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ASSET RETIREMENT OBLIGATION: (Details)
$ in Millions
1 Months Ended 9 Months Ended
Jun. 24, 2019
Apr. 30, 2024
USD ($)
Sep. 30, 2024
USD ($)
item
Sep. 30, 2023
USD ($)
Jan. 31, 2024
USD ($)
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         $ 87.7
Asset retirement obligation activity          
Balance at the beginning of the year     $ 612.5 $ 585.3  
Changes in estimates     (12.3)    
Closure payments       (0.3)  
Accretion expense     21.3 19.3  
Balance at the end of the year     $ 621.6 $ 604.3  
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    
Change in asset retirement liability   $ (3.2)      
Mexico          
ASSET RETIREMENT OBLIGATION:          
Change in asset retirement liability     $ (9.1)