The expansion – which includes the construction of a new flotation plant and the development of underground mining – represents a total capital investment of $490 million (100% basis), to be deployed across FY27 and FY28.
The investment breaks down across three key areas: a flotation plant ($240M), underground pre-production development ($220M) and non-processing infrastructure ($30M).
At the current spot spodumene price of approximately US$2,700/t SC6, the payback period is expected to be less than one year¹.
The flotation plant and underground mining program are expected to deliver meaningful improvements to the Mt Marion operation, supporting mine life through access to additional mineral resources below the existing open pit.
The projects will also guide improved plant recoveries, targeting approximately 70%, increased installed capacity from ~500ktpa SC6 to 600ktpa SC6 and remove the lower-grade SC3.5 product to deliver a single SC5 product.
Tendering for an underground mining contractor is already underway, with central underground development expected to commence in Q1 FY27.
From FY28, Mt Marion will operate as a combined open pit and underground mine, with underground ore from open stoping expected to supplement up to 40% of processing feed.
The flotation circuit will be built alongside the existing dense media separation plant to recover fine spodumene currently lost to tailings, constructed and operated by MinRes' Mining Services division. Construction is targeted to begin in Q1 FY27, with commissioning and ramp-up scheduled for 2H FY28.
Minimal disruption to existing operations is expected during construction and commissioning. The site's accommodation camp will also be expanded from 500 to 750 rooms to support both projects.
MinRes Managing Director Chris Ellison welcomed the decision.
"This high-return brownfield investment sets up Mt Marion for decades to come. Underground mining and flotation will work together to access deeper high-grade ore, lift recoveries and produce a single 5% product,” Ellison said.
"I thank our partner Ganfeng for their collaboration on the design and commitment to these projects, which will ensure we unlock the full potential of Mt Marion."
Learn more about the MinRes Lithium business.
¹ Payback period based on current spot spodumene price of approximately US$2,700/t SC6.