Currently if you have a Infernal Brimstone WQ available you can glitch it so you won't complete the WQ even though you get the Brimstones thus you can farm it indefinitely.
What you want to do:

Attack Brimstone DestroyerKite it right to the edge of the WQ zoneKill itRun out of the WQ zone but stay in range so you can mine itStart mining it before the WQ isn't active anymore (as you are out of the zone)Rinse and repeatJust read another recent thread with a similar bug, this probably works with any similar world quest
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