This is a great start! I'm excited to see what you add.
UI
Sometimes, especially at the edge of the screen, the pointer finger of the mouse cursor and the head of the pick cursor do not match up. This makes it really hard to manually mine.
The font makes it difficult to distinguish numbers. I could not tell the difference between the 3 and 8, or the 5 and 2 at first glance.
Gameplay
That was a satisfying but short loop. I definitely agree with another poster that we should be able to move mining lodges, or at least destroy and replace them. Sometimes the pathfinding for the soldiers and the monsters would be a bit silly and they would walk parallel to each other. I wish there were more upgrades and relics besides just move faster or dealing more damage. The best combat relic being locked behind the final boss is also not useful, as there's nothing left to do with it after that.
Bugs
I had a worker stuck inside a miner's lodge until the end of the game. I'm not sure if it got inside by accident, or if I accidentally placed the lodge on top of it.