On this page of our treasure guide to Uncharted 3 Drake's Deception you can find valuable information about all collectibles available in chapter 18. Only one treasure can be found in this chapter - Calcite Statue of a Female Figure. Stop for a while after you've reached the well during your journey through the desert.
Calcite Statue of a Female Figure
After you reach the well for the first time, walk around it to find a vase. Shoot it  to collect the treasure.