There is nothing on the ground in the well cave. There are a couple malachite veins there, but it is much easier to get to them before triggering the cutscene with Zagan than afterwards.
As Joram said, you can return to the mine tower in Broken Valley; the tower and the top of the walls are above the poison gas.
For the Bounty Hunter achievement, there is another set of wanted posters inside the harbour building.
Go inside, turn right, forward a bit and take the stairs up on the right.
