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REVENUE - Provisional Copper and Gold Sales (Details)
ozt in Thousands, lb in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2019
USD ($)
$ / ounce
$ / pound
ozt
lb
Dec. 31, 2018
USD ($)
$ / pound
ozt
lb
Disclosure of Disaggregation of Revenue [Line Items]    
Percent change in commodity prices used for sensitivity analysis 10.00%  
Copper    
Disclosure of Disaggregation of Revenue [Line Items]    
Average price of hedging instrument | $ / pound 2.80 2.71
Volumes subject to final pricing Copper (millions) Gold (000s) | lb 39 51
Impact on net income before taxation of 10% movement in market price US$ $ 11 $ 14
Gold[member]    
Disclosure of Disaggregation of Revenue [Line Items]    
Average price of hedging instrument | $ / ounce 1,524  
Volumes subject to final pricing Copper (millions) Gold (000s) | ozt 15 0
Impact on net income before taxation of 10% movement in market price US$ $ 2 $ 0