Hold on - you say "we find more gold every day" and then go on to suggest that the money supply doesn't actually need to keep up with economic growth?

If we had the technology to maintain 0% inflation, we would do that. We can't, and rather than risk deflation we instead target low positive inflation. This is because deflation leads to nightmare spirals where people start stuffing money into their mattresses instead of investing in useful things because holding has risk-free guaranteed returns that the unpredictable real world can't match.

The amount of gold being mined is not sufficient to keep up with economic growth and gold is therefore inherently deflationary. It's not a good way to store value, because a coin that's going to double in value over two years or whatever is obviously not a stable store of value.

You can argue about corrosion resistance or whatever other physical properties gold might have, but unless the civilization collapses you will find just as much luck storing your wealth in the database of a major bank. Needless to say, designing a civilization around the idea that it could collapse at any moment is unnecessary and expensive.