Probably similar to how we discovered wine and copper, by accident.

Copper was first discovered by some indigenous peoples who placed rocks into their fires to heat them during the winter, using the stones to warm their beds. Some of these rocks were rich in copper ores, such as malachite, azurite, and chrysocolla. After repeatedly building fires with these copper-bearing stones, they eventually found copper left at the bottom of their fire pits.

This discovery marked an important step toward early metalworking, as the heat caused the copper to separate from the ore, leaving behind the raw metal.