Cast the mixture, we hear, as a source of uranium (11)
I believe the answer is:
pitchblende
'a source of uranium' is the definition.
(I've seen this before)
'cast the mixture we hear' is the wordplay.
I cannot quite understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
'mixture' could be 'blend' (blend is a kind of mixture) and 'blend' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'as' acts as a link.
Can you help me to learn more?
(Other definitions for pitchblende that I've seen before include "Brown or black mineral containing radium" , "source of uranium" , "Uranium ore" .)