Large mineral aggregate around one river in Europe (5)
I believe the answer is:
loire
'river in europe' is the definition.
'Loire' can be an answer for 'river' (Loire is an example). I'm unsure of the 'in europe' bit.
'large mineral aggregate around one' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'mineral aggregate' becomes 'ore' (I've seen this before).
'around' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'ore' enclosing 'i' is 'oire'.
'l'+'oire'='LOIRE'
Can you help me to learn more?
(Other definitions for loire that I've seen before include "valley famous for its wines" , "French river (Orleans, Tours, Nantes)" , "flower found amid vineyards" , "Longest French river" , "French department" .)