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Significant accounting principles and policies (Details Textual)
Dec. 31, 2017
Dec. 31, 2016
Written put options [member]    
DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory [Line Items]    
Closing foreign exchange rate 0.3082 0.2976
Purchased call options [member]    
DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory [Line Items]    
Closing foreign exchange rate 0.3088 0.2983
Sociedad Minera Cerro Verde S.A.A. [Member] | Written put options [member]    
DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory [Line Items]    
Closing foreign exchange rate 3.245 3.360
Sociedad Minera Cerro Verde S.A.A. [Member] | Purchased call options [member]    
DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory [Line Items]    
Closing foreign exchange rate 3.238 3.352