Thalumbra Chests for the Keys

Within Thalumbra, the Ever Deep you can start several timed quests that reward you with a key.
 * Gold Key needs a Gold Chest
 * Platinum Key needs a Platinum Chest

The thing is once a a chest got opened it will respawn at a other semi random location within Thalumbra, the Ever Deep. The "normal" track from scouts will show those chests.
 * Q:But why semi random?
 * A:the amount possible locations of the chests seems to be limited

Known Gold chest locations

 * Above the entrace to Maldura

Known Platinum chest locations

 * under water near the "an empty mushroom cart"