Chañarcillo is a town and mine in the Atacama Desert of Copiapó Province , Atacama Region , Chile , located near Vallenar and 60 km from Copiapó . It is noted for its silver mining . The town grew after the Chañarcillo silver mine, discovered on May 16, 1832, by Juan Godoy , sparkled the Chilean silver rush . It grew in prominence in the second half of the nineteenth century and became important in the Atacama mining industry and one of the most important mines to the Chilean economy. It was connected by railway before 1862. Today the settlement is largely in ruins.
51-423: The Chanarcillo District produced at least $ 100 million in silver before abandonment. This production from up to 20 mines was limited to a third of a square mile. From 1860 until 1885, 2,500,000 kg of silver was produced. Most production occurred before 1930 and since then until 1960, only minor amounts of silver were produced by removing pillars in mines or from the dump material. In 1870, 1,570 miners worked in
102-405: A decollement . Extensional decollements can grow to great dimensions and form detachment faults , which are low-angle normal faults with regional tectonic significance. Due to the curvature of the fault plane, the horizontal extensional displacement on a listric fault implies a geometric "gap" between the hanging and footwalls of the fault forms when the slip motion occurs. To accommodate into
153-860: A plate boundary. This class is related to an offset in a spreading center , such as a mid-ocean ridge , or, less common, within continental lithosphere , such as the Dead Sea Transform in the Middle East or the Alpine Fault in New Zealand. Transform faults are also referred to as "conservative" plate boundaries since the lithosphere is neither created nor destroyed. Dip-slip faults can be either normal (" extensional ") or reverse . The terminology of "normal" and "reverse" comes from coal mining in England, where normal faults are
204-582: A fault hosting valuable porphyry copper deposits is northern Chile's Domeyko Fault with deposits at Chuquicamata , Collahuasi , El Abra , El Salvador , La Escondida and Potrerillos . Further south in Chile Los Bronces and El Teniente porphyry copper deposit lie each at the intersection of two fault systems. Faults may not always act as conduits to surface. It has been proposed that deep-seated "misoriented" faults may instead be zones where magmas forming porphyry copper stagnate achieving
255-410: A fault often forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. The level of a fault's activity can be critical for (1) locating buildings, tanks, and pipelines and (2) assessing the seismic shaking and tsunami hazard to infrastructure and people in
306-408: A fault's age by studying soil features seen in shallow excavations and geomorphology seen in aerial photographs. Subsurface clues include shears and their relationships to carbonate nodules , eroded clay, and iron oxide mineralization, in the case of older soil, and lack of such signs in the case of younger soil. Radiocarbon dating of organic material buried next to or over a fault shear
357-421: A recovery rate as low as 40% in some cases, room and pillar mining cannot compete in terms of profitability with many modern, more mechanized types of mining such as longwall or surface mining . Abandoned mines have a tendency to collapse. In remote areas, collapses can be dangerous to wildlife, but subsidence of abandoned mines can be hazardous to infrastructure above and nearby. Significant amount of coal
408-432: Is a stub . You can help Misplaced Pages by expanding it . Room and pillar 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
459-415: Is also the line commonly plotted on geologic maps to represent a fault. A fault zone is a cluster of parallel faults. However, the term is also used for the zone of crushed rock along a single fault. Prolonged motion along closely spaced faults can blur the distinction, as the rock between the faults is converted to fault-bound lenses of rock and then progressively crushed. Due to friction and
510-616: Is an oxidized and supergene sulfide enriched rock. Oxidized ores occur above the water table and supergene sulfide enrichment below. In the oxidized zone, ore minerals include native silver and argentite have been replaced by cerargyrite , iodobromite , bromyrite , embolite , and iodyrite . In the supergene sulfide enriched zone, ore minerals include pearceite , proustite , tetrahedrite , polybasite , and pyrargyrite . Groups of large crystals have been found at Chañarcillo, including proustite , stephanite , chlorargyrite and adamite . This Atacama Region location article
561-461: Is left on the pillars as roof support. Note Fault (geology) In geology , a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth 's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as
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#1732765126360612-543: Is often critical in distinguishing active from inactive faults. From such relationships, paleoseismologists can estimate the sizes of past earthquakes over the past several hundred years, and develop rough projections of future fault activity. Many ore deposits lie on or are associated with faults. This is because the fractured rock associated with fault zones allow for magma ascent or the circulation of mineral-bearing fluids. Intersections of near-vertical faults are often locations of significant ore deposits. An example of
663-492: 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. The room and pillar system is used in mining coal , gypsum , iron , limestone , and uranium ores, particularly when found as manto or blanket deposits, stone and aggregates , talc , soda ash , and potash . It has been used worldwide from
714-434: Is released in part as seismic waves , forming an earthquake . Strain occurs accumulatively or instantaneously, depending on the liquid state of the rock; the ductile lower crust and mantle accumulate deformation gradually via shearing , whereas the brittle upper crust reacts by fracture – instantaneous stress release – resulting in motion along the fault. A fault in ductile rocks can also release instantaneously when
765-463: The Chesapeake Bay impact crater . Ring faults are the result of a series of overlapping normal faults, forming a circular outline. Fractures created by ring faults may be filled by ring dikes . Synthetic and antithetic are terms used to describe minor faults associated with a major fault. Synthetic faults dip in the same direction as the major fault while the antithetic faults dip in
816-537: The United States Gypsum Sperry mine, near Mediapolis, Iowa , opened in 1961. This room-and-pillar mine, 620 feet (190 m) below the surface, has square pillars 37 feet (11 m) on a side separating rooms of the same width in a gypsum bed about 10 feet (3.0 m) thick. Many salt mines use room and pillar layouts. The Sifto salt mine in Goderich, Ontario , the largest in the world,
867-630: The Chañarcillo mines; however the mines were exhausted by 1874 and mining largely ended in 1888 after the mines were accidentally flooded. Despite this, Chañarcillo was the most productive mining district in 19th century Chile. Chanarcillo is on the south flank of a dome , the Sierra de Chanarcillo, characterized by radial fractures and northwest striking faults . Silver ore occurs in nearly vertical veins within these fractures and faults within interbedded limestones and tuffs . This ore zone
918-609: The Czech Republic to China to the US. Planning for the development of room and pillar mines operates in much the same way as other mining methods, and begins with establishing ownership of the mine. Following this, the geology of the mine must be analysed, as this will determine factors like the lifespan of the mine, the production requirements, and the cost to develop and maintain. Next, mine layout should be determined, as factors like ventilation, electrical power, and haulage of
969-654: The United States since the late 18th century. It is still in use throughout the US, but has slowed or stopped entirely in parts of Europe. Coal mining in the United States has nearly always operated with a room and pillar layout, although originally operated with significantly more manpower. Room and pillar mining of gypsum was used in Iowa beginning in 1892, and was phased out of use in 1927 due to low recovery and development of technologies that made surface mining more practical, safe, and cost effective. More recently,
1020-556: The capacity of the mined material determines the pillar size. Random mine layout makes ventilation planning difficult, and if the pillars are too small, there is the risk of pillar failure. In coal mines, pillar failures are known as squeezes because the roof squeezes down, crushing the pillars. Once one pillar fails, the weight on the adjacent pillars increases, and the result is a chain reaction of pillar failures. Once started, such chain reactions can be extremely difficult to stop, even if they spread slowly. To prevent this from happening,
1071-414: The crust. A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°. Thrust faults typically form ramps, flats and fault-bend (hanging wall and footwall) folds. A section of a hanging wall or foot wall where a thrust fault formed along a relatively weak bedding plane is known as a flat and a section where the thrust fault cut upward through
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#17327651263601122-415: The decreasing cost of surface mining. Room and pillar mining is not particularly dependent on the depth of the deposit. At particularly deep depths, room and pillar mining can be more cost effective compared to strip mining due to the fact that significantly less overburden needs to be removed. This means that today, room and pillar mining is mostly used for high grade, but small, deep deposits. Due to
1173-481: The deposit is "undercut", where a slot is cut as deep as possible along the bottom of a section of ore. This undercut allows for a manageable pile of rock in later stages. The second step is the drilling and blasting of the section. This creates a pile of ore that is loaded and hauled out of the mine—the final step of the mining process. More modern room and pillar mines use a more "continuous" method, that uses machinery to simultaneously grind off rock and move it to
1224-433: The direction of extension or shortening changes during the deformation but the earlier formed faults remain active. The hade angle is defined as the complement of the dip angle; it is the angle between the fault plane and a vertical plane that strikes parallel to the fault. Ring faults , also known as caldera faults , are faults that occur within collapsed volcanic calderas and the sites of bolide strikes, such as
1275-409: The fault (called a piercing point ). In practice, it is usually only possible to find the slip direction of faults, and an approximation of the heave and throw vector. The two sides of a non-vertical fault are known as the hanging wall and footwall . The hanging wall occurs above the fault plane and the footwall occurs below it. This terminology comes from mining: when working a tabular ore body,
1326-459: The fault is the horizontal component, as in "Throw up and heave out". The vector of slip can be qualitatively assessed by studying any drag folding of strata, which may be visible on either side of the fault. Drag folding is a zone of folding close to a fault that likely arises from frictional resistance to movement on the fault. The direction and magnitude of heave and throw can be measured only by finding common intersection points on either side of
1377-465: The fault movement. Faults are mainly classified in terms of the angle that the fault plane makes with the Earth's surface, known as the dip , and the direction of slip along the fault plane. Based on the direction of slip, faults can be categorized as: In a strike-slip fault (also known as a wrench fault , tear fault or transcurrent fault ), the fault surface (plane) is usually near vertical, and
1428-428: The footwall moves laterally either left or right with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults and those with right-lateral motion as dextral faults. Each is defined by the direction of movement of the ground as would be seen by an observer on the opposite side of the fault. A special class of strike-slip fault is the transform fault when it forms
1479-531: The footwall. The dip of most normal faults is at least 60 degrees but some normal faults dip at less than 45 degrees. A downthrown block between two normal faults dipping towards each other is a graben . A block stranded between two grabens, and therefore two normal faults dipping away from each other, is a horst . A sequence of grabens and horsts on the surface of the Earth produces a characteristic basin and range topography . Normal faults can evolve into listric faults, with their plane dip being steeper near
1530-429: The geometric gap, and depending on its rheology , the hanging wall might fold and slide downwards into the gap and produce rollover folding , or break into further faults and blocks which fil in the gap. If faults form, imbrication fans or domino faulting may form. A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate compressive shortening of
1581-491: The implied mechanism of deformation. A fault that passes through different levels of the lithosphere will have many different types of fault rock developed along its surface. Continued dip-slip displacement tends to juxtapose fault rocks characteristic of different crustal levels, with varying degrees of overprinting. This effect is particularly clear in the case of detachment faults and major thrust faults . The main types of fault rock include: In geotechnical engineering ,
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1632-464: The largest faults on Earth and give rise to the largest earthquakes. A fault which has a component of dip-slip and a component of strike-slip is termed an oblique-slip fault . Nearly all faults have some component of both dip-slip and strike-slip; hence, defining a fault as oblique requires both dip and strike components to be measurable and significant. Some oblique faults occur within transtensional and transpressional regimes, and others occur where
1683-418: The megathrust faults of subduction zones or transform faults . Energy release associated with rapid movement on active faults is the cause of most earthquakes . Faults may also displace slowly, by aseismic creep . A fault plane is the plane that represents the fracture surface of a fault. A fault trace or fault line is a place where the fault can be seen or mapped on the surface. A fault trace
1734-399: The mine is divided up into areas or panels. Pillars known as barrier pillars separate the panels. The barrier pillars are significantly larger than the "panel" pillars and are sized to allow them to support a significant part of the panel and prevent progressive collapse of the mine in the event of failure of the panel pillars. Traditionally, the act of mining consists of three steps. First,
1785-608: The mine's entrance. After the pillars are removed, the roof (or back) is allowed to collapse behind the mining area. Pillar removal must occur in a very precise order to reduce the risks to workers, owing to the high stresses placed on the remaining pillars by the abutment stresses of the caving ground. Retreat mining is a particularly dangerous form of mining. According to the Mine Safety and Health Administration (MSHA), pillar recovery mining has been historically responsible for 25% of American coal mining deaths caused by failures of
1836-408: The miner stood with the footwall under his feet and with the hanging wall above him. These terms are important for distinguishing different dip-slip fault types: reverse faults and normal faults. In a reverse fault, the hanging wall displaces upward, while in a normal fault the hanging wall displaces downward. Distinguishing between these two fault types is important for determining the stress regime of
1887-407: The mines, but also includes factors like the number and type of entries, roof height, ventilation, and cut sequence. Room and pillar mines are developed on a grid basis except where geological features such as faults require the regular pattern to be modified. The size of the pillars is determined by calculation. The load-bearing capacity of the material above and below the material being mined and
1938-435: The most common. With the passage of time, a regional reversal between tensional and compressional stresses (or vice-versa) might occur, and faults may be reactivated with their relative block movement inverted in opposite directions to the original movement (fault inversion). In such a way, a normal fault may therefore become a reverse fault and vice versa. In a normal fault, the hanging wall moves downward, relative to
1989-494: The opposite direction. These faults may be accompanied by rollover anticlines (e.g. the Niger Delta Structural Style). All faults have a measurable thickness, made up of deformed rock characteristic of the level in the crust where the faulting happened, of the rock types affected by the fault and of the presence and nature of any mineralising fluids . Fault rocks are classified by their textures and
2040-405: The ore must be considered in cost analysis. Due to the non-homogeneous nature of mineral deposits typically mined by room and pillar, mine layout must be mapped very carefully. It is desirable to keep the size and shape of rooms and pillars consistent, but some mines strayed from this formula due to lack of planning and deposit characteristics. Mine layout includes the size of rooms and pillars in
2091-412: The right time for—and type of— igneous differentiation . At a given time differentiated magmas would burst violently out of the fault-traps and head to shallower places in the crust where porphyry copper deposits would be formed. As faults are zones of weakness, they facilitate the interaction of water with the surrounding rock and enhance chemical weathering . The enhanced chemical weathering increases
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2142-423: The rigidity of the constituent rocks, the two sides of a fault cannot always glide or flow past each other easily, and so occasionally all movement stops. The regions of higher friction along a fault plane, where it becomes locked, are called asperities . Stress builds up when a fault is locked, and when it reaches a level that exceeds the strength threshold, the fault ruptures and the accumulated strain energy
2193-414: The risk of subsidence unless properly maintained, however, maintenance does not often occur. Room and pillar mining is one of the oldest mining methods. Early room and pillar mines were developed more or less at random, with pillar sizes determined empirically and headings driven in whichever direction was convenient. Room and pillar mining was in use throughout Europe as early as the 13th century, and
2244-422: The roof or walls, even though it represents only 10% of the coal mining industry. Retreat mining cannot be used in areas where subsidence is not acceptable, reducing profitability. Sometimes retreat mining is not used and the underground space is repurposed as climate controlled storage or office space instead. Many room and pillar mines have been abandoned for as long as 100 years. This drastically increases
2295-420: 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
2346-404: The strain rate is too great. Slip is defined as the relative movement of geological features present on either side of a fault plane. A fault's sense of slip is defined as the relative motion of the rock on each side of the fault concerning the other side. In measuring the horizontal or vertical separation, the throw of the fault is the vertical component of the separation and the heave of
2397-416: The stratigraphic sequence is known as a ramp . Typically, thrust faults move within formations by forming flats and climbing up sections with ramps. This results in the hanging wall flat (or a portion thereof) lying atop the foot wall ramp as shown in the fault-bend fold diagram. Thrust faults form nappes and klippen in the large thrust belts. Subduction zones are a special class of thrusts that form
2448-400: The surface, then shallower with increased depth, with the fault plane curving into the Earth. They can also form where the hanging wall is absent (such as on a cliff), where the footwall may slump in a manner that creates multiple listric faults. The fault panes of listric faults can further flatten and evolve into a horizontal or near-horizontal plane, where slip progresses horizontally along
2499-429: The surface. Other processes, such as backfill , where discarded tailings are unloaded into mined-out areas, can be used, but are not required. Retreat mining (below) is an example of a process like this. Retreat mining is often the final stage of room and pillar mining. Once a deposit has been exhausted using this method, the pillars that were left behind initially are removed, or "pulled", retreating back towards
2550-582: The vicinity. In California, for example, new building construction has been prohibited directly on or near faults that have moved within the Holocene Epoch (the last 11,700 years) of the Earth's geological history. Also, faults that have shown movement during the Holocene plus Pleistocene Epochs (the last 2.6 million years) may receive consideration, especially for critical structures such as power plants, dams, hospitals, and schools. Geologists assess
2601-474: Was opened in 1959. It taps a salt bed 30 metres (98 ft) thick 533 metres (1,749 ft) below the surface, mostly under Lake Huron . The Cargill salt mine 1,700 feet (520 m) below the surface, mostly under Lake Erie at Cleveland, Ohio is similar. Modern room and pillar mines can be few and far between. This is due to many factors, including the dangers to miners associated with subsidence, increasing use of other methods with more mechanization, and
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