Interested Party in UK:
Thank you for your kind words!
The book
Mammy Pleasant's Partner by Helen O'Donnell Holdredge (1954) contains a brief account of a Cocos Island treasure recovery. The proceeds were used to purchase the famous New Almaden quicksilver mine in California. Apparently the plunder had only been hidden a short time - this appears to have been in the gray area between treasure hunting and theft.
Our Search for the Missing Millions (of Cocos Island) by One of the Searchers (1904) is a very interesting account of a failed treasure hunt. Privately printed in San Francisco, I believe most copies were destroyed in the Fire and Earthquake of 1906. You can read about the venture in the excellent
Voyage of the Herman. Had the author of that excellent work known about
Our Search... some gaps in the story might have been filled.
Many readers have found E.F. Knight's
The Cruise of the "Alerte" in Search of Treasure (1891) to be interesting. I know I have. Knight was a newspaper correspondent along with Stephen Crane and Richard Harding Davis during the Spanish American War. He lost an arm in World War I and continued to enjoy yachting - giving more truth to the term "single-handed sailing" than he probably cared for.
For summaries of many famous treasures and treasure hunts - and certainly more accurate accounts than most (including a chapter on Oak Island) it's difficult to match Robert Nesmith's
Dig for Pirate Treasure (1958). When I first started collecting treasure literature I purchased many items from Bob's old Foul Anchor Archives mailorder operation. From time to time you can still find books and pamphlets with his sticker on the inside back or front cover.
You might enjoy William La Verre's
Gold, Diamonds and Orchids (1935) and
Southward Ho! A Treasure Hunter in South America (1940). I highly recommend Bingham's
Lost City of the Incas (not a very original suggestion, I'm afraid) and the first-rate
Valverde's Gold - which will probably lead you to several other books.
Percy Fawcett's
Lost Trails, Lost Cities (1953) is one you are probably familiar with. David Grann's recent
The Lost City of Z; A Tale of Deadly Obsession in the Amazon (2010) I found quite good.
Hope these titles provide you with some clues to further reading!
Good luck to all,
~ The Old Bookaroo