I've witnessed the following problem back in 6.3, and it seems still active in 6.42. There is a maximum range to where Mass Drivers work. When you open a colony around a second very distant star of a system for example (likely though a lagrange point), then mass drivers wont be able to carry any mining results back, forcing you to use costly freighters.
Looks like this:
I calculated that one freighting trip of 20 holds currently costs me around 10kt Sorium, so exporting mining results would be 1t Sorium per 12.5t of mixed material.
The mineral packages just stay there forever now, and would just keep stacking up if I didn't cancel them being sent. If someone has an idea on how to clean them up, I want to know of course.(they might take calculation resources)