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BUSINESS ACQUISITION (Details) (USD $) In Millions, except Share data, unless otherwise specified | 12 Months Ended | 0 Months Ended | 1 Months Ended | 12 Months Ended | 0 Months Ended | 12 Months Ended | 6 Months Ended |  | 0 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010 | Jan. 24, 2012 Minera Andes | Jan. 31, 2012 Minera Andes | Dec. 31, 2012 Minera Andes | Jan. 24, 2012 Minera Andes Replacement options | Dec. 31, 2012 Minera Andes Replacement options | Jun. 30, 2011 Minera Andes Robert R. McEwen | Dec. 31, 2012 Minera Andes Robert R. McEwen | Jan. 24, 2012 Minera Andes McEwen Mining
BUSINESS ACQUISITION |  |  |  |  |  |  |  |  |  |  |
Exchange ratio |  |  |  | 0.45 |  |  |  |  |  |  |
Exchangeable Shares received by shareholders of acquiree | 7,800,000 |  |  |  | 127,331,498 |  |  |  | 38,700,000 |  |
Shareholding of combined company (as a percent) |  |  |  | 48.00% |  |  |  |  |  |  | 52.00%
Shareholding of combined company on a diluted basis (as a percent) |  |  |  | 47.00% |  |  |  |  |  |  | 53.00%
Percentage of shares of the company owned |  |  |  |  |  |  |  |  |  | 25.00% |
Ratio for exchange of exchangeable shares |  |  |  |  |  | 1 |  |  |  |  |
Estimated fair value of the vested portion of the replacement options |  |  |  |  |  |  |  | $ 3.2 |  |  |
Principal assumptions used in applying the Black-Scholes option pricing model |  |  |  |  |  |  |  |  |  |  |
Risk-free interest rate, low end of range (as a percent) |  | 1.74% | 2.18% |  |  |  | 0.02% |  |  |  |
Risk-free interest rate, high end of range (as a percent) |  | 2.33% | 2.97% |  |  |  | 0.39% |  |  |  |
Volatility factor of the expected market price of common stock, low end of range (as a percent) |  | 90.00% | 87.00% |  |  |  | 46.00% |  |  |  |
Volatility factor of the expected market price of common stock, high end of range (as a percent) |  | 100.00% | 94.00% |  |  |  | 77.00% |  |  |  |
Weighted-average expected life of option | 6 years | 6 years 7 months 6 days | 6 years 4 months 24 days |  |  |  | 1 year 4 months 24 days |  |  |  |

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- Definition The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References No definition available. + Details
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