I recommend reviewing this thread when taking into consideration the above.
It is possible to effectively mint a coin if a group has a decided upon quality to go for for their minimum coin denomination. Silver and gold do not carry a quality, so Steel, Wrought Iron, Iron, Bronze, Copper and Tin coins will need to be what's decided upon as the smallest denomination in addition to its quality.
The thread I gave a link to suggest Steel coins Q<17.
Through Quality of fuel manipulation, and the Kiln and of the rest of the metallurgic process you're then creating a specialized system for the said group's mint.