mother lode vs wealth

mother lode

noun
  • Any source of valuable or useful material. 

  • A large or rich vein of gold or of another precious mineral from which other branches extend. 

wealth

noun
  • Riches; a great amount of valuable assets or material possessions. 

  • A great amount; an abundance or plenty. 

How often have the words mother lode and wealth occurred in a corpus of books? (source: Google Ngram Viewer )