Source of wealth in mint built just around the corner (8)
I believe the answer is:
imminent
'just around the corner' is the definition.
(thesaurus)
'source of wealth in mint built' is the wordplay.
'source of wealth' becomes 'mine' (I've seen this before).
'in' is an insertion indicator.
'built' indicates an anagram.
'mint' anagrammed gives 'imnt'.
'mine' inserted within 'imnt' is 'IMMINENT'.
(Other definitions for imminent that I've seen before include "About to happen, looming" , "Likely to occur at any moment" , "Likely to happen at any moment" , "Happening any moment now" , "About to happen very soon" .)