Very very cool. Kinda reminded me of the old flash game Motherlode, and had a similar gameplay loop (between having to come up to the surface to refuel, avoid taking damage from mining, a number of upgrades to each part of the miner, etc). Some small thoughts/tweaks that could further improve the game --

1) I think other commenters suggested implementing an elevator or something like that to the game. I think just reducing the fuel penalty for falling (or make it zero) and then an "auto-fall" feature might be nice.

2) Animations for bombs, rockets, etc. I think I saw some quick animations both, but would be nice to have a better indicator that a bomb was used, etc.

3) Maybe instead of using upper-case letters for the rock/ore types, those could just be filled tiles of a solid color? (like 1-bit graphics) Then the enemies can be upper-case ASCII characters and it might be a bit more readable. 

I'll add more if I think of anything else. I really enjoyed this entry though. It just needs some catchy music and I'd be hooked :)

Such a really nice take! It was a bit sad to not have any kind of background music or just sounds in general, but I really wanted to just go deeper and deeper to see what new minerals I could find!

What a great game! Fits the genre perfectly, is very fun, and is a good looking game that clearly conveys the necessary map information. Well done!

mixing a traditional RL with motherload is a great idea. i wish the economic scanner actually showed your total instead of just making you multiply it in your head. the fact that there's no "carryover" for quotas is an interesting idea, but i'd kinda prefer to have a bit of leeway, especially since a lucky set of upgrades can have you able to clear out most of the money in the earlier bits for an insane over-quota score.

I especially like the asymmetry of movement. Both because of the costs of going through different rock, but also not being able to drill “up.” It creates a real sense of space, and you develop patterns for how to move efficiently. And the continuity between days creates opportunities for like “highways” you use over and over, and leaving resources for future days when you’re doing well, etc.

Speaking of highways, I wonder if there are opportunities to build things in the mine? That’s a core mining idea, and I could see that working really nicely here. An elevator, for example. Or you place a drill and the next day it has drilled out a direction. Or turrets that protect your core areas from enemies.

Good tutorialization, too. Love the just-in-time messages.

I've been thinking for a long time about what a roguelike mining game would look like. Merging the tense, strategic gameplay of a roguelike with the ore gathering and exploration of a mining game is a fresh and interesting twist.  
It would be interesting if certain resources also lead to different upgrades and the upgrade to dig upwards should be removed. It takes away a challenge.