Copper tools

I know this has been suggested over and over again but it would be an insanely good implementaation.

Copper tools were humankind's introduction to metallurgy, before the Bronze Age (they experimented several alloys before finding out that bronze was the best out of them, ending the "Chalcolithic" and beginning the Bronze Age). However I believe that you could still mine iron with stone tools even if copper tools are added (after all, stone tools were still widely used irl throughout the Bronze Age), but perhaps iron could be made even rarer.

Personally it would make sense for a player to first make stone tools, then copper, then iron, it would beautifully reflect human history. Same applies to armor.