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1. Literally, a mine where gold ore is found and excavated. Also written as "goldmine." More than 500 workers have become trapped in a gold mine after a minor earthquake cause the mineshaft to collapse.
2. An enterprise, opportunity, or resource that is or has the potential to be extremely profitable. The social networking site has since become a veritable gold mine, attracting millions of new users every month and generating staggering amounts of money from ad revenue. If we can secure the merger deal with the pharmaceutical giant in London, I'm sure it will prove to be a gold mine!
3. A person, place, or thing containing a plentiful amount of something valuable or desirable. Who knew that my grandfather's attic would turn out to be a gold mine of priceless antiques? This database is a gold mine for anyone interested in medical research trials. Our professor is a gold mine of information about medieval French literature.
be sitting on a gold mine
To have immediate access to a plentiful amount of something valuable or desirable, especially something that one has not yet profited from. Who knew that my grandfather was sitting on a gold mine of priceless antiques all these years? If your social networking site is attracting millions of new users every month, then you guys are definitely sitting on a gold mine.
gold mine of information
Something that yields a lot of valuable or useful information. I've never met any of these relatives before, so your photo albums will be a gold mine of information.
(a) gold mine of information
Fig. someone or something that is full of information. Grandfather is a gold mine of information about World War I. The new encyclopedia is a positive gold mine of useful information.
A rich, plentiful source of wealth or some other desirable thing, as in That business proved to be a gold mine, or She's a gold mine of information about the industry. [First half of 1800s]