Quickly gathering ore's not exactly rocket science! (9)
I believe the answer is:
aerospace
'rocket science' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'quickly gathering ore's not exactly' is the wordplay.
'quickly' becomes 'apace' (synonyms).
'gathering' means one lot of letters goes inside another.
'not exactly' indicates an anagram.
'ores' with letters rearranged gives 'eros'.
'apace' enclosing 'eros' is 'AEROSPACE'.
Can you help me to learn more?
(Other definitions for aerospace that I've seen before include "Technology of flight" , "Nasa's speciality" , "zone near Earth" , "Opera case (anag)" , "The aviation world" .)