Miner's strike (4)
I believe the answer is:
lode
'miner's strike' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lode that I've seen before include "Rich source" , "Deposit of valuable ore running through other rocks" , "Vein of metallic ore sounds heavy" , "Vein of metal in the earth" , "A deposit of ore, say gold" .)