Gold only found in old lady’s stately tomb (9)
I believe the answer is:
mausoleum
'stately tomb' is the definition.
(building containing a tomb)
'gold only found in old lady's' is the wordplay.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'only' becomes 'sole' (synonyms).
'found in' indicates putting letters inside.
'old lady' becomes 'mum' (I've seen this before).
'au'+'sole'='ausole'
'ausole' going into 'mum' is 'MAUSOLEUM'.
(Other definitions for mausoleum that I've seen before include "Housing for a tomb" , "gloomy site" , "One may lie impressively in this" , "Large, stately tomb" , "Sepulchre" .)