There is an art to mining large quantities of Adamantite. Know the zones it pops up in, in what amounts, and in what locations. Install Gatherer or Cartographer to record your finds. It may freak people out, but if you see someone mining a node, ride or fly to it, dismount, and try to 'tag' it (but don't loot the ore), so you have it on your map. Set aside some time, rather than doing 5-10 minutes here or there. Every Outland zone has 1 Khorium Vein that instantly re-pops elsewhere when you mine it. Your mining productivity will increase dramatically when you get a flying mount.
Hellfire= Fel Iron, Khorium. Best place to mine Fel Iron if that's all you need. Motes of Fire come swiftly here too. Mount up and do circuits around the perimeter (hug the edge of the world where possible, detour to any outcrops of rock/hills/mountains in the center of the map).
Zangamarsh= Fel Iron, Adamantite, Khorium. Not a good place to mine at all, best saved if every other location is packed with farmers. Few nodes, with a lot of space between them. Circle the edges, then do sweeps over the deep water in the center. The 'contested' cave with the Sporelings is sometimes good for 3 nodes, as is the Ogre cave in the far west.
Terrokar, Blades Edge, Nagrand, Shadowmoon, Netherstorm= Fel Iron, Adamantite, Rich Adamantite, Khorium.
Terrokar: There's a lot of 'edge' to Terrokar, circle all of it. Detour through the center, anywhere you see a mountain. At ground level it's just basic Adamantite nodes and Fel Iron, so not an ideal mining zone; the thing that saves it are the two locations you need a flying mount for, namely Skettis (south east of Terrokar, above the Bone Wastes) and the area above and behind the Aldor Rise in Shattrath. Both of these areas can spawn Rich Adamantite as well as regular (which won't happen at ground level in the rest of Terrokar. Skettis is filled with 70-72 mobs, including patrolling elite giants, be careful up there :o)
Blades Edge: I find mining here can be rewarding, but very time consuming, a 'back-up' location like Zangamarsh, but with more nodes. A flying mount is a must here, as there are so many mountains and valleys to poke around in. Never found a good reliable circuit here.
Nagrand: One of the best zones, if not the best. Insane amount of nodes of all flavours. A good circuit; fly out of Shatt (over the back of the Aldor rise (q.v), and head west over Nesingwary's camp. Cross the road and hug the mountains, then sweep the lake. Pick up the mountains edge again near the Throne of the Elements, and continue west to the Ogre camp (detouring south to the little hills nearby.
Passing over the Ogre camp, continue west, cross the road, and fly up and round the 'outside' of the mountain in front of you (border of Nagrand and Zangarmarsh) untill you see some patrolling ogres on the left. Scout in their cave, then mount back up and continue round the edge of Nagrand. Check the very high camp in the center-west (watch for elites), then bear towards Osh'gun. Circle the area around this mountain, looking for little hills (and a rare spawn called Voidhunter Yar).
After a full circle of this area, resume your 'edge' circuit, taking in the large humanoid camp in the east, as well as the ogre camp to the north of it (check the cave), and fly north till you are parallel with the arena. Fly down the center of the ravine nearby, always heading in the direction of Halaa, and stopping near the 2 ogre caves. Lastly, fly over the large lake nearby, and dive in if you see a node.
Shadowmoon: Although a high level zone, I find the mining exceedingly poor in SMV. Good quantities of Fel Iron around the Hand of Gul'dan. The Forge area in the center, and the Naga cavern in the north are reliable spots, but the amount of mobs in these areas renders the whole thing frustrating.
Netherstorm: The other good mining zone. Fly north of Area 52, scan the ruins. Fly over the gap to the north. Clear the large cave under the manaforge, then do a circuit round it. Fly north to Soccrethar's Seat, circle it. Fly east to the Forge camps, then north to the northmost Ecodome.
Go east from here to the hill with dog/eye mobs on it, then south to the Eco dome. Circle it, then fly out to the Etherium area, circle round that, and the manaforge nearby, then into the mine beneath the manaforge.
I have never found good quantities on the 'island' with Cosmowrench on it, or the 'undead' island, or the starter island (with Area 52 on it). There are nodes to be found there, just not in the same quantities.
I may add more if anything occurs to me
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