Space mining could be huge in a few more decades if we find that some asteroids contain solid metal. We know metal is created when a star explodes (bigger star, bigger explosion, and more energy to create heavier metals). We know that the earth has a solid molten iron core. We know the moon has a core (likely metallic) because Earth's gravity skewed the moon's core towards us, hence the moon does not rotate.
Asteroid cores, asteroid contents? I don't think we know, other than statistically what should be in them based on what is in Earth. if there's solid metal in some of them, and we can find those which contain solid metal with a good degree of confidence, then space mining using robots will be very profitable. Not for the run of the mill metals, but for gold and platinum. If we find those are just floating out there in big chunks under a few dozen feet of dusty rock, a lot of people will be sending robots up to find it.