Gaming

I played Mines of Mars years ago and ran into the same wall near the end.

That second to last boss is basically immune to brute force. Rockets and snipers barely matter. You need the alien weapon from the trading pit, the one that bypasses armor. Without it the fight drags forever and feels broken.

Mining all rocks does trigger extra content, but it is not a huge secret ending. You mainly unlock lore and a short payoff, not a new dungeon or sequel hook.

If you want to finish cleanly, grab the alien weapon first, then come back. Otherwise you are just burning ammo.