River left mineral deposit skirting island (5)
I believe the answer is:
loire
'river' is the definition.
(Loire is an example)
'left mineral deposit skirting island' is the wordplay.
'left' becomes 'l' (common abbreviation).
'mineral deposit' becomes 'ore' (I've seen this before).
'skirting' indicates putting letters inside.
'island' becomes 'i'.
'ore' placed around 'i' is 'oire'.
'l'+'oire'='LOIRE'
(Other definitions for loire that I've seen before include "banker" , "part of France" , "European river" , "France's longest river" , "Longest French river" .)