The minting of gold and silver coins was under the complete control of the Roman Emperor.  As the Roman Prefect in Judea, Pontius Pilate would only be allowed to mint bronze coins.  This had been true long before Pontius Pilate came on the scene. The previous Roman Prefects, as well as the earlier Herodian and Hasmonean rulers of Judea, could only mint bronze coins.

Even though Pontius Pilate had the authority to mint bronze coins he did so only three times, in the 16th, 17th and 18th years of his rule. He ruled from 26-36 AD so his coins are dated 29/30, 30/31 and 31/32 AD. Why did he mint coins only during these particular years?  It is not known.

The other mystery is where these coins were minted. There are two solid possibilities. The coins could have been minted in Jerusalem. There had been a mint established there previouly under the rule of Herod Archelaus.  Pontius Pilate could have reestablished that mint and used the resources already there or he could have established a mint at Caesarea, where for most of the year he lived and ruled from.