Have riches perhaps in American vault (6)
I believe the answer is:
abound
'have riches perhaps' is the definition.
(I've seen this before)
'american vault' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'vault' becomes 'bound' (I've seen this before).
'a'+'bound'='ABOUND'
'in' acts as a link.
(Other definitions for abound that I've seen before include "Exist in large quantities" , "Be plentiful, proliferate" , "Be in plentiful supply" , "flourish" , "rich" .)