SYDNEY -- BHP Billiton ( BHP), the world's biggest mining company, said Wednesday it plans to return $10 billion to its shareholders after soaring iron ore and copper prices helped its first-half net profit jump 71.5%. The Melbourne-based mining giant said in a statement it was more than doubling its share buyback from the $4.2 billion it announced in November. BHP said it plans to complete the initiative by the end of 2011. BHP's net profit for the six months ended Dec. 31 was $10.52 billion, up from $6.14 billion a year earlier, it said in a statement. Revenue was up 39% to $34.17 billion from $24.58 billion. The company credited its boost in profit to strong demand from emerging markets, such as China, and tight supply for its key commodities, which pushed prices higher. Tough weather conditions in many producing countries, such as Australia -- which has experienced record flooding in recent months -- cut into supplies of coal, iron ore and copper. The company said it was "cautiously optimistic" about the short-term outlook for the global economy. "While we expect a slowdown in the growth rate of global commodity demand in calendar year 2011, the economic environment still underpins a robust near term outlook for our products," the company said in a statement. BHP declared an interim dividend of 46 cents a share, up from 42 cents in the prior corresponding period. Rival Rio Tinto ( RIO)announced its own massive stock buyback last week. The Anglo-Australian miner said it planned to buy back $5 billion of its shares by the end of 2012.