Influence of a sandstone washout on the properties of an underlying coal seam

Abstract

Properties of coals, either washed products or seam samples, from the Ryhope Five Quarter seam (Middle Coal Measures, Westphalian B) at Vane Tempest colliery, County Durham, UK, show significant differences over restricted areas of seam workings. The differences can be shown to be systematically related to roof lithology: where the properties of the coal indicate lower rank, the seam is overlain by a washout sandstone, whereas a mudstone/shale roof covers the higher-rank parts of the worked seam. No single unequivocal reason can be proposed to explain the lithological influence upon the coal properties, although differing thermal conductivities and rock permeabilities may play their part, but equally possible is early oxidation of the coal or differing degrees of degradation of the organic biomass at the time of deposition under either sands or muds. The importance of precise mapping of sand bodies overlying coal seams is stressed because of the deleterious effect that a sand body can have on the coking potential of a coal seam.