Gold exploration had been going on for thousands of years which means every new piece of gold is being discovered at much higher cost. So while supply increases, prices don't go down.
Of the additional 80% gold I'd guess about half represents profit for gold miners or tax or mining royalties. So 40% of the gold supply has come at zero marginal cost.
Also keep in mind that a technological breakthrough could produce a sudden glut in gold supply, as we have seen recently with oil and gas fracking.
The main reason the price has gone up is that the world population is in aggregate far richer than in 1980. What's more, Indians and Chinese (who are culturally inclined to invest in gold) have seen their wealth grow particularly rapidly, so the proportion of world assets stored in gold has likely increased.
If you ask your Shaman to produce a poison and send it to every gold miner in the world and as a result no new gold will be mined, you still won't dig up much by simply putting shovel in your backyard. You would have to go to the last crust level they been at and start to dig from there, which makes it incredible expensive and complicated.
Meanwhile, if for any reason, including breaking a Bitcoin blockchain by state-sponsored actor (or someone powerful enough; or simply forcing ISPs to ban traffic on mining ports now that NN is gone), when miners stop or move to something else, you can pick up from where they left off of and alone mine one bitcoin a minute on your mediocre laptop.
Whether someone will pick up these coins from you at $15k per pop, that's a different story.
> or simply forcing ISPs to ban traffic on mining ports now that NN is gone
If the government can force ISPs to implement content-neutral routing, what on earth would stop the government from forcing ISPs to mandate content-neutral routing for everything except mining ports, or going even further to demand that DPI be used to investigate the content of all ports to prohibit mining activity?
There is 80% more gold aboveground today than there was in 1980.