The resource regeneration seems to attempt to balance itself actively based on the frequency certain things are mined. If, for example, players are mining an abundance of gems, the game will seed fewer gems back into the world than was gathered. If players are not finding enough gems, it will seed more gems back into the world. This helps prevent resources from becoming either over abundant or too rare. The best way to maximize your mining is to explore many regions frequently. Return to your own mine after exhausting another mine some place else.