PERTH (miningweekly.com) – A 34% increase in the ore reserve tonnage at the Mt Cattlin lithium operation in Western Australia, has confirmed the mine-life extension, ASX-listed Allkem said on Friday, with the company also flagging a potential underground operation.

The company told shareholders that the ore reserve tonnage at Mt Cattlin was now estimated at 7.8-million tonnes grading 1.2% lithium oxide and 130 parts per million tantalum pentoxide.

The miner noted that the ore reserve and the planned mining schedule suggested a projected life-of-mine for the next four to five years, out to 2027 or 2028, via openpit mining methods.

The next stage of mining at Mt Cattlin will consist of two separate cutbacks to optimise ore presentation, with the mining proposal for Stage 4 having been submitted to the Western Australian regulators and is anticipated to be received by the end of 2023.

The Stage 4 operation at Mt Cattlin is expected to have an operating cost of some $953/t, incorporating the remainder of the current Stage 3 openpit and Stage 4 openpits and processing the end-of-life stockpiles from April this year to the end of the mine life.

Stage 4 operations are expected to generate a net present value of some A$1.7-billion, with the project to require a capital investment of around A$115-million.

Allkem’s board has approved mining of the first cutback of the openpit, which is expected to result in continued spodumene production into 2026. In the second cutback, the increasing waste to ore strip ratio at depth using the openpit mining method is being evaluated against an alternate underground mining option, and Allkem told shareholders that the company was seeing significant opportunity to transition Mt Cattlin to an underground mine, including unlocking greater orebody extension potential and prolonging the mine-life.

A feasibility study on the underground development is expected in the first quarter of next year, Allkem said, and would allow for a variety of scenarios to be modelled to ensure an optimised future mining method is selected.