The stope may be backfilled or left empty, depending on the rock conditions. Open stope mining leaves these caverns with no additional bracing or external support. In 1994, stope leaching of copper was reported at 16 mines in the US. Three methods of stope mining are commonly used. During the excavation, three stories below ground level, they came across an old stope. The empty stope is filled with cement fill. Inside, the veins have been removed and debris carefully stacked within the stope. These are essential to remove the material where the stope is unprotected from top. The operation maintained a completely unsupported "show stope" with dimensions of high, wide, and long. A slot is required in every stope to provide the initial void. The stope is then sealed to prevent access. A stope can be created in a variety of ways. The stope is blasted in slices of about 5 meter or so using explosives. Stope fill, plus remnant supergene silver and sulphide ore characterize the ore reserve. When the cleaning work is complete, the stope is abandoned and access is prohibited.