The way that the geo teams work when surveying a planet is each build phase there is a chance of finding more minerals and a chance of finishing the survey so no more minerals can be found. The higher the team rating is the better the chance of finding minerals and the lower the chance to finish is. Also you will tend to get results much faster on planets while asteroids are very slow to find any minerals on. This sort of compensates for the amount/scarcity of the minerals found. That will match the normal generation chance for the type of body (terrestrial/chunk ect) that you are on. Asteroids have much higher availabilities in general.
If there is an alien colony you can still land your team. They may get attacked in which case you will lose them as they don't have a combat value. They can perform the mineral survey but anybody who has a colony on the planet will benifit from what they find.
Brian
