"We have stopped all production but the furnaces are still switched on while the search for a new investor continues," a company spokesman said. "If a new investor is found we would be able to restart work quickly."
The company, based in Duisburg in central Germany, had in the last seven days cut its workforce from 310 to 80, the spokesman said.
"We have to keep the furnaces alight while the search for a new investor continues," the spokesman said. "If they are turned off we would have to reapply for a licence to produce metal here."
"Under current environmental protection rules it is very unlikely we would be permitted to operate at this location again. The company is over 100 years old and we are now surrounded by houses."
Sudamin Metallhuette had said in May its financial problems stemmed largely from a sharp rise in zinc concentrate prices on aggressive Chinese buying on the world market.
Energy costs had also risen sharply.
Sudamin's output was sold largely to other parts of Germany's metals industry with ThyssenKrupp AG a major customer.
Germany's non-ferrous metals industry has been hit by plant closures this year. Two major aluminium plants, Hamburger Aluminium and Stade, are also ending production largely because of high electricity costs.