There are as many mining methods of extraction to choose from as there are sizes and shapes of orebodies. The shape and orientation of an orebody, the strength of the ore and surrounding rock and the manner in which the valuable minerals are distributed are different for each ore zone. These and other factors will influence the selection of a mining method and the overall plan for developing the orebody.
Operating mines range in size from small underground operations (some of which have only a few production levels and may produce under 100 tonnes of ore per day) to the large open pits (some of which move thousands of tonnes or ore and waste rock per day).
The primary opening into an underground mine can he either a shaft, a decline (also called a ramp) driven down into the earth, or an adit, a horizontal opening driven into the side of a hill or mountain. All have the same purpose — to provide access for people, materials and equipment and to provide a way for ore to be brought to surface.
Shafts are usually vertical (although they can be inclined) and are equipped with hoists and head- frames, structures at the top that enclose the hoist.
Ramps, on the other hand, usually spiral downward at a gradient of about 15% to allow access into the mine by rubber-tired mobile equipment. In some cases, ramps are driven in a straight line to accommodate conveyor belts, or have straight runs with switch back points. Ramps are generally less expensive to develop than shafts. But depending on the angle of the decline, the size of the opening and the ground conditions encountered, the total cost may be higher than the cost of developing a shaft to reach the same depth.
Horizontal or level mine workings are called crosscuts and drifts. Sometimes it is useful to open vertical workings between levels in an underground mine; these are called raises or winzes.