mother lode

• mother-lode

Probably a calque of Spanish veta madre (“mother lode”).

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mother lode (plural mother lodes)

1. (geology) A large or rich vein of gold or of another precious mineral from which other branches extend.
   • 1912, Jack London, Smoke Bellew, ch. 7:

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

2. (idiomatic, by extension) Any source of valuable or useful material.
   • 2000, Dick Thompson, "The Feds Step Up the Pace," Time, 10 April:

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