But U.S. Attorney Charles Miller said his investigation is ongoing and did not rule out the possibility that individuals might be charged with violating federal mine safety laws.
"It's our hope this sends a message to the coal industry," Miller said.
Mine Safety and Health Administration spokeswoman Amy Louviere said the $1.7 million civil penalty was the agency's highest ever against a coal company. The $2.5 million criminal penalty was the second-highest.
State and federal investigators say an overheated conveyer belt caused the Jan. 19, 2006, fire at Aracoma Coal Co.'s Alma No. 1 mine.
Two miners — 33-year-old Don Bragg and 47-year-old Ellery Elvis Hatfield — died after they were separated from the rest of their mining crew. Weeks earlier, a mine explosion killed 12 miners at Sago Mine in northern West Virginia, owned by International Coal Group.
Both incidents led to sweeping federal and state mine safety law revisions.
Bragg's and Hatfield's widows attended Tuesday's announcement, but declined comment. Their lawyer, Bruce Stanley, said they hoped the "penalties will help convince all operators that money will never be more important than miners' lives."
Last month, Richmond, Va.-based Massey Energy agreed to settle a wrongful death lawsuit filed by the families. The terms of that settlement were not disclosed.