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Note 8 - Stockholders' Equity (Tables) | 3 Months Ended
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Mar. 31, 2018
Notes Tables |
Schedule of Potential Per Share Dividend Amounts Quarterly Price Levels [Table Text Block] |
Quarterly average realized silver price per ounce |  |  | Quarterly dividend per share |  |  | Annualized dividend per share |
| $30 |  |  |  | $0.01 |  |  |  | $0.04 |
| $35 |  |  |  | $0.02 |  |  |  | $0.08 |
| $40 |  |  |  | $0.03 |  |  |  | $0.12 |
| $45 |  |  |  | $0.04 |  |  |  | $0.16 |
| $50 |  |  |  | $0.05 |  |  |  | $0.20 |

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- References No definition available. + Details
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