You might interested in several threads from the FAQ section on "The Golden Age of Piracy, Life of a Pirate and Other Related Topics" as well as a recent search:

• How frequently (if ever) did pirates actually bury treasure? Were treasure maps ever really used? - 55 comments, over 1 year old.
• This thread goes into a few notable examples and summarize the spread of the idea of "buried pirate treasure" as well as the more ordinary goods that pirates generally dealt in.
• Has there ever been documented evidence of anyone finding (pirate) buried treasure? - 47 comments, over 2 years old.
• The commenters here give a great deal of context for pirates during the Golden Age to explain the (lack of) prevalence for buried treasure.
• Did pirates really bury treasure? - 26 comments, over 11 months old.
• The commenters in this thread goes into detail on the spread of the "buried pirate treasure" throughout popular fiction.