Tractor shifted boulder containing separate traces of lead and zinc (9)
I believe the answer is:
bulldozer
'tractor' is the definition.
(bulldozer is a kind of tractor)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for bulldozer that I've seen before include "Powerful tractor for clearing ground" , "Clearer" , "One pushes" , "For heavy machinery" , "heavy tractor" .)