The Hyesan Mine , located in Masan - dong , Hyesan - si , and Ryanggang - do , has been in operation since 1970 .
Is the largest copper mine in the country .
The Hyesan Mine , located in Masan - dong , Hyesan - si , and Ryanggang - do , has been in operation since 1970 and is the largest copper mine in the country .