and reverse circulation (RC) drilling samples from a variety of sites in the Goldfields to crush, screen and assay to develop a snapshot of responses to this approach.”

Samples were crushed where necessary and screened into up to six size fractions, with a finer set of screens used for the RC samples to accommodate the difference in particle size distributions.

As expected, gold sites displayed significant variation in response, while all nickel sites tested showed significant upgrade in the finer fractions of both nickel and cobalt. RC samples were a compelling sample option due to their prevalence and self-preparation for screening, however there remains a question as to the legitimacy of the results they generate.

“Gold samples produced varied data with the majority of sites producing low to moderate upgrades on average,” Dr Dyer said.

“The RC samples generated greater variation and often decreased in grade at the finest size fractions, likely due to particles being below liberation size, creating issues with the response ranking fit.”

The Kal Hub research also showed nickel produced far more consistent behaviour with all sites producing moderate to high responses for both nickel and cobalt. While for some samples the nickel and cobalt response rankings matched well, in others the nickel upgraded significantly better.

These results are explored in greater detail in the whitepaper – ‘Grade Deportment by Size - Initial characterisation of deposits in the Western Australia Gold Fields at the small scale’ available from

The Kalgoorlie-Boulder Mining Innovation Hub continues to work with several participants on a variety of projects throughout the Goldfields that are enabling optimised resource extraction.

Download the Grade by Size whitepaper.

Find out more about the Kalgoorlie-Boulder Mining Innovation Hub.

Learn about Grade Engineering.

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