After gold box, share score (13)
I believe the answer is:
orchestration
'score' is the definition.
(orchestration is scoring musically)
'after gold box share' is the wordplay.
'after' means one lot of letters go next to another.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'box' becomes 'chest' (chest is a kind of box).
'share' becomes 'ration' (a ration is a share of a limited resource).
'or' put next to 'chest' is 'orchest'.
'orchest'+'ration'='ORCHESTRATION'
(Other definitions for orchestration that I've seen before include "Scoring for strings, brass, woodwind and percussion" , "Composer's skill" , "Stage-management" , "Note arrangement" , "Arrangement for instruments - short reaction (anag)" .)