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Note 11. Derivative Instruments (Tables) | 3 Months Ended
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Mar. 31, 2012
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] |
March 31, 2012 |  | Metric tonnes under contract |  |  | Average price per pound |
|  | Zinc |  |  | Lead |  |  | Zinc |  |  | Lead |
Contracts on provisional sales |  |  |  |  |  |  |  |  |  |  |  |
2012 settlements |  |  | 6,250 |  |  |  | 1,300 |  |  | $ | 0.94 |  |  | $ | 0.96 |
Contracts on forecasted sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2012 settlements |  |  | 11,850 |  |  |  | 5,100 |  |  | $ | 1.12 |  |  | $ | 1.13 |
2013 settlements |  |  | 8,675 |  |  |  | 13,250 |  |  | $ | 1.13 |  |  | $ | 1.15 |
December 31, 2011 |  | Metric tonnes under contract |  |  | Average price per pound |
|  | Zinc |  |  | Lead |  |  | Zinc |  |  | Lead |
Contracts on provisional sales |  |  |  |  |  |  |  |  |  |  |  |
2012 settlements |  |  | 9,600 |  |  |  | 2,600 |  |  | $ | 0.86 |  |  | $ | 0.89 |
Contracts on forecasted sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2012 settlements |  |  | 20,500 |  |  |  | 15,900 |  |  | $ | 1.12 |  |  | $ | 1.12 |
2013 settlements |  |  | 8,275 |  |  |  | 11,150 |  |  | $ | 1.14 |  |  | $ | 1.17 |

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- Definition Tabular disclosure of the notional amounts of outstanding derivative positions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5579245-113959 + Details
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Namespace Prefix: | us-gaap_
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