My games are heavily influenced by harn. One aspect of Harn I adopted was the coinage system. The reason for this is that it gave gold back it's place of pride. The finding of a cache of gold coins returned to be a momentous event.
The trick is that everything is silver based. The average coin a NPC or player sees is the silver penny struck at 256 pennies per pound of silver. For convenience we will just say that 250d (d for denarius or a roman silver penny) equal 1 pound for encumberance
Gold coins are typically struck in Crowns weighing in at 1 oz or 16 per pound of gold. 320 silver pennies equal a gold crown. 16 pennies per 1 oz of metal times 20 the historical ratio of the value of gold to silver.
Lesser used coins are gold pennies which weigh the same as a silver penny and are valued at 20d to one gold penny.
More common are silver marks which are silver bars with a mint or maker's mark worth 240d. They weigh nearly 1 lb.
There are farthings which are worth 1/4 penny each. If found in coin form they are a copper however most of the time they are really quarter bit of a penny. Most pennies are minted with lines to allow them to be easily broken up into farthings.