State in which mineral has almost disappeared (6)
I believe the answer is:
oregon
'state' is the definition.
(I know that Oregon is a state)
'mineral has almost disappeared' is the wordplay.
'mineral' becomes 'ore' (ore is a kind of mineral).
'has' means one lot of letters go next to another.
'almost' means to remove the last letter (most of the word but not all of it).
'disappeared' becomes 'gone' (going is a kind of disappearing).
'gone' with its final letter taken off is 'gon'.
'ore'+'gon'='OREGON'
'in which' is the link.
(Other definitions for oregon that I've seen before include "America's Beaver State" , "area of the US" , "US state, capital Portland" , "Part of the US" , "Gooner (anag) - US state" .)