I really liked the early gameplay loop, a bit of work to get going but then it snowballs quickly. Had a few issues; the gem/treasure collection noise would not stop at a certain point when the whole container filled up, and would dearly love a "leave mine" button because at a certain point it becomes impossible to run out of stamina. It seems a bit strange that fewer rocks/extra dirt layers show up the deeper you go; I would expect it to get harder not easier to mine layers and there to be better rewards further down, but the item pool seems consistent. That'd incentivize buying the tool upgrades.
A really good framework to build a game on though! I had fun.
+1 for please add an option to disable the screenshake. Had difficulties aiming at the spot I actually wanted to mine a lot; would be nice if that was pointer driven (like Stardew Valley - you'd still have to be fairly close for it to work). The artwork and seeing the gems drop into the sidebar was my favourite part. <3