I'm Level 51 and just got a Daily Quest to mine 80 titanium. Since the titanium mine isn't available until Level 61 (and I'm not likely to gain 10 levels quickly), it is safe to say that quest is effectively impossible. I've cancelled it, of course, but it shouldn't have been there in the first place.
Some recent change has drastically increased the cost of some of the Daily Quests (used to be 240 horses; now 80 cannons, etc), but up until this one they were possible - expensive and probably not worth it, but possible - but this one just isn't.
I think whatever algorithms controls these things (and was tweaked to increase the requirements) needs revisiting.