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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)
 16 Months Ended 28 Months Ended 12 Months Ended
Dec. 31, 2013
Dec. 31, 2014
Dec. 31, 2014
El Gallo mine      
Stockpiles, Material on Leach Pads, In-process Inventory, Precious Metals Inventory and Materials and Supplies      
Cumulative metallurgical recovery rate for gold production (as a percent) 61.00%mux_PercentageOfCumulativeMetallurgicalRecoveryForGoldProduction
/ mux_MineralPropertyNameAxis
= mux_ElGalloComplexMember		 56.00%mux_PercentageOfCumulativeMetallurgicalRecoveryForGoldProduction
/ mux_MineralPropertyNameAxis
= mux_ElGalloComplexMember		  
Minimum      
Stockpiles, Material on Leach Pads, In-process Inventory, Precious Metals Inventory and Materials and Supplies      
Recovery percentage of leach pads of the recoverable ounces in the first year of leaching     50.00%mux_OreOnLeachPadsRecoveryPercentageOfRecoverableOuncesInFirstYearOfLeaching
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum      
Stockpiles, Material on Leach Pads, In-process Inventory, Precious Metals Inventory and Materials and Supplies      
Recovery percentage of leach pads of the recoverable ounces in the first year of leaching     95.00%mux_OreOnLeachPadsRecoveryPercentageOfRecoverableOuncesInFirstYearOfLeaching
/ us-gaap_RangeAxis
= us-gaap_MaximumMember