He promised investors 10% gains. Now, he’s accused of using their money for sailing excursions in an alleged Ponzi scheme

A financier has been extradited from the United Kingdom to the United States to face allegations that he cheated investors who were promised monthly 10% gains in what was actually a Ponzi scheme, authorities said.

Matthew Melton, 61, of Boulder, Colorado, has remained jailed at a federal lockup in Brooklyn after appearing in court Saturday to face securities fraud and wire fraud charges. His lawyer did not immediately respond to a message seeking comment.

Authorities said Melton...