Girl with mark that locates treasure chest (6)
I believe the answer is:
thorax
'chest' is the definition.
(I know that chest can be written as thorax)
'girl with mark that locates treasure' is the wordplay.
I cannot really see how this works, but
'girl' could be 'ora' and 'ora' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for thorax that I've seen before include "Between the neck and belly" , "Insect's upper body" , "Part of the body between the head and abdomen" , "Part of the human torso between neck and diaphragm" , "Chest" .)