The resignations have been effective since December 22.
Both Turner and Erhard are representatives of ArcLight Capital Partners and joined the Patriot board after the 2008 acquisition of Magnum Coal.
"We have enjoyed working with Patriot's board and management team since the Magnum transaction and have been impressed with the broad business capabilities of both the board and management,” Turner said.
He noted that the decision would allow both men more time to manage other portfolio investments.
Patriot announced the resignation of its president and chief operating officer Paul Vining in August.
Assuming the role of senior vice-president and chief operating officer was three-decade coal veteran Charles Ebetino Jr, who was previously Patriot’s senior vice-president of corporate development since the producer’s 2007 spin-off.
As part of the organizational adjustment, chief executive officer Richard Whiting took on the role of president and continued in his capacity as CEO.
Patriot Coal has 14 mining complexes in the Appalachian region and Illinois Basin and controls about 1.8 billion tons of proven and probably coal reserves.