From Guild Wars 2 Wiki
Dwarven Relics,Sparkfly Essence, and other such materials, needed to complete certain Dynamic Events. Most commonly, an NPC will request from the players in the area to collect certain items within a clearly marked geographical location on the map, and bring them back to him. Once the NPC has collected enough items, he will generally run back and make something with them, such as a new environmental weapon, food or other item, and offer the item for sale. The resultant product is generally only available for sale for a few minutes after the event ends.Event Items are collectible goods, such as
They very rarely have any value outside the event, or can be sold for merely 1 copper, so they can be destroyed or sold if possible without consequence.