If it gave you four gold I think it would be too good, haha.
Consider other ramp cards like Murfolk Prospector, Gemscout Owl and Galina. (or Rich Earth) typically they take multiple turns to pay off. Owl costs one and returns one. Rich Earth costs three and returns one per turn. Galina costs two and returns two only if you've got four green units. Most of these cards pay for themselves in one turn then generate a profit only after that.
Rickety Mine costs two and returns three guaranteed. So it's actually really good as a gold generation card. Generating a profit if it survives one turn. It's just, it's kind of hard to keep it alive as red. And then beyond that it's kind of hard to justify the card cost when Red already struggle with cards and don't hugely struggle with gold.
The damage to your base and sacrificing itself is actually fine IMO, it's flavourful and as a downside it's like, yeah, I could care less about two damage to base.
Honestly paying two gold to get an average return of six gold is crazy good. I just think I'm struggling to find useful ways to spend all of that gold in Mono-Red and it's just a huge risk to play the mine at all given that it's really easy to destroy and doesn't help the board at all.
I need to think about including mine in some multi-colour decks with like, Growth or other good starting options.