| In millions, except per share items | Dec-31-22 | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Revenue: | | | | | | | | |
| Sale of metals (Note 17) | 23.3 | 25.6 | 5.6 | 7.7 | 7.2 | 6.7 | 6.4 | 8.1 |
| Sale of metals (Note 17) growth | -9.0% | 354.1% | -27.1% | 7.1% | 7.9% | 4.5% | -20.7% | 3334.5% |
| Total revenue | 23.3 | 25.6 | 5.6 | 7.7 | 7.2 | 6.7 | 6.4 | 8.1 |
| Total revenue growth | -9.0% | 354.1% | -27.1% | 7.1% | 7.9% | 4.5% | -20.7% | 3334.5% |
| Costs and expenses: | | | | | | | | |
| Cost of metals sold (exclusive of depreciation shown below) (Note 17) | -17.5 | -13.3 | | | | | | |
| Exploration expense | -9.6 | -5.3 | -5.0 | -4.1 | -3.9 | -3.1 | -3.7 | -3.6 |
| El Quevar project expense | -0.6 | -0.3 | -0.6 | -2.0 | -1.3 | -0.8 | -0.5 | |
| Administrative expense | 4.5 | 4.8 | 3.7 | 3.6 | 3.4 | 3.5 | 3.9 | 4.2 |
| Stock-based compensation | -0.7 | -1.6 | -0.9 | -0.8 | -0.2 | -0.3 | -0.6 | -0.5 |
| Reclamation expense | -0.3 | -0.3 | -0.2 | -0.2 | -0.2 | | | |
| Other operating income, net | 1.6 | 0.5 | 0.0 | 3.2 | 5.1 | 2.1 | 1.8 | -0.5 |
| Depreciation and amortization | 0.4 | 0.6 | 1.0 | 1.1 | 1.2 | 1.0 | 1.5 | 4.5 |
| Total costs and expenses | 33.4 | 27.1 | 14.4 | 12.8 | 9.2 | 10.6 | 12.7 | 38.2 |
| Loss from operations | -10.1 | -1.5 | -8.8 | -5.0 | -2.0 | -3.9 | -6.3 | -30.2 |
| Operating margin | -43.6% | -5.7% | -156.1% | -65.3% | -27.2% | -57.7% | -98.8% | -373.7% |
| |
| Other income (expense): | | | | | | | | |
| Interest and other income (expense), net (Note 18) | | | -0.1 | -0.2 | 0.1 | 0.1 | | |
| Gain on foreign currency transactions | 0.3 | 0.2 | -0.1 | -0.1 | -0.1 | -0.1 | -0.1 | -0.1 |
| Total other income (expense) | 0.7 | 0.0 | -0.2 | -0.3 | -0.1 | -0.1 | -4.3 | 4.8 |
| Loss from operations before income taxes | -9.8 | -1.6 | -9.0 | -5.4 | -1.9 | -3.9 | -10.7 | -25.4 |
| Income taxes (Note 15) | -0.1 | -0.5 | 0.0 | 0.0 | 0.0 | 0.0 | | |
| Net loss | -9.9 | -2.1 | -9.1 | -5.4 | -1.9 | -3.9 | -10.7 | |
| |
| Net loss per common share - basic | | | | | | | | |
| Net loss per common share - basic | ($0.06) | ($0.01) | ($0.07) | ($0.05) | ($0.02) | ($0.04) | ($0.13) | ($0.48) |
| |
| Weighted-average shares outstanding - basic | 165.5 | 161.9 | 131.8 | 101.1 | 94.0 | 90.5 | 81.7 | 53.0 |