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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue, fixed assets (Details)
3 Months Ended
Apr. 30, 2019
USD ($)
item
MT
Apr. 30, 2018
USD ($)
Jan. 31, 2019
USD ($)
Revenue from Contract with Customer [Abstract]      
Royalty Revenue $ 5,361,790 $ 6,646,670  
Base overriding royalties, first tier portion percentage 90.00%    
Base overriding royalties, first tier shipment ceiling (in million tons) | MT 4    
Base overriding royalties, second tier portion percentage 85.00%    
Base overriding royalties, second tier shipment ceiling (in million tons) | MT 2    
Base overriding royalties, third tier portion percentage 25.00%    
Base overriding royalties, third tier shipment threshold (in million tons) | MT 6    
Base overriding royalties, number of volume thresholds for transaction price | item 4    
Base overriding royalties, volume threshold for transaction price | MT 1    
Accrued income receivable $ 3,377,580   $ 2,339,060
Contract asset 1,294,804   $ 56,357
Base Overriding Royalties      
Revenue from Contract with Customer [Abstract]      
Royalty Revenue 3,068,019 3,857,485  
Bonus Royalties      
Revenue from Contract with Customer [Abstract]      
Royalty Revenue 2,106,957 2,634,231  
Fee Royalties      
Revenue from Contract with Customer [Abstract]      
Royalty Revenue $ 186,814 $ 154,954