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Goodwill (Tables)
12 Months Ended
Dec. 31, 2018
Changes in goodwill [abstract]  
Summary of Key Assumptions Used for Assessing the Recoverable Amount of Goodwill
 
 
2018
 
 
 
Gold price ($/oz)
 
$1,275 - $1,300

Discount rate
 
5
%
Conversion factor of resources and exploration potential to proven and probable reserves
 
21
%
Fair value per ounce of resources and exploration potential beyond proven and probable reserves
 

$140