An extensive drilling programme carried out by the former British Coal Opencast Executive (BCOE) between 1975 and 1985 established that the geology is relatively simple.

The two coal seams to be worked by the mine are the Sharlston Top (1.16 metres thick) and the Sharlston Low (1.42 metres thick).  There may also be extraction in the Sharlston Yard seam, although this is still to be decided.

Two areas of coal have been defined; the Northern area is a fully proven recoverable reserve consisting of Sharlston Top ( 351,800 tonnes) and Sharlston Low (411,300 tonnes).

It is separated from the Southern area by the North Anglers Fault. The Southern area is a resource that has been determined from boreholes and a detailed examination of colliery abandonment plans in the vicinity. It consists of Sharlston Top (896,100 tonnes) and Sharlston Low (1,074,900 tonnes). The depth to the basal seam (Sharlston Low) varies from 45 to 130 metres.