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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, 2020 oz lb $ / oz $ / lb | Dec. 31, 2019 oz lb $ / oz $ / lb
Silver 2020 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz | 910 | 2,556
Average price per ounce/pound (in USD per Ounce) | $ / oz | 23.53 | 17.20
Gold 2020 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz | 2 | 10
Average price per ounce/pound (in USD per Ounce) | $ / oz | 1,948 | 1,481
Zinc 2020 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 23,975 | 21,550
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.02 | 1.04
Lead 2020 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 5,512 | 5,159
Average price per ounce/pound (in USD per Ounce) | $ / lb | 0.84 | 0.88
Zinc 2020 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 827 | 441
Average price per ounce/pound (in USD per Ounce) | $ / lb | 0.94 | 1.13
Lead 2020 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 8,543 | 11,740
Average price per ounce/pound (in USD per Ounce) | $ / lb | 0.81 | 0.98
Silver 2021 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz | 0 |
Gold 2021 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz | 0 |
Zinc 2021 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 6,945 |
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.12 |
Lead 2021 Settlements for Provisional Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 0 |
Silver 2020 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz | 0 |
Gold 2020 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz | 0 |
Silver 2021 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz | 0 |
Gold 2021 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | oz | 0 |
Zinc 2021 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 27,448 |
Average price per ounce/pound (in USD per Ounce) | $ / lb | 1.06 |
Lead 2021 Settlements for Forecasted Sales [Member] |  |
Ounces/pounds under contract (Ounce) | lb | 12,136 |
Average price per ounce/pound (in USD per Ounce) | $ / lb | 0.86 |

X
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