Ore deposit (4)
I believe the answer is:
lode
'ore deposit' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lode that I've seen before include "Vein of metallic ore sounds heavy" , "mine to some extent" , "A deposit of ore, say gold" , "Mineral vein" , "Deposit of valuable ore running through other rocks" .)