On: A 3K-year-old copper smelting site could be key to understanding origins of iron

[pjc50]

This is similar to the "rare earth tailings" phenomenon, isn't it. A mine is built to extract one metal, the most profitable at that time, and everything else unextracted ends up in mine tailings or refinery slag. But, in addition to truly worthless silicates, that "waste" includes a bunch of other metals at low purity which may eventually be economic to extract.

[IAmBroom → pjc50]

Leadville Colorado was the site of a very minor gold rush, that mostly produced large piles of lead tailings.

Until someone noticed the lead tailings were not lead, but oxidized silver.