Coin minting should not be a 1:1 ratio by default.
Incentivize using better metals.
Lesser metal should give lesser yields, with only precious metals being 1:1 if any at all.
Example:
1 lead bar = 60 coins
1 tin bar = 60 coins
1 copper bar = 65 coins
1 bronze bar = 75 coins
1 iron bar = 75 coins
1 wrought iron bar = 80-85 coins
1 steel bar = 90 coins
1 gold/silver/rosegold/meteor bar = 95-100 coins