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Financial Instruments - Summary of Assets and Liabilities Measured at Fair Value by Level within Fair Value Hierarchy (Detail) - USD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Disclosure of fair value measurement of assets and liability [line items]      
Environmental trust funds $ 109.6 $ 98.8 $ 88.1
Windfall Project – contingent and exploration considerations 245.4 0.0  
Borrowings 1,236.5 1,079.3  
Financial liabilities measured at fair value | C$300.0 million contingent consideration – initial fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Windfall Project – contingent and exploration considerations 202.5 0.0  
Financial liabilities not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Borrowings 1,249.9 1,089.6  
Investments – listed | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Investments – listed 65.7 34.5  
Environmental trust funds | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Environmental trust funds 0.0 2.9  
Environmental trust funds | Financial assets not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Environmental trust funds 109.6 95.9  
Trade receivables from provisional copper sales | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Trade receivables from provisional copper sales 18.2 29.6  
Asanko redeemable preference shares | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Asanko redeemable preference shares 99.7 60.3  
Loan advanced – contractor | Financial assets not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Loan advanced – contractor 0.0 23.4  
Level 1 | Financial liabilities measured at fair value | C$300.0 million contingent consideration – initial fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Windfall Project – contingent and exploration considerations 0.0 0.0  
Level 1 | Financial liabilities not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Borrowings 1,010.5 1,006.1  
Level 1 | Investments – listed | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Investments – listed 65.7 34.5  
Level 1 | Environmental trust funds | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Environmental trust funds 0.0 0.0  
Level 1 | Environmental trust funds | Financial assets not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Environmental trust funds 0.0 0.0  
Level 1 | Trade receivables from provisional copper sales | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Trade receivables from provisional copper sales 0.0 0.0  
Level 1 | Asanko redeemable preference shares | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Asanko redeemable preference shares 0.0 0.0  
Level 1 | Loan advanced – contractor | Financial assets not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Loan advanced – contractor 0.0  
Level 2 | Financial liabilities measured at fair value | C$300.0 million contingent consideration – initial fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Windfall Project – contingent and exploration considerations 0.0 0.0  
Level 2 | Financial liabilities not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Borrowings 0.0 0.0  
Level 2 | Investments – listed | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Investments – listed 0.0 0.0  
Level 2 | Environmental trust funds | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Environmental trust funds 0.0 2.9  
Level 2 | Environmental trust funds | Financial assets not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Environmental trust funds 109.6 95.9  
Level 2 | Trade receivables from provisional copper sales | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Trade receivables from provisional copper sales 18.2 29.6  
Level 2 | Asanko redeemable preference shares | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Asanko redeemable preference shares 0.0 0.0  
Level 2 | Loan advanced – contractor | Financial assets not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Loan advanced – contractor 0.0 0.0  
Level 3 | Financial liabilities measured at fair value | C$300.0 million contingent consideration – initial fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Windfall Project – contingent and exploration considerations 202.5 0.0  
Level 3 | Financial liabilities not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Borrowings 239.4 83.5  
Level 3 | Investments – listed | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Investments – listed 0.0 0.0  
Level 3 | Environmental trust funds | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Environmental trust funds 0.0 0.0  
Level 3 | Environmental trust funds | Financial assets not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Environmental trust funds 0.0 0.0  
Level 3 | Trade receivables from provisional copper sales | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Trade receivables from provisional copper sales 0.0 0.0  
Level 3 | Asanko redeemable preference shares | Financial assets measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Asanko redeemable preference shares 99.7 60.3  
Level 3 | Loan advanced – contractor | Financial assets not measured at fair value      
Disclosure of fair value measurement of assets and liability [line items]      
Loan advanced – contractor $ 0.0 $ 23.4