HELENA - The U.S. Supreme Court is expected to announce this week whether it will hear a case over Montana's 1998 ballot initiative that prohibited new cyanide "heap-leach" gold mines.

A Colorado-based mining venture has fought a long legal battle over the ban in the courts, and its claims have already been turned aside by the state Supreme Court.

Canyon Resources Corp. is hoping the Supreme Court will take the case, and ultimately find that the ban constituted an illegal taking of property. The company estimates its loss from roughly $80 million it sunk into the McDonald project near Lincoln to as much as $550 million for the value of the minerals it could have mined.

U.S. Supreme Court justices met Friday to discuss the case and will announce a decision on Tuesday, according to the court's schedule.

The mine operators say their property rights were denied when the state passed the ban on the use of cyanide in new gold mines. The company needed to use the banned process, which separates precious metals from ore, to profitably mine gold at the proposed Lincoln and should be compensated for the loss.

A favorable decision from the Supreme Court could produce a settlement on its losses, the company said.

The state argues that Montana's high court has already made a sound decision, and no further review is warranted. Canyon Resources and Seven-Up Pete never had a vested right to mine using the cyanide heap-leach process, the Montana Attorney General argued in a brief filed with the U.S. Supreme Court.

The mining venture estimates there is about 9 million ounces of gold and 20 million ounces of silver at to be mined at the Lincoln location, and more than half could be recovered by using cyanide.

The conservation group Montana Environmental Information Center has supported the state in defending the ban, while a conservative legal group called the Mountain States Legal Foundation is supporting the company.

James Hesketh, President & CEO of Canyon Resources Corporation, said the 1998 ban was a big blow to the company, and it has only now started to recover.

"It's been a huge impact on the company, and hugely destructive to our shareholder wealth," he said.

Hesketh said Montana should be obligated to pay if it wants to decide to ban a process it had made investments on.

"We believe we have a strong case," Hasketh said. "The trick in the Supreme Court is to get heard."

Hesketh said the company still has a case brewing at the District Court level if the Supreme Court rejects its claim.

"We have fiduciary responsibility to our shareholders to recover their losses," he said.