The marriage is on Cornwall OPC Database, and says:
Married 12th October 1779 at Mawgan in Pydar
John Roberts, residing at St Austle (sic) to Ann Dungey
No other details.
There are a number of burials for John Roberts, in and around St Austell!
But this one looks good?
7th June 1830, at St Austell, John Roberts, 73, of Charlestown