Bellevue told the ASX on Tuesday probable reserves had increased 29 per cent to 6.8 million tonnes at 6.1g/tonne for 1.34 million ounces of contained gold.

The company said this was an increase of 300,000 ounces on the stage two feasibility study, and meant the life of mine reserves and mineral inventory had risen to 1.85Moz, underpinning an increase in mine life to 10 years, up from eight years.

Bellevue said the reserve had been independently verified by leading mining consultant Entech, and were calculated at a conservative gold price of $1750/oz.

The company last month said its mineral resource had grown to 9.8Mt at 9.9g/t gold for 3.1Moz, up from 3Moz at 10g/t, while the indicated resource had increased to 4.6Mt at 11.2g/t gold for 1.7Moz, up from 1.4Moz at 11g/t.

“Production in the first five years is forecast to average 200,000 ounces per annum at a bottom-quartile all-in-sustaining cost of $1000-1100/oz,” the company said on Tuesday.

Bellevue said this meant the project was set to boast some of the lowest operating costs among ASX-listed gold producers.

The company had previously indicated first production would be in the June quarter next year, and reiterated this on Tuesday while saying commercial production would begin in the second half of 2023.

Bellevue said it would generate average free cash flow of $231m a year before tax across the 10 years, including $254m pre-tax annually for the first five years of production.

This would add up to $2.1 billion across the 10-year mine life based on a gold price of $2500/oz, while the pre-tax internal rate of return would be 68 per cent.

It noted the project remained fully funded to production, with existing cash reserves of $151m and the undrawn $200m Macquarie debt facility.

Bellevue said pre-production costs were set to meet previous forecasts, with more than 90 per cent of these expenses either committed or locked in via tenders.

“By locking in 90 per cent of our pre-production costs and underpinning our 10-year mine life with 1.34Moz in reserves, we have significantly de-risked the project and put us on a path to realising the immense value of this exceptional asset,” managing director Steve Parsons said.

The Bill Beament-led Develop Global started work on the construction of the underground mine last month after winning the $400m contract in April.

“A total of 4.8km of the planned 14km of pre-production development has been completed to date, with mining costs locked in for the remainder of the pre-production period,” the company said.

“First development ore from the northern decline is expected in the September 2022 quarter, with only 70m of further development required before the first high-grade ore is encountered at the Armand lode.

“More than 53 per cent of the camp construction is completed.

“The remaining camp construction is expected to be completed in the September 2022 quarter.”

The company said its 1Mtpa nameplate capacity processing plant had been designed to be expanded to 1.5Mtpa throughput with additional capital requirements, which created the opportunity for further organic growth at the project supported by ongoing resource growth.

Bellevue said the early works engineering, procurement and construction contract had been awarded to GR Engineering Services, allowing the capital required for the key plant components to be fixed.

“Long lead items including the ball mill, crushing equipment, screens, agitators and leach and tailings thickeners have been or are in the process of being ordered,” the company said.

“The full EPC contract is well advanced and anticipated to be signed in coming weeks.

“Tenders for the power purchase agreement and bulk civil earthworks have been received and the company is currently working towards awarding these contracts.

“Approvals for full project execution are well advanced with completed permits in place for camp construction and underground development.

“Remaining required approvals to deliver the processing facility and remaining infrastructure are on track for the September 2022 quarter.”

Bellevue also reiterated the project was forecast to be the lowest carbon emitter per ounce of ASX-listed gold producers with a forecast range of 0.15t-0.20t of carbon dioxide equivalent per ounce.