South African gold miner Gold Fields said on Thursday it had exercised an option to take a 40 percent stake in a gold-copper project in the Philippines, the next step in its strategy to diversify out of its home base.

Gold Fields, the world's fourth-largest bullion producer, said in a statement it had taken the stake after making a $110 million down payment this week and retained the option to acquire an additional 20 percent in the Far Southeast Project.

It acquired the 40 percent from Liberty Express Assets, a private holding company. The remaining 20 percent, if exercised, would be bought from Philippine-listed Lepanto Consolidated Mining.

The mine is in an existing camp near established infrastructure such as roads and power, a significant selling point at a time when miners are grappling with soaring costs.

South Africa's gold mines are the world's deepest and producers face a perfect cost storm from growing depths and rising power rates and wages, while uncertainty remains on the policy front as the ruling ANC considers steep tax hikes on the industry.

Other South African gold miners in southeast Asia include Gold Fields' smaller rival Harmony, which is investing heavily in its promising Wafi-Golpu project in Papua New Guinea.