First off you have to equip a shield. If you go up to a warp gate and use the AoE shield smash ability bound to the "2" key you can push the warp gate from it's current position. Keep doing this until the warp gate is at the very edge or outside of the green misty nurgle looking zone that its in. After that you can destroy the gate no problem. I tried this three times without fail. I also noticed that enemies are invincible inside that nurgle zone as well. Hope this helps!