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DERIVATIVE INSTRUMENTS (Details Textual)
 12 Months Ended
Dec. 31, 2018
$ / Ounce-oz
Oct. 31, 2017
lb
Disclosure of derivative instruments [Line Items]    
Strike price of put options at the time of purchasing | $ / Ounce-oz 1,230  
Strike price of call options at the time of selling | $ / Ounce-oz 1,300  
Purchased put options [Member]    
Disclosure of derivative instruments [Line Items]    
Strike price of copper price option contracts | lb   3.00
Written call options [Member]    
Disclosure of derivative instruments [Line Items]    
Strike price of copper price option contracts | lb   3.37