That's a really interesting concept. Would these assembly lines by automated or manned? On the same concept, you could perhaps build spaceships, research stations, and more factories and refineries in space from the materials you mine, which would consume less fuel getting them from the Earth into space. It could make colonizing other planets much easier as well. Wouldn't it be interesting to hitch a ride on a resource-rich asteroid, and use the mined materials to create facilities and spaceships on/inside the asteroid as it hurtles off in whichever direction... it could, in essence, become a mothership to help build a mothership, and you could even perhaps build thrusters to help propel it along even faster.
Space is exciting! Let's also not forget the Ocean depths, which are pretty much as mysterious. As to mining, I recently read that Planetary Resources was acquired by an Ethereum-centric blockchain startup. Also, it's not just metals, Helium-3 mining on the moon could be very profitable as well.
Thanks for posting,
The Cyberius team.