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v3.21.1

Accounting policies - Summary of Key assumptions used in the Income and Market Approach (Detail) | 12 Months Ended |  |  |
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Dec. 31, 2020 $ / per_oz | Dec. 31, 2019 $ / per_oz | Dec. 31, 2020 $ / oz | Dec. 31, 2019 $ / oz | Dec. 31, 2018 $ / per_oz
Disclosure of Detailed Information of Key Assumptions Used in the Income and Market Approach Explanatory [line items] |  |  |  |  |
Resource value per ounce (with infrastructure) | $ / per_oz | 76 | 70 |  |  |
Discount rates - real | 8.40% | 8.50% |  |  |
Life of mine | 7 years | 10 years |  |  |
US Dollars [member] | Year 4 [member] |  |  |  |  |
Disclosure of Detailed Information of Key Assumptions Used in the Income and Market Approach Explanatory [line items] |  |  |  |  |
Gold price | 1,500 | 1,350 | 1,500 | 1,350 | 1,300
US Dollars [member] | Year 1 To 3 [member] | Bottom of range [member] |  |  |  |  |
Disclosure of Detailed Information of Key Assumptions Used in the Income and Market Approach Explanatory [line items] |  |  |  |  |
Gold price |  |  | 1,600 | 1,400 |
US Dollars [member] | Year 1 To 3 [member] | Top of range [member] |  |  |  |  |
Disclosure of Detailed Information of Key Assumptions Used in the Income and Market Approach Explanatory [line items] |  |  |  |  |
Gold price |  |  | 1,800 | 1,500 |

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