You can get gears by:
- breaking minerals;
- popping bubbles;
- unlocking mineshafts in the mine;
- breaking gates;
- unlocking the mine exit.
To get more gears, increase your gear multiplier. To do this, try to pop bubbles with a gear icon in the mines. The more bubbles like this you pop, the higher your multiplier becomes, which means you will get more gears.