Band of ore (4)
I believe the answer is:
seam
'band of ore' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for seam that I've seen before include "Join in material - layer of coal" , "Sewing join" , "Stratum of ore or coal" , "Joint between two edges" , "Join round cricket ball" .)