1) Usually a vertical or near vertical excavation which gives men access to the minerals underground.
The earliest OED examples noted are connected with mining, either in Durham or in Cornwall. In Yorkshire the references are from the latter period: 1600 libertie for digging and gettinge … and making waies and shafts, Northowram
1668 a shaft put downe cost Ł18, Tan Hill. The meaning of this word may be self-evident but it is of interest because of the way it came to symbolise the ability of a lessee to gain access to the riches underground and the landowners’ need to control that access. In 1739, for example, a lease to John Kaye of Lepton finished with the words and shall not get Coals with above one shaft at a time. It was occasionally used of a horizontal gallery.