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ASSET RETIREMENT OBLIGATION: (Details)
$ in Millions
1 Months Ended 3 Months Ended 12 Months Ended
Jun. 24, 2019
Jan. 31, 2022
USD ($)
Mar. 31, 2022
USD ($)
item
Mar. 31, 2021
USD ($)
Dec. 31, 2019
USD ($)
ASSET RETIREMENT OBLIGATION:          
Maximum annual guarantees secured 50.00%        
Percentage of guarantee for Lima complex     50.00%    
Percentage of security for LOC     50.00%    
Total guarantees   $ 66.3      
Asset retirement obligation activity          
Balance at the beginning of the year   562.9 $ 562.9 $ 545.0  
Changes in estimates     43.3    
Closure Payments     (2.0) (0.2)  
Accretion expense     6.5 6.1  
Balance at the end of the year     $ 610.7 $ 550.9  
Peru          
ASSET RETIREMENT OBLIGATION:          
Period after which successive reviews are required by the law (in years)     5 years    
Number of units with future closure costs recognized as an asset retirement obligation | item     3    
Asset retirement obligation activity          
Changes in estimates         $ 28.1
Mexico          
Asset retirement obligation activity          
Changes in estimates   $ 43.3