Rich vein of ore

• Profitable source
• Gold miner's bonanza
• Vein of ore
• Jackpot
• Prospector's dream
• In the ___, there's the greatest concentration of ___
• Miner's dream

Wikipedia Word definitions in Wikipedia
Motherlode is a 1988 James Brown compilation album . Created as a follow-up to the successful 1986 compilation In the Jungle Groove , it similarly focuses on Brown's funk recordings of the late 1960s and early 1970s. It includes live performances and remixes ...

Wiktionary Word definitions in Wiktionary
n. 1 (context literally English) The main, central lode of a natural resource, near which smaller deposits of the same ore etc. exist. 2 (context figuratively English) The main prize, best cut or pick etc. by far, dwarfing all others.