A worked vein.
The lode varied from six feet to just a few inches in the roof on some stopes. The miners would have stood on timbers set across the vein and picked away as high as they could to retrieve the metal.
As far as mines go, this part of Bradda is very dry and the timbers are in a state of rot. There are many hidden dangers such as the flooded shaft at the bottom of the picture. There are several false floors made of wood in the level and should not be crossed.