Bring a Libram of Protection, 1 Pristine Black Diamond, 2 Large Brilliant Shards, and 1 Frayed Abomination Stitching to Lorekeeper Lydros in Dire Maul to receive an Arcanum of Protection.
He wept like an infant at the loss of this libram. Mind you, I myself have wept over texts - there is no greater loss than that of knowledge and history - but to cry over this nearly useless jumbling of incantations? Preposterous! It left me to believe that the Prince was doing him a favor in flaying the flesh from his bones.
Bring the Libram along with a pristine black diamond, large brilliant shards, and a frayed abomination stitching and I shall recreate the Arcanum.
Oh, and check the north wing.
Details
The Libram of Protection drops off trash mobs and bosses within the Dire Maul instance. Pristine Black Diamonds drop in any of the high level instances. Large Brilliant Shards are often disenchanted from high level rare items. Frayed Abomination Stitchings drop off the abominations in Stratholme.