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Derivative financial instruments (Details 1)
 12 Months Ended
Dec. 31, 2017
USD ($)
DMT
Dec. 31, 2016
USD ($)
DMT
Disclosure of derivative financial instruments [Line Items]    
Current derivative financial liabilities $ 0 $ 1,524,000
Copper [Member]    
Disclosure of derivative financial instruments [Line Items]    
Quantity of Metal | DMT 24,846 29,121
Period of quotations January – March January - April
Current derivative financial liabilities $ 2,508,000 $ 397,000
Gold [Member]    
Disclosure of derivative financial instruments [Line Items]    
Quantity of Metal | DMT 64,898 15,370
Period of quotations January – March January – February
Current derivative financial liabilities $ 1,066,000 $ 481,000
Silver [Member]    
Disclosure of derivative financial instruments [Line Items]    
Period of quotations January – April January - April
Current derivative financial liabilities $ 1,815,000 $ (1,825,000)
Lead [Member]    
Disclosure of derivative financial instruments [Line Items]    
Quantity of Metal 22,735 23,636
Period of quotations January – April January - April
Current derivative financial liabilities $ 229,000 $ (801,000)
Zinc [Member]    
Disclosure of derivative financial instruments [Line Items]    
Quantity of Metal | DMT 54,603 29,407
Period of quotations January – April January – March
Current derivative financial liabilities $ 1,806,000 $ (172,000)
Bottom of range [member] | Copper [Member]    
Disclosure of derivative financial instruments [Line Items]    
Provisional quotation 6,645.36 2,985.28
Future quotation 7,112,500 5,535,760
Bottom of range [member] | Gold [Member]    
Disclosure of derivative financial instruments [Line Items]    
Provisional quotation 1,256.45 1,139.75
Future quotation 1,258,000 1,151,000
Bottom of range [member] | Silver [Member]    
Disclosure of derivative financial instruments [Line Items]    
Provisional quotation 16.02 16.32
Future quotation 16,070 16,420
Bottom of range [member] | Lead [Member]    
Disclosure of derivative financial instruments [Line Items]    
Provisional quotation 2,333.23 1,871.58
Future quotation 2,488,000 2,017,000
Bottom of range [member] | Zinc [Member]    
Disclosure of derivative financial instruments [Line Items]    
Provisional quotation 3,103.72 2,291.08
Future quotation 3,226,500 2,578,000
Top of range [member] | Copper [Member]    
Disclosure of derivative financial instruments [Line Items]    
Provisional quotation 6,841.95 5,824.00
Future quotation 7,275,000 5,642,250
Top of range [member] | Gold [Member]    
Disclosure of derivative financial instruments [Line Items]    
Provisional quotation 1,317.67 1,145.90
Future quotation 1,317,100 1,179,400
Top of range [member] | Silver [Member]    
Disclosure of derivative financial instruments [Line Items]    
Provisional quotation 18.00 19.35
Future quotation 17,210 16,660
Top of range [member] | Lead [Member]    
Disclosure of derivative financial instruments [Line Items]    
Provisional quotation 3,110.69 2,380.60
Future quotation 2,579,750 2,080,000
Top of range [member] | Zinc [Member]    
Disclosure of derivative financial instruments [Line Items]    
Provisional quotation 3,275.47 2,732.10
Future quotation $ 3,343,500 $ 2,612,500