Optimising underground metalliferous mine ore recovery

Minova, in partnership with Round Oak Minerals, has lifted ore recoveries in an unmined area of the Bentley mine in Western Australia by 20 per cent. How did Minova do it?

There are many projects that a mining or METS (mining equipment, technology and services) company will say yes to.

For Minova, it said yes to going underground into areas that have not been mined for many years.

This happened at the Bentley copper-zinc underground mine, which is part of the Jaguar operations north of Kalgoorlie in Western Australia.

Its history dates back to 2011 when Jabiru Metals offloaded the site in a deal with IGO.

Seven years later, Round Oak Minerals (formerly known as CopperChem) acquired the Jaguar operation from IGO to reposition itself as a significant base metals producer in Australia.

In line with this strategy, Round Oak sought Minova’s trusted assistance in maximising ore recovery and improving extraction outcomes in the unmined areas of the Bentley mine.

Minova has used its many years of experience to assess the project and underground conditions to ensure a successful outcome.

One of the principal mining methods that was historically used at the Bentley mine was the Avoca method.

This required all development in a given area to be complete before stoping began in a bottom-up sequence. Stope voids were sequentially back-filled with loose run-of-mine waste rockfill.

Minova grouted large volumes of rockfill, allowing the redesign of the stopes below the rockfill, which improved the overall recovery.

“The Bentley mine had a stope design which was limited by having rockfill above the stopes, so grouting the rockfill changes the design options,” Minova product lead Douglas Pateman tells Australian Mining.

“In turn, Round Oak implemented another mining system in Bentley to work in conjunction with our grouting program. They used cemented-aggregate fill in conjunction with the Minova grout system to improve the total ore recovery.”

This strategy allowed the height of the primary stopes to extend to their full height, including the originally-designed ore sill pillars, which translated to an increase in the available ore that can be mined.

The result was an average 20 per cent increase in ore tonnes on the initial design for these stopes.

“It’s a fantastic success,” Pateman, who provided Round Oak with engineering support during the initial set up of the project on-site, says.

“The additional ore that the Round Oak team has been able to recover is quite significant. It’s also high-grade ore, which means the additional value that’s been generated is a good outcome for the mine.”

Three contractors have worked day and night shifts for a period of three weeks to bring the project to completion.

Minova provided a specialist worker who operated the pump each shift, and trained another contractor to inject grout into the rockfill.

But one of the biggest challenges in the project was to ensure the quality of the water was compatible with the Minova-chosen grout, FB200.

This was selected for its unique rapid gel times, quick strength, low viscosity and high-water content, allowing for controlled placement through borehole patterns to gain maximum penetration of the unconsolidated rockfill.

“The grout that we used required a greater volume of water compared with that required by traditional grout,” Pateman says.

“We did a lot of testing to ensure the compatibility of the water with our grout, with different formulations for different types of water.”

Moving and storing this high volume of grout underground was also another challenge.

Scheduling, according to Pateman, was an important part of this project, given the large number of truck and vehicle movement required to get the grout underground.

“Safety was an absolute priority in this project,” he says. “We used specially designed equipment that is safe for use in underground coal mines, which have greater legislative requirements.”

Minova also aimed to minimise the movement of machinery to reduce worker exposure to mobile equipment.

“In this project, our greatest risk was interaction with mobile equipment, so most of the time our work was done in a safe location,” Pateman, who has eight years of practical and theoretical knowledge with Minova, says.

Minova also injected the grout into the rockfill at a safe working height instead of working above the head, while implementing appropriate dust control and area ventilation.

The company has developed its expertise since undertaking a project of similar nature in an underground gold mine in Western Australia back in 2001.

It has been involved in a number of projects across Australia and Indonesia since then, building its capacity in maximising ore recovery despite the unique challenges presented by individual mines.

This article also appears in the March edition of Australian Mining.

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