A mine is a place beneath the surface of the earth where raw materials are found and cultivated.
The shaft is the portal through which you get to the place below. From the surface, it is the evidence that an excavation has already taken place and that access to what is available has already been established. This is a fairly common dream image and indicates that there may be a need to revisit the dark and scary places below the surface of your consciousness in order to reap the benefit that is hidden in those realms.
If the mine shaft seems abandoned, you are revisiting some insight or awareness that you have already mined, so look to past wisdom for your answers to today’s questions.... Complete Dictionary of Dreams