The extension and infrastructure projects exceed Sibanye's 15 percent hurdle rate after tax and inflation and have internal rates of return of 20 to 30 percent. Read also: Sibanye expects leap in earnings to June Sibanye shares have more than doubled this year and climbed 5.9 percent to a record R67.67 at 9:23 a.m. in Johannesburg. The twin boost of higher gold prices and a weaker rand, in which it pays costs, have helped widen profit margins and turn the producer's aging, previously high-cost operations into mines that are on course to generate 10 billion rand of free cash flow this year.