Seam-style ore deposits will be returning to Mining in Dragonflight Patch 10.0.7, having not made an appearance in game since Battle for Azeroth.
Large Seams of Serevite and Draconium have been spotted in the new Forbidden Reach zone. These large deposits yield about twice as much Serevite Ore and Draconium Ore as normal mining deposits. You can get more with higher Finesse:
