Nurse briefly with certain valuables (8)
I believe the answer is:
Here is my best explanation:
'valuables' is the definition.
(I've seen this before)
'nurse briefly with certain' is the wordplay.
'nurse' becomes 'treat' (I've seen this before).
'briefly' means to remove the last letter.
'with certain' becomes 'sure' (synonyms. I am not sure about the 'with' bit.).
'treat' with its last letter taken off is 'trea'.