This is quite a fun experience. I enjoy mining games in general and find them very satisfying. I loved the pixel artstyle of each of the items and found all the sound effects amusing. Also trying to figure out what items are needed for upgrades was fun. I didn't have problems with the combat, but I did find that ifyou hit the ghosts just when they appear they die in one hit, regardless of what weapon I used.
I did find a bug though where everytime I crafted the advanced gem, it would spawn in my inventory with 0 quantity, so I couldn't actually use it :(. It would disappear the moment I would click on it, so I could not really craft anything golden and I couldn't fight the final boss. I tried twice to craft the advanced gem (using 9 blue gems) and it bugged out both times.
Also, being able to drag items around in the inventory and organize them would be a really big improvement.
Overall, quite fun concept! Keep up the good work