As far as I know, they will be randomized the next time. How many fields your colony will have is decided when you create your colony. Here is some info on colonizing and planet fields. http://www.bulfleet.org/viewtopic.php?t=24311
One thing that post doesn't remind you is to take resources with you. I don't have the exact numbers, but if you take about 5,500 metal and 2,000 crystal, you will be able to build your new colony up very quickly, without waiting for the mines to produce.