Thank you Steve for this...it always struck me as odd that the dudes on earth could find minerals at a drop of a hat, yet it took them YEARS UPON YEARS to poke around a rock that is not more then 100 diameter at average....
And I vote for A and B.
When initially geosurveyed set the max amount and accessability that you can eventually get too. You of course have a fair chance of NOT finding those numbers right off the bat. For that you need to do some actual work instead of watching girlies on your computer while it scans the planet. So you send in the geosurvey teams! The mighty men with picks! And they putz around, and putz around...and they find things...much like they do now...major amount of the time its just adding up to what the original max amounts are. But some of the time its adding above and beyond them. Now, this goes on for however long, you have discovered (or overdiscovered) the orginal amounts that where rolled up with the initial geosurvey. Now, you have your diminishing returns with each discovery, and by diminishing I mean the chances for the next discovery, not the amounts found. Each new discovery after this should give less of a chance to find the next discovery. And so on.
So you have this :
Geosurvery 'We totally watched some por...er...scanned the planet...sir...ya...'
Geo Team up to original max 'Sir, we have like...TOTALLY gotten our robots to do a good ol' job of rooting around in the ground'
Geo Team up to x chance after originals passed 'Sir, I can't believe it, but Bob over there totally went off the trail to take a leak and found a nice new lode!'
Geo team past x chance after originals passed 'Sir....you gotta be kidding us....Fish eyed sam, you know, the guy who's mom screamed in horror when his mom was handed him as a baby?...ya..him...seriously sir, he's got more of a chance to hook up with that dancer over on Titan that everyones talking about then we do of finding something more for your slavedriver type self to dig up...'
But, I leave it up to you math man to figure out the deep stuff....
And speaking of planetoids, pluto is a damn planet! PLANET! SCREW THEM ASTRONOMERS! Just because you found new ones doesn't mean you need to change the one...ONE!.. old one. pffft...