Coal mining along the Warfield Fault, Mingo County, West Virginia: a tale of ups and downs

Abstract

Mine development along a 15-mile (24 km) section of the Warfield Fault in Mingo County, West Virginia has broadened the geological understanding of the fault and its related structures. The fault has been exposed in two new road cuts, one in the northeast-trending segment at Neely Branch and one in the eastern east-trending segment at the head of Marrowbone Creek. Both exposures show a well-defined normal fault with a 45° to 55° N dip, juxtaposing sandstone/shale packages from the roof and the floor of the Coalburg seam. The fault is associated with a thin gouge zone, some drag folding, and parallel jointing. Its trace tends to run parallel to the crest of the adjacent Warfield Anticline. Based on underground mine development and detailed core drilling, the vertical offset along the fault plane ranges from a maximum of 240 ft (73 m) in the central part of the area near the structural bend to less than 100 ft (30 m) in western and eastern directions. The fault is located along the relatively steeply dipping (locally in excess of 25%) southern limb of the Warfield Anticline, and appears related to a late phase of extension involving folded Pennsylvanian strata. On a regional scale, the lithological variations across the fault do not suggest any appreciable strike-slip component. Underground room and pillar mines in the Coalburg seam north and south of the fault have been greatly impacted by the Warfield structures. Due to the combined (and opposite) effects of the folding and faulting, the northern mines are located up to 400 ft (125 m) higher in elevation than the southern ones. Overland conveyor belts connect mining blocks separated by the fault. The practical mining limit along the steep slopes toward the fault is around 15%. Subsidiary normal faults with offsets in the 5- to 15-ft (1.5–4.5 m) range are fairly common and form major roof control and production hurdles. Overall, the Warfield structures pose an extra challenge to mine development in this part of the Appalachian Coalfields.