BP33 portal cut at Finniss: design and geotechnical notes for mine planners
Reviewed by Joe Ashwell
First reported on International Mining – News
30 Second Briefing
Portal cutting at Core Lithium’s BP33 deposit has started the underground decline at the Finniss lithium project in Western Australia, establishing the transition from open pit to long-life underground operations. BP33 is planned as a low-cost underground production base with a mine life exceeding 10 years, supporting spodumene concentrate output from the existing Grants open pit and processing plant near Darwin. The move signals a shift to deeper, higher-grade ore extraction, with geotechnical focus now on decline ground support, water management and long-term stope stability.
Technical Brief
- Portal cutting at BP33 establishes the physical interface between surface infrastructure and the new underground decline.
- Development sequencing at BP33 will now be driven by decline advance rates and underground access constraints.
- Transition to underground at BP33 implies a shift to more intensive ground support and water control regimes.
- Long-life underground status at BP33 will require progressive stope design updates as geology and structure are better defined.
Our Take
The BP33 portal development effectively complements the recent restart of open-pit mining at the Grants deposit within the Finniss lithium project, suggesting Core Lithium is moving towards a multi-source feed strategy to sustain a mine life exceeding 10 years.
In our database of lithium coverage, Finniss in Australia stands out as one of the few hard-rock operations where underground access (BP33) is being advanced in parallel with open-pit activity, which typically improves flexibility in matching ore supply to volatile spodumene pricing.
The recent A$290 million funding package referenced in May 2026 coverage of Core Lithium, together with the second offtake for Finniss material, underpins the capital-intensive transition to underground mining at BP33, reducing execution risk on the longer mine-life profile reported for the project.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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