Good find by the geo team on Earth. However, I have had a high skill team find five or six deposits before saying they could find no more. Five high accessibility minerals turns a habitable but otherwise useless rock into a prize, even if it only has 100,000 of each. For most minerals 100k is a couple decade's worth.
When surveying, the game makes rolls against the team's skill level (the exact mechanics are in the wiki somewhere). The first roll determines if a find is made for the given time period. This is why low skill teams can take years to find a deposit, and high skill teams may find one two months in a row. A second roll is made to determine if the team can find any more minerals. If this roll is failed, no survey team can ever again find new deposits on that planet. Low skill teams will almost always take a long time and only find one deposit; that is why it is best to start them on an uninhabitable and otherwise useless rock. When their skill level hits 150+, use them on places you will colonize or will place mines anyway.
Anyway, to summarize, I would counsel against sending your team to Mars or any other potentially habitable planet, or any place that already has useful mineral deposits, until you get their skill built up. Like you, I learned this the hard way.