gold mine vs plethora

gold mine

noun
  • A plentiful stockpile of something sought after. 

  • A mine for gold ore or metal. 

  • A very profitable economic venture. 

plethora

noun
  • An excessive amount or number; an abundance. 

  • Excess of blood in the skin, especially in the face and especially chronically. 

How often have the words gold mine and plethora occurred in a corpus of books? (source: Google Ngram Viewer )