South Africa-based gold producer AngloGold Ashanti plans to boost gold output in Guinea by investing over $400 million in the next eight years, according to an agreement reached this week with the West African country.

Guinea is a significant producer of bauxite and iron ore and is also seeking to expand its gold production. This latest deal with AngloGold extends another agreement that had been set to expire in 2019.

"Initially, they will invest $117 million and they will add an additional $294 million during this period," a senior official at the ministry of mines told Reuters on condition of anonymity.

"Older areas are depleted. They promised to change the operating method by going deeper, instead of being confined to the surface," the source said.

AngloGold Ashanti's operations are at the Siguiri mine in the east of Guinea. Its affiliate Societe Aurifere de Guinee produces about 300,000 ounces of gold each year.

This new deal is expected to maintain output and fund new exploration in the area.