The blasts are a key milestone in the transition of Mt Marion to a combined open-pit and underground mining operation.
In May, MinRes announced a $490 million investment with joint venture partner Jiangxi Ganfeng Lithium to develop underground mining and construct a flotation plant at the mine, located 40km south-west of Kalgoorlie.
MinRes Underground Mining Manager Shannon McMahon said the blasts were successfully delivered with underground mining contract partner Macmahon.
“This first portal blast creates the entrance to underground mining at Central pit and the access we need to reach the first underground ore at Mt Marion,” she said.
“Exploration has confirmed we’ve barely scratched the surface of what the orebody can deliver and the shift to underground is the next step in realising Mt Marion’s full potential.”
The underground project spans two pits, Central and North, with five portals planned across the sites. Portals are the entry points from the surface into the underground mine.
The Central pit portal blasts in October follow the restart of underground development at North pit in September. At North pit, the decline is planned to reach 850m below the surface, while the decline at Central pit will extend to a depth of 540m.
First ore from underground stoping, the method of extracting ore from underground, is expected in Q4 FY27. Stoping production at Central pit is planned for Q4 FY27, with North pit to follow in Q4 FY28.
From FY28, Mt Marion will operate as a combined open-pit and underground mine, with underground ore expected to supplement up to 40% of the processing feed.
MinRes Executive General Manager Commodities Joe Brown said underground mining and the flotation plant represented a high-return brownfield investment.
"These projects set up Mt Marion for the decades ahead. Underground mining and a flotation plant gives us access to higher-grade ore, lift recoveries and increase installed capacity by 20%,” he said.
FY27 guidance for MinRes’ 50% share of Mt Marion volume is 200,000 to 240,000 tonnes of spodumene concentrate (SC6), which is exported via the Port of Esperance to international customers.
