Australia's St Barbara has confirmed strong economics for its Simberi expansion project in Papua New Guinea, following the completion of a prefeasibility level plant study and an updated life-of-mine plan (LOMP).

The study outlines an expanded operation capable of producing more than 220 000 oz/y of gold from the 2028 financial year, peaking following an initial ramp-up to 90 000 oz/y in 2027. Total gold output over the 13-year LOMP is forecast at 2.2-million ounces, based solely on proved and probable reserves.

All-in sustaining costs are projected to fall to between $1 200/oz and $1 300/oz from 2029 to 2036. These estimates now include the cost of a proposed enhanced royalty package for local landowners and communities.

Initial project capital is estimated at $235-million, with pre-expansion growth capital of between $40-million and $60-million to be invested between 2026 and 2027. This will fund early works, including a camp upgrade, road construction and a reverse osmosis plant.

“This is a robust opportunity to deliver value for St Barbara shareholders,” said MD and CEO Andrew Strelein. “Our current work shows a project with significantly higher production, a lower operating cost and a mine life extending to 13 years without including any exploration targets.”

Assuming a gold price of $2 500/oz, the project yields a post-tax net present value of $717-million and an internal rate of return of 62%, with payback expected in 3.6 years.

The expansion, designed by Pitch Black Group and supported by AMC Consultants and Paradocs Metallurgy, transitions Simberi from free-milling oxide ore to processing harder sulphide ore. This will require a flotation circuit to produce a gold concentrate and upgrades to the comminution circuit. Oxide ore will continue to be treated via the existing carbon-in-leach plant.

Capital costs also cover new power generation capacity and construction of a wharf to enable concentrate export. Operating costs are estimated at $58.6/t milled over the life-of-mine.

The company expects to make a final investment decision in the first half of the 2026 financial year, pending resolution of an ongoing tax assessment in Papua New Guinea.