Mineral aggregate originally rife in outskirts of Odense (3)
I believe the answer is:
ore
'mineral aggregate' is the definition.
(I've seen this before)
'originally rife in outskirts of odense' is the wordplay.
'originally' suggests taking the first letters.
'in' is an insertion indicator.
'outskirts of' suggests removing the centre.
'odense' with its centre removed is 'oe'.
The first letter of 'rife' is 'r'.
'r' placed into 'oe' is 'ORE'.
(Other definitions for ore that I've seen before include "Danish currency" , "Valuable resource" , "Raw metal" , "it could be gold" , "Mineral-bearing rock" .)