How to reveal the treasure
Interact with Inconspicuous Landmark for 
Cuergo's Gold. The reference event creates this temporary treasure; it is not a permanent chest spawn.
The quest requires 
Cuergo's Key. Follow its page for the associated pirate drops.
Relevant locations
Classic in-game map · No outdoor coordinates supplied. Not live spawn tracking.
Coordinates and linked records
Where to find it
Temporary quest treasure in Tanaris; interact with the Inconspicuous Landmark. No fixed treasure pin supplied.
Baseline placements, not live spawn tracking. Coordinates are percentages of the named area map; an instance location has no outdoor pin.
Summon Pirate Treasure and Trigger Mob