Stoping is the process of extracting the desired ore or other mineral from an underground mine, leaving behind an open space known as a stope. [1] Stoping is used when the country rock is sufficiently strong not to collapse into the stope, although in most cases artificial support is also provided.
The earliest forms of stoping were conducted with hand tools or by fire-setting; later gunpowder was introduced. From the 19th century onward, various other explosives, power-tools, and machines came into use. As mining progresses the stope is often backfilled with tailings, or when needed for strength, a mixture of tailings and cement. In old mines, stopes frequently collapse at a later time, leaving craters or flashes at the surface. They are an unexpected danger when records of underground mining have been lost with the passage of time.
Stoping is considered "productive work", and is contrasted with "deadwork", the work required merely to access the mineral deposit, such as sinking shafts and winzes, carving adits, tunnels, and levels, and establishing ventilation and transportation. [2]
A stope can be created in a variety of ways. The specific method of stoping depends on a number of considerations, both technical and economical, based largely on the geology of the ore body being mined. These include the incline of the deposit (whether it is flat, tilted or vertical), the width of the deposit, the grade of the ore, the hardness and strength of the surrounding rock, and the cost of materials for supports. [3]
It is common to dig shafts vertically downwards to reach the ore body and then drive horizontal levels through it. Stoping then takes place from these levels.
When the ore body is more or less horizontal, various forms of room and pillar stoping, cut and fill, [4] or longwall mining can take place. In steeply-dipping ore bodies, such as lodes of tin, the stopes become long narrow near-vertical spaces, which, if one reaches the surface is known as a gunnis or goffen. [1] A common method of mining such vertical ore bodies is stull stoping, see below.
Open stoping is generally divided into two basic forms based on direction: overhand and underhand stoping, which refer to the removal of ore from above or below the level, respectively. It is also possible to combine the two in a single operation.
Underhand stoping, also known as horizontal-cut underhand or underbreaking stoping, is the working of an ore deposit from the top downwards. Like shrinkage stoping, underhand stoping is most suitable for steeply dipping ore bodies. [5] Because of the mechanical advantage it offers hand tools being struck downward (rather than upward, against gravity), this method was dominant prior to the invention of rock blasting and powered tools. [6]
In overhand stoping, the deposit is worked from the bottom upward, the reverse of underhand stoping. With the advent of rock blasting and power drills, it became the predominant direction of stoping. [3]
In combined stoping, the deposit is simultaneously worked from the bottom upward and the top downward, combining the techniques of overhand and underhand stoping into a single approach.
Breast stoping is a method used in horizontal or near-horizontal ore bodies, where gravity is not usable to move the ore around. [7] Breast stoping lacks the characteristic "steps" of either underhand or overhand stoping, being mined in a singular cut. Room and pillar is a type of breast stoping.
Stull stoping is a form of stoping used in hardrock mining that uses systematic or random timbering ("stulls") placed between the foot and hanging wall of the vein. The method requires that the hanging wall and often the footwall be of competent rock as the stulls provide the only artificial support. This type of stope has been used up to a depth of 3,500 feet (1,077 m) and at intervals up to 12 feet (3.7 m) wide. [8] The 1893 mining disaster at Dolcoath mine in Cornwall was caused by failure of the stulls holding up a huge weight of waste rock. [9]
Square-set timbering was invented in the Comstock Lode, Virginia City, Nevada in the 1860s.
Square-set stoping is a historical method of stoping which relies on interlocking timbers set into place forming a grid, wedged tightly against the rock. As the mining progresses, generally upwards, new timber sets are added to fill the void. Ore is dropped through the sets freely or fed into chutes and either loaded into ore cars or mucked out from there.
Depending on rock conditions and other technical considerations, once the stope has reached its engineered height, it may be left open or backfilled for support. A common historical method of hydraulic fill involved dumping waste rock into a completed stope, then slurrying in a mixture of mill sand and water. The water drains away leaving the sand to lock the fill in place. Other methods of hydraulic fill using cement and mill sand, such as paste fill, are more contemporary methods of stoping and unlikely used in conjunction with the antiquated method of squareset timbering.
Shrinkage stoping is most suitable for steeply dipping ore bodies (70°—90°). In shrinkage stoping, mining proceeds from the bottom upwards, in horizontal slices (similar to cut and fill mining), with the broken ore being left in place for miners to work from. Because blasted rock takes up a greater volume than in situ rock (due to swell factor), some of the blasted ore (approximately 40%) must be removed to provide working space for the next ore slice. Once the top of the stope is reached all the ore is removed from the stope. The stope may be backfilled or left empty, depending on the rock conditions. [10]
This section possibly contains original research .(June 2020) |
Long hole stoping as the name suggests uses holes drilled by a production drill to a predetermined pattern as designed by a mining engineer. Long hole stoping is a highly selective and productive method of mining and can cater for varying ore thicknesses and dips (0 – 90 degree). It differs from manual methods such as timbered and shrinkage as once the stope has begun blasting phase it cannot be accessed by personnel. For this reason the blasted rock is designed to fall into a supported drawpoint or removed with remote control LHD (load, haul, dump machine).
The biggest limitation with this method is the length of holes that can be accurately drilled by the production drill, larger diameter holes using in the hole hammer drills can be accurate to over 100 m in length while floating boom top hammer rigs are limited to ~30 m.
Holes drilled underground are generally drilled perpendicular, in a radial pattern around the drive. For the blastholes to successfully extract the ore material they must be able to fire into a void in front. A slot is required in every stope to provide the initial void. The slot is often the most difficult, costly and highest risk component of mining a stope. Depending on the shape, height and other factors, different methods to create a slot can be used such as:
A gunnies, gunnis, or gunniss is the space left in a mine after the extraction by stoping of a vertical or near vertical ore-bearing lode. The term is also used when this space breaks the surface of the ground, but it can then be known as a coffin or goffen. It can also be used to describe the deep trenches that were dug by early miners in following the ore-bearing lode downwards from the surface – in this case they are often called open-works; their existence can provide the earliest evidence of mining in an area. William Pryce, writing in 1778, also used the term as a measure of width, a single gunnies being equal to three feet.
Underground hard-rock mining refers to various underground mining techniques used to excavate "hard" minerals, usually those containing metals, such as ore containing gold, silver, iron, copper, zinc, nickel, tin, and lead. It also involves the same techniques used to excavate ores of gems, such as diamonds and rubies. Soft-rock mining refers to the excavation of softer minerals, such as salt, coal, and oil sands.
Open-pit mining, also known as open-cast or open-cut mining and in larger contexts mega-mining, is a surface mining technique that extracts rock or minerals from the earth.
A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water, other liquids, or gases. It may also be part of a geotechnical investigation, environmental site assessment, mineral exploration, temperature measurement, as a pilot hole for installing piers or underground utilities, for geothermal installations, or for underground storage of unwanted substances, e.g. in carbon capture and storage.
The tin mining industry on Dartmoor, Devon, England, is thought to have originated in pre-Roman times, and continued right through to the 20th century, when the last commercially worked mine closed in November 1930. From the 12th century onwards tin mining was regulated by a stannary parliament which had its own laws.
Borehole Mining (BHM) is a remote operated method of extraction (mining) of mineral resources through boreholes based on in-situ conversion of ores into a mobile form (slurry) by means of high pressure water jetting (hydraulicking). This process is carried-out from a land surface, open pit floor, underground mine or floating vessel through pre-drilled boreholes.
Surface mining, including strip mining, open-pit mining and mountaintop removal mining, is a broad category of mining in which soil and rock overlying the mineral deposit are removed, in contrast to underground mining, in which the overlying rock is left in place, and the mineral is removed through shafts or tunnels.
Shaft mining or shaft sinking is the action of excavating a mine shaft from the top down, where there is initially no access to the bottom. Shallow shafts, typically sunk for civil engineering projects, differ greatly in execution method from deep shafts, typically sunk for mining projects.
Minas da Panasqueira or Mina da Panasqueira is the generic name for a set of mining operations between Cabeço do Pião and the village of Panasqueira, which has operated in a technically integrated and continuous manner practically since the discovery of ore there. Subsequently, it was agglomerated into a single administrative entity called Couto Mineiro da Panasqueira which had its last demarcation on 9 March 1971 and later on in the present C-18 Mining Concession. The mining facilities are currently centralized in the area of Barroca Grande – Aldeia de São Francisco de Assis (Covilhã) through which the current underground operation, ore extraction and processing facilities are accessed.
Mine exploration is a hobby in which people visit abandoned mines, quarries, and sometimes operational mines. Enthusiasts usually engage in such activities for the purpose of exploration and documentation, sometimes through the use of surveying and photography. In this respect, mine exploration might be considered a type of amateur industrial archaeology. In many ways, however, it is closer to caving, with many participants actively interested in exploring both mines and caves. Mine exploration typically requires equipment such as helmets, head lamps, Wellington boots, and climbing gear.
Kidd Mine or Kidd Creek Mine is an underground base metal (copper-zinc-silver) mine 24 km (15 mi) north of Timmins, Ontario, Canada. It is owned and operated by Swiss multinational Glencore Inc. The mine was discovered in 1963 by Texas Gulf Sulfur Company. In 1981, it was sold to Canada Development Corporation, then sold in 1986 to Falconbridge Ltd., which in 2006 was acquired by Xstrata, which in turn merged with Glencore in 2013. Ore from the Kidd Mine is processed into concentrate at the Kidd Metallurgical Site, located 27 km (17 mi) southeast of the mine, which until 2010 also smelted the ore and refined the metal produced. Following the closure of the majority of the Met Site, concentrate is now shipped to Quebec for processing. Kidd Mine is the world's deepest copper-zinc mine.
Room and pillar or pillar and stall is a variant of breast stoping. It is a mining system in which the mined material is extracted across a horizontal plane, creating horizontal arrays of rooms and pillars. To do this, "rooms" of ore are dug out while "pillars" of untouched material are left to support the roof – overburden. Calculating the size, shape, and position of pillars is a complicated procedure, and an area of active research. The technique is usually used for relatively flat-lying deposits, such as those that follow a particular stratum. Room and pillar mining can be advantageous because it reduces the risk of surface subsidence compared to other underground mining techniques. It is also advantageous because it can be mechanized, and is relatively simple. However, because significant portions of ore may have to be left behind, recovery and profits can be low. Room and pillar mining was one of the earliest methods used, although with significantly more manpower.
In-situ leaching (ISL), also called in-situ recovery (ISR) or solution mining, is a mining process used to recover minerals such as copper and uranium through boreholes drilled into a deposit, in situ. In-situ leach works by artificially dissolving minerals occurring naturally in the solid state.
The following outline is provided as an overview of and topical guide to mining:
Mining in the Upper Harz region of central Germany was a major industry for several centuries, especially for the production of silver, lead, copper, and, latterly, zinc as well. Great wealth was accumulated from the mining of silver from the 16th to the 19th centuries, as well as from important technical inventions. The centre of the mining industry was the group of seven Upper Harz mining towns of Clausthal, Zellerfeld, Sankt Andreasberg, Wildemann, Grund, Lautenthal und Altenau.
The Kemi Mine is owned by Outokumpu Chrome Oy, a subsidiary of Outokumpu Oyj. It is located in Elijärvi, in the municipality of Keminmaa, to the north of Kemi. The Kemi Mine is the largest underground mine in Finland, with an annual production capacity of 2.7 million tonnes of ore. It is also part of the integrated ferrochrome and stainless steel manufacturing chain owned by Outokumpu in the Kemi-Tornio region. The Kemi Mine has approximately 400 employees every day, both employees of Outokumpu and contractors.
Zinc mining is the process by which mineral forms of the metal zinc are extracted from the earth through mining. A zinc mine is a mine that produces zinc minerals in ore as its primary product. Common co-products in zinc ores include minerals of lead and silver. Other mines may produce zinc minerals as a by-product of the production of ores containing more valuable minerals or metals, such as gold, silver or copper. Mined ore is processed, usually on site, to produce one or more metal-rich concentrates, then transported to a zinc smelter for production of zinc metal.
The Sumdum mine is one of the largest lead and zinc mines in United States. The mine is located in north-western United States in Alaska. The mine has reserves amounting to 24 million tonnes of ore grading 0.37% zinc and 79.1 million oz of silver.
The Pogo mine is a gold mine in the state of Alaska. By 31 December 2017 Pogo had produced 3.6 million ounces of gold at a grade of 13.6 g/t. Annual production for 2020 was 205,878 ounces. At 31 December 2019 the mine had Proven and Probable Reserves of 1.5 million ounces of gold at a grade of 7.5 g/t (JORC). It is located 30 miles (48 km) northeast of Delta Junction and 90 miles (145 km) east of Fairbanks. Northern Star Resources Ltd announced in May 2020 that it had entered into an agreement with the Japan-based Sumitomo Metal Mining Co and Sumitomo Corp to acquire the Pogo Gold mine.
The Rajpura Dariba Mine VRM disaster took place in Dariba, Udaipur, India on 28 August 1994 at a mine operated by Hindustan Zinc Ltd.