Deep seam mining

Underground soft rock mining is a group of underground mining techniques used to extract coal, oil shale, potash and other minerals or geological materials from sedimentary ("soft") rocks. Because deposits in sedimentary rocks are commonly layered and relatively less hard, the mining methods used differ from those used to mine deposits in igneous or metamorphic rocks (see Underground mining (hard rock)). Underground mining techniques also differ greatly from those of surface mining.

The number sign, or hash sign (#) is often used as shorthand to denote shaft or seam, as in 4# (4 shaft or seam depending on context).

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