Near-Earth asteroid mining? Is there anything close and worth mining? AFAIK most asteroids, including those containing valuable heavy metals like platinum, are in the asteroid belt between Mars and Jupiter orbits. Which is significantly farther than Mars.
I more easily believe in mining rocks on Moon as cool souvenirs. (And as a first step in developing the technology.)
Just as with scientific research, asteroid mining will be the domain of robots. There's no economic case for sending humans for that job, and AI is improving year on year. So sadly no Belters, whatever the value of mining space rocks.
Even a completely useless piece of rock is already a piece of rock in space. It can be used for shielding, counterweight for a spinning habitat, melted into simple shapes to support your habitats, etc.. You can even use it for propulsion - fling it away with a mass driver or vaporize with an arc-jet through a thruster nozzle!
I more easily believe in mining rocks on Moon as cool souvenirs. (And as a first step in developing the technology.)