River gold in Ohio county (7)
I believe the answer is:
orinoco
'river' is the definition.
(I know that Orinoco is a river)
'gold in ohio county' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'ohio' becomes 'O' (abbreviation for Ohio).
'county' becomes 'co'.
'or'+'in'+'o'+'co'='ORINOCO'
(Other definitions for orinoco that I've seen before include "banker" , "South American river - lazy Womble" , "Womble; S. Amer. river" , "Common character" , "Colombia/Venezuela river" .)