Solid entry. Pretty frantic and I loved the lemmings feel :) Best I was able to get was 19 gems.
I liked the music but noticed it didn't loop when it was done (and I couldn't hear their screams in the next playthrough).
This feels like it could work as a multi-level game with gem targets per level to give a sense of progression, but I also had fun just trying to see how far down I could dig.
Oh, and I had trouble getting the mouse-wheel to scroll only the level and not the webpage, so I had to use the arrows to move the camera. Definitely would have preferred the mouse wheel.
Great game!