From Longman Dictionary of Contemporary Englishmother lodeˈmother lode, motherlode /ˈmʌðələʊd $ -ðərloʊd/ noun [countable usually singular] American English 1 HETIa mine that is full of gold, silver etc2 LOT/LARGE NUMBER OR AMOUNTa place where you can find a lot of a particular type of objectmother lode of The Sharper Image catalog is a mother lode of men’s gadgets and toys.3 → hit the mother lode
Examples from the Corpus
mother lode• The region is a mother lode of potential support for his candidacy. 