What is the opening of a shaft, drift, or slope mine called?

The opening of a shaft, drift, or slope mine is referred to as a portal. This term specifically denotes the entry point or access way into a mining excavation. Portals are essential as they provide both access for personnel and machinery, and a means for hauling materials in and out of the mine. In mining operations, the design and location of a portal can significantly impact the efficiency and safety of the mining process, making it a fundamental aspect of mine development.

Other terms mentioned in the choices refer to different concepts within mining: a gob typically relates to the area of mined-out space in a coal mine where the roof has collapsed; a room often describes a space created within the mine where coal is extracted; and a face is the exposed surface of the coal seam that is currently being mined. While these terms are important in their own right, they do not accurately represent the entry point into a mine, which is why portal is the correct choice here.