mother lode

1. In mining, the main source of a mineral in given area. We haven't hit the mother lode of silver quite yet—but we will!

2. By extension, an abundance of something. I wasn't looking to expand my record collection, but I sure hit the mother lode when I cleaned out my parents' attic! It's an exciting time to be a researcher in this field, as a mother lode of new data was recently released.