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Mineral Property, Plant and Equipment (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2020 | Dec. 17, 2020
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | $ 2,933.4 |  |  |
Mineral property, plant and equipment | 2,933.4 |  | $ 3,101.3 |
Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | 4,138.0 | $ 3,846.4 |  |
Additions | 243.0 | 277.8 |  |
Revisions | 17.1 | 13.3 |  |
Disposals | (5.6) | (1.9) |  |
Transfers | 0.0 |  |  |
Mineral property, plant and equipment | 4,138.0 | 3,846.4 | 4,466.6 |
Accumulated depreciation, amortisation and impairment [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | (1,204.6) | (1,033.1) |  |
Amortization | 164.3 | 171.6 |  |
Disposals | (4.6) | (1.2) |  |
Mineral property, plant and equipment | (1,204.6) | (1,033.1) | (1,365.3) |
Right of Use Assets |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Revisions |  | 2.4 |  |
Amortization | 1.0 | 1.1 |  |
Plant and Equipment [Member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | 750.9 |  |  |
Mineral property, plant and equipment | 750.9 |  | 888.7 |
Plant and Equipment [Member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | 1,320.3 | 1,194.6 |  |
Additions | 94.1 | 125.2 |  |
Revisions | 0.0 | 0.0 |  |
Disposals | (5.6) | (1.9) |  |
Transfers | 121.2 |  |  |
Mineral property, plant and equipment | 1,320.3 | 1,194.6 | 1,530.0 |
Plant and Equipment [Member] | Accumulated depreciation, amortisation and impairment [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | (569.4) | (502.9) |  |
Amortization | 75.5 | 66.6 |  |
Disposals | (4.6) | (1.2) |  |
Mineral property, plant and equipment | (569.4) | (502.9) | (641.3) |
Plant and Equipment [Member] | Right of Use Assets |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Revisions |  | 2.4 |  |
Amortization | 1.0 | 1.1 |  |
Mineral Property - Depletable [Member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | 1,824.4 |  |  |
Mineral property, plant and equipment | 1,824.4 |  | 1,909.0 |
Mineral Property - Depletable [Member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | 2,450.8 | 2,305.6 |  |
Additions | 101.5 | 131.9 |  |
Revisions | 17.1 | 13.3 |  |
Disposals | 0.0 | 0.0 |  |
Transfers | 0.0 |  |  |
Mineral property, plant and equipment | 2,450.8 | 2,305.6 | 2,624.2 |
Mineral Property - Depletable [Member] | Accumulated depreciation, amortisation and impairment [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | (626.4) | (521.4) |  |
Amortization | 88.8 | 105.0 |  |
Disposals | 0.0 | 0.0 |  |
Mineral property, plant and equipment | (626.4) | (521.4) | (715.2) |
Mineral Property - Depletable [Member] | Right of Use Assets |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Revisions |  | 0.0 |  |
Amortization | 0.0 | 0.0 |  |
Mineral Property - Non-Depletable [Member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | 104.9 |  |  |
Mineral property, plant and equipment | 104.9 |  | 16.9 |
Mineral Property - Non-Depletable [Member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | 104.9 | 95.8 |  |
Additions | 33.2 | 9.1 |  |
Revisions | 0.0 | 0.0 |  |
Disposals | 0.0 | 0.0 |  |
Transfers | (121.2) |  |  |
Mineral property, plant and equipment | 104.9 | 95.8 | 16.9 |
Mineral Property - Non-Depletable [Member] | Accumulated depreciation, amortisation and impairment [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | 0.0 | 0.0 |  |
Amortization | 0.0 | 0.0 |  |
Disposals | 0.0 | 0.0 |  |
Mineral property, plant and equipment | 0.0 | 0.0 | 0.0 |
Mineral Property - Non-Depletable [Member] | Right of Use Assets |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Revisions |  | 0.0 |  |
Amortization | 0.0 | 0.0 |  |
Exploration and evaluation assets [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | 253.2 |  |  |
Mineral property, plant and equipment | 253.2 |  | 286.7 |
Exploration and evaluation assets [member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | 262.0 | 250.4 |  |
Additions | 14.2 | 11.6 |  |
Revisions | 0.0 | 0.0 |  |
Disposals | 0.0 | 0.0 |  |
Transfers | 0.0 |  |  |
Mineral property, plant and equipment | 262.0 | 250.4 | 295.5 |
Exploration and evaluation assets [member] | Accumulated depreciation, amortisation and impairment [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Property, plant and equipment | (8.8) | (8.8) |  |
Amortization | 0.0 | 0.0 |  |
Disposals | 0.0 | 0.0 |  |
Mineral property, plant and equipment | (8.8) | (8.8) | $ (8.8) |
Exploration and evaluation assets [member] | Right of Use Assets |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Revisions |  | 0.0 |  |
Amortization | 0.0 | $ 0.0 |  |
Trillium |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Mineral property, plant and equipment |  |  |  | $ 19.3
Trillium | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Additions | 19.3 |  |  |
Trillium | Plant and Equipment [Member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Additions | 0.0 |  |  |
Trillium | Mineral Property - Depletable [Member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Additions | 0.0 |  |  |
Trillium | Mineral Property - Non-Depletable [Member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Additions | 0.0 |  |  |
Trillium | Exploration and evaluation assets [member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Additions | 19.3 |  |  |
Island Gold [Member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Additions | 54.8 |  |  |
Island Gold [Member] | Plant and Equipment [Member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Additions | 0.0 |  |  |
Island Gold [Member] | Mineral Property - Depletable [Member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Additions | 54.8 |  |  |
Island Gold [Member] | Mineral Property - Non-Depletable [Member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Additions | 0.0 |  |  |
Island Gold [Member] | Exploration and evaluation assets [member] | Gross carrying amount [member] |  |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |  |
Additions | $ 0.0 |  |  |

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- Definition The amount of additions to property, plant and equipment other than those acquired through business combinations. [Refer: Business combinations [member]; Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2020-01-01 -Paragraph 73 -Subparagraph e -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2020-en-r&anchor=para_73_e_i&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The amount of depreciation of property, plant and equipment. [Refer: Depreciation and amortisation expense; Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2020-01-01 -Paragraph 73 -Subparagraph e -Clause vii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2020-en-r&anchor=para_73_e_vii&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2020-01-01 -Paragraph 75 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2020-en-r&anchor=para_75_a&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The increase (decrease) in property, plant and equipment resulting from transfers. [Refer: Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 16 -IssueDate 2020-01-01 -Paragraph 73 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2020-en-r&anchor=para_73_e&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The amount of tangible assets that: (a) are held for use in the production or supply of goods or services, for rental to others, or for administrative purposes; and (b) are expected to be used during more than one period. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2020-01-01 -Paragraph 73 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2020-en-r&anchor=para_73_e&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 54 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_54_a&doctype=Standard -URIDate 2020-01-01 + Details
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