Cache of raw mineral under street (5)
I believe the answer is:
store
'cache' is the definition.
(I've seen this in another clue)
'raw mineral under street' is the wordplay.
'raw mineral' becomes 'ore' (I've seen this in another clue).
'under' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'street' becomes 'st' (abbreviation).
'ore' put after 'st' is 'STORE'.
'of' acts as a link.
(Other definitions for store that I've seen before include "Supermarket" , "Save" , "Reserve, shop" , "Shop; repository" , "Shop; hoard" .)