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Inventories
 12 Months Ended
Dec. 31, 2017
Classes of current inventories [abstract]  
Inventories
7.   Inventories
 
  
December 31,
    
December 31,
  
 
  
2017
    
2016
  
 
            
Concentrates
  
$
1,391
    
$
1,266
  
Ore stockpiles
    
2,877
      
161
  
Spare parts and supplies
    
5,098
      
5,191
  
 
  
$
9,366
    
$
6,618
  

The amount of inventories recognized as an expense during the year ended December 31, 2017 was $40.0 million (2016: $46.1 million). During the year ended December 31, 2017, the concentrates and ore stockpiles, and spare parts and supplies write-down to net realizable value included in cost of sales was $0.4 million and $0.3 million, respectively (2016: $1.0 million and $0.1 million, respectively).