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Acquisition of Richmond Mines Ltd. (Schedule of Asset Acquisition) (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Net assets acquired |  |  |
Cash and cash equivalents | $ 220.5 | $ 182.8 | $ 206.0
Equity securities (note 15) | 43.7 | 22.8 |
Mineral property, plant and equipment | 3,101.3 | 2,933.4 |
Current liabilities | (146.9) | (127.3) |
Deferred tax liabilities | $ (559.9) | $ (513.7) |

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