so on the second minute of gameplay I reached the moon and continued my journey to infinity and beyond, flying on my very first blue gem
Ok, now no kidding! I liked the project a lot. Get ore -> get reward -> get more resources to progress -> repeat until reached the final objective - I like this kind of gameplay!
SFX is nice! You want to hear this sound of coins, you hear the crash when digging the rocks etc. The sounds are good.
The game leaks more juice, such as screen shake upon dirt digging and maybe some effect of earning gold besides the SFX only by itself. Though the game is not very long, some nice peaceful music would cheer the player up I suppose so the repetitive gameplay wouldn't feel as boring. Don't get me wrong, the game is not bad or tedious, but repetitiveness makes you sometimes think "oh well more digging".
Also IMHO something like a counter that shows you how many more fossils/minerals you need to bring to make the client happier.
While playing, I've encountered some bugs. I suppose you already know about them, but I think it still can be useful:
1) Happy icon of the merchant does not dissapear if relationship gets worse, so different smiley faces start to overlap each other (see screenshots)
2) Fossils and gems can get stuck in the ground
3) Not a bug, but an optimization problem: a lot of light from torches causes minor FPS lowering.
Overall, I liked the game. It's simple, easy to understand and cute. If the game grew in some way and enhanced, I'd even buy it for a few dollars. Well done!