Pantoro (ASX:PNR) said it plans to start the development of its third producing underground mine at the Norseman gold project in Western Australia early in fiscal year 2027, according to a Tuesday Australian bourse filing.

The company said development toward the high-grade O'Briens Reef will begin in early FY27 following completion of dewatering and rehabilitation of the Bullen Decline, with first ore development expected during the December 2026 quarter.

Ore from O'Briens is expected to deliver average diluted mill grades exceeding 6 grams per tonne over the life of the current mineral resource, the filing added.

Development of the Crown South ore zone is expected to begin in the March 2027 quarter, Pantoro said.

Pantoro added that a fifth underground drill rig is scheduled to arrive at Norseman in April and will be deployed to accelerate exploration across the Mainfield.

Drilling in the main Crown Reef area is underway, intending to commence additional decline development into the zone within the next 12 months, the filing said.

The company added that resource modelling across the Crown, Crown South, and expanded O'Briens areas is also underway, with an updated mineral resource and ore reserve expected during the September quarter.

The company's shares fell 17% in recent Tuesday trade, earlier reaching their lowest since August 2025.