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BUSINESS ACQUISITION (Details) (Minera Andes, USD $) In Millions, except Share data, unless otherwise specified | 1 Months Ended | 9 Months Ended | 1 Months Ended | 9 Months Ended | 3 Months Ended |  | 1 Months Ended
--- | --- | --- | --- | --- | --- | --- | ---
Jan. 31, 2012 | Sep. 30, 2012 | Jan. 31, 2012 Replacement options | Sep. 30, 2012 Replacement options | Jun. 30, 2011 Robert R. McEwen | Sep. 30, 2012 Robert R. McEwen | Jan. 31, 2012 McEwen Mining
BUSINESS ACQUISITION |  |  |  |  |  |  |
Exchange ratio | 0.45 |  |  |  |  |  |
2012 Exchangeable Shares received by shareholders of acquiree | 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 |  |  |  |  |  | 25.10% |
Ratio for exchange of 2012 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) |  |  | 0.02% |  |  |  |
Risk-free interest rate, high end of range (as a percent) |  |  | 0.39% |  |  |  |
Volatility factor of the expected market price of common stock, low end of range (as a percent) |  |  | 46.00% |  |  |  |
Volatility factor of the expected market price of common stock, high end of range (as a percent) |  |  | 77.00% |  |  |  |
Weighted-average expected life of option |  |  | 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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