Bad news for the Libertarians: silver was historically way more common for money than gold was, to the point that languages like Irish and French use the same word for money as for silver.

This is because there was (and is) way less gold than silver, so gold is way more valuable. As such, gold coins were only used to buy things like houses, horses, and suits of armour. Silver coins were much more practical; the linked article mentions that Ptolemaic Egypt had to export large quantities of grain to bring in enough silver to pay their army despite there being gold in Egypt.

But more than that, if there is a complete societal collapse, the metal you’ll want is iron. Societal collapse doesn’t mean things continue as they have been except there are no safety or food quality laws. It means everybody goes back to peasant agriculture using tools made of wood and iron (well, steel, which is iron with extra stuff in it). If money is used, it might well be something where no coins actually change hands; everybody just remembers how much they owe their neighbours, and how much their neighbours owe them. That, if course, assumes that in the event of complete societal collapse, we don’t decide to give local communism a try.