Opt for crucible? (7,3)
I believe the answer is:
melting pot
'for crucible?' is the definition.
('melting pot' can be a synonym of 'crucible')
'opt' is the wordplay.
I cannot really see how this works, but
an anagram of 'opt' is 'pot' which is located in the answer.
The remaining letters 'melting' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for melting pot that I've seen before include "Vessel - place for mixture" , "Crucible'" , "Place where different peoples mingle" , "Dissolving container" , "In which to mix metals, immigrants" .)