I'd suggest the fact that the cost of mining quadrupled in 10...

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.