mother lode

plural mother lodes · alternative mother-lode · alternative motherlode

1. geographyA large or rich vein of gold or of another precious mineral from which other branches extend.

   Undeterred, reasoning from the coarseness of the gold that it had not traveled far, they had set out in search of the mother lode.

   1912, Jack London, “The Little Man”, in Smoke Bellew

2. broadlyidiomaticAny source of valuable or useful material.

   Emerging, but No Longer a Mother Lode of Profits [title]

   2014 March 4, Landon Thomas Jr., “Emerging, but No Longer a Mother Lode of Profits”, in New York Times

   1 more example

   It is also letting them probe the genomes of other organisms for DNA that could turn out to be a mother lode for medicine.

   2000 April 10, Dick Thompson, “The Feds Step Up the Pace”, in Time