US Mine Safety and Health Administration spokeswoman Amy Louviere said the fatality occurred at Patriot subsidiary Midland Trail Energy's Five Mile Prep Plant.
MSHA believes a hydraulic pump burst on a belt press just after 4pm. The names of the workers have not yet been released.
It is West Virginia's first coal-mining fatality of the year and the second nationally.
The plant has only had a few safety citations from MSHA, with the most recent in December.
Louviere said an order was issued to close the plant immediately after the fatality and a federal investigator was enroute.
