Setting of gold part encircling box (13)
I believe the answer is:
orchestration
'setting' is the definition.
(thesaurus)
'gold part encircling box' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'part' becomes 'ration' (ration is a kind of part).
'encircling' is an insertion indicator.
'box' becomes 'chest' (chest is a kind of box).
'or'+'ration'='orration'
'orration' enclosing 'chest' is 'ORCHESTRATION'.
'of' acts as a link.
(Other definitions for orchestration that I've seen before include "Composer's skill" , "Arrangement for instruments - short reaction (anag)" , "Note arrangement" , "Stage-management" , "Arrangement of string, brass, woodwind and percussion parts" .)