Investor number one set up gold reserves, perhaps (7)
I believe the answer is:
bullion
'gold reserves perhaps' is the definition.
(bullion refers to gold in bar form)
'investor number one set up' is the wordplay.
'investor' becomes 'bull' (bull is a kind of investor).
'number' becomes 'no' (abbreviation for 'number').
'one' becomes 'i' (Roman numeral).
'set up' shows that the letters should be reversed in order.
'no'+'i'='noi'
'noi' back-to-front is 'ion'.
'bull'+'ion'='BULLION'
(Other definitions for bullion that I've seen before include "Gold or silver in bars or ingots" , "eg Gold bars" , "Bars of precious metal" , "Gold or silver in bulk" , "expensive bars" .)