Mineral Resources (ASX:MIN) and joint venture partner Jiangxi Ganfeng Lithium approved a final investment decision to build a new flotation plant and develop underground mining at the Mt Marion lithium operation in Western Australia, with total capital investment estimated at AU$490 million, according to a Tuesday filing with the Australian bourse.

The project, funded across fiscal 2027 to fiscal 2028, includes AU$240 million for the flotation plant, AU$220 million for underground pre-production works, and AU$30 million for supporting infrastructure, with a payback period of under one year at current spodumene prices, per the filing.

The expansion is anticipated to prolong the mine's operational life, improve recovery rates to nearly 70%, raise installed capacity to 600,000 tonnes per year SC6 equivalent from roughly 500,000 tonnes per year, and simplify output to a single SC5 product stream, the filing said.

Underground development and construction of the flotation circuit are both scheduled to begin in the first quarter of fiscal 2027, with the flotation circuit expected to be commissioned in the second half of fiscal 2028, the filing added.