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Acquisition of Richmond Mines Ltd. (Schedule of Asset Acquisition) (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | --- | ---
Net assets acquired |  |  |
Cash and cash equivalents | $ 182.8 | $ 206.0 | $ 200.8
Equity securities | 22.8 | 7.8 |
Mineral property, plant and equipment | 2,933.4 | 2,813.3 |
Current liabilities | (127.3) | (131.9) |
Deferred tax liabilities | $ (513.7) | $ (491.5) |

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