European agreed mineral deposit is blot on the landscape (7)
I believe the answer is:
eyesore
'blot on the landscape' is the definition.
(I've seen this before)
'european agreed mineral deposit' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'agreed' becomes 'yes' (I've seen this before).
'mineral deposit' becomes 'ore' (I've seen this before).
'e'+'yes'+'ore'='EYESORE'
'is' acts as a link.
(Other definitions for eyesore that I've seen before include "Horrible sight" , "Hideous sight" , "terrible prospect" , "offensive to viewers" , "Ugly building" .)