The Mars missions suggest we're close to having the tech to get robots onto asteroids, some of which might have a fuel source that can sustain an unmanned operation that launches minerals along trajectories back toward .. the moon perhaps. It seems infeasible to ferry the minerals back and forth, although the value of the minerals might be high enough to justify it.

I wonder what the timeframe is for starting something? Space X has gone from start to regular orbital missions in 10 years and $800 million. Would it be so far-fetched to think of a 20 year timeframe for asteroid mining?