Not difficult if you start with native copper and native tin.

Neolithic technology includes using fire in pre-smelting ways, both for firing ceramics and for tempering flint to make it even tougher for use in tools. Somewhere along the line they built their kilns with rocks that, under heat, yielded tin or copper.

I've always thought there was a certain amount of experimentation going on, rather than these all being dumb luck discoveries.

Copper ores can be extracted with basalt hammers, by heating and quenching the rock face so it shatters, and by determined sand drilling. These ores were not necessarily tougher than other stones they were used to manipulating.