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Significant accounting policies (Tables)
12 Months Ended
Dec. 31, 2017
Significant Accounting Policies Details Narrative  
Schedule of estimated useful lives

Depreciation of assets is determined using the straight-line method over the estimated useful lives of such assets as follows:

 

  Years
Buildings and other constructions:  
Administrative facilities Between 35 and 48
Main production structures Between 30 and 49
Minor production structures Between 20 and 35
Machinery and equipment:  
Mills and  horizontal furnaces Between 42 and 49
Vertical furnaces, crushers and grinders Between 23 and 36
Electricity facilities and other minors Between 12 and 35
Furniture and fixtures 10
Transportation units:  
Heavy units Between 11 and 21
Light units Between 8 and 11
Computer equipment 4
Tools Between 5 and 10