A lot of places bootstrapped with bog iron, which is the same process, except that the iron-eating bacteria deposits were accumulating on a large scale over many years.
And once you have iron picks, you can think about mining. (And iron plows so that you can feed your specialized miners, etc. There are so many tech ladders of making tools to make tools to make tools…)
Perhaps bogs again? If someone takes peat moss from a murky bog, with iron-eating bacteria, to burn as fuel, then they’re going to keep finding funny stuff in the residue of their fire. If they knew about other funny stuff like copper, tin and gold, they could add up the fingers.
