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Note 11 - Derivative Instruments - Summary of Forward Sales Contracts (Details) oz in Thousands, lb in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 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 | 1,399 | 1,295
Average price per ounce/pound (in USD per Ounce) | $ / oz | 17.18 | 16.29
Gold 2017 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz | 5 | 4
Average price per ounce/pound (in USD per Ounce) | $ / oz | 1,298 | 1,172
Zinc 2017 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 19,070 | 19,070
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.33 | 1.18
Lead 2017 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 2,535 | 7,441
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.07 | 0.97
Zinc 2018 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 2,370 |
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.38 |
Zinc 2017 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 441 | 35,384
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.23 | 1.19
Lead 2017 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 2,866 | 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 | 39,463 | 13,779
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.27 | 1.21
Lead 2018 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 17,968 | 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 | 14,330 |
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.3 |
Lead 2019 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 8,267 |
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.07 |
Silver 2020 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz |  |
Gold 2020 Settlements for Forecastedl Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz |  |
Zinc 2020 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 3,307 |
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.27 |
Lead 2020 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 2,205 |
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.07 |

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