Possibly copper’s sphere of operation (7)
I believe the answer is:
element
This clue is a double definition.
'possibly copper's' is the first definition.
(copper is a chemical element)
'sphere of operation' is the second definition.
(Other definitions for element that I've seen before include "of the weather" , "silver perhaps?" , "An abstract part of something" , "fire, perhaps, once" , "Constituent -- habitat" .)