Fortune-hunter in favour of area seizing power (10)
I believe the answer is:
prospector
'fortune-hunter' is the definition.
'in favour of area seizing power' is the wordplay.
'in favour of' becomes 'pro' (I've seen this before).
'area' becomes 'sector' (sector is a kind of area).
'seizing' indicates putting letters inside.
'power' becomes 'p'.
'sector' going around 'p' is 'spector'.
'pro'+'spector'='PROSPECTOR'
(Other definitions for prospector that I've seen before include "Searcher for minerals" , "Clementine's father, perhaps?" , "Gold-digger" , "One searching for valuable minerals" , "Searcher after valuable ores" .)