Story of silver buried in South America (4)
I believe the answer is:
saga
'story' is the definition.
(a saga is a long story)
'silver buried in south america' is the wordplay.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'buried in' indicates putting letters inside (inserted letters get buried).
'south america' becomes 'SA' (abbreviation).
'ag' placed inside 'sa' is 'SAGA'.
'of' acts as a link.
(Other definitions for saga that I've seen before include "long series of events" , "Long narrative" , "Medieval Icelandic legend" , "A long story or poem - it's a gas" , "Norse epic" .)