The approval will set in progress the engineering and procurement of long-lead time items for the sulphide project at Copler, which will add an additional 22 years of production time to overall operations at the mine.

It follows the release of a feasibility update into the expansion project last month, and will bring life-of-mine gold production at Copler to 3.9 million ounces at all-in sustaining costs of $US637 per ounce.

The company intends to transition from oxide to sulphur production over time at Copler, with sulphide ore production scheduled to commence in late 2017.

Alacer president and chief executive Rod Antal said the board approval was a big step for the sulphide project.

"The board's decision to approve the advancement of the sulphide project represents a significant milestone for both the Copler gold mine and Alacer," he said.

"We remain focused on further de-risking the sulphide project and I am confident that we have the resources and expertise in place to advance the project into the execution phase."

Land permits required to begin construction on the project have progressed through the regulatory process and are currently awaiting final approval, while the environmental impact assessment has been approved.

The projected Copler mine life extends to 2039.

Last month, the company announced it had improved is gold recovery model to allow metallurgical recovery rates of 72%, resulting in a 36% increase to oxide reserves and a 21% increase to sulphide reserves on an all-recoverable ounce basis.

Total probable mineral reserves at Copler across oxide and sulphide operations measure 65.2 million tonnes at 2.1 grams per tonne for 4.3 million ounces.

Oxide reserves account for 21Mt at 1.2gpt for 999,000oz, while sulphide reserves cover 40.2Mt at 2.6gpt for 3.3Moz.

Alacer owns an 80% share in Copler.

Shares in Alacer closed at $A2.89 yesterday.