I could be remembering incorrectly, and the stats themselves might well be very eurocentric, but didn’t the bubonic plague cause the only historically recorded downturn in global human population?
I’d like to point out that today there is a much higher level of education among the general populace, and many more books in existence, than in ancient times. It would not be possible for us to lose the art of writing, as happened in the collapse of the Aegean Civilization (c. 1100 BC - 800 BC, the first European “Dark Age”) or to lose all scientific knowledge as in the second Dark Age (c. 500 AD - 1000 AD). There would always be people around who would know or could find out from books how to keep homes supplied with electricity through water power, wind, etc., and how to modify vehicles to run on alternative fuels. Interstate trade would be no problem. 5000 years ago copper from Michigan was traded as far south as Peru. I’d say we’d revert back to something like the early 1900’s.
I’m talking long-term. Much of that metal could be exhausted quickly or may already be unusable without extensive work. Which might not be possible.
Mines that already are open would be a help though, assuming it could be transported.
I think metals would be one of the few things in relative abundance. You’re assuming we’d need metals in the same quantities as we do now, and without mining, we’d be in trouble.
However, if we reverted to some lesser level of technology… say 1800-1850, we’d have FAR less use for metal than we do now. Just think about how far one cargo ship would go, metal-wise. Or how much rusted-out crap in junkyards there is?
In a sense, our modern Dark-agers would have a leg up on the people in the past- it’s significantly less trouble to recycle already refined metal than to smelt it from ore. Plus, depending on who was still alive and what they knew, you could even segregate the different types of metals and alloys for different uses- cast iron, steel, etc… Even aluminum would be available through recycling, which was not the case until about 1900 or thereabout, with the advent of the Hall-Heroult process for smelting aluminum.
Personally, I think that the main thing that would define the post-crash civilizations would be access to our knowledge. Anybody that could get the Haber process up and running, as well as some other basic 20th century industrial processes would be a long way to rebuilding society. (the Haber process fixes atmospheric nitrogen- a vital component of fertilizer, allowing more than subsistence farming).