One Bee Gee's heart of gold (5)
I believe the answer is:
auric
'of gold' is the definition.
(auric means relating to gold)
'one bee gee's heart' is the wordplay.
'one bee gee' becomes 'Maurice' (Maurice Gibb, member of the Bee Gees).
'heart' indicates the central letters.
The central letters of 'maurice' are 'AURIC'.
(Other definitions for auric that I've seen before include "French composer" , "Pertaining to gold" , "Of or containing gold" , "made of gold" , "Relating to a form of gold" .)