Conceive of silver being found in excavation on island (7)
I believe the answer is:
imagine
'conceive of' is the definition.
('imagine' can be a synonym of 'conceive of')
'silver being found in excavation on island' is the wordplay.
'silver' becomes 'ag' (Ag is the chemical symbol for silver).
'being found in' is an insertion indicator.
'excavation' becomes 'mine' (mine is a kind of excavation**).
'on' says to put letters next to each other.
'island' becomes 'i'.
'ag' put inside 'mine' is 'magine'.
'magine' after 'i' is 'IMAGINE'.
(Other definitions for imagine that I've seen before include "Picture in mind, envisage" , "Picture mentally" , "Picture, conceive" , "John Lennon classic (just think of it!)" , "Form a mental image in the mind" .)