noun (n)

• an especially rich vein of precious ore(noun.object)

  source: wordnet30
• a sudden happening that brings good fortune (as a sudden opportunity to make money)(noun.event)

  Synonym:
  boom, bunce, godsend, gold rush, gravy, manna from heaven, windfall
  

  source: wordnet30
• In mining, a rich mine or vein of silver or gold; hence, anything which is a mine of wealth or yields a large income.(noun)

  source: webster1913