I did a run with the pickaxe, I was lazy to take a screenshot, but it was funny, more gems than you could ever imagine. I got past the final boss too. :)
The actual reason I didn't post was because I discarded a good gem by mistake, a pearl, and I didn't want to show off my blunder, ahaha. But yeah it was doable, no problem. You need a level or so to stack up gems while using the pickaxe only for deathblows, then you can use it as your main weapon and wreck havoc.