That's the same gate I used, too; good ol' Snarby takes the heat off later. I made a really stupid move in the one Aurora Isles level: I opened an energy door that I forgot leads to staring down nine turrets, and I didn't have the proper gun to deal with them. Still not sure how I survived that one with that single health bar. I really thought I was done when I drew a Candlestick Keep level in T3 at the random selection, since those are usually a nightmare to solo, but I managed to pull it off by playing like a total wimp. But hey, at least there were no Devilites...*shudder*.
I still need those two achievements myself, along with Free Spirit; I've done a couple of FSC runs with random parties, but I don't feel like I'm equipped to take on the boss-man yet, unless someone drags my corpse through it. As far as I know, the mineral one is a cumulative count, so you don't have to dump that all at once; I got the previous achievements by just tossing in small amounts over time.