I'd suggest the fact that the cost of mining quadrupled in 10 years suggest it was.
There were other factors such as rising energy & labour costs etc.
Much of which has been removed to a great degree.
Some of the reason why gold was only twice the cost of production as a lot of old mines were re-opened & previously uneconomic gold was being mined.
There was over production.
If it wasn't in a bubble gold would have corrected less than 20%.
The fact that it corrected around 45% says it all.
