Benchmark prices for the coal used in steelmaking have plunged an additional 15% from levels that had already hit a six-year low, likely heaping more pain on several miners facing a financial brink, coal industry reports show. Japanese buyers are signing contracts that pay $93 a metric ton, the lowest price since 2004 for so-called metallurgical coal, Doyle Trading Consultants LLC and IHS Inc. IHS -0.30 % ’s “Inside Coal,” a trade publication, both said on Wednesday. Japanese steelmakers and Australian suppliers agree to contracts every quarter, setting the global benchmark. Prices have fallen more than 70% from a high of $330 a metric ton just four years ago. That spike had inspired a raft of multibillion-dollar deals among miners eager to sell at record-high prices. But their new supply flooded the market just as once-rampant Chinese demand slumped, and prices went into a tailspin that has lasted longer […]