Rio Tinto invests $341M in Arizona copper studies

　　DENVER - Shares of Rio Tinto PLC slid Monday after the British mining company said it would invest $341 million to support ongoing pre-feasibility studies on a major copper deposit in Superior, Ariz. 　　London-based Rio Tinto said it expects the studies of the deposit at Resolution Copper Mining LLC operations to be completed by 2012. It hopes to start production by 2020 and gradually increase it to about 560,000 U.S. tons of copper per year. 　　Rio Tinto, which owns 55 percent of the deposit, said its partner will help finance the studies, putting the overall cost at $652 million. BHP Copper Inc., a BHP-Billiton plc subsidiary, owns the remaining 45 percent. 　　Copper prices have shot up in the last few years, due to rising demand from the world's quickly developing emerging markets. 　　Last year, Rio Tinto generated $3.5 billion in copper sales - making the metal the company's biggest earner. 　　Shares of Rio Tinto fell $22.46, or 5.7 percent, to $372.06 Monday.