In favour of going back into mine to make money (6)
I believe the answer is:
profit
'make money' is the definition.
'in favour of going back into mine' is the wordplay.
'in favour of' becomes 'for' (I've seen this before).
'going back' says the letters should be written backwards.
'into' indicates putting letters inside.
'mine' becomes 'pit' (down the pit).
'for' back-to-front is 'rof'.
'rof' placed inside 'pit' is 'PROFIT'.
'to' is the link.
(Other definitions for profit that I've seen before include "Money made" , "Clean up" , "returns" , "financial advantage" , "Gain from employment of capital" .)