The 47-year-old defendant, unnamed in the Norwegian media, appeared in Kongsberg District Court Monday and confessed he had used dynamite to blast out holes in the old mines, enter them and take out silver and rock crystals worth hundreds of thousands of dollars, broadcaster NRK reported.
The Drammen, Norway, father of two said he didn't do it for the money, but was overindulging his hobby of prospecting through the long-closed mines to make rare finds.
The mines, located on the scenic Hardangervidda mountain plateau in central southern Norway, are protected under the country's Cultural Heritage Act, and police say the man destroyed, polluted, drilled, blasted and excavated large quantities of silver -- which he then stole.
The man said in court Monday he first became interested in minerals in 1988. A few years later, he took a mountaineering course during which several climbers entered the silver mines and made large mineral findings in old slag heaps, where it was then still legal to look.
But in 1992, the area was put under the Cultural Heritage Act, and in 2003 the old Kongsberg Silver Mines were permanently protected from all traffic without special permission from Buskerud County officials.
The defendant said he was aware of the laws, but the excitement felt after finding silver and other precious minerals was too alluring, NRK reported.
"Unfortunately I could not stay away from the mines," he said, adding his intent wasn't to cause any harm and that he never saw his blasting as irresponsible, even though the area is a popular with hikers.
"I never thought to put anyone's life in danger," he said.
Southern Buskerud Police Inspector Hans Egil Seljordslia told the Norwegian daily Dagbladet the man was arrested red-handed while emerging from a mine in May 2012.
He said some of the stolen minerals were sold to Norwegian Mining Museum in Kongsberg -- the same museum responsible for managing the mines.
Silver believed linked to the Kongsberg mines and the rare mineral anatase were taken from the man's home, along with explosives. About 50 kilograms (110 pounds) of dynamite were found at his home, while another 1.5 kilograms (3.3 pounds) were taken from his holiday homes in Nore and Uvdal.
Police needed two cars to transport the silver, minerals, mining equipment and climbing equipment to the police station, with the total value of the seized materials put at about $335,000, Kongsberg Police Chief Morten Ole Pedersen told Norway's TV2.
The defendant's lawyer, Frederick Neumann, told the court this case is a special one.
"The case is unique in the sense that it is not common that individuals go into the mines to pick through them and blow up silver and crystals," he said. "The defendant admits that his hobby has gotten out of control."