South Africa's Harmony Gold has entered into foreign exchange hedging contracts to the value of $400 million, a third of its projected gold sales this year, it said on Tuesday.

Harmony, which produces most of its bullion in South Africa, has seen earnings climb as the rand currency weakened more than 16 percent over the past four months.

The hedging contracts are spread over 12 months with an average floor price of 15.59 rand per dollar and an average cap price of 18.60 rand, the company said.

"The weakness in and volatility of the rand presented an opportunity to Harmony to establish a very attractive minimum exchange rate on the US dollars we receive when we sell our gold, while leaving our shareholders fully exposed to the upside in the US$ gold price," the company said.