Arduous experience in gold trade (6)
I believe the answer is:
'arduous experience' is the definition.
(I know this)
'gold trade' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'trade' becomes 'deal' (synonyms).
'in' acts as a link.
(Other definitions for ordeal that I've seen before include "Prolonged distressing experience" , "Tough test in Laredo" , "A difficult and harrowing experience" , "A difficult or harrowing time" , "Difficult and testing experience" .)