gold mine

noun3

1. •
   A mine for gold ore or metal.

   • South Africa has many goldmines.
2. •
   A very profitable economic venture.

   • This oil deposit is a regular gold mine. We make more and more money every year!
3. •
   A plentiful stockpile of something sought-after.

   • The Smithsonian Institution is a goldmine of knowledge, but like most mines, you have to dig for the good stuff.