Five gold cases aunt misappropriated somewhere in South Pacific (7)
I believe the answer is:
vanuatu
'somewhere in south pacific' is the definition.
'five gold cases aunt misappropriated' is the wordplay.
'five' becomes 'V' (Roman numeral).
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'cases' is an insertion indicator (forms a case around).
'misappropriated' is an anagram indicator.
'aunt' anagrammed gives 'nuat'.
'au' enclosing 'nuat' is 'anuatu'.
'v'+'anuatu'='VANUATU'
(Other definitions for vanuatu that I've seen before include "Archipelago, formerly known as New Hebrides" , "Country of the south-west Pacific" , "Southwest Pacific island hit by Cyclone Pam in March" , "Pacific island country, formerly New Hebrides" , "South Pacific Ocean nation of 80 islands" .)