salt a mine
salt the mine
1. To make a mine appear profitable by filling it with ore containing the desired material. It turned out that they'd salted the old abandoned mine with low-grade gold deposits to convince us to buy, then skipped town with the money.
2. To plant false information about something to fraudulently increase its value, potency, or desirability. After the dossier circulated the media, nearly culminating in the president's impeachment, it came to light that the senator's campaign had heavily "salted the mine" with falsified accounts of witnesses who'd been paid to cooperate.