Criticise fool with a mining tool (7)
I believe the answer is:
nitpick
'criticise' is the definition.
(nitpicking is a kind of criticising)
'fool with a mining tool' is the wordplay.
'fool' becomes 'nit' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'a mining tool' becomes 'pick'.
'nit'+'pick'='NITPICK'
(Other definitions for nitpick that I've seen before include "Raise petty objections" , "Find little fault" , "Find fault in petty way" , "Be fussy and pedantic" , "Carp" .)