Pests in silver mine (6)
I believe the answer is:
vermin
'pests' is the definition.
(I've seen this before)
'in silver mine' is the wordplay.
'in' indicates a hidden word.
'VERMIN' is hidden within 'silver mine'.
(Other definitions for vermin that I've seen before include "despicable people!" , "cockroaches, for example" , "Odious creatures" , "Animals that spread disease" , "Rats, foxes, mice etc" .)