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STOCK-BASED COMPENSATION (Details) (USD $) In Millions, except Per Share data, unless otherwise specified |  | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended
--- | --- | --- | --- | --- | ---
Jan. 19, 2012 | Sep. 30, 2012 Stock Options | Sep. 30, 2011 Stock Options | Sep. 30, 2012 Stock Options Oz | Sep. 30, 2011 Stock Options Oz | Sep. 30, 2012 Minera Andes Stock Options | Sep. 30, 2012 Minera Andes Stock Options | Sep. 30, 2012 Chief Operating Officer | Sep. 30, 2011 Certain employees, directors and consultants
STOCK-BASED COMPENSATION |  |  |  |  |  |  |  |  |
Number of shares of common stock reserved for issuance before amendment | 9 |  |  |  |  |  |  |  |
Number of shares of common stock reserved for issuance | 13.5 |  |  |  |  |  |  |  |
Stock options granted (in shares) |  |  |  |  |  |  |  | 0.3 | 0.9
Exercise price of options granted (in dollars per share) |  |  |  |  |  |  |  | $ 5.80 | $ 7.10
Vesting period of options |  |  |  |  |  |  |  |  | 3 years
Exercise period of options |  |  |  |  |  |  |  |  | 10 years
Stock option expense |  | $ 0.7 | $ 0.7 | $ 2.8 | $ 1.9 | $ 0.1 | $ 1.1 |  |
Principal assumptions used in applying the Black-Scholes option pricing model for the awards |  |  |  |  |  |  |  |  |
Risk-free interest rate (as a percent) |  |  |  | 0.97% |  |  |  |  |
Risk-free interest rate, low end of range (as a percent) |  |  |  |  | 1.82% |  |  |  |
Risk-free interest rate, high end of range (as a percent) |  |  |  |  | 2.33% |  |  |  |
Volatility factor of the expected market price of common stock (as a percent) |  |  |  | 75.00% |  |  |  |  |
Volatility factor of the expected market price of common stock, low end of range (as a percent) |  |  |  |  | 90.00% |  |  |  |
Volatility factor of the expected market price of common stock, high end of range (as a percent) |  |  |  |  | 100.00% |  |  |  |
Weighted-average expected life of option |  |  |  | 6 years | 6 years 7 months 6 days |  |  |  |
Weighted-average grant date fair value (in dollars per share) |  |  |  | 3.80 | 4.97 |  |  |  |

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph g(1) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 64 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=6793087&loc=d3e301413-122809 + Details
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- Definition Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.D.2) -URI http://asc.fasb.org/extlink&oid=6793087&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section D -Subsection 2 + Details
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- Definition The estimated measure of the 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 Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph e(2)(b) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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