I also like this idea returning to gold coins..
All Precious metals can be involved.
Unless they made the value of gold coins very, very high, they would not circulate. For example, were I running the monetary system of the USA, I might make a gold coin the size of the old (pre-1933) $10 gold piece (0.48 oz of actual gold, and some copper to harden the coin) worth, say, $1000 (vs. actual gold value of about $575 or so).
A silver coin the size of a US quarter I would have it worth some $15 perhaps. Or make it a little smaller and stamp "$10" on it.
Even doing the above (fiat value WAY above metal value) might still not be enough to prevent hoarding of such coins ("Gresham's Law": bad money chases out the good).
So, IMO, best not to use gold as "money". Silver might work better as a "Monetary Metal".