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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 |
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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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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