Treasure chests can be found randomly on all sizes of Uncharted Isles in the Arc. There are three different tiers of treasure chests to be found on uncharted isles; opening the chest will reward players a scaling number of taijitu, with the higher tiers offering the best rewards. The different tiers can be found on all sizes of uncharted isles. Longer voyages have a better chance of spawning higher tiers.
Once a treasure chest has been opened it will permanently stay open, even if players were to visit the isle again; claiming an isle with an opened treasure chest on it will not allow the chest to be opened again.