If you're doing destruction magic as your primary damage dealer, I wouldn't even worry about weapons at all. Dual casted destruction will stagger enemies with the Impact perk, which is insanely useful. Also, destro is pretty dang strong on its own when you get up to Adept level spells and above.
I've yet to use any conventional weapon in the game and I am just fine.
You could also use "Bound" weapons, which are summoned using Conjuration. --- My channel. Enjoy: http://www.youtube.com/zer0din
For a PURE mage? I'd have to say that you start with either dual destruction spells or one destruction spell and a ward spell in the other. Then when magika runs low swap to a scroll in one hand and a staff/Daedric weapon in the other. But to answer this question properly you would really have to know your idea of a pure mage...
In my mind, a pure mage is someone who doesn't use armor or weapons of any kind other then staffs OR summond Daedric weapons... Some would say that a pure mage can still use daggers or small swords and wear light armor so they would dissagree with my load-out. It's really up to you how you feel would best suit your character and how you want to play... --- Cigarettes are a lot like hamsters... Completely harmless until you put one in your mouth and set it on fire. GT:BMAN270