But in a July filing with the court, Horsehead’s financial adviser said the company’s assets were worth an estimated $280 million to $375 million. The main reason for the decline? The company’s decision to write down to almost zero the new zinc plant in Mooresboro it built for $550 million.

What accounts for the almost total loss in the plant’s value? Lazard, adviser to Horsehead in the bankruptcy, said it based its valuation on prices of the company’s debt and equity, both of which are naturally depressed by the company’s Chapter 11 filing. Lazard also referred vaguely to its consideration of “the latest 12 months revenue multiples of selected comparable guideline companies.”

This makes some of Horsehead’s shareholders suspicious.

“The major issue is how the company has been urging the court to believe that hundreds of millions of dollars of value vanished into thin air and a brand-new factory was deemed to be worthless,” said Thomas I. Boswell of Boswell Capital Management in Hong Kong, operator of the Intrinsic Value Limited Partnership, which owns 250,000 Horsehead shares. “To say that they’re writing off a $500 million plant basically because the share price of our stock and the prices of our bonds have fallen is ludicrous.”

Horsehead did not respond to an email seeking comment.

Christopher S. Sontchi, the federal judge overseeing the bankruptcy proceeding in Delaware, has raised questions of his own about the steep decline in the company’s worth. In an unusual ruling in May, he allowed the formation of an equity committee, giving Horsehead shareholders a chance to participate in the process. More than 1,000 individual investors own the stock.

“To put it bluntly, something doesn’t smell right to the court,” Judge Sontchi said, according to a court transcript. “There was a certain valuation scenario that existed pre-petition and there’s a radically different valuation scenario that exists post-petition, and there’s a sufficient amount of ambiguity as to what’s right and who’s right, that I believe it’s appropriate in this unique circumstance to appoint an equity committee.”