TL;DR
The mining drill can extract different tipes of ores if there is a mixed field. What if you let people select the kind of ores they will extract?What ?
Let electric mining drills selkect the kind of ores to extract as priority or to ignore others at all and drill only 1 kind of ores.Why ?
The idea was almost useless until 0.14, but with introduction of uranium if you have a mixed field near the starting area you cannot extract freely ores until you have tecnologies for extracting the uranium ores. The mine will stop extracting ores having reached the uranium and the mine is totally locked as production.If this is not a good idea for you, a good alternative solution is to let player select if build an uranium mine or a generic one. This way you can work on other materials and leave uranium alone or choose to extract uranium too.
A good idea for the second solution is to give drills a sort of flag for let them extract or not uranium ores.
This will not force players to restart a good map just because they get a lot of uranium scattered on other ore fields...