Treasure is a Epic element. Strictly seen, Treasure dragons are very rare Metal element dragons, but they refuse to live in Metal Habitats and the branch of Metallomancy associated with them, Argentomancy, is as powerful as an Epic style of magic and can be used without any mastering of Metallomancy so it is often regarded as an element on its own.
Characteristics of Treasure Dragons
Many Treasure dragons are centered around a specific precious metal, and, with that association, also share features from it. They are also known to hoard treasures.