Obuasi, set in the Ashanti region of southern Ghana, is undergoing a redevelopment project to create a more modern, mechanised operation.
It has been under care and maintenance since 2016, and the new project is expected to produce first gold by the end of this year.
Veolia, which designs and provides water, waste and energy management solutions, has been attached to the project for a three-year period.
Under the new contract, Veolia Ghana, 70% owned by Veolia Africa and 30% by West African Surface Solutions Ghana, will be responsible for operating and maintaining six water-treatment facilities - four waste-water treatment and two drinking water treatment plants - for the Obuasi open-cut and underground mines.
The Ghanaian operation has to manage its waste water and process residue in order to comply with the local Environmental Protection Agency's requirements for discharge into the ecosystem.
Veolia said the water-intensive mining sector is one of its major growth areas, adding that it was "working hand-in-hand with players in the industry to find solutions to the challenges they face in Africa", and elsewhere in the world.
Christophe Maquet, director of Veolia's Africa and Middle East zone, said the new contract highlights the company's "operational expertise in water and discharge treatment".
"By optimising the process water treatment for the Obuasi gold mine, we have an opportunity to improve the productivity of this crucial operation," he added.