Convict returns with mineral — and plenty of it (6)
I believe the answer is:
galore
'plenty of it' is the definition.
'convict returns with mineral' is the wordplay.
'convict' becomes 'lag' (I've seen this before).
'returns' says the letters should be written backwards.
'with' is a charade indicator (letters next to each other).
'mineral' becomes 'ore' (ore is a kind of mineral).
'lag' written backwards gives 'gal'.
'gal'+'ore'='GALORE'
'and' is the link.
(Other definitions for galore that I've seen before include "'Whisky ------!', classic Ealing comedy of 1949" , "abundantly" , "Pussy ---, Bond girl" , "Existing in great numbers" , "In profusion" .)