Mineral Resources (MinRes) has confirmed a final investment decision (FID) to expand operations at its Mt Marion lithium project in Western Australia, jointly owned with Jiangxi Ganfeng Lithium.

The planned expansion will introduce both a flotation plant and underground mining at the site.

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The total capital investment for these projects will be A$490m ($351.2m) on a 100% basis, with spending scheduled for the 2027 and 2028 financial years.

Of this amount, A$240m is allocated for the flotation plant, A$220m for preliminary underground development, and A$30m earmarked for non-processing infrastructure.

Based on a current spot price for spodumene of roughly $2,700 per tonne of spodumene concentrate (SC6), the companies estimate that the investment could be recouped in less than a year.

Mt Marion is situated about 590km east of Perth, on the traditional lands of the Marlinyu Ghoorlie People, and is approximately 70km south of Kalgoorlie.

The development will involve the construction of the flotation circuit alongside the existing dense media separation facility to recover fine spodumene material that is presently lost to tailings.

MinRes’ Mining Services division will construct and operate the flotation plant.

The construction is targeted to start in the first quarter of FY27 and commissioning planned for the second half of FY28.

Following the expansion, the site aims to improve plant recoveries, targeting approximately 70%.

Installed SC6 capacity is projected to increase from about 500,000 tonnes a year to 600,000 tonnes, with the lower-grade SC3.5 product to be replaced by a single SC5 product.

From FY28, operations at Mt Marion will combine open pit and underground mining, with ore from underground workings expected to make up as much as 40% of the processing feed.

The process of selecting a contractor for underground mining has begun.

Core underground development activities are expected to start in the first quarter of FY27.

According to the company, minimal disruption is anticipated for existing operations during the construction and commissioning phases.

MinRes managing director Chris Ellison said: “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.”

In November 2025, MinRes and POSCO Holdings signed a binding agreement to form a lithium joint venture partnership.