Newmont gave the go-ahead to the US$186 million underground project last year, which is expected to add between 150,000-200,000 ounces per annum for the first five years of its initial 10-year life.

Ahafo began commercial production in 2006 and is this year expected to produce 435,000-465,000oz at a consolidated all-in sustaining cost of $900-$980/oz.

Combined with the Ahafo mill expansion expected in the second half of 2019, Newmont said Subika would help improve Ahafo's average AISC by $250-$350/oz compared with 2016.

In 2016, Ahafo produced 349,000oz at an AISC of $1,152/oz sold.

"In addition to increasing gold production and lowering costs at Ahafo, Subika Underground leverages the operation's existing infrastructure and experienced workforce to further extend mine life," CEO Gary Goldberg said.

As the company's newest mine, Subika Underground features semi-autonomous loading operations, proximity detection for vehicles, personnel tracking, and planned installation of ventilation-on-demand systems, Newmont said.

It said it represented Newmont's third profitable expansion in 2018 and was one of its 10 new mines and expansions on four continents, completed on or ahead of schedule and at or below budget, since 2013.

Newmont traded above $33 briefly yesterday before closing up 1c in New York to $32.47, capitalising it close to $17.3 billion.