Decide to put off quarry (9)
I believe the answer is:
determine
'decide' is the definition.
(I know that decide is a more specific form of determine)
'put off quarry' is the wordplay.
'put off' becomes 'deter' (both can mean to discourage).
'quarry' becomes 'mine' (type of mine).
'deter'+'mine'='DETERMINE'
'to' acts as a link.
(Other definitions for determine that I've seen before include "Choose" , "Come to a decision" , "Establish" , "fix" , "Discover" .)