gold mine

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A rich or plentiful source of something desired.

from The Century Dictionary.

• noun A place whore gold is or may be mined.
• noun Anything productive of great wealth.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A mine for gold ore or metal.
• noun idiomatic A very profitable economic venture.
• noun idiomatic A plentiful stockpile of something sought after.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a good source of something that is desired
• noun a mine where gold ore is found
• noun a good source of something that is desired
• noun a mine where gold ore is found