The Collaborative International Dictionary of English v.0.48:

Free coinage \Free coinage\
   In the fullest sense, the conversion of bullion (of any
   specified metal) into legal-tender coins for any person who
   chooses to bring it to the mint; in a modified sense, such
   coinage when done at a fixed charge proportionate to the cost
   of the operation.
   [Webster 1913 Suppl.]