Gold coins pretty much disappeared from Western Europe in the early middles ages, the Byzantine Empire and the the Islamic states were pretty much the only significant source of gold for a time so that makes sense in a way.

Interestingly enough the first coins minted in the Islamic Caliphate and based on the Roman Solidus actually had portraits (they just removed the Christian symbols) on them for a while:

https://en.wikipedia.org/wiki/File:First_Umayyad_gold_dinar,...