mother lode

mother lode
ˈmother lode , moth‧er‧lode /ˈmʌðələʊd $ -ðərloʊd/ noun [countable usually singular] American English
1. a mine that is full of gold, silver etc
2. a place where you can find a lot of a particular type of object
    mother lode of
    The Sharper Image catalog is a mother lode of men’s gadgets and toys.
3. hit the mother lode informal to produce or find something that will make you very rich, happy, or successful:
    They hit the mother lode with their second album.