Turnover of old bar in valley where wealth abounds (2,6)
I believe the answer is:
el dorado
'where wealth abounds' is the definition.
(mythical city of gold)
'turnover of old bar in valley' is the wordplay.
'turnover' says the letters should be written in reverse.
'of' becomes 'o'.
'old bar' becomes 'rod' (I've seen this in other clues. I am not sure about the 'old' bit.**).
'in' indicates putting letters inside.
'valley' becomes 'dale' (dale is a kind of valley).
'rod' put within 'dale' is 'darodle'.
'o'+'darodle'='odarodle'
'odarodle' in reverse letter order is 'EL DORADO'.
(Other definitions for el dorado that I've seen before include "Famed place of wealth" , "Mythical land of gold" , "Place of great wealth, from fictitious city on the Amazon" , "One who can't give something up" , "'Imaginary place of great wealth and opportunity (2,6)'" .)