Stoping

Stoping is a process accommodating the ascent of magmatic bodies from their sources in the mantle (geology) or lower crust to the surface. The process involves the mechanical disintegration of the surrounding country/host rock, typically through fracturing due to pressure increases associated with thermal expansion of the host rock in proximity of the interface with the melt. Once fractures are formed, melt and/or volatiles will typically invade, widening the fracture and promoting the foundering of host rock blocks (i.e. stoped blocks). Once suspended in the melt, stoped blocks may either sink or float depending upon the density of the block relative to that of the melt. Additionally, blocks submerged within melt are subject to further thermally-induced fracturing which may account for the often observed "lack of evidence" for the process of stoping.

Mining method

Stoping also refers to a mining method where steeply dipping ores are removed by explosives and the shattered ore removed from a tunnel at a lower level. The resulting cavity, called a stope, is then backfilled, often with tailings or concrete. Before explosives, stopes were formed by fire-setting and mechanical attack, many examples of such stopes being found by mining at a much later time. Stopes are a feature of deep mines since miners tried as far as possible to use opencast or open pit methods wherever possible since it was much safer to have free access of air. The dangers of working in enclosed spaces was increased by the use of fire-setting, which produced large volumes of noxious gases as the rock faces were heated by wood fires, and then quenched with streams of water. The thermal shock encouraged fracture and disintegration of the rock.

The miners also left pillars of rock (often still containing veins) to support the stopes, collapse being a common hazard where large volumes of material had been removed. Backfilling was one way in which such stopes could be stabilised, and saved effort in removing waste debris. In old mines, stopes frequently collapse at a later time, leaving craters at the surface. They are an unexpected danger when all records of underground mining have been lost due to the passage of time.