But scrap metal is still purer than any ore.

And ferrous mineral recycling accounts for roughly 33% of present production (2018 data, most current available):

<https://www.epa.gov/facts-and-figures-about-materials-waste-...>

That's a loss of 2/3 of production to non-scrap effluvia on an annual basis. I'll let you work out the ultimate resource depletion cycle from that. Recycling is useful, but it's no magic bullet, and there are always losses.

The most heavily recycled metal in the US is lead, per USGS data and prior comments of mine, with recovery rates of about 75%, accounting for 40% of net production.

<https://news.ycombinator.com/item?id=20164506>

<https://news.ycombinator.com/item?id=26412585>

Source citation: "USGS 2020 Minerals Yearbook: Recycling — Metals"

<https://www.usgs.gov/centers/nmic/recycling-statistics-and-i...>

>That's a loss of 2/3 of production to non-scrap effluvia

Considering that the amount of stuff in our world made from steel at any one time is steadily increasing this makes sense.

>The most heavily recycled metal in the US is lead, per USGS data and prior comments of mine, with recovery rates of about 75%, accounting for 40% of net production.

There's little to no "post consumer pre-recycler" use for lead whereas every tom dick and harry can find a use for some old pipes or beams or whatever.

That just means it's currently more economical to mine iron ore than it is to mine landfills.

And we are presumably still adding to the total stock of iron in human circulation.