<P> Some mining, including much of the rare earth elements and uranium mining, is done by less - common methods, such as in - situ leaching: this technique involves digging neither at the surface nor underground . The extraction of target minerals by this technique requires that they be soluble, e.g., potash, potassium chloride, sodium chloride, sodium sulfate, which dissolve in water . Some minerals, such as copper minerals and uranium oxide, require acid or carbonate solutions to dissolve . </P> <P> Surface mining is done by removing (stripping) surface vegetation, dirt, and, if necessary, layers of bedrock in order to reach buried ore deposits . Techniques of surface mining include: open - pit mining, which is the recovery of materials from an open pit in the ground, quarrying, identical to open - pit mining except that it refers to sand, stone and clay; strip mining, which consists of stripping surface layers off to reveal ore / seams underneath; and mountaintop removal, commonly associated with coal mining, which involves taking the top of a mountain off to reach ore deposits at depth . Most (but not all) placer deposits, because of their shallowly buried nature, are mined by surface methods . Finally, landfill mining involves sites where landfills are excavated and processed . </P> <P> Sub-surface mining consists of digging tunnels or shafts into the earth to reach buried ore deposits . Ore, for processing, and waste rock, for disposal, are brought to the surface through the tunnels and shafts . Sub-surface mining can be classified by the type of access shafts used, the extraction method or the technique used to reach the mineral deposit . Drift mining utilizes horizontal access tunnels, slope mining uses diagonally sloping access shafts, and shaft mining utilizes vertical access shafts . Mining in hard and soft rock formations require different techniques . </P> <P> Other methods include shrinkage stope mining, which is mining upward, creating a sloping underground room, long wall mining, which is grinding a long ore surface underground, and room and pillar mining, which is removing ore from rooms while leaving pillars in place to support the roof of the room . Room and pillar mining often leads to retreat mining, in which supporting pillars are removed as miners retreat, allowing the room to cave in, thereby loosening more ore . Additional sub-surface mining methods include hard rock mining, which is mining of hard rock (igneous, metamorphic or sedimentary) materials, bore hole mining, drift and fill mining, long hole slope mining, sub level caving, and block caving . </P>

Two methods of mining used by indigenous miners