Hard to imagine a scenario where anything mined on an asteroid can be as lucrative of a proposition as mining the same things here on earth.
So it has to be that what they will find on the asteroid is useful and not available here on earth... or that we have run out of and have no more of the same substance here on earth.
I see a lot of R&D up front to make that happen.
Why does it have to be that? Could it be the environment and processes that provide the economic advantage?