Once a body (planet/asteroid ect) has been surveyed you can think of the minerals showing as the easily found stuff.  When a geology team goes to that body they are looking for harder to detect deposits.  What they find is then added to the total.  This is basically the fluff for how the geology team works.  The mechanics are that a team has a chance to find new minerals and a chance to have the survey finish with no further chance of finding any minerals.  The higher the teams rating then better the chance to find minerals, and the less chance of ending the survey there is.  This means that you always want a very skilled team available for those important locations.  They will have the best chance of finding new minerals and not being shut down to soon.  Once ANY team gets the survey done message no further teams can improve on that colony.  I have noticed a way to get around this however if you can have multiple colonies on a single body then each colony can have a team look for minerals independantly. 

Brian

Geology teams are needed to uncover more resources.

No just the speed it completes the survey