Game with clubs over diamonds - profit not unknown - could spades help make your fortune here? (9)
I believe the answer is:
goldfield
'could spades help make your fortune here?' is the definition.
(place to dig for gold)
'game with clubs over' is the wordplay.
'game' becomes 'field game' (field game is a kind of game).
'with' is a charade indicator (letters next to each other).
'clubs over' becomes 'gold' (I can't explain this - if you can you should believe this answer much more).
'field' put after 'gold' is 'GOLDFIELD'.
'diamonds profit not unknown' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
(Another definition for goldfield that I've seen is " Where to dig up a nugget".)