mother lode noun
plural ∼ lodes [count] chiefly US : the place where the largest amount of gold, silver, etc., in a particular area can be found — usually singular ▪ a gold miner who struck/hit the mother lode [=who found the place containing the largest amount of gold] — often used figuratively ▪ The library's collection of old newspapers has proven to be a mother lode of information about the town's early history.
