Ore investigator like Leo? (7)
I believe the answer is:
assayer
'ore investigator' is the definition.
(someone who tests minerals)
'like leo?' is the wordplay.
'like' becomes 'as'.
'leo?' becomes 'Sayer' (Leo Sayer, the English-Australian singer).
'as'+'sayer'='ASSAYER'
(Other definitions for assayer that I've seen before include "Tester of chemicals on metal" , "One analyses metals" , "(Precious metal) analyst" , "He allocates marks" , "One does chemical tests on metals" .)