You will get one of the following: the Queens auto rifle, scour rifle, pulse rifle, hand Cannon, fusion rifle, sniper rifle, shotgun, machine-gun, or rocket launcher. You have a possibility of obtaining an exotic weapon. The two small weapons can give you strange coins and motes of light. But please note that you can only open the big golden chest if you have a treasure key in the consumables section of your inventory. So be sure to always have a key in your inventory before doing a Prison of Elders run. I hope I helped.