Beautiful game with great sound design. I never bothered buying any of the things in the shop because the cave wasn't that big, and I didn't see a reason not to sell everything I gathered (though since I had to click to sell them all individually, I had wondered at first if there was going to be crafting or something else to encourage me to hold onto different ores - perhaps that was in the shop and I overlooked it (?) but it was fun collecting everything either way).
The character design is great, and the only other comments on the visuals is 1) there's an occasional 1-pixel discrepancy that causes lines to appear. I had this in my game too, and after googling, I learned that I could round to 0.001 when laying out my background tiles to help cover those gaps. And 2) when I got to the center of the core, I couldn't really see my progress bar since it was white and the core was white, so it would be nice if it had a small dark outline so I could see it better on the bright background.
I had a lot of fun finishing this one - great job!