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COMMITTMENTS AND CONTINGENCIES: (Details 4) (USD $)
 2 Months Ended 3 Months Ended 1 Months Ended 3 Months Ended 6 Months Ended
Dec. 31, 1997
Jan. 31, 2005
Minera Mexico, S.A. de C.V. (the "Transaction")
Oct. 31, 2010
Asarco LLC
American Mining Corporation ("AMC") merger transaction
Jun. 30, 2011
American Mining Corporation ("AMC") merger transaction
Oct. 31, 2010
American Mining Corporation ("AMC") merger transaction
Jun. 30, 2011
Peruvian operations.
Toquepala and Cuajone mines
Jun. 30, 2010
Peruvian operations.
Toquepala and Cuajone mines
Jun. 30, 2011
Peruvian operations.
Tia Maria
Litigation matter                
Number of purported class action derivative lawsuits filed   3 2   4      
Number of purported class action derivative lawsuits which are consolidated   3            
Number of consolidated purported class action derivative lawsuits   1            
Period of trial (in days)       4        
Other commitments:                
Percentage of royalty expense, low end of the range (as a percent)           1.00%    
Percentage of royalty expense, high end of the range (as a percent)           3.00%    
Royalty charge           $ 31,800,000 $ 27,600,000  
Period for which the first resolution of approval process is suspended (in days)               180
Term of power purchase agreement related to sale of power plant (in years) 20              
Total budget for the project               1,000,000,000
Number of new jobs generated in construction phase               4,000
Number of direct and indirect permanent jobs generated in construction phase               4,100
Estimated annual production of copper cathodes (in tons)               120,000
Amount invested in mine and leach equipment and required studies               $ 442,000,000