Anyone mentioned Clonk yet?
http://www.clonk.de/?lng=enScreenie of the last free version here.
http://www.clonk.de/gallery.php?lng=en&sec=ce&img=settlement1.jpgDig a mine, keep it from flooding, and sell gold, oil, and other misc. rocks.
You can build a pretty darn large mining town in the sandbox mode if you have enough time and you don't mess up.

hmmm... what else do I remember about it...
-You can build explosives from sulfer.
-Power is generated from windmills and coal power plants.
-Power is connected with electrical lines.
-Electricity can be used to power drills, elevators, and oil pumps.
-There's a multiplayer mode, where you try and blow each other up.
-There are various creeps, like dinosaurs and sharks.
-Fish can be sold for $$$
-The water physics are decent, but there's no water pressure.
-The controls can be a bit clunky.
-100% destructible terrain, pixel based