July 28 (Reuters) - Australia's Boss Energy (BOE.AX) , opens new tab on Monday flagged operational challenges at its flagship Honeymoon uranium project in South Australia, sending its shares to a three-year low.

The uranium miner, which owns 100% of the Honeymoon project, warned that issues in ramping up operations could delay reaching full capacity, after the site exceeded production guidance for fiscal 2025.

Sign up here.

The Subiaco-headquartered company also flagged a rise in cash costs for fiscal 2026, citing shorter processing times and changes to the chemical mix used in extraction.

"Honeymoon continues to ramp up, however the removal of nameplate targets and increased cost outlook have cast doubts over the project's long-term value," Jefferies analysts said in a note.

Boss Energy said it expects to spend between A$27 million and A$30 million ($17.73 million-$19.70 million) on the project in fiscal 2026, which Jefferies said is higher than its estimates.

"Higher costs are expected to negatively impact the project's profitability and BOE's future earnings," said George Ross, senior analyst at Argonaut.

"FY26 guidance has shocked the market... significant increase in production capital costs was not anticipated by the market."

The stock fell as much as 44.7% to A$1.880, its lowest since July 14, 2022, before closing 44% lower. It was the top loser on the broader ASX200 benchmark index (.AXJO) , opens new tab, which ended 0.4% higher.

Jefferies analysts said the recent board changes have reduced the chances of Boss Energy engaging in acquisitions as they are more focused on internal growth.

Boss Energy, which went public in 2007, said last week Chief Executive and Managing Director Duncan Craib would step down from the roles later this year and transition to a non-executive director role in 2026. Craib has been with the firm since 2017.

Chief Operating Officer Matt Dusci was named as his successor, effective October 1.

($1 = 1.5232 Australian dollars)

https://www.reuters.com/business/energy/australias-boss-energy-flags-honeymoon-uranium-project-challenges-shares-plunge-2025-07-28/