COLUMBUS, Ohio (AP) — A judge says an ex-treasure hunter should remain jailed on contempt-of-court charges.

Federal Judge Algenon Marbley Marbley has held Tommy Thompson in contempt since December 2015 for violating terms of a plea deal by refusing to respond to questions about the location of 500 missing gold coins.

Thompson's attorney argues federal law prohibits holding someone under such conditions for longer than 18 months.

Marbley denied the request Friday after a short hearing, saying Thompson is still refusing to follow his plea deal.

Thompson's attorney said he'll appeal Marbley's order.

The coins are valued at up to $4 million and were minted from gold taken from the S.S. Central America. It sank in an 1857 hurricane.