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Share-based payment arrangements - Summary of assumptions ised to estimate the fair value of options granted (Details)
12 Months Ended
Dec. 31, 2020
CAD ($)
$ / oz
Dec. 31, 2019
CAD ($)
$ / oz
Disclosure of range of exercise prices of outstanding share options [line items]    
Expected dividends | $ $ 0 $ 0
Bottom of range    
Disclosure of range of exercise prices of outstanding share options [line items]    
Risk-free interest rate 0.25% 1.34%
Expected volatility (range) 63.00% 59.00%
Expected life (range) 1.96 1.98
Top of range    
Disclosure of range of exercise prices of outstanding share options [line items]    
Risk-free interest rate 0.95% 1.80%
Expected volatility (range) 70.00% 63.00%
Expected life (range) 3.96 3.98