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MINERAL PROPERTY INTERESTS AND ASSET RETIREMENT OBLIGATIONS (Details) (USD $)
 3 Months Ended 9 Months Ended 12 Months Ended 9 Months Ended 9 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Dec. 31, 2011
Sep. 30, 2012
Gold
item
Sep. 30, 2012
Tonkin Complex
Sep. 30, 2012
Gold Bar Complex
Sep. 30, 2012
Limo Complex
Sep. 30, 2012
Battle Mountain Complex
Sep. 30, 2012
Other United States Properties
item
Dec. 31, 2007
Other United States Properties
Sep. 30, 2012
Los Azules Copper Project
Sep. 30, 2012
Other Argentina exploration properties in San Juan, Argentina
Sep. 30, 2012
Cerro Negro Region
Sep. 30, 2012
Other Argentina exploration properties in Santa Cruz, Argentina
Sep. 30, 2012
Other Argentina exploration properties in Catamarca, Argentina
Sep. 30, 2012
Other Argentina exploration properties in Chubut, Argentina
Sep. 30, 2012
El Gallo Complex
Sep. 30, 2012
Other Mexico Exploration Properties in Sinaloa, Mexico
Sep. 30, 2012
Tonkin property and Magistral mine portion of the El Gallo Complex
item
Sep. 30, 2012
Minera Andes
Jan. 24, 2012
Minera Andes
MINERAL PROPERTY INTERESTS                                              
Quantity produced (in ounces)           298                                  
Number of claims allowed from Nevada properties                     3                        
Reduction in the deferred tax liability and recovery of future income taxes                     $ 1,000,000                        
Property written-off                     1,900,000                        
Total 785,278,000   785,278,000   245,454,000   52,204,000 77,012,000 50,098,000 31,106,000 19,107,000 2,900,000 431,190,000 7,819,000 80,889,000 19,194,000 2,362,000 248,000 9,469,000 4,580,000      
Mineral property interests                                             541,702,000
Increase in mineral property interests since acquisition     539,800,000                                     541,700,000  
Number of most significant properties subject to reclamation obligations                                         2    
Undiscounted estimated reclamation costs             3,000,000                       4,600,000        
Cash bonding for mineral properties in the United States 5,190,000   5,190,000   5,190,000                                    
Changes in the asset retirement obligations                                              
Asset retirement obligation liability - opening balance     6,253,000 6,153,000 6,153,000                                    
Settlements     (24,000)   (82,000)                                    
Accretion of liability 110,000 134,000 342,000 400,000 524,000                                    
Adjustment reflecting updated estimates     (79,000)   (342,000)                                    
Asset retirement obligation liability - ending balance 6,492,000   6,492,000   6,253,000                                    
Current portion of the asset retirement obligation $ 323,000   $ 323,000   $ 512,000