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Note 11 - Derivative Instruments - Summary of Forward Sales Contracts (Details) oz in Thousands, lb in Thousands | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2017 oz lb $ / oz $ / lb | Dec. 31, 2016 oz lb $ / oz $ / lb
Silver 2017 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz | 1,379 | 1,295
Average price per ounce/pound (in USD per Ounce) | $ / oz | 17.14 | 16.29
Gold 2017 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz | 7 | 4
Average price per ounce/pound (in USD per Ounce) | $ / oz | 1,259 | 1,172
Zinc 2017 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 15,873 | 19,070
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.21 | 1.18
Lead 2017 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 6,724 | 7,441
Average price per ounce/pound (in USD per Ounce) | $ / lb | 0.97 | 0.97
Zinc 2017 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 6,834 | 35,384
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.26 | 1.19
Lead 2017 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 6,504 | 17,637
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.05 | 1.03
Zinc 2018 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 28,329 | 13,779
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.23 | 1.21
Lead 2018 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 16,314 | 5,732
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.05 | 1.05
Zinc 2019 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 1,102 |
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.21 |
Lead 2019 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 1,102 |
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.06 |

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- Definition Specified interest rate, security price, commodity price, foreign exchange rate, index of prices or rates for a derivative contract measured in mass but not the derivative contract itself. + References No definition available. + Details
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