The main screen should have a button/link/something that goes to the mining. It took me a few minutes to figure out that it's under Control Panel -> Mine -> that.. Exit looking button bottom corner.
Otherwise it looks like.. I start with 0 dollars, can't build any of the three things, and can't upgrade any of the three things in Control Panel.. nothing to do -> broken game -> give up.
I kept looking because it looked neat (and so far, it is!), but a lot of players might not.
Other suggestions:
1. Let me hold down the mouse button to keep mining instead of clicking.
2. The value of higher tier ores should scale better with the tophat bonuses; right now I get $9 for dirt, $10 for stone... and wish I hadn't upgraded that minecart since dirt is so much faster to mine.
3. Drag and drop lemming/s to the mine for auto-mining
4. SAVE GAME (auto-save ideally). Very very important