Video games have largely misled us here. Iron ore is incredibly common, it’s not a rare resource at all. The limiting factor for steel production has historically been energy, not ore, and in the modern context the ability to produce pure oxygen for carbon reduction. Historically iron mines were put near forests for fuel, not wherever the richest ore was.

The advantage of re-using slag isn’t that it’s richer in metal, iron oxides being pretty easy to get, it’s that it would take less energy or Oxygen to finish refining.

Recommended reading: Bret Devereaux’s blog series about iron & steel production. https://acoup.blog/2020/09/18/collections-iron-how-did-they-...

I wonder how much silver comes from recycling old copper, lead and zinc.

Only about a quarter of « new » silver comes from silver mines. The rest as a byproduct of other mineral mining where they separate out the silver.

https://www.globalxetfs.com/silver-explained/