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REVENUE - Provisional Copper and Gold Sales (Details)
lb in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2018
USD ($)
lb
Dec. 31, 2017
USD ($)
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]    
Volumes subject to final pricing Copper (millions) Gold (000s) | lb 51 57
Impact on net income before taxation of 10% movement in market price US$ | $ $ 14 $ 19