One who believes about gold speculator (8)
I believe the answer is:
theorist
'speculator' is the definition.
(I've seen this before)
'one who believes about gold' is the wordplay.
'one who believes' becomes 'theist' (someone who believes in a god).
'about' means one lot of letters goes inside another.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'theist' placed around 'or' is 'THEORIST'.
(Other definitions for theorist that I've seen before include "Creator of hypothesis" , "An expert in abstract principles" , "Thinker" , "Speculator" , "Expert in established hypotheses" .)