gold vein; vein of gold
Literal geological meaning: a vein or seam of gold in rock. Also used metaphorically for a rich source of wealth.
It is said that a vein of gold runs through this mountain.
The prospectors kept searching for a new gold vein.
financial backing; source of funds; money connection
Figurative use: a person or organization that provides money, or a reliable source of funding. Often used in business or political contexts.
He secured a solid source of funds for the election.
The company found a new financial connection overseas.
The survey team discovered a new gold vein deep in the mountains.
The reporter tried to look into the politician's financial backing.
After the scandal, his source of funding dried up.